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Combined effect of light harvesting strings, anti-reflective coating, thin glass, and high ultraviolet transmission encapsulant to reduce optical losses in solar modules
Abstract
Optical losses are a major source for current and power reduction in solar modules. Hence, various improvements aiming at reducing these losses have been suggested. In this work, we have evaluated the effects of anti-reflective coating, front glass thickness, polyvinyl butyral ultraviolet+ encapsulant, and light harvesting strings on the module performance individually and in combination. The individual and combined contributions were quantified by spectrally resolved optical measurements on the module components and simulations as well as electrical measurements on 1-cell and 54-cell modules. Optical gains and their impact on short circuit current are discussed in relation to a maximum current obtained from the solar cells internal quantum efficiency. The results of the electrical characterization are in good agreement with the optical analysis substantiating our approach. They show that a combined, relative current enhancement of 5% can be obtained for an optimized module, which compares to an increase of 1% absolute efficiency. Copyright © 2014 John Wiley & Sons, Ltd.
... In PV modules, there is a spectral interaction of the optical properties of all components such as the glass, the encapsulant, the solar cell, and the backsheet [7]. Hence, a systematic assessment of the impact of the glass on the module performance requires the setup of fully functional modules. ...
... Note that the glasses are structured on both sides leading reducing the reflection on the two surfaces and therefore doubling the effect. With optical data from all components in the modules and the quantum efficiency data from the solar cells, the expected module currents and optical loss mechanisms can be calculated (see Fig.4) [5][6][7][8]. A short circuit current for the reference glass of J SC,ref =38mA/cm² and for the AR1 glass of J SC,AR1 =39mA/cm² is expected. ...
... or +2.1% rel. . This is comparable to other ARC data published earlier [7]. ...
This works presents a new functionalization concept for front glasses of PV modules and an analysis of their anti-reflective and anti-soiling properties. The described functionalization technology is based on surface structuring and modification obtained by a low cost chemical treatment. The functionalized, nanostructured surface is part of the original glass and no additional coating is required, which makes it more reliable. Nanostructured glasses are compared to conventional anti-reflective coated and untreated reference glasses. The optical and self-cleaning properties of the glasses are investigated by spectrally resolved optical analysis and by a newly developed anti-soiling test method, respectively. Additionally, the performance of 1-cell modules equipped with these glasses is simulated on the basis of optical data and measured electrically in solar simulators. 60-cell modules with different glasses are compared for their electrical performance. It is shown that the anti-reflective behavior of a glass with nanostructured surface without any additional anti-reflective coating is as good as conventional solar glass with standard anti-reflective coating. Furthermore, it is shown that loss in integral transmission after soiling process is significantly reduced (25 % relative) by a proper wet chemical surface treatment. This reduces solar module operation costs in arid regions.
... This characterization gives the electrical characteristics of the PV modules typically until 1200 nm and do not consider the heat sources of the module which influence the performance of the PV modules. More detailed PV module indoor characterizations also target the cell-tomodule power ratios [1,2], but do not consider the heat sources and wider range of wavelengths. ...
... This means that the glass bulk properties for AR and non-AR versions are almost similar. The electrical properties of the solar cells are similar to the cell measured in ref. [4,2]. ...
... The share of each power loss due to each reduction factor can be calculated by (2). ...
Incident light on solar modules is either lost in reflection or heat generation or generates desired electricity. In this work, we introduce and extended evaluation of PV modules by means of simulation and measurements and quantify optical reflection losses, heat sources and electricity values in PV modules with different bill of materials based on the material stack level. We introduce our optical and electrical loss analysis model which evaluates PV modules in spectral dependent optical and voltage dependent electrical analysis which can be used for any defined spectrums in any location in the word. We show that almost 75% of the incoming incident light turns into heat sources with different loss mechanism while 7% to 10% of incoming light can be reflected out of the stack. We also show that modules with anti-reflection coating can benefit about 2-4%rel. extra efficiency compared to the modules with similar glass and no AR properties. The reduced reflection in glass level increases the efficiency as well as the heat sources of the module. The Module with UV+ polymer (Polyvinylbutyral, PVB) shows a low UV (Ultraviolet) absorption in the polymer in UV range and decreases the degradation effects such as discoloration. Furthermore, modules with PVB encapsulation materials show about 2.5% extra electricity generation in module level compared to the similar module with encapsulant without UV+ properties (ethylene vinyl acetate, EVA).
... Vogt et al. demonstrated a complex multi physic simulation to quantify the heat sources in solar modules with FEM and ray tracing simulation [3] which shows good accuracy but needs complex FEM models and high computation time. In our previous work [4], we have shown the influence of optimized and modified module components on the electrical power of the module in moderate and desert areas by means of simulation and measurement. In this work, we introduce a practical and easy multi-physic approach to estimate the optical reflection losses, electricity generation and heat sources in the relevant layers of a solar module. ...
... Four mini-modules were manufactured from 3.2 mm glass with anti-reflection coating, EVA as the encapsulation material, backsheet and solar cells. The cells are six inches pseudo-square ALBSF selective emitter solar cells (SE) with 2 busbars [4]. The solar cells were characterized by the loss evaluation tool LOANA to determine the quantum efficiency and power characteristics of the cells before and after lamination. ...
... a Below band gap energy absorption As shown in Fig. 7-right, the light which enters the solar cell will be either absorbed by the solar cell in above or equal to the band gap energy range or be reflected from the rear side metallization of solar cell in the below band gap energy range. The back reflected light in the rear side of solar cell in the below band gap energy range will either leave the solar cell or be reflected multiple times (continued ) Relative power loss due to the reflectance of the light in glassjpolymer interface once f 4 ðlÞ Spectrally resolved reduction factor due to absorption in polymer p 4 ðlÞ Spectrally resolved power density after absorption in polymer P 4 Power loss in due to absorption in polymer DP rel$f4 : ...
Solar modules convert light in wanted electricity, unwanted heat and reflected incident light. Light absorbed in the silicon of the solar cells generates free charge carriers which are converted into electricity by the photovoltaic effect. Some of the energy absorbed in free charge carriers as well as all other absorption in non-photoactive layers generates heat. PV modules are mainly characterized in standard test conditions (STC) but quantification of reflection losses and heat sources in PV modules helps to evaluate the yield of PV modules in different spectrums and environmental conditions such as desert regions where the module temperature can influence the energy yield. In this work, we introduce a practical method for calculating spectrally resolved absorption and voltage resolved electrical conversion mechanisms in order to quantify electricity and heat generating processes by means of common characterization devices. The model only needs optical characterization of module components and typical electrical characterization of the cells and modules. Based on the performance of individual components, the share of each loss phenomena and electricity production in the complete solar module can be determined. Comparison of simulation results with experimental measurements shows a good correlation. The measured and simulated short-circuit current density are in good agreement with about 1% deviation due to additional back reflections and measurement noise. The cell to module (CTM) current loss are simulated and measured for 2.63% and 1.85% respectively. The results show that for the measured modules, 7% of the incoming solar power on the module is reflected while 75.58% of it turns to heat. The usable energy as electricity is simulated and measured for 17.44% and 17.72%, respectively. We show that more than half of the incoming energy dissipates as heat due to thermalization and thermodynamic losses.
... Bearing in mind that PV modules often are subject to irradiance of oblique incidencewhether, for example, due to diffuse sunlight caused by clouds or simply direct sunlight that is not normally incident on the stationary PV module due to the time of daya number of optical concepts to recapture the light incident of all angles of incidence on the dead areas of PV modules have been presented in the literature [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These optical concepts rely on redirecting the incident light into the active area of the PV module by diffractive optics [4,5], reflection [6][7][8][9] and refraction [10][11][12] of incident light as well as recovering the back-scattered light off front contacts via total internal reflection off the inside of the cover glass [13,14]. ...
... Bearing in mind that PV modules often are subject to irradiance of oblique incidencewhether, for example, due to diffuse sunlight caused by clouds or simply direct sunlight that is not normally incident on the stationary PV module due to the time of daya number of optical concepts to recapture the light incident of all angles of incidence on the dead areas of PV modules have been presented in the literature [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These optical concepts rely on redirecting the incident light into the active area of the PV module by diffractive optics [4,5], reflection [6][7][8][9] and refraction [10][11][12] of incident light as well as recovering the back-scattered light off front contacts via total internal reflection off the inside of the cover glass [13,14]. One disadvantage of any diffractive optics based approach is the strong dependence on the angle of incidence and wavelength, which limits the ability to redirect incident light into the active area of the PV module for the entire solar spectrum and for arbitrary angles of incidence [4,5]. ...
