Figure - available from: Advanced Functional Materials
This content is subject to copyright. Terms and conditions apply.
a) Schematic of PCBM photodimerization and thermal decomposition processes in a supported thin film, as well as simultaneous exposure to light and thermal stress following a time‐varying profile, relevant for the practical use of solar cells. Conditions of b) isothermal stress and c) thermal ramping, with (red) and without (black) illumination. The top panels show the PCBM dimer concentration estimated by UV–vis spectroscopy (shown here for a 0.65:0.35 PS:PCBM sample); the middle and bottom panels show the temperature and illumination profiles (1 Sun equivalent). Shaded areas correspond to conditions of neutron reflectivity (NR) measurements and markers (▶) indicate points of AFM measurements. All samples used in this study have the architecture Si/PEDOT:PSS/PS:PCBM and varying blend ratios, with φ(PCBM) = 0.2, 0.35, 0.5, 0.65, 0.8 mass fraction.
Source publication
The combined effects of illumination and thermal annealing on the morphological stability and photodimerization in polymer/fullerene thin films are examined. While illumination is known to cause fullerene dimerization and thermal stress their dedimerization, the operation of solar cells involves exposure to both. The competitive outcome of these fa...
Similar publications
Piezoelectric structures on flexible substrates are fabricated by using spray deposition of polyvinylidene fluoride (PVDF) film on conductive polymer, serving as electrode. The spray deposition conditions are optimized in term of uniform film with high piezoelectric phase content. It was found that the best piezoelectric dynamic and static response...
As a thermoelectric (TE) material suited to applications for recycling waste-heat into electricity through the Seebeck effect, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) is of great interest. Our research demonstrates a comprehensive study of different post-treatment methods with nitric acid (HNO3) to enhance the ther...
We demonstrate a flexible and light-weight supercapacitor based on bacterial nanocellulose (BNC) incorporated with tin oxide (SnO2) nanoparticles, graphene oxide (GO) and poly(3,4-ethylenedioxyiophene)-poly(styrenesulfonate) (PEDOT:PSS). The SnO2 and GO flakes are introduced into the fibrous nanocellulose matrix during bacteria-mediated synthesis....
In order to achieve a high performance-to-cost ratio to photovoltaic devices, the development of crystalline silicon (c-Si) solar cells with thinner substrates and simpler fabrication routes are important steps. Thin-film heterojunction solar cells (HSCs) with dopant-free and carrier-selective configurations look like ideal candidates in this respe...
Citations
... [19] This is valid for most binary blend systems and highly related to the material selection. Typically, fullerene derivative acceptors are known to present aggregation and phase coarsening forming oversize domains and large crystals even under slight thermal stress due to their diffusive ability with spherical structure, [20,21] which are detrimental to exciton dissociation, photo-generated charge carrier and consequently short-circuit current density (J SC ). [22,23] Moreover, the spontaneous spinodal demxing of deeply quenched polymer:fullerene blends occurs even at room temperature, resulting in abnormal burn-in degradation with large J SC loss at the early stage of device operation. ...
Organic solar cells (OSCs) achieved performance booming benefiting from the emerging of non‐fullerene acceptors, while inadequate device stability hampers their further application. At present, the prevalent belief attributes the inevitable thermal degradation of OSC device to morphological instability caused by excessive phase separation and crystallization in the active layer during device operation. However, it is inapplicable for state‐of‐art Y6‐based devices which strongly degrade before large‐scale morphology change. Herein, an alternative degradation mechanism is elucidated wherein molecular orientation change and demixing induced performance degradation in Y6‐based devices. Distinct from IT‐4F‐based counterpart, Y6‐based devices suffer severe thermal degradation dominated by open‐circuit voltage (VOC) and fill factor (FF) losses. The VOC loss is attributed to molecular orientation transition of polymer donors from edge‐on to face‐on, leading to a strong built‐in potential reduction and increase in non‐radiative loss due to energy level shifting. As for FF decay, discontinuous acceptor phases result in electron mobility decrease by over orders of magnitude, originating from the increased molecular stacking and phase separation. This work reveals the thermal degradation mechanism for Y6‐based devices and correlates the photoelectric properties with morphology instability, which will offer guidance for improving the stability of high‐performance OSCs.
... Fullerene derivatives as the most extensively employed guest components with short-wavelength absorption still suffer from the defects of intrinsic instability and decreased film robustness owing to the formation of dimers or clusters under light irradiation. [15][16][17][18] As for the morphology optimization, the addition of third component possibly produces adverse effects on the original optimized nanoscale phase-separated morphology by deteriorating the balance of the binary system. [11,19,20] Thus, the third component needs to be meticulously and elaborately designed in order to simultaneously improve all photovoltaic parameters. ...
