Martin C. Schubert

Martin C. Schubert
Fraunhofer Institute for Solar Energy Systems ISE | ISE

Dr. rer. nat.

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252
Publications
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5,560
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Publications

Publications (252)
Article
One drawback of passivating contacts in crystalline silicon solar cells is the current loss due to parasitic absorption within the involved material layers. When employed on an illuminated side of the cell, the full spectrum of the incident light will be partly absorbed before reaching the silicon bulk. Additionally, near-infrared (NIR) absorption...
Article
Full-text available
Gallium-doped silicon material has been rapidly gaining importance in the photovoltaic industry as a boron-oxygen defect-free material with promising minority carrier lifetime. We investigate the influence of different cell process flows [passivated emitter and rear cell tunneling-oxide-passivating contact, and a “hot oxidation” process] on the bul...
Article
In order to push silicon solar cell efficiencies further towards their limit, as well as to ensure accuracy of luminescence based characterization techniques, an accurate modeling of radiative recombination is important. It is well-known that the radiative recombination coefficient Brad of silicon shows a substantial charge carrier density dependen...
Article
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Recent progress in surface passivation technology and wafer pretreatment already resulted in significant improvements in the achievable minority charge carrier lifetime of crystalline silicon. This work further exemplifies this by studying the lifetime on lowly doped crystalline silicon wafers passivated by poly-Si. To ensure credible lifetime meas...
Article
Full-text available
By investigating the formation of the light‐ and elevated temperature‐induced degradation (LeTID) defect under dark annealing conditions alongside the formation of the boron‐hydrogen‐complex, we have found both formations being limited by presumably the same reaction. Starting with this observation, two possible mechanisms of LeTID defect formation...
Article
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Czochralski‐grown gallium doped silicon wafers are now a mainstream substrate for commercial passivated emitter and rear (PERC) solar cells and allow retention of established processes while offering enhanced cell stability. We have assessed the carrier lifetime potential of such Czochralski‐grown wafers in dependence of resistivity, finding effect...
Article
Full-text available
Commercial silicon is prone to form silicon oxide precipitates during high-temperature treatments typical for solar cell production. Oxide precipitates can cause severe efficiency degradation in solar cells. We have developed a model describing the nucleation and growth of oxide precipitates that considers silicon self-interstitial defects and surf...
Article
The interest in cast mono silicon is increasing due to its lower energy consumption and resulting smaller carbon footprint, lower oxygen content and resulting less oxygen-related defects as well as easy scalability to large wafer formats like 210 × 210 mm² full square. As a cast silicon alternative to high performance multicrystalline (hpm) silicon...
Article
Full-text available
Czochralski-grown gallium-doped silicon wafers are now a mainstream substrate for commercial passivated emitter and rear cell (PERC) devices and allow retention of established processes while offering enhanced cell stability. We have assessed the carrier lifetime potential of such Czochralski-grown wafers in dependence of resistivity, finding effec...
Article
Full-text available
The effect of light- and elevated temperature-induced degradation (LeTID) can be nonpermanently reversed by charge carrier injection below the degradation temperature (commonly used degradation temperatures are above ~70 °C). In this study, we show that the rate of temporary recovery depends strongly on the excess carrier density. We observe that t...
Article
As the electrical characteristics of silicon solar cells depend significantly on their temperature T of operation, it is vital to analyze and understand the contributions of the various cell properties in detail in order to optimize silicon solar cells for improved energy output in realistic operation conditions. Within a detailed electro-optical s...
Article
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An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
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This review explores the current state of the art in spatially resolved characterization of mixed‐halide perovskite solar cells. As the size of perovskite cells and modules continues to grow, quantification of the spatial distribution of key cell parameters will become increasingly valuable in predicting ultimate cell‐level performance and tracking...
Article
Full-text available
The silicon surface texture significantly affects the current density and efficiency of perovskite/silicon tandem solar cells. However, only a few studies have explored fabricating perovskite on textured silicon and the effect of texture on perovskite films because of the limitations of solution processes. Here we produce conformal perovskite on te...
Article
Full-text available
In this paper we present a contactless transient carrier spectroscopy and imaging technique for traps in silicon. At each pixel, we fit the transient decay of the trap emission which allows us to obtain both the trap time constant and trap concentration. Here we show that this technique allows for high-resolution images. Furthermore, this technique...