... One disadvantage of any diffractive optics based approach is the strong dependence on the angle of incidence and wavelength, which limits the ability to redirect incident light into the active area of the PV module for the entire solar spectrum and for arbitrary angles of incidence [4,5]. While tailored contacts [6,7,13,14], triangular voids inside the encapsulation of a PV module [8,9], and prismatic covers [10][11][12] successfully demonstrated the ability to redirect light by geometrical optics in the entire solar spectrum, they either suffer from low performance at large angles of incidence or are not compatible with the conventional combination of an encapsulation layer and a front glass cover. Advanced optical concepts, such as contact grids with subwavelength photonic structures, promise to minimize the reflection losses off the electrical contacts. ...
The vast majority of conventional photovoltaic (PV) module technologies suffer from inactive areas, for example, due to the front contact finger grids or interconnection lines, which are essential for efficient extraction of the photocurrent. Invisibility cloaking by freeform surfaces is a new concept to guide incident light of the entire solar spectrum and all angles of incidence away from these inactive areas to the active areas of the PV modules. In this work, a freeform surface design is incorporated into a standard encapsulation layer of conventionally front glass covered PV modules. For a copper indium gallium diselenide (CIGS) thin-film PV module, a relative improvement in power conversion efficiency of 6.5% is presented, which demonstrates that the entire optical losses of the inactive area can be recovered. The design of the freeform surface is optimized based on rigorous ray-tracing simulations, which further allow discriminating and quantifying the underlying optical effects. Moreover, in order to demonstrate the scalability of the freeform surface cloak, a prototype CIGS thin-film PV module (comprised of nine monolithically interconnected solar cells) exhibiting fully-cloaked interconnection lines is presented.
... Bearing in mind that PV modules often are subject to irradiance of oblique incidencewhether, for example, due to diffuse sunlight caused by clouds or simply direct sunlight that is not normally incident on the stationary PV module due to the time of daya number of optical concepts to recapture the light incident of all angles of incidence on the dead areas of PV modules have been presented in the literature [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These optical concepts rely on redirecting the incident light into the active area of the PV module by diffractive optics [4,5], reflection [6][7][8][9] and refraction [10][11][12] of incident light as well as recovering the back-scattered light off front contacts via total internal reflection off the inside of the cover glass [13,14]. ...
... Bearing in mind that PV modules often are subject to irradiance of oblique incidencewhether, for example, due to diffuse sunlight caused by clouds or simply direct sunlight that is not normally incident on the stationary PV module due to the time of daya number of optical concepts to recapture the light incident of all angles of incidence on the dead areas of PV modules have been presented in the literature [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These optical concepts rely on redirecting the incident light into the active area of the PV module by diffractive optics [4,5], reflection [6][7][8][9] and refraction [10][11][12] of incident light as well as recovering the back-scattered light off front contacts via total internal reflection off the inside of the cover glass [13,14]. One disadvantage of any diffractive optics based approach is the strong dependence on the angle of incidence and wavelength, which limits the ability to redirect incident light into the active area of the PV module for the entire solar spectrum and for arbitrary angles of incidence [4,5]. ...
... One disadvantage of any diffractive optics based approach is the strong dependence on the angle of incidence and wavelength, which limits the ability to redirect incident light into the active area of the PV module for the entire solar spectrum and for arbitrary angles of incidence [4,5]. While tailored contacts [6,7,13,14], triangular voids inside the encapsulation of a PV module [8,9], and prismatic covers [10][11][12] successfully demonstrated the ability to redirect light by geometrical optics in the entire solar spectrum, they either suffer from low performance at large angles of incidence or are not compatible with the conventional combination of an encapsulation layer and a front glass cover. Advanced optical concepts, such as contact grids with subwavelength photonic structures, promise to minimize the reflection losses off the electrical contacts. ...
In this work, detailed energy yield modelling based on experimental data of all-angle invisibility cloaks for solar cell contact fingers is used to underline their high improvement potential under realistic conditions.
... In essence, the baseline module is built with standard solar glass and EVA encapsulant , whereas glass with an AR coating and reduced thickness (2mm instead of 3.2mm) and PVB encapsulant is used for the improved module. The experimental investigations of the modules and the module materials used are presented in Schneider et al. [11]. ...
... Turek and Eiternick [5] and Schneider et al. [11] compared modules built with light-harvesting strings (LHS, textured tabs made by Schlenk) and without them: LBIC measurements taken on both modules are presented in Fig. 5. ...
... (a) Irradiated AM1.5g solar spectrum[12], spectral response function of selective emitter (SE) cells, and resulting weighting function. (b) Relative power losses due to various optical processes in the front stack of a baseline module compared with a module optimized with an AR coating on glass, thinner glass and high UV transmittance encapsulant[11]. ...
The output power of a solar module is the sum of the powers of all the individual cells in the module multiplied by the cell-to-module (CTM) power ratio. The CTM ratio is determined by interacting optical losses and gains as well as by electrical losses. Higher efficiency and output power at the module level can be achieved by using novel ideas in module technology. This paper reviews methods for reducing different optical and electrical loss mechanisms in PV modules and for increasing the optical gains in order to achieve higher CTM ratios. Various solutions for optimizing PV modules by means of simulations and experimental prototypes are recommended. Finally, it is shown that designing PV modules on the basis of standard test conditions (STC) alone is not adequate, and that, to achieve higher CTM ratios by improving the module designs in respect of environmental conditions, an energy yield analysis is essential.
https://store.pv-tech.org/store/investigation-of-celltomodule-ctm-ratios-of-pv-modules-by-analysis-of-loss-and-gain-mechanisms/
... Gains and losses originating from the encapsulation of the solar cell within the photovoltaic module are commonly calculated at standard testing conditions STC [5,7,14] and consider optical, electrical and geometrical effects. Additional models are available for isolated physical effects or module components [6,8,[14][15][16][17][18]. ...
... Gains and losses originating from the encapsulation of the solar cell within the photovoltaic module are commonly calculated at standard testing conditions STC [5,7,14] and consider optical, electrical and geometrical effects. Additional models are available for isolated physical effects or module components [6,8,[14][15][16][17][18]. ...
Models for the calculation of losses in PV systems are widely applied but typically focus on single components (i.e. the solar cell). We discuss relevant models and combinations thereof to analyze losses from wafer to system. We propose a holistic approach to analyze losses from laboratory to environmental conditions. The proposed approach focusses on practically relevant interfaces (i.e. STC module power) and is based on separated influence factors.
... To improve the module efficiency/ power, various advanced technologies can be incorporated, such as multibusbar [1,2], halved-cell [3,4] and light-trapping ribbon [5,6]. These technologies have yielded promising results in terms of improving module performance. ...
... In this case, the light reflected at the ribbon will be totally internally reflected at the front glass-air interface and redirected onto the solar cells, thus increasing the module current generation potential. Such a ribbon can be termed a lighttrapping ribbon (LTR) or a lightharvesting string (LHS) [5,12]. Fig. 2 shows the light path in a module with a textured ribbon (V groove). ...
... One of the effective ways to overcome this limitation is to fabricate a multi-junction (e.g., tandem) device by strategically stacking multiple photoactive layers with complementary absorption spectra [54][55][56][57][58][59][60][61]. In a tandem cell, each photoactive layer captures a different energy part of the solar spectrum, which is beneficial to mitigating the transmission and thermalization losses during the photonto-electron conversion process, possibly resulting in performance enhancement ( Figure 1b) [62][63][64][65][66][67][68]. However, complex device structure includes additional processing steps for recombination layers between sub-cells and therefore complicates the fabrication process. ...
Recently, emerging third-generation photovoltaic technologies have shown rapid progress in device performance; the power conversion efficiencies (PCEs) of organic bulk heterojunction (BHJ) and perovskite solar cells (PSCs) are now surpassing 19% and 25%, respectively. Despite this dramatic enhancement, their efficiencies are theoretically limited based on the detailed balance model which accounts for inevitable loss mechanisms under operational conditions. Integrated solar cells, formed by monolithically integrating two photoactive layers of perovskite and BHJ with complementary absorption, provide a promising platform for further improvement in solar cell efficiency. In perovskite/BHJ integrated solar cells (POISCs), high bandgap perovskite offers high open-circuit voltage with minimal losses while low bandgap organic BHJ extends absorption bandwidth by covering the near-infrared region, resulting in additional photocurrent gain. Different from conventional tandem solar cells, integrated solar cells contain merged photoactive layers without the need for complicated recombination layers, which greatly simplifies fabrication processes. In this review, we summarize the recent progress in POISCs, including operational mechanism and structural development, and remaining challenges on the road toward efficient devices.