Fluorination strategy is demonstrated to be a successful approach for optimizing the electron distribution and morphology of organic photovoltaic materials. The previous works focus on introducing only a few C(sp²)─F bonds into conjugated backbone or C(sp³)─F bonds into sidechains. Herein, a new strategy by introducing C(sp³)─F polyfluoride unit into the backbone is proposed, wherein the fluorine atoms are not involved into the conjugation but can promote the intermolecular interaction between backbones. Two wide‐bandgap fluoropolymers are prepared and employed as the third component for ternary organic solar cells. As expected, even if there are six fluorine atoms in a single repeat unit, the relevant fluoropolymers possess complementary absorption and aligned energy levels. More importantly, the polyfluoride backbone affords adequate non‐covalent interactions, consequently enhancing the polymer aggregation and packing order, which is verified by a fibril‐like morphology in the blend film with the host polymer PM6 and only 10 wt.% fluoropolymer. In addition, the decreased surface energy caused by polyfluoride unit is beneficial for the improvement of domain purity and the formation of nanoscale phase separation between donor and acceptor materials. As a result, the fluoropolymer‐assisted ternary device displays a higher efficiency of 18.74% compared with the binary device (17.39%).
... Under real operation conditions, the possible factors concurring to the degradation of new PV devices' generation may arise from an intrinsic instability (such as carrier recombination [41], phase separation [42] and residual lattice strain [43]) of the devices, as well as from extrinsic factors, such as mechanical stress [44], irradiation [45,46], heating [47,48] and exposure to O 2 and H 2 O [49][50][51]. In particular, thermal degradation [52][53][54], photo-oxidation [55,56] and other photo-chemical/photo-physical processes [45,57,58] were found to dramatically affect the morphology of the active layer as well as of the carrier's transport layers and the contact interfaces, with consequent detrimental effects on the overall performances of the device [59][60][61]. ...
In the present work, an insight on the morpho/structural properties of semitransparent organic devices for buildings’ integrated photovoltaics is presented, and issues related to interface and bulk stability are addressed. The organic photovoltaic (OPV) cells under investigation are characterized by a blend of PM6:Y6 as a photo-active layer, a ZnO ETL (electron transporting layer), a HTL (hole transporting layer) of HTL-X and a transparent electrode composed by Ag nanowires (AgNWs). The devices’ active nanomaterials, processed as thin films, and their mutual nanoscale interfaces are investigated by a combination of in situ Energy Dispersive X-ray Reflectometry (EDXR) and ex situ Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and micro-Raman spectroscopy. In order to discriminate among diverse concomitant aging pathways potentially occurring upon working conditions, the effects of different stress factors were investigated: light and temperature. Evidence is gained of an essential structural stability, although an increased roughness at the ZnO/PM6:Y6 interface is deduced by EDXR measurements. On the contrary, an overall stability of the system subjected to thermal stress in the dark was observed, which is a clear indication of the photo-induced origin of the observed degradation phenomenon. Micro-Raman spectroscopy brings light on the origin of such effect, evidencing a photo-oxidation process of the active material in the device, using hygroscopic organic HTL, during continuous illumination in ambient moisture conditions. The process may be also triggered by a photocatalytic role of the ZnO layer. Therefore, an alternative configuration is proposed, where the hygroscopic HTL-X is replaced by the inorganic compound MoOx. The results show that such alternative configuration is stable under light stress (solar simulator), suggesting that the use of Molybdenum Oxide, limiting the photo-oxidation of the bulk PM6:Y6 active material, can prevent the cell from degradation.
... For a decade, PCBM has been investigated for use in various thin-film organic electronics applications. [11][12][13][14][15] In semiconductors, PCBM is not used alone but is typically blended with C 60 and poly(3-hexyltiophene) (P3HT). PCBM-C 60 -P3HT blends are the most commonly used n-type compounds for fabricating organic solar cells. ...
Functionalized fullerenes are known as high-performance molecules. Herein, the interaction of C60 fullerene with Phenyl-C61-butyric-acid-methyl-ester (PCBM) is investigated by means of density functional theory (DFT) method to elucidate the structures and electronic states of C60-PCMB complexes. C60-PCBM blends are typically used in solar cell. Studying the electronic structure of C60-PCBM is important for elucidating the mechanism of solar cells. The intermolecular distances for C60 and PCBM dimers were calculated to be 3.70 and 2.34 Å, respectively. In C60 dimer, the five membered ring of C60 interacted with the six membered ring of neighbour C60. Two hydrogen bonds between side chains of PCBM are connected in the PCBM dimer. The binding energies were 1.4 kcal/mol (C60 dimer) and 2.6 kcal/mol (PCBM dimer). In the C60-PCBM complex, five different structures were found to be stable. The binding energies were distributed in the range 1.6-3.7 kcal/mol. The electronic states and excitation energies of C60-PCBM complexes and the basis set superposition error (BSSE) were discussed on theoretical results.