Poster
Full-text available
The poster shows investigations of the lifetime at the highest level. We reached a lifetime of 135 ms on p-type material and a lifetime of 1/3 s on n-type material. We determine the J0 for the surface as well as the limitation of the lifetime, possibly by SRH recombination.
Article
Hybrid metal halide perovskite‐based thin‐film photovoltaics have the potential to become the next generation of commercialized PV technology with certified power conversion efficiencies reaching 24 % on 0.1 cm2 area devices. Recent efforts in upscaling of this technology resulted in an efficiency of 12.6 % for 354 cm2 modules. Still, upscaling los...
Conference Paper
Full-text available
In this work the existing SRH parametrizations for the FeGa defect are re-evaluated by a deliberately iron contaminated sample set of varied doping densities. The evolution of the cross-over point is analyzed for this aim, due to its characteristic dependency on the defect parameters of the metastable iron states. It can give insight into the defec...
Conference Paper
In this work we present results of a series of experiments to investigate the origin of the defects causing light and elevated temperature induced degradation (LeTID). It has been demonstrated that LeTID effects can be observed even in high purity monocrystalline silicon. The experiments are therefore performed on float-zone silicon and feature a v...
Conference Paper
Edge losses in silicon solar cells are becoming more important in current photovoltaic research, especially in shingled cell modules with high perimeter to area ratios. Hence, in this study a new approach is presented to quantify edge recombination losses by using photoluminescence (PL) measurements combined with device modelling. The main focus of...
Conference Paper
Full-text available
To understand and maximize the annual energy output of silicon based photovoltaic modules beyond standard testing conditions (STC) it is of utmost importance to get insight into the temperature dependent device properties of silicon solar cells. In this study we demonstrate an approach which allows for both a global and a local characterization of...
Preprint
To maximize the annual energy output of silicon based photovoltaic modules beyond standard testing conditions (STC), it is important to assess temperature dependent device properties of silicon solar cells. In this study we characterize the temperature dependence of the dark saturation current density J 0 of diffused regions (e.g. emitter layers)....
Article
Multicrystalline solar cells made from n‐type silicon feedstock have shown record efficiencies of 22.3% in a TOPCon cell structure. Still, material related carrier recombination limits the attainable efficiency. In this article, we summarize findings of metallic impurity and structural defect concentration present in n‐type mc silicon and elaborate...
Article
In this study, we present a method to predict the local temperature-dependent performance of silicon solar cells from wafer lifetime images, which enables local investigation of silicon solar cell parameters under realistic operation conditions. The multicrystalline silicon wafers investigated underwent high-temperature steps equivalent to emitter...
Article
Full-text available
Understanding the origin of thermomechanical stress in solar cells is a key factor to extend the lifetime of photovoltaic modules. However, the methods to determine the stress are very limited. With the confocal micro-Raman spectroscopy, we present a contactless method, which is able to measure through the front glass and is well-known in the field...
Article
In this work, the established method of iron imaging is transferred from B‐doped silicon to Ga‐doped material. For this purpose, the pairing and splitting conditions are investigated and a preparation procedure suggested that ensures a sufficient fraction of iron–gallium pairing and splitting, respectively. Furthermore the defect parameters availab...
Article
In order to systematically improve perovskite-based solar cell technologies, it is crucial to identify performance limits and determine both global and local loss mechanisms quantitatively. One of the most important steps toward competitiveness is the upscaling of perovskite solar cells, which can be achieved, e.g., via solution-based blade coating...
Article
We present a novel method to analyze the local current-voltage I-V characteristics of both solar cells and cell precursors. The method, which we call “Suns-ILIT”, is based on illuminated lock-in thermography (ILIT) measurements and photoluminescence imaging (PLI) in open-circuit conditions with varying illumination intensities. Compared to conventi...
Conference Paper
Full-text available
In this study, we present a method to predict the local temperature dependent performance of silicon solar cells from wafer lifetime images which enables local investigation of silicon solar cell parameters under realistic operation conditions. The multicrystalline silicon wafers investigated underwent high temperature steps equivalent to emitter d...
Article
Correlations between defect-related luminescence (DRL) and recombination mechanisms of multicrystalline silicon wafers are investigated by hyperspectral photoluminescence (PL) imaging at cryogenic temperatures (∼80 K) and by PL-based techniques for charge carrier lifetime at room temperature. This unique combination of measurement techniques is use...