... Also, the roundness of the circular wire geometry in the MBB design assists to reflect the incident light from the ribbon surface onto the wafer surface and it makes less losing the received energy in comparison with the standard interconnection ribbons [9]. Besides, the MBB design uses high number of small round wires to decrease the busbar width and it results in an increase of the number of current paths to associate more uniform current distribution [10]. However, the MBB connector may suffer manufacturing errors associated with the non-homogeneity of solder coating around the copper-wire which results in earlier solder failure and crack (up to 21 %) [11,12]. ...
As the solar PV harvesting energy system are becoming more important sector of renewable energy day to day, improving the efficiency of the solar PV module and reducing the cost of modules are receiving more attentions of PV module manufacturers. Design of the PV module interconnection ribbons is one of the main focus for developing the efficiency of the PV modules and improving the reliability of the modules. In the last decade, new designs for the PV module interconnection ribbon have been introduced, however, there is still a need to optimize their configuration and geometry to achieve higher reliability without dropping the efficiency of the PV modules. Indeed, solely using the wider interconnection ribbons (to provide more joint length) may increase the reliability of the module, but it directly reduces the efficiency of module due to more shading effect. This study provides the results for determining the optimal design for long-term reliability of PV module interconnections. Three main PV module ribbon interconnection designs including Conventional Ribbon (CR), Light-Capturing Ribbon (LCR), and Multi-Busbar (MBB) interconnections are compared in terms of number of cycles to creep-fatigue failure. This study uses the FEM simulation and creep-fatigue reliability formulations to find the effect of the main geometrical parameters on the failure of different PV module ribbon interconnection designs. The finding showed that the MBB interconnections has up to 15 % higher creep-fatigue lifetime compared to the LCR and the CR interconnections.
... The texturing profile was far from optimal. In 2013, Schneider et al. measured a 2.5 % gain in Jsc with structured ribbons, but the total coverage of the cell is unknown [56]. In 2016, Holst et al. have studied the increasing of light harvesting by such structured cell interconnection ribbons, experimentally and with ray-tracing [57]. ...
Photovoltaic modules with higher efficiency can be envisaged by limiting the optical and electrical performance losses caused by cell integration. This thesis is mainly dedicated to the modelling of PV modules made up of silicon heterojunction solar cells (SHJ). There are already many tools for modelling the performance of a photovoltaic module, but it is necessary to adapt them to account for specificities of this technology, as well as latest developments in module design and interconnection. An optical and electrical model – mainly analytical – has been developed. A standardized classification of performance losses within the module was defined and enriched on the basis of previous work in the literature. Two loss items are analysed in more detail. The first is electrical: in order to reduce resistive losses, modules made up of cut cells have become the standard. The performance losses associated with cutting silicon heterojunction cells were missing data from the literature. An edge recombination current of 8 nA / cm has been measured before and after cutting, as well as a loss of photo-generated current. The impact on module performance has been modelled for different cutting geometries. The second is optical: new encapsulants material exhibit significant diffusive behaviour. A 4-flux model is developed to characterize its optical constants from spectrophotometric measurements in reflection and transmission, total and diffuse. A new item in performance losses is proposed, caused by backscattering of light. The impact on the photo-generated current of the module was analysed for two diffusive, UV opaque and transparent encapsulants.
... In a similar way, the cell interconnection ribbon (and wires) can shade the cell, but considering reflection on the ribbons and at the glass / air interface, the effective shading is lower than 100%. With EQE measurements, we obtained an effective shading of 30% for V-groove structured ribbons in module and 90% for flat ribbons, in good agreement with previous studies [14][15][16][17]. Considering wires in module, we use an effective shading of 60%. ...
Today, an increasing number of companies are working with heterojunction technology because of its higher efficiency potential and decreasing LCOEs compared to traditional solar cells [1] [2]. One of the major challenges for SHJ solar cells is the use of low temperature silver paste for metallization because of 1) their lower conductivity and 2) their need of alternative interconnection strategies as described by Faes et. al. [2]. As heterojunction technology is relatively new and as new wafer sizes are about to be adopted, metallization and interconnection are facing challenges and opportunities [3]. To screen quickly the multiple possibilities, a specific modelling for heterojunction has to be developed. The parameters describing the metallization and interconnection of a module are numerous and highly interdependent. In this field, performance optimization is always a compromise to be made mainly between the additional series resistance of the elements (TCO, finger, busbar, ribbons) and their impact on the photo-generated current. Optimal results are expressed in term of finger width, grid pitch, number of busbar and ribbons, section of ribbons, etc. Even under standard conditions (STC), the optimizations are obviously dependent on the parameters of the non-metallized cell. Also, the results differ whether the optimization criterions include the cost of the individual elements (€/Wp). For these reasons, CTMOD, a multidimensional prediction model of the performance and material cost of each possible architecture, is essential.
... A direct method to enhance light harvesting involves reduction of incident-light reflection losses by introducing an antireflective microstructure on the front side of the device. 20,21 On the other hand, light can be concentrated and amplified in the active layer by integrating nanostructures within the device combined with optimizing device construction. For example, plasmonic nanostructures have been employed extensively in optoelectronic devices because the incident light can be effectively trapped and coupled inside the active layer by plasmonic light scattering, surface plasmon polariton (SPP) effects, and localized surface plasmon resonance (LSPR) effects. ...
Metal electrodes are playing an increasingly important role in controlling photon absorption and in promoting optimal light management in thin-film semiconductor devices. For organic optoelectronic devices, the conventional fabrication approach is to build the device on top of a transparent electrode, with metal electrode deposition as the last step. This makes it challenging to control the surface of the metal electrode to promote good light management properties. An inverted fabrication approach that builds the device on top of a metal electrode, makes it possible to control the morphology of the metal surface independently of the organic semiconductor active layer to achieve a variety of photonic and plasmonic behaviors useful for devices. Yet, there are few reports of inverted fabrication of organic optoelectronic devices and its impacts on device properties. Silver (Ag) is the most suitable metal for fabrication of nanostructured electrodes with plasmonic behavior (i.e., plasmonic electrodes) because of its low parasitic absorption loss and high reflectivity. In this project, we describe the facile fabrication of silver nanoparticle (AgNP) aperiodic plasmonic metasurfaces and study their physical and optical characteristics. Then, we investigate the photonic and electrical behavior of the aperiodic plasmonic metasurfaces when interfaced with poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) organic semiconducting polymer thin films. The luminescence quantum yield of F8BT thin films increases from 29% on planar Ag up to 66% on AgNP metasurfaces (AgNP MS) due to the Purcell Effect and the improved extraction of emission coupled to surface plasmon polariton (SPP) modes. In particular, we show that plasmonic enhancement can overcome ohmic losses associated with metals and metal-induced exciton quenching. According to the current-voltage characteristics of hole-only devices with and without aperiodic plasmonic metasurfaces, we conclude that AgNP aperiodic plasmonic metasurfaces have comparable electrical behavior to planar metal electrodes while having superior light management capability.
... Reflections from the cover glass of photovoltaic (PV) modules represent approximately 4% of the incident light, which reduces the power conversion efficiency (PCE) of PV modules. To suppress these reflections and improve the PCE of PV modules, antireflection coatings (ARCs) are widely applied on the light incoming side of the cover glass (Agustin-Saenz et al., 2019;Agustín-Sáenz et al., 2019;Huh et al., 2019;Schneider et al., 2014;Yao et al., 2017). The use of silica-based ARCs with sufficiently high porosity and desired thickness formed via a solgel method has been recognized as a low-cost strategy for improving the PCE (Buskens et al., 2016;Guo et al., 2016;Sun et al., 2014;Xu et al., 2014aXu et al., , 2014bYe et al., 2013). ...
Silica-based antireflection coatings (ARCs) used in photovoltaic (PV) modules often encounter soiling problems, which has been recognized as one of the most serious problems degrading the power output of PV modules. In this work, four kinds of silica-based ARCs were prepared to investigate the effects of surface morphology and chemistry on their anti-soiling properties under Ningbo’s climate. To reveal the influences of surface morphology, hollow silica nanoparticle (HSN)- and solid silica nanoparticle (SSN)-based ARCs were prepared and compared. To understand the surface chemical effects, we comparatively studied the soiling behavior of hydrophilic and hydrophobic HSN ARCs postmodified with methyl and fluorinated groups (named CH3-HSN and F-HSN, respectively). After half-year field tests, we found that the HSN ARCs with a rougher surface exhibited better anti-soiling performance than the SSN ARCs. On the other hand, the hydrophilic ARCs showed better soiling resistance than the hydrophobic controls because of the role of rain cleaning in the soiling mitigation of the hydrophilic samples installed at a moderate tilt angle under a typical coastal climate. Comparing the hydrophobic samples modified with methyl and fluorinated groups, the former was superior to the latter in both laboratory and outdoor tests because of the larger adhesion force between contaminants and the surface in the fluorinated-HSN ARCs. These findings provide constructive guidance for the applications of silica-based ARCs in PV modules installed in coastal areas, which is the key to maximizing the power output of PV modules in practice.