... Thus far, there have been a few reports of using PCBM as the guest component for ternary all-PSCs to improve device efficiencies 41,42 . Despite the good electron-accepting property of PCBM, its intrinsic instability remains a non-ignorable factor impairing device stability 43,44 . For instance, it has been found that PCBM molecules tend to dimerize under light illuminance and the dimerization significantly reduces the chargetransporting capacity of PCBM 45,46 . ...
Fullerene acceptors typically possess excellent electron-transporting properties and can work as guest components in ternary organic solar cells to enhance the charge extraction and efficiencies. However, conventional fullerene small molecules typically suffer from undesirable segregation and dimerization, thus limiting their applications in organic solar cells. Herein we report the use of a poly(fullerene-alt-xylene) acceptor (PFBO-C12) as guest component enables a significant efficiency increase from 16.9% for binary cells to 18.0% for ternary all-polymer solar cells. Ultrafast optic and optoelectronic studies unveil that PFBO-C12 can facilitate hole transfer and suppress charge recombination. Morphological investigations show that the ternary blends maintain a favorable morphology with high crystallinity and smaller domain size. Meanwhile, the introduction of PFBO-C12 reduces voltage loss and enables all-polymer solar cells with excellent light stability and mechanical durability in flexible devices. This work demonstrates that introducing polyfullerenes as guest components is an effective approach to achieving highly efficient ternary all-polymer solar cells with good stability and mechanical robustness.
... [11][12][13] In our previous work, film-depth-dependent light absorption spectroscopy (FLAS) was developed to determine the vertical composition distribution in films, [14][15][16] which is of low cost and easily accessible as compared with other methods, such as secondary ion mass spectroscopy (SIMS) [17][18][19] and neutron reflectivity. [20][21][22] FLAS is applied to different organic thin film samples to understand and optimize their electrical and optoelectronic properties. [23][24][25][26][27] The setup for FLAS mainly consists of a plasma etching instrument and an optical system that can measure the light absorption spectra during the etching process. ...
Organic thin films usually feature vertical phase segregation, and film-depth-dependent light absorption spectroscopy is an emerging characterization method to study the vertical phase separation of active layer films in organic electronics field. However, the interference effects on thin films can lead to optical errors in their characterization results. In this work, the interference effects on fluctuations of peak intensity and peak position of film-depth-dependent light absorption spectroscopy are investigated. Subsequently, a numerical method based on inverse transfer matrix is proposed to obtain the optical constants of the active layer through the film-depth-dependent light absorption spectroscopy. The extinction coefficient error in the non-absorbing wavelength range caused by interference effect is reduced by ∼95% compared with the traditional film-depth-dependent light absorption spectroscopy measurement. Thus, the optical properties of the thin film and quantitative spectrographic analysis based on these optical constants largely avoid the effects of interference including fluctuations of peak intensity and peak position. It is concluded that for many morphologically homogenously films, the spatial (film-depth) resolution of this film-depth-dependent light absorption spectroscopy can be optimized to be <1 nm. Subsequently, this modified film-depth-dependent light absorption spectroscopy approach is employed to simulate the local optical properties within devices with a multilayer architecture.
... NR studies can also inform the study of other energy-related materials systems and devices. This is the case for PS:PCBM (6,6-phenyl-C 61 -butyric acid methyl ester-polystyrene) thin films where NR provided essential new insight into the stability of these organic solar cell materials under operating conditions of light exposure and temperature [128]. Another example is provided by the operando NR measurements of the bulk c-Si electrode where Li + transport, distribution, and concentration were monitored inside the working electrode [129]. ...
Design and implementation of advanced membrane formulations for selective transport of ions and molecular species are critical for creating the next generations of fuel cells and separation devices. It is necessary to understand the detailed transport mechanisms over time- and length-scales relevant to the device operation, both in laboratory models and in working systems under realistic operational conditions. Neutron scattering techniques including quasi-elastic neutron scattering (QENS), reflectivity (NR) and imaging (NI) are implemented at beamline stations at reactor and spallation source facilities worldwide. With the advent of new and improved instrument design, detector methodology, source characteristics and data analysis protocols, these neutron scattering techniques are emerging as a primary tool for research to design, evaluate and implement advanced membrane technologies for fuel cell and separation devices. Here we describe these techniques and their development and implementation at the ILL reactor source (Institut Laue-Langevin, Grenoble, France) and ISIS Neutron and Muon Spallation source (Harwell Science and Technology Campus, UK) as examples. We also mention similar developments under way at other facilities worldwide, and describe approaches such as combining optical with neutron Raman scattering and X-ray absorption with neutron imaging and tomography, and carrying out such experiments in specialised fuel cells designed to mimic as closely possible actual operando conditions. These experiments and research projects will play a key role in enabling and testing new membrane formulations for efficient and sustainable energy production/conversion and separations technologies.