Article
The main goal of a solar cell's contact is to simultaneously minimize the contact resistivity ρ $_\text{cont}$ and the effective recombination, the latter often expressed via $J_\text{0, cont}$ . To model the resulting solar cell characteristics, the simplest approach is to use those two measurable quantities as an effective boundary condition. W...
Article
Photoluminescence imaging is a fast and powerful technique to extract information about the nonuniformity of the recombination properties of silicon wafers and solar cells. In conventional photoluminescence imaging, where a uniform illumination is used, lateral carrier flows within the sample lead to smeared and quantitatively inaccurate results. I...
Article
N-type multicrystalline silicon (mc-Si) is a promising alternative to the dominant p-type mc-Si for solar cells because it combines the cost advantages of mc-Si while benefiting from higher tolerance to transition metal contamination. A detailed understanding of the relative roles of point defect and precipitated transition metals has enabled advan...
Conference Paper
We demonstrate a novel method to measure the lateral distribution of the recombination current without an external load, hence without the need to establish an electrical contact. In combination with photoluminescence imaging, which can be used to calculate the lateral implied open-circuit voltage iVOC distribution, accurate local current-voltage I...
Conference Paper
Full-text available
GLOBAL cell efficiencies are measured at standardized testing conditions (STC) to be able to compare technology improvements worldwide in a systematic manner. However, these STC are rarely met in real operation conditions of solar cells as especially temperature and irradiation intensity differ a lot to laboratory standards. In this study we presen...
Conference Paper
Silicon is the most studied semiconductor, having almost every aspect of it being investigated. All this information is spread over a large set of publications, review articles and textbooks and cannot be found in a single location. Furthermore, the available data is not always consistent and depends on the techniques and samples used. This problem...
Article
We report on the formation of wrinkle-patterned surface morphologies in cesium formamidinium based CsxFA1-xPb(I1-yBry)3 perovskite compositions with x = 0–0.3 and y = 0–0.3 under various spin-coating conditions. By varying the Cs and Br content, perovskite precursor solution concentration, and spin-coating procedure, the occurrence and characterist...
Article
Full-text available
A central quantity to assess the high quality of monocrystalline silicon (on scales beyond mere purity) is the minority charge carrier lifetime. We demonstrate that the lifetime in high purity float zone material can be improved beyond existing observations, thanks to a deeper understanding of grown-in defects and how they can be permanently annihi...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
In this work, we show the latest progress in the confocal micro-Raman spectroscopy for determination of stress within embedded solar cells. We present measurements proving that the module front glass has no influence on the stress measurement. We also present the first large area stress mapping on a quarter solar cell within a single-cell laminate....
Article
In this contribution, we present our recent results for high efficiency multicrystalline silicon solar cells. Based on n-type high-performance multicrystalline silicon substrates in combination with the TOPCon solar cell concept featuring a full area passivating back contact and a boron-diffused emitter as well as a plasma-etched black-silicon text...
Article
An approach that determines the charge carrier lifetime from photoluminescence (PL) imaging that is virtually not affected by lateral charge carrier drift and diffusion and image smearing due to photon scattering is proposed. The approach attempts to create a laterally uniform charge carrier density within a sample with non‐homogeneous recombinatio...
Article
Full-text available
A new approach to model edge recombination in silicon solar cells is presented. The model accounts for recombination both at the edge of the quasi-neutral bulk as well as at an exposed space-charge-region (SCR), the latter via an edge-length-specific diode property with an ideality factor of 2: a localized J $_{02}$ , $_{edge}$ . The model is imple...
Chapter
In the following sections some practical aspects of using lock-in thermography in the functional diagnostics of electronic components will be discussed and illustrated by measurement examples of a typical, thermally thin sample (solar cell) and a thermally thick one (integrated circuit). All these discussions are based on the theoretical findings p...
Chapter
In Sect. 3.1, a number of thermography and lock-in thermography approaches from literature are described and discussed, both steady-state and non-steady-state, showing the large variety of thermography measurement possibilities. Many of these systems are not called thermography but rather thermo-AFM, or photothermal or thermo-elastic investigations...