... T-EVA is a recently developed advanced functional encapsulant that allows 1% power gain compared with conventional C-EVA because it transmits entire UV radiation. 16 But using T-EVA as a front and rear encapsulant can cause discoloration/delamination at the backsheet interface in the PV module. 17 Hence, the weather stability of the T-EVA encapsulant is still not known. ...
Commercially different variants of ethylene‐vinyl acetate (EVA) encapsulants are available in the photovoltaic (PV) market. Photobleaching and discoloration are the two most commonly observed phenomena, and their initiation may be different for different encapsulants. To investigate the EVA encapsulant photobleaching and discoloration, solar cell laminates having different EVA films (UV‐transparent [T], UV‐cut [C], and combination of the two [TC]) were tested in Xenon test chamber. High temperatures are created in the laminates during the aging tests by using a thick insulation layer behind the backsheet. The UV fluorescence images and grayscale profile show clear signs of photobleaching and discoloration. It is found that the oxygen diffusion coefficient of the T sample is four and nine times slower than the TC and C samples, respectively, in the photobleached region. Fluorescence imaging and spectra and Raman spectra were taken before and after the accelerated test and indicate that discoloration causing fluorophores generation is higher after the photobleached region for transparent and combined EVAs, whereas higher at the center for UV‐cut EVA laminates. A colorimeter was used to measure the Yellowness Index of the samples before and after the accelerated aging test. This work will help in the early detection of photobleaching and discoloration of any encapsulant used in the PV modules. This method will also help to study the behavior of encapsulants in different climatic conditions like hot, cold, dry, humid, and their combinations by simulating the same in an accelerated weathering chamber by using the different insulation thickness.
... In the literature, different methods to quantify energy distribution and mitigate losses in PV modules have been put forward [15][16][17]. Some of them analyzed optical losses of PV modules and evaluated the impacts of different approaches to reduce these losses, while other losses, especially heat source, are not mentioned in these studies [18,19]. Rodolphe et al. [20] and Dupre et al. [21] proposed some strategies to minimize thermal losses in solar photovoltaics, whereas heat generation was not considered. ...
Efficiency improvements of PV modules has come under heated discussions. The conversion efficiency is hindered by losses that occur in the whole physical process, which poses a great challenge to classify and quantify the energy distribution. Many researchers have analyzed specific loss processes in theory, while the real situation is more complicated than the models that have been provided. To analyze the power loss and quantify the energy distribution in the PV module, this paper discusses the loss mechanisms in detail, based on material characteristics (optical coefficient and cell bandgap), operation mechanisms (carriers' generation, transportation, and recombination mechanisms) and environmental factors (temperature and solar irradiance). A comprehensive energy distribution model under standard test condition is then developed, and the electrical characteristics and thermal performance of PV modules are investigated. Finally, the model is verified for both PV cells and modules. The results indicate that, for a PV module, about 57.25% of the total incident solar energy is lost in the carriers' generation, while the remaining 1.28%, 23.47% and 2.10% are lost in the carriers' transportation, recombination and cell to module process, respectively. As a result, approximately 72.16% of the incident energy is dissipated as heat, resulting in the increase of cell temperature, and almost 11.94% of solar energy finally leaves the module due to multilayer reflection. The study also demonstrates that when the module temperature rises, the decrease in power output mainly originates from the increase in recombination loss of the PV cell. Furthermore, some potential suggestions are provided to control energy conversion losses and improve cell performance.
... The proposed strategies encompass diffractive optics, 71 reflective optics, 72,73 refraction at "free-form surfaces", 74,75 as well as recovering backscattered light via total internal reflection. 76 However, it should be noted that these concepts are at a much lower level of technological readiness than the metallization schemes discussed above, and they are mentioned here simply in the spirit of an outlook on possible directions for future research and development. ...
The remarkable recent progress in perovskite photovoltaics affords a novel opportunity to advance the power conversion efficiency of market-dominating crystalline silicon (c-Si) solar cells. A severe limiting factor in the development of perovskite/c-Si tandems to date has been their inferior light-harvesting ability compared to single-junction c-Si solar cells, but recent innovations have made impressive headway on this front. Here, we provide a quantitative perspective on future steps to advance perovskite/c-Si tandem photovoltaics from a light-management point of view, addressing key challenges and available strategies relevant to both the 2-terminal and 4-terminal perovskite/c-Si tandem architectures. In particular, we discuss the challenge of achieving low optical reflection in 2-terminal cells, optical shortcomings in state-of-the-art devices, the impact of transparent electrode performance, and a variety of factors which influence the optimal bandgap for perovskite top-cells. Focused attention in each of these areas will be required to make the most of the tandem opportunity.
... Singh et al. showed that combined approach of multi-busbar technology and halved-cell technology reduces the resistive losses in PV module and thus increases the module performance up to approximately 4% [1]. Research studies have also been devoted to investigate the impact of module materials (BOM) on module performance [2]- [3]. It has been suggested that modification of module BOM (i.e. ...
... The record efficiency for a SHJ solar cell with front contacts is lower (25.1 % by Kaneka [2]) due to reflection of light at the contact finger grid and the bus bars and due to parasitic absorption within the transparent conductive oxide (TCO) layer [3] as schematically shown in Fig.1a. A huge research effort is being made to develop less absorbing TCOs [4][5][6][7][8], less reflective contact grids [9][10][11][12][13][14][15][16] and various other approaches [17][18][19][20][21] to overcome these losses. We have recently reported a new front contact design that can replace the finger grid as well as the TCO [22]. ...
We have developed effectively transparent contacts (ETCs) that allow for increased current in heterojunction solar cells. Micro-meter scaled triangular cross-section grid fingers with micro-meter scaled distance redirect light efficiently to the active area of the solar cell and hence, omit losses through reflection at the front finger grid. Furthermore, the grid fingers are placed close together such that only a very thin layer of transparent conductive oxides (TCO) is necessary which avoids parasitic absorption and can decrease material costs. In this paper we experimentally show current enhancement of ~2 mA/cm^2 in silicon heterojunction solar cells using ETCs. 1 mA/cm^2 is gained through less parasitic absorption and 1 mA/cm^2 is gained by efficient redirection of light and therefore, absent shadowing losses.
... Similar losses were reported in Refs. [14,15,18,22,23,72]. Note that the losses are given in short-circuit current, not in generation current, because we know coll precisely. ...
This paper develops a procedure to analyse the optical losses of both crystalline Si cells in air and of modules in an industrial environment. We evaluate EQE and reflectance (R) measurements on the cell, and R measurements on various spots of the module by combining the recently developed module ray tracer from PV Lighthouse with established Sentaurus device modeling. The IQE is the product of absorptance (Aeh) in Si due to e-h pair generation and their collection efficiency (ηcol). With Sentaurus device modeling of our PERC cells, we can model ηcol to high precision and compute Aeh from the IQE. At long wavelengths, this Aeh allows us to quantify light trapping in both the cell in air and the cell in the module without fitting internal reflectance etc. At short wavelengths, the parasitic absorptance Apar in the front SiNx layer is precisely evaluated with ellipsometry, photothermal deflection spectroscopy (PDS), and ray tracing. In the module, we reproduce the R measurements with the ray tracer and obtain R at the backsheet and the ribbon by iteration and evaluate their Lambertian factor by consistency. The ray tracing model, based on these measurements and with the achieved consistencies, then gives us an optical loss analysis of all parts of the cell and the module and allows us to evaluate possible improvements to high precision.
... 12) Direct optical coupling gain (reduced reflectance) arises because of the increasing refractive indices of the encapsulation layers. In addition, the scattering of light incident on the cell-gap area [13][14][15][16][17] (backsheet) and on the tabbing ribbons of a PV module [18][19][20][21] (Fig. 2) contributes to cell-to-module optical gains. Light scattered at an angle greater than the total internal reflection angle for the glass-air interface (approximately 42°) undergoes total internal reflection at the front glass-air interface and redirects back to the solar cell for absorption as shown in Fig. 2. ...
Reducing levelized cost of electricity (LCOE) is important for solar photovoltaics to compete against other energy sources. Thus, the focus should not only be on improving the solar cell efficiency, but also on continuously reducing the losses (or achieving gain) in the cell-to-module process. This can be achieved by choosing the appropriate module material and design. This paper presents a detailed and systematic characterization of various photovoltaic (PV) module materials (encapsulants, tabbing ribbons, and backsheets) and an evaluation of their impact on the output power of silicon wafer-based PV modules. Various characterization tools/techniques, such as UV–vis (reflectance) measurement, external quantum efficiency (EQE) measurement and EQE line-scan are used. Based on the characterization results, we use module materials with the best-evaluated optical performance to build "optimized modules". Compared to the standard mini-module, an optical gain of more than 5% is achievable for the "optimized module" with selected module materials.