... In the bare PCBM case, the absorption around 310-330 nm range shows an obvious enhancement mostly due to the degradation or dimerization of fullerene, which is in agreement with previous reports. [38,45,46] The absorption of PCBM around 320-340 nm shows an enhancement and blue shift after UV aging due to the molecular structural damage. In comparison, the UV-vis absorption had almost no changes for the PCBM film with Bphen additive, as shown in Figure 2b. ...
It is crucial to make perovskite solar cells sustainable and have a stable operation under natural light soaking before they become commercially acceptable. Herein, a small amount of the small molecule bathophenanthroline (Bphen) is introduced into [6,6]-phenyl-C61 -butyric acid methyl ester and it is found that Bphen can stabilize the C60 -cage well through formation of much more thermodynamically stable charge-transfer complexes. Such a strengthened complex is used as an interlayer at the in-light perovskite/SnO2 side to achieve a champion device with efficiency of 23.09% (certified 22.85%). Most importantly, the stability of the resulting devices can be close to meeting the requirements of the International Electrotechnical Commission 61215 standard under simulated UV preconditioning and light-soaking testing. They can retain over 95% and 92% of their initial efficiencies after 1100 h UV irradiation and 1000 h continuous illumination of maximum power point tracking at 60 °C, respectively.
... [49] The photo-oxidation for fullerene acceptors can cause the photopolymerization of fullerene molecules. [50] The conventional fullerene acceptor bis(1- [3-(methoxycarbonyl)propyl]-1-phenyl)- [6,6]C62 (PC 60 BM) can undergo a severe photodimerization after the exposure to sunlight. [51] Kim et al. identified a three-phase degradation process for non-fullerene acceptors O-IDTBR and O-IDFBR which contains a first photoinduced conformational change, followed by photo-oxidation and fragmentation and a complete chromophore bleaching at the final stage. ...
The organic solar cell (OSC) is a promising emerging low-cost thin film photovoltaics technology. The power conversion efficiency (PCE) of OSCs has overpassed 16% for single junction and 17% for organic-organic tandem solar cells with the development of low bandgap organic materials synthesis and device processing technology. The main barrier of commercial use of OSCs is the poor stability of devices. Herein, the factors limiting the stability of OSCs are summarized. The limiting stability factors are oxygen, water, irradiation, heating, metastable morphology, diffusion of electrodes and buffer layers materials, and mechanical stress. The recent progress in strategies to increase the stability of OSCs is surveyed, such as material design, device engineering of active layers, employing inverted geometry, optimizing buffer layers, using stable electrodes and encapsulation materials. The International Summit on Organic Photovoltaic Stability guidelines are also discussed. The potential research strategies to achieve the required device stability and efficiency are highlighted, rendering possible pathways to facilitate the viable commercialization of OSCs.
... 10, 16,17 However, fullerenes have been known to undergo photo-induced reactions under UV or visible illumination 18−21 and aggregate into large particles under thermal stress. 22,23 Fortunately, the first issue about photostability of fullerenes can be negligible for inverted planar-structured PSCs because most of the high-energy photons are absorbed by the perovskite layer, which acts as an optical filter. 10 Sequentially, thermally induced fullerene aggregation becomes the remaining issue that should be urgently solved for improving the thermal stability of fullerenebased ETLs in PSCs, but it has rarely been studied heretofore largely due to lack of a powerful tool to identify the precise bonding for understanding the interaction and aggregation of fullerene derivatives in ETLs. ...
The structure-dependent thermal stability of fullerene electron transport layers (ETLs) and its impact on device stability have been underrated for years. Based on co-crystallographic understanding, herein, we develop a thermal stable ETL comprising of a hybrid layer of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) and [6, 6]-phenyl-C61- propylbenzene (PCPB). By tuning the weight ratios of PCBM and PCPB to influence the non-covalent intermolecular interactions and packing of fullerene derivatives, we obtained a champion device based on the 20PCPB (20 wt% addition of PCPB into the mixture of PCBM: PCPB) ETL and excellent thermal stability of 500 h under 85 oC thermal aging in N2 atmosphere in the dark. The present work exemplifies that co-crystallography can be a precise tool to probe interaction and aggregation of fullerene derivatives in ETLs, and mixed fullerene derivatives can be sought as promising ETLs to enhance the long-term stability of PSCs under high-temperature working environment.