Chapter
Some applications of Lock-in Thermography for the investigation of a thermally thin sample (solar cell) and a thermally thick one (IC) were already presented in the examples given in Chap. 5. In the following section we will present some more applications, showing the universal applicability of this technique to different fields of functional diagn...
Chapter
In this book, the technique of lock-in thermography is being reviewed with special emphasis on its application to the characterization and functional testing of electronic components. The investigation of shunting phenomena in solar cells, which our lock-in thermography originally was developed for, among a lot of other applications is presented to...
Chapter
First, in Sect. 2.1 the general basics of infrared (IR) thermography are briefly reviewed, which are also applicable to IR camera based lock-in thermography. In Sect. 2.2, the principles of the lock-in technique itself and of its digital realization are described.
Chapter
The following sections will outline the heat diffusion theory underlying lock-in thermography experiments. First, in Sect. 4.1, the effects of the heat conduction on the surrounding of the sample will be discussed, presenting the definitions of a thermally thin and a thermally thick sample, and of the quasi-adiabatic state of a measurement. In Sect...
Article
An accurate electrical device characterization of hybrid organic-inorganic halide perovskite solar cells (PSCs) is an important prerequisite for further improvement and industrial transfer of this promising photovoltaic technology. In this work, we study the nonlinearity of current versus irradiance as well as the temperature dependence of PSCs in...
Article
This paper discusses degradation phenomena in crystalline silicon. We present new investigations of the light- and elevated temperature-induced degradation of multicrystalline silicon. The investigations provide insights into the defect parameters as well as the diffusivity and solubility of impurity species contributing to the defect. We discuss p...
Article
Full-text available
Relating crystallization of the absorber layer in a perovskite solar cell (PSC) to the device performance is a key challenge for the process development and in-depth understanding of these types of high efficient solar cells. A novel approach that enables real-time photo-physical and electrical characterization using a graphite-based PSC is introdu...
Article
Multicrystalline (mc) n-type silicon has proven to be a suitable substrate for the fabrication of highly efficient mc-Si solar cells. In this paper, we elaborate the impact of base material parameters on the efficiency potential of n-type mc-Si solar cells featuring a boron-diffused front side emitter and a full-area passivating rear contact (TOPCo...
Article
A study of the spatial occurrence of iron precipitation in a high performance multicrystalline silicon (HPMC-Si) sample is presented. The separated effects of grain-boundaries, sparse intra-granular dislocations, and dislocation clusters are investigated by combining the Fei imaging method with glow discharge mass spectroscopy, electron backscatter...
Article
Full-text available
Minimizing carrier recombination at interfaces is of extreme importance in the development of high-efficiency photovoltaic devices and for bulk material characterization. Here, we investigate a temporary room temperature superacid-based passivation scheme, which provides surface recombination velocities below 1 cm/s, thus placing our passivation sc...
Article
Full-text available
In this contribution, we demonstrate a route for efficiencies exceeding 22% with n-type multicrystalline (mc) silicon solar cells based on the TOPCon cell concept featuring a boron-diffused front side emitter and a full-area passivating rear contact. By applying a “high-performance” (HP) crystallization process with an adapted seed structure in ord...
Article
Full-text available
Light- and elevated temperature-induced degradation (LeTID) in multicrystalline silicon can reduce the efficiency of solar cells significantly. We analyse the influence of the firing temperature profile on the degradation behaviour of neighbouring mc-Si wafers, varying peak temperatures above 800°C (measured) as well as heating and cooling ramps. T...
Article
Confocal micro-Raman spectroscopy allows for spatially resolved measurements of the phonon energy in silicon, which is correlated to mechanical stress. Mechanical stress is a tensorial quantity. For the confocal measurement geometry and certain crystal orientations approximations have been derived in the past which correlate the shift of the Raman...
Article
Full-text available
For solar cell application, the stability of interface passivation quality to in-field conditions is crucial. We have performed an experiment to test the resilience of different aluminium oxide based passivation schemes to illumination at 75 °C. Different thermal treatments to activate the passivation and/or simulate contact firing were performed b...
Conference Paper
Full-text available
A new approach to model the impact of edge recombination within silicon solar cells using a 3D simulation of the entire cell geometry within Quokka3 is presented. The contribution of edge recombination within the space charge region (SCR), which is not directly accounted for in Quokka3's skin concept, is included by an effective property, a localiz...