... They are featuring the inherent disadvantage of a flat topside that reflects incident light out of the module which is then lost for power generation. Other concepts have been presented in the past to improve cell interconnection, for instance round wires or light harvesting connectors that have been proven to reflect more light onto the cell and show higher optical efficiencies [1][2][3][4][5][6][7][8]. ...
Different approaches like round wire interconnectors, shingled or back-contact cells have been presented in the past to improve the cell-to-module efficiency ratio by reducing the shading losses of interconnector ribbons.
We present a new cell interconnector design based on a triangular cross section to further improve modules based on interconnector ribbons. We analyze the optical behavior of the concept and compare it with rectangular ribbons and round wire interconnectors. An evaluation of the new concept using optical ray tracing is performed. Results show an advantage in optical performance of 2.35% of the new concept compared to standard interconnector ribbons under perpendicular irradiation as well as 1.94% compared to round wires. An analysis using irradiation data (DNI) shows a superior optical performance of the TriCon-Concept. We find that in an elevation tracked module using TriCon 2.32% more light reaches the cell surface over the year compared to rectangular interconnectors (5BB) and 2.02% compared to round wires.
... The highest power conversion efficiency for silicon photovoltaics of 26.3% was achieved using silicon heterojunction solar cells with IBCs. 4 Although IBCs can be considered as the best option in terms of optical performance, they are more difficult and expensive to fabricate and a front contact scheme with similar optical properties would be more desirable. Therefore tremendous research effort has been devoted to the development of more transparent TCOs, 5-10 metal grids with improved shape, [11][12][13][14][15][16] nanomaterial contacts, 17-22 sophisticated encapsulation layer geometries [23][24][25] and other approaches. 26,27 In most of these approaches, improved transparency comes at the cost of reduced electrical performance as the sheet resistance increases. ...
We demonstrate silicon heterojunction solar cells with microscale effectively transparent front contacts (ETCs) that redirect incoming light to the active area of the solar cell. Replacing standard contact electrodes by ETCs leads to an enhancement in short circuit current density of 2.2 mA cm^(−2) through mitigation of 6% shading losses and improved antireflection layers. ETCs enable low loss lateral carrier transport, with cells achieving an 80.7% fill factor. Furthermore, dense spacing of the contact lines allows for a reduced indium tin oxide thickness and use of non-conductive, optically optimized antireflection coatings such as silicon nitride. We investigated the performance of ETCs under varying light incidence angles, and for angles parallel to the ETC lines find that there is no difference in photocurrent density with respect to bare indium tin oxide layers. For angles perpendicular to the ETC lines, we find that the external quantum efficiency (EQE) always outperforms cells with flat contact grids.
... The record efficiency for a SHJ solar cell with front contacts is lower (25.1 % by Kaneka [2]) due to reflection of light at the contact finger grid and the bus bars and due to parasitic absorption within the transparent conductive oxide (TCO) layer [3] as schematically shown in Fig.1a. A huge research effort is being made to develop less absorbing TCOs [4][5][6][7][8], less reflective contact grids [9][10][11][12][13][14][15][16] and various other approaches [17][18][19][20][21] to overcome these losses. We have recently reported a new front contact design that can replace the finger grid as well as the TCO [22]. ...
... Light management approaches are crucial to further increase the efficiency of photovoltaic devices [1][2][3]. One topic that is currently under investigation within the research community is the optimization of light management in solar modules, i.e. to redirect light that is incident on optically non-active module components, such as front side contacts, to the area of the solar cell absorber material [4]. ...
We inscribed phase gratings into the cover glass of a solar module using femtosecond laser pulses to guide light around the front side metallization. Photocurrent and efficiency of the module increased by 1 % (relative).
... It has been a rather widespread concept in the PV industry, that the unique function of the PV module materials are the PV cell protection (glass, encapsulants, backsheets and frame) [5] and electrical contact establishment (tab ribbons and junction box). Nowadays, and with the aim to make profitable the whole involved materials in the PV device [6], PV module materials are being considered as an active device part which can positively contribute to solve relevant problems like potential induced degradation [7] or to improve PV module efficiency by a suitable PV cell to PV module technology transfer [8]. ...
Selective emitter diffusion technology has demonstrated a direct PV cell efficiency increase, due to a good ohmic contact and high blue response. These PV devices will be assembled to fabricate the final and commercial PV modules where the power enhancement is the most valuable one. The traditional encapsulant material is ethylene-vinyl-acetate (EVA) which ultraviolet wavelength cut off is placed in the region where selective emitter technology improvement is performed. Photovoltaic industry has developed innovate materials to overcome these issues. Among them, a low ultraviolet cut off EVA can be easily acquired. Our study demonstrates that with the correct PV module encapsulant configuration, part of the developed PV cell efficiency improvement related to selective emitter technology can be successfully translated at the end of the value chain; that is, the final PV module.
... A second attempt is to use many small round ribbons called smart wire technology (SWT) [2]. The third approach is to use the total reflection effect in combination with the glass/air interface and the structured ribbons [3][4][5][6]. These ribbons are called light harvesting (LHR) or light capturing ribbons (LCR). ...
The optical loss due to the busbar grid and soldered interconnector ribbons on a three
busbar standard multicrystalline silicon solar cell’s front side is at 2.3%. One way to
reduce this optical loss on cell level and in a photovoltaic (PV) module is to use deep
structured ribbons as cell connectors. The standard soldered, flat ribbon is replaced with
a glued, multiple structured ribbon. The investigation of shiny soldered flat ribbons and
multiple structured ribbons in single-cell mini modules demonstrates the light angle
dependency and the benefit for the structured alternative. Additional yield measurements
for conventional photovoltaic modules with soldered flat and glued multiple structured
ribbons technologies were studied under laboratory conditions as well as in outdoor
measurements. The simulations and the experimental findings confirmed that the new
structured ribbon design increases the short circuit current and the yield by about
2%.
... In the wavelength range between 400 and 1100 nm, we determine a reduction of the reflectivity from 3.7 ± 0.5% to 1.9 ± 0.5% absolute due to the ARC. Additional losses by absorption in the lamination foil can be reduced by using an encapsulant that is transparent for ultra-violet light [175][176][177]. ...
This work presents a new laser microspot welding process for the interconnection of aluminum
metallized crystalline silicon solar cells and the investigation of this process. Furthermore,
it demonstrates the application of laser welding for interconnection of back-junction
back-contacted solar cells.
In the current production, the majority of silicon solar cells is interconnected by soldering
a solder-coated copper ribbon to its front and rear side. This process induces thermomechanical
stress in the brittle silicon solar cells and demands metal surfaces free of stable
oxides, e.g., silver. In this work, a pulsed laser welding process for solar cell interconnection
is developed to minimize the mechanical stress and to omit the use of cost-intensive silver
by contacting aluminum. The interconnects consist of a 10-µm-thick aluminum layer. It is
attached to a substrate, which is transparent for the laser irradiation. A laser irradiates the
aluminum layer through this substrate in order to weld it to the aluminum metallization of
the solar cell. The so-called aluminum-based mechanical and electrical laser interconnection
(AMELI) process is analyzed for pulse durations of 20 ns and 1.3 µs and the process windows
for these laser sources are determined. The electrical contact resistivity of the laser welded
interconnections is determined to be less than 10 µΩ cm². Mechanical tear-off stresses of
up to 450 kPa are measured. Additionally, the laser induced damage to the silicon surface
passivation and silicon crystal is investigated using specially designed test structures.
Silicon samples with aluminum layers as thin as one micrometer can be electrically and
mechanically contacted without inducing any detectable laser damage.
The thermal processes involved in the laser interconnection process are investigated by
microscopic surface analysis and the finite element method simulations. They show that
a transparent substrate is indispensable for the welding process. For an aluminum layer
thickness up to 5 µm, the process is dominated by thermal diffusion. For thicker layers, the
melting at the irradiated surface that is in contact with the substrate results in material
expansion causing a breakage of the solid layer and ejection of molten aluminum.
The impact of the laser interconnection process on back-junction back-contacted solar cells
is studied. The full performance of the solar cells can be transferred to the module level
by the laser process. The modules reach efficiencies of up to 20.4%. In artificial aging,
laser interconnected modules experience no significant degradation of the fill factor after
1402 humidity-freeze cycles proving their longterm stability. Additionally, the successful
interconnection of solar cells with a thickness of 90 µm is demonstrated. To avoid losses
associated with the busbars required for solder interconnection, solar cells without busbars
are interconnected. This results in an efficiency increase from cell to module of 4% relative
and an absolute efficiency of 22.1%. Detailed analysis of the characteristic I-V -parameters
show that this increase is caused by a reduction of the series resistance by a factor of three.
This leads to module fill factors of 80.5%. Additionally, the process is further developed for
the interconnection of solar cells with two dimensional contact structures by employing the
high lateral precision of laser systems.
The results of this work suggest that laser welding is an alternative to the widely used
soldering process. Laser microspot welding enables a significant reduction of material consumption,
has proven its longterm stability, and opens new opportunities for advanced solar
cell designs with improved efficiencies.
... There is a significant interest within the industry to improve light transmission into the cell in order to increase the short circuit current of the device. One approach to accomplish this is to provide an anti-reflective coating on the front surface of the glass [184]. There is, however, very little literature on the reliability of this coating and how it might impact module performance in the long-term. ...
This article is the third and final article in a series dedicated to reviewing each process step in crystalline silicon (c-Si) photovoltaic (PV) module manufacturing process: feedstock, crystallization and wafering, cell fabrication, and module manufacturing. The goal of these papers is to identify relevant metrology techniques that can be utilized to improve the quality and durability of the final product. The focus of this article is on the module manufacturing process. The c-Si PV module fabrication process can be divided into three primary areas; (1) stringing and tabbing, (2) lamination, and (3) integration of junction box and bypass diode(s). Each of these processing steps can impact the reliability and durability of PV modules in the field. The ultimate goal of this article is to identify appropriate metrology techniques and characterization methods that can be utilized within a module manufacturing facility to improve the reliability and durability of the final product. Additionally, a gap analysis is carried out to identify areas in need of further research and a discussion is provided that addresses new challenges for advanced materials and emerging technologies.
... Light management approaches are crucial to further increase the efficiency of photovoltaic devices [1][2][3]. One topic that is currently under investigation within the research community is the optimization of light management in solar modules, i.e. to redirect light that is incident on optically non-active module components, such as front side contacts, to the area of the solar cell absorber material [4]. ...
Highly efficient volume phase gratings have been fabricated in low-iron soda lime glass using femtosecond (fs) laser pulses with 1030 nm wavelength and 270 fs pulse duration. Optical simulations based on rigorous coupled-wave analysis theory were performed to determine optimal grating parameters and designs for the application of the gratings for light management in solar modules, suggesting a very effective blazedlike design. Several of such blazed phase gratings have been fabricated and analyzed by measuring their diffraction efficiencies into first and higher orders. Up to 77% of the incoming light in the wavelength region relevant for silicon-based photovoltaics were diffracted by these gratings. Typical induced refractive index changes between 0.002 and 0.006 were derived by comparing the experimental efficiencies with the simulation results.
... Owing to light reflection on the front side of the module, the module efficiency is a little lower than the efficiency of cells. Decreasing the reflection losses is one way in which the technology is improving [25]. ...
After 30 years of development, photovoltaic (PV) technology has been recognised to be capable of contributing significantly to future energy supply. The global cumulative installed PV power now exceeds 180 GWp, and the annually installed power exceeds 40 GWp. The cost of electrical energy produced by PV systems is now close to that from conventional sources. This study discusses the physics, construction and manufacture of PV cells and modules, taking into account current trends in technology. All parts of PV systems that influence the cost of the electrical energy produced are considered. Three generations of PV module are described. Crystalline silicon (c-Si) is and will remain the dominant PV material at least until 2020 because of its high efficiency, long service time and relatively low cost. It represents nearly 90% of total module production. There are no material supply constraints to limit production and a decrease in c-Si PV module cost to below 0.4 €/Wp before 2017 can be expected. PV power generation will reach industrial grid parity before 2020 and a cumulative installed power of 1 TWp is expected before 2025.
... Another important field of applications concerns the spectral resolved loss analysis of PV modules and its components. [5] A lock-in or Fourier transform technique can be used to determine the EQE. [6] In this work, great emphasis was placed on a method which is applicable to any LED-based solar simulator. ...
A new generation of solar simulators is based on light emitting diode illumination sources. These measurement systems offer the opportunity to adjust the light spectrum as close as possible to the AM1.5G reference spectrum. Additionally, they provide the technical basis to combine power measurements with a spectral resolved analysis. Such an application is the determination of the quantum efficiency, which results in valuable additional cell information such as front and rear surface recombination, diffusion length, or emitter dead layer thickness. In this work, a fast method to determine the external quantum efficiency (EQE) of a solar cell using a LED solar simulator is presented. The measurement time of our LED-EQE approach could be reduced to less than half a second as no mechanical parts such as monochromators are involved. Due to the finite spectral band-width of the LEDs an adapted data analysis approach has been developed, which leads to results that show excellent agreement with standard EQE measurements.
This paper develops a coupled optical-electrical-thermal loss model of a photovoltaic (PV) module under various conditions. Validation shows that the coupled optical-electrical-thermal loss model is accurate and effective, ranging from 0.17% to −1.88%, which are smaller than limit error in the IEC standard. The developed model is then applied to investigate energy distributions of a PV module under standard test conditions (STC) and dynamic conditions by qualitative and quantitative evaluations. Results show that the energy distributions under dynamic conditions are similar to those under STC. The power output, optical and thermal losses are 16%, 16% and 68%, respectively. The optical losses mainly result from transmission loss (43.4%), reflection loss at air-glass interface (25.5%) and reflection loss at PV layer (25%). As for complicated thermal losses, they are caused by thermalization loss (38.4%), sub-bandgap loss (21.6%), angle mismatch loss (12.9%) and voltage drop loss due to non-radiative recombination (11.6%). Furthermore, some optical suggestions (anti-reflection film, velvet surface and light trapping structure) and thermal suggestions (up conversion, down conversion, stacked structure, surface recombination optimization and the photovoltaic/thermal technology) are proposed to optimize the PV power output.
Over the last few years, perovskite solar cells have arisen as a technology to potentially side with mainstream silicon photovoltaics to help drive the transition towards renewable sources of energy. The coupling of perovskites with silicon in a tandem configuration may accelerate this development owing to the remarkably high power-conversion efficiencies possible with such devices. However, most of the perovskite/silicon tandem achievements so far have been confined to the lab environment, with only a few reported tests under outdoor conditions, using packaged devices. Nevertheless, one of the major challenges for perovskite/silicon tandem technologies, besides scale-up, lies in the cell-to-module (CTM) translation, which for the perovskite/silicon tandem concept is complicated by perovskite-imposed constrains such as a low temperature resilience, imposing challenges regarding tabbing and lamination, as well as a high sensitivity to moisture ingress, mandating the search for adequate encapsulation materials and methods. In this article, we describe and assess these challenges in depth and give a perspective on future directions towards module design, tailored for perovskite/silicon tandem photovoltaics, combining high performance with excellent durability. Our discussion also holds relevance for all-perovskite and other emerging photovoltaic technologies seeking market entry.
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In this work, a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system has been employed to fabricate diamond-like carbon (DLC) films for the application in crystalline silicon solar cells. The morphological, structural and optical properties of the synthesised DLC films were investigated under different deposition times, different plasma discharge powers, different CH4 flow rates, and different substrate temperatures, respectively. It is shown that, when the plasma discharge power was 100 W, the CH4 flow rate was 60 sccm, and the substrate temperature was 100 °C, the synthesised DLC film features a high transmittance of 95%, a low surface reflectivity of approximately 14%, a wide optical band gap of 2.6 eV, as well as a uniform and dense texture. Subsequently, the DLC films with different thicknesses were grown on the surface of crystalline silicon solar cells as anti-reflection coatings. The solar cell current-voltage characteristic testing system was used to investigate the change of solar cell performance parameters, i.e., Jsc, Voc, FF and η. After the growth of a DLC film with a deposition time of 20 min on the surface of a crystalline silicon solar cell, the photovoltaic conversion efficiency of the solar cell increases from 4.12% to 5.2%. This work demonstrates that the DLC film has a promising application potential as an anti-reflection layer in crystalline silicon solar cells.
Ethylene-vinyl acetate (EVA) is the predominating material of choice for making the encapsulant film for photovoltaic (PV) modules. The easy accessibility, low cost, high transparency, long track record, widespread know-how on processability and performance, and to some extent, ignorance of the criticality of encapsulant film on the long-term performance of PV modules have made EVA, a dominant player in the PV industry. In parallel, due to economic reasons, the majority of encapsulant development has moved to a direction of compromising the quality to meet the cost target. In recent years, the PV industry has started recognizing, polyolefin-based encapsulants as technically superior when compared to EVA. Polyolefin-based encapsulant comes in either a crosslinked or thermo-plastic version. Thermoplastic polyolefin offers several advantages related to processability and performance over the crosslinked version. In the current study, we compare a newly developed thermoplastic polyolefin-based encapsulant and a state of the art EVA encapsulant from different aspects of fundamental material properties, like optical, thermal, mechanical, etc. and discuss their implication on the performance of a solar module.
Figure 1: Multi-domain approach in Daidalos. a) Module domain containing the glass, encapsulation, CIR, cells and back sheet. b) Front finger domain containing the fingers. c) Front texture domain containing the texture with the cells front ARC. d) Monofacial rear local contact domain containing the local contact, rear dielectric coating and a slice of the rear metallization. ABSTRACT: Today, the PV module energy conversion efficiency is below the efficiency of the cells prior to module integration. Using optical ray tracing simulations, we show how to increase module efficiencies beyond the efficiency of the solar cells. To achieve this we follow two basic principles: First, we minimize optical losses of the module components by minimizing the absorption in the glass and the encapsulation as well as by introducing multilayer glass ARC coatings that reduce the surface reflection. Second, we exploit the internal reflection at the glass-air interface by using light guiding structures in the cell gaps and as cell connects. This improves the light trapping by reducing the cell front side reflection losses. In our specific example presented in this work, the optimization leads to a module efficiency of 20.9%, which is a 0.1%abs above that of the non-encapsulated cells with an efficiency of 20.8%.
We present a module fabrication process enabling gap-free interconnection of c-Si solar cells using solder-based interconnection technology with ribbons or wires. The interconnect-shingling process increases the module efficiency by avoiding the gaps between the solar cells. The process is applicable to bifacial cells and uses well-proven interconnection technologies. In contrast to previous adhesive-based shingled modules, the current transport is supported by interconnects, thus reducing the silver consumption for the cells’ metallization and avoiding cell overlap. We lay down the cells on structured encapsulant layers to reduce mechanical stress at the cell edges during lamination. Alternatively, the lamination process can be adapted to allow the encapsulant to reflow. This also results in a low pressure at sensitive cell parts. Both approaches avoid crack formation. We demonstrate the interconnect-shingling process with a proof-of-concept module having a aperture area efficiency of 22.1%. Applying 200 thermal cycles does not cause any crack formation.
The device physics of commercially dominant diffused-junction silicon solar cells is well understood, allowing sophisticated optimization of this class of devices. Recently, so-called passivating-contact solar cell technologies have become prominent, with Kaneka setting the world's silicon solar cell efficiency record of 26.63% using silicon heterojunction contacts in an interdigitated configuration. Although passivating-contact solar cells are remarkably efficient, their underlying device physics is not yet completely understood, not in the least because they are constructed from diverse materials that may introduce electronic barriers in the current flow. To bridge this gap in understanding, we explore the device physics of passivating contact silicon heterojunction (SHJ) solar cells. Here, we identify the key properties of heterojunctions that affect cell efficiency, analyze the dependence of key heterojunction properties on carrier transport under light and dark conditions, provide a self-consistent multiprobe approach to extract heterojunction parameters using several characterization techniques (including dark J-V, light J-V, C-V, admittance spectroscopy, and Suns-Voc), propose design guidelines to address bottlenecks in energy production in SHJ cells, and develop a process-to-module modeling framework to establish the module's performance limits. We expect that our proposed guidelines resulting from this multiscale and self-consistent framework will improve the performance of future SHJ cells as well as other passivating contact-based solar cells.
Photovoltaic (PV) modules are not only an opto-electrical system, but also opto-thermal one, where the optical, electrical, and thermodynamic domains are strongly coupled. The means to suppress both light and heat losses in PV modules remains undeveloped. Herein, a universal route to realize both radiative cooling and light management via the ultra-broadband versatile textures is proposed, originating from the interaction with the visible, near-infrared, and mid-infrared electromagnetic waves (EMWs) via geometric, diffractive, and subwavelength optical effects. The sol–gel imprinted ultra-broadband textures exhibited a near-unity infrared emissivity over 0.96 at the atmospheric window between 8 to 13 μm for radiative cooling, and a solar transmittance and haze above 0.94 and 0.95 at the wavelengths from 350 to 750 nm, respectively, for light management. Applying the ultra-broadband textures imprinted glass to silicon PV modules as an encapsulant cover, the short-circuit current and conversion efficiency were increased by 5.12 and 3.13% in relative terms, respectively. The fabrication of such ultra-broadband versatile textures was photolithography-free, scalable, and PV industry compatible, which provided a cost-effective, long-term durable, and energy-efficient means to both light and thermal management through ultra-broadband matter-EMW interaction not only in PV modules, but also various opto-electro-thermal devices.
We reported a facile and bio-inspired strategy for obtaining antireflective (AR) coating through polymerization-induced self-wrinkling. Upon irradiation of light, the complex wrinkle micro-patterns with different morphologies were generated spontaneously on the surface of coating during photo-cross-linking, which enables the photo-curing coating can decrease reflection. The resulting photo-curing coating exhibits a high transmittance over 90% and low reflection below 5%. ∼. 8%, with an efficiency anti-reflection of 4% ∼ 7% compared to the flat blank coating. The successful application of these AR coatings with wrinkles pattern to encapsulate the thin film solar cells results in appreciable photovoltaic performance improvement of more than 4%. ∼. 8%, which benefits from the decrease of the light reflection and increase of optical paths in the photoactive layer by the introduction of wrinkling pattern. Furthermore, the efficiency improvements of the solar cells are more obvious, with a remarkable increase of 8.5%, at oblique light incident angle than that with vertical light incident angle.
This work demonstrates a performance improvement of state-of-the-art silicon solar cells by cloaking their metal contact fingers. The cloaking free-form surfaces are fabricated on silicon heterojunction solar cells using direct laser writing of polymers and subsequent soft imprinting. Cloaking performance is determined experimentally by measuring spatially resolved and angle-resolved current generation and the spectral response of the cell. The short-circuit current density of the cell increases by 7.3%; its power-conversion efficiency is enhanced by 9.3%. Overcompensation of the shadowing loss is found to be caused by improved light-gathering and light-trapping in the polymer layer. The experimental findings are in good agreement to ray-tracing simulations.
We process a photovoltaic (PV) module with 120 half passivated emitter and rear cells that exhibits an independently confirmed power of 303.2 W and a module efficiency of 20.2% (aperture area). The cells are optimized for operation within the module. We enhance light harvesting from the inactive spacing between the cells and the cell interconnect ribbons. Additionally, we reduce the inactive area to below 3% of the aperture module area. The impact of these measures is analyzed by ray-tracing simulations of the module. Using a numerical model, we analyze and predict the module performance based on the individual cell measurements and the optical simulations. We determine the power loss due to series interconnection of the solar cells to be 1.5%. This is compensated by a gain in current of 1.8% caused by the change of the optical environment of the cells in the module. We achieve a good agreement between simulations and experiments, both showing no cell-to-module power loss.
A key for increasing the module efficiency is improved light harvesting. The structuring of solar cell interconnection ribbons (CIR) is a promising option for improved light harvesting as it can easily be integrated into current module production. We perform ray tracing simulations of complete PV modules in 3D exhibiting geometric features such as profiled CIR and surface textured cells. We evaluate the increase in module performance by a light harvesting string (LHS) under realistic irradiation conditions with respect to angular and spectral distribution. Using the realistic irradiation for a location in Germany, a location at the polar circle and a location at the equator we simulate the enhancement of short-circuit current density Jsc resulting from the use of LHS. Our results show Jsc gains between 1.00% and 1.86% depending on the location and module orientation. We demonstrate the applicability of our model by comparing measurements and simulations for a one-cell module that we measure and simulate under various angles of the light incidence.
Effectively transparent front contacts for optoelectronic devices achieve a measured transparency of up to 99.9% and a measured sheet resistance of 4.8 Ω sq^(−1). The 3D microscale triangular cross-section grid fingers redirect incoming photons efficiently to the active semiconductor area and can replace standard grid fingers as well as transparent conductive oxide layers in optoelectronic devices.
We employ coordinate transformations to design two different optical structures for cloaking of reflective front contacts on solar cells. The cloaking performance is verified in a proof-of-principle experiment and using ray tracing simulations.
Recent reports about new cell efficiency records are highlighting the continuing development of passivated emitter and rear cells (PERC). Additionally, volume production has started, forming the basis for cutting edge solar modules. However, transferring the high efficiency of the cells into a module requires an adaptation of the conventional front metallization and of the cell interconnection design. This paper studies and compares the module output of various cell interconnection technologies, including conventional cell interconnection ribbons and wires. We fabricate solar cells and characterize their electrical and optical properties. From the cells, we build experimental modules with various cell interconnection technologies. We determine the optical and electrical characteristics of the experimental modules. Based on our experimental results, we develop an analytical model that reproduces the power output of the experimental modules within the measurement uncertainty. The analytical model is then applied to simulate various cell interconnection technologies employing halved cells, optical enhanced cell interconnectors, and multiwires. We also consider the effect of enhancing the cell-to-cell spacing. Based on the experimentally verified simulations, we propose an optimized cell interconnection for a 60-PERC module that achieves a power output of 323 W. Our simulations reveal that wires combined with halved cells show the best module performance. However, applying light-harvesting structures to the cell interconnection ribbons is an attractive alternative for upgrading existing production lines.
In order to interconnect industrial solar cells with a front grid pattern, flat solder-coated copper wires are usually soldered to 2 or 3 busbars on the front surface. In order to minimize the resistive power loss in the wires and minimize stress in the cells, these wires are thin and wide, and the shading of the cells by these wires represents a significant power loss in the encapsulated modules. In order to eliminate this power loss component, researchers are exploring more complicated and expensive cell designs whereby all contacts are either placed on or are led to the rear side of the cells. We have developed a much simpler and more cost effective solution whereby the effective shading of the wires is greatly reduced. This is accomplished by forming triangular grooves on the top surface of the wire and coating the surface with a reflective layer such as silver. The grooves are designed so that incident light is reflected up toward the glass coversheet of the module at an angle shallow enough that it undergoes total internal reflection at the glass-air interface and is reflected back down onto the solar cell. As much as 80% of the light hitting the busbars can potentially be recaptured. Experiments with industrial solar cells have shown a 2% relative gain in encapsulated cell current and power with use of this light-capturing interconnect wire as compared to the controls with standard wire. Further gains are expected with reoptimization of the wire width. Only minor modifications are needed to a tabber-stringer to enable the use of this wire. A method to manufacture and store the wire has been developed by Schlenk Metallfolien, and sampling has begun to interested module manufacturers. Module reliability tests are ongoing, but initial data on thermal cycling and damp heat testing shows no degradation in the short circuit current benefit vs. the controls. The concept applies to interconnection of discrete thin-film cells as well as to Si-wafer cells.
The polyvinyl butyral (PVB) encapsulant material is being evaluated as a candidate for use in photovoltaic solar cells encapsulation process due to high stability against UV radiation and the high adhesive force to glass. This material is used for a long time in automotive technology, building integrated vitrification and security glazing. The long experience in this sector can direct be carried over to the photovoltaic industry. The purpose of this experimental investigation is to better understand the electrical properties and thermal stability of PVB based encapsulant material and their dependence on temperature will be presented. An overview of some main electrical and thermal properties of PVB is compared to EVA.
Optical losses in a photovoltaic (PV) module consist of reflectance (R) losses and parasitic absorptance losses (Apara.mod) in the front layers of the module. In this paper, a method for quantifying the optical losses associated with the cover glass and the encapsulant material of silicon wafer based PV modules is presented. The method involves measuring the spectral reflectance (R) and the full-area external quantum efficiency (EQE) of a silicon wafer solar cell before and after encapsulation. The approach used is to first obtain the full-area internal quantum efficiency (IQE) of the cell using R and EQE of the cell before encapsulation. Assuming that the IQE of the cell is not changed by the encapsulation process, the spectrally resolved parasitic absorptance loss (Apara.mod) associated with the cover glass and the encapsulant material is calculated with the aid of EQE and R measurements of the encapsulated cell. Using this method, the optical losses (at near normal incidence) of single-cell monocrystalline silicon wafer PV modules with various glass structures (textured, planar, antireflection coated) and encapsulant materials (EVA, ionomer) are investigated and compared. Ionomer encapsulated modules are found to show higher Apara.mod because of a higher absorption coefficient of the material. Modules with textured glass show a higher Apara.mod due to the longer optical pathlength resulting from refraction of light at the glass-air interface.
This paper reports on a set of experiments to determine what efficiency gain can be achieved by using AR coated glass and to evaluate the weatherability of the coatings. AR coated glass from three different vendors was evaluated by building and testing full size modules. Only one of the three vendors' glass produced consistent increases in STC efficiency on the order of 2.4 to 3%. All of the three types of coated glass successfully passed the accelerated stress tests from IEC 61215. Modules made with the glass that consistently produced STC efficiency gains were then deployed outdoors for extended time periods in order to measure the energy production. Preliminary results indicate that the energy production difference between the AR coated glass and the standard low iron glass is in excess of the gain measured at STC. A pilot run of 231 modules achieved a similar STC efficiency gain. Modules from this trial have now been deployed outdoors to in a large system to determine energy gain from the AR coated glass.
In this work, we report a very efficient and low-cost method to estimate the cell-to-module (CTM) power loss of 60-cell module from one-cell module. Moreover, we compare two different kinds of Selective Emitter (SE) solar cell with Homogeneous Emitter (HE) solar cell. According to one baseline experiment of real 60-cell PV module, one model is built to qualitatively estimate PV module performance from one-cell level by considering optical effect and electrical effect. In this case, we compare two different kinds of SE cells and one HE cell. SE cells with higher blue response have higher CTM power loss after module due to the higher absorption in the short wavelength range of encapsulated materials.
Optical losses in a photovoltaic (PV) module consist of reflectance losses and parasitic absorptance losses in the front layers of the module. A method for quantifying the optical losses associated with the cover glass and encapsulant material of silicon wafer based PV modules is presented. The method involves measuring the spectral reflectance (R) and the external quantum efficiency (EQE) of a silicon wafer solar cell before and after encapsulation. The approach used is to first obtain the internal quantum efficiency (IQE) of the cell using R and EQE of the cell before encapsulation. Assuming that the IQE of the cell is not changed by the encapsulation process, the spectrally resolved parasitic absorptance loss (Apara.mod) associated with the cover glass and the encapsulant material is calculated with the aid of EQE and R measurements of the encapsulated cell. Using this method, the optical losses (at near normal incidence) of single-cell multicrystalline silicon wafer PV modules with two different ethylene vinyl acetate (EVA) encapsulants (conventional and super-clear EVA) are investigated and compared. Compared to conventional EVA, the module encapsulated with super-clear EVA is found to have much lower Apara.mod at short wavelengths.
As an evaluation method of the photovoltaic (PV) system, it is necessary to clarify loss factor which decreases system efficiency. One of the factors mentioned is the reflection loss that depends on an incident angle. It is believed that the factor is simulated by reflections and transmissions in a module. Using the optical performance of a four-layer encapsulation, a simulation was made on the reflection loss according to Fresnel's law. Further, the incident angle modification factor as the coefficient for evaluating energetic reflection loss was described by a computer program simulation. The result was that the modification factor is between 0.96 and 0.98. Consequently, to obtain the optical property of module materials, the module tilt angle and its latitude location, the simulation could give the evaluation of annual reflection losses by such a factor at various regions.
An optical model for arbitrary layers is developed and a one-dimensional steady-state thermal model is applied to analyze the energy balance of silicon solar cell modules. Experimental measurements show that simulations are in good agreement, with a maximum relative error of 8.43%. The wind speed vwind, ambient temperature Tamb and irradiance G are three main factors influencing the temperature of a photovoltaic panel. Over the course of a day the electrical output is reduced by the module temperature to only 32.5% of the rated value. Optical studies reveal that before 8:00 hours and after 16:00 hours, significant incident energy is lost by reflection because of the large angle of incidence θin, while at other times of day optical losses are nearly the same due to only small changes of transmission for θin
An industrial sol–gel process to coat solar glass with a porous SiO2 antireflection (AR) layer has been recently developed. This paper presents the first detailed study obtained on sets of commercial multicrystalline silicon solar cells encapsulated with patterned low-iron glasses, with or without this AR coating. Measurements under standard test conditions (STC) show a current gain of 2.65% with the AR glass, whereas an additional current gain is obtained at high light incidence angle. Based on the mini-module results and on the outdoor monitoring of test modules to evaluate temperature effects, simulations were performed to asses the yearly photovoltaic energy yield gain at different locations. A significant energy yield increase of 3.4–3.7% is expected with the new AR glass.
Herstellung und Veredlung von Dünnglas für PV-Anwendungen, 9 Photovoltaik- Modultechnik
- T Keyser
Keyser T. Herstellung und Veredlung von Dünnglas
für PV-Anwendungen, 9. Workshop " Photovoltaik-
Modultechnik ", TÜV Rheinland, Köln (2012).
Optical loss reduction by combining innovative solar module technologies
- J Schneider
Optical loss reduction by combining innovative solar module technologies
J. Schneider et al.