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Journal articleZhang L, Lee S, Park SY, et al., 2024,
High Thickness Tolerance in All-Polymer-Based Organic Photovoltaics Enables Efficient and Stable In-Door Operation.
, Adv Sci (Weinh), Vol: 11Organic photovoltaics (OPVs) have great potential to drive low-power consumption electronic devices under indoor light due to their highly tunable optoelectronic properties. Thick devices (>300 nm photo-active junctions) are desirable to maximize photocurrent and to manufacture large-scale modules via solution-processing. However, thick devices usually suffer from severe charge recombination, deteriorating device performances. Herein, the study demonstrates excellent thickness tolerance of all-polymer-based PVs for efficient and stable indoor applications. Under indoor light, device performance is less dependent on photoactive layer thickness, exhibiting the best maximum power output in thick devices (34.7 µW cm-2 in 320-475 nm devices). Thick devices also exhibit much better photostability compared with thin devices. Such high thickness tolerance of all-polymer-based PV devices under indoor operation is attributed to strongly suppressed space-charge effects, leading to reduced bimolecular recombination losses in thick devices. The unbalanced charge carrier mobilities are identified as the main cause for significant space-charge effects, which is confirmed by drift-diffusion simulations. This work suggests that all-polymer-based PVs, even with unbalanced mobilities, are highly desirable for thick, efficient, and stable devices for indoor applications.
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Journal articleAlsufyani M, Moss B, Tait CE, et al., 2024,
The Effect of Organic Semiconductor Electron Affinity on Preventing Parasitic Oxidation Reactions Limiting Performance of n-Type Organic Electrochemical Transistors.
, Adv Mater, Vol: 36A key challenge in the development of organic mixed ionic-electronic conducting materials (OMIEC) for high performance electrochemical transistors is their stable performance in ambient. When operating in aqueous electrolyte, potential reactions of the electrochemically injected electrons with air and water could hinder their persistence, leading to a reduction in charge transport. Here, the impact of deepening the LUMO energy level of a series of electron-transporting semiconducting polymers is evaluated, and subsequently rendering the most common oxidation processes of electron polarons thermodynamically unfavorable, on organic electrochemical transistors (OECTs) performance. Employing time resolved spectroelectrochemistry with three analogous polymers having varying electron affinities (EA), it is found that an EA below the thermodynamic threshold for oxidation of its electron polarons by oxygen significantly improves electron transport and lifetime in air. A polymer with a sufficiently large EA and subsequent thermodynamically unfavorable oxidation of electron polarons is reported, which is used as the semiconducting layer in an OECT, in its neutral and N-DMBI doped form, resulting in an excellent and air-stable OECT performance. These results show a general design methodology to avoid detrimental parasitic reactions under ambient conditions, and the benefits that arise in electrical performance.
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Journal articleYang EJ, Luke J, Fu Y, et al., 2024,
Unraveling the Impact of Solution Filtration on Organic Solar Cell Stability
, Advanced Functional Materials, Vol: 34, ISSN: 1616-301XDespite major advances in efficiency, the operational stability of organic photovoltaic (OPV) devices remains poor. Therefore, understanding the degradation mechanisms and identifying potential solutions to improve device stability is critical to enabling the widespread commercialization of OPVs. Herein, simple filtration of the PBDB-T:ITIC photoactive layer (PAL) solution prior to film deposition is demonstrated to enhance OPV device operational stability without compromising initial device performance. The effect of filtration, a commonly used but poorly understood OPV fabrication step, is investigated using a range of chemical, structural, and optoelectronic methods, on solutions and films. Filtration is found to remove large aggregates from solution without disrupting nanoscale preaggregation, resulting in enhanced acceptor ordering in PBDB-T:ITIC thin films, significantly improving morphological stability and photostability. This simple and facile method is confirmed to be a general strategy that also works for other PBDB-T-containing OPV blends, including Y6-based systems, and highlights how subtle changes in morphology can result in dramatic differences in operational stability.
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Journal articleFu Y, Xu L, Li Y, et al., 2024,
Enhancing inter-domain connectivity by reducing fractal dimensions: the key to passivating deep traps in organic photovoltaics
, Energy and Environmental Science, Vol: 17, Pages: 8893-8903, ISSN: 1754-5692The detrimental impact of non-geminate recombination on high-performance organic photovoltaics has been recognised and primarily attributed to bimolecular recombination. However, the recent surge in Y-series acceptor-based systems has drawn attention to deep-trap-assisted monomolecular recombination. This study reveals the morphological origin of deep traps in the prototypical PM6:Y6 system, identifying isolated crystalline and amorphous Y6 domains as key contributors. The findings underscore the importance of improving inter-acceptor domain connectivity for effective trap passivation. For the first time, we have pinpointed a crucial metric for inversely quantifying the inter-acceptor domain connectivity: the crystalline domain fractal dimension (Df). Due to the self-similar nature of fractal structures, the fractal dimension propagates across multi-length scales and can be controlled by tuning local intermolecular aggregation motifs. Remarkably, combining diiodide benzene (DIB) as the additive and layer-by-layer (LBL) processing effectively promotes the more extended backbone order of Y6 molecules, consequently reducing the fractal dimensions and passivating deep traps. By applying this strategy to another high-performance system, D18:L8BO, a benchmark efficiency of 19.6% is achieved, among the highest efficiencies reported for LBL OPVs.
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Journal articleBlakesley JC, Bonilla RS, Freitag M, et al., 2024,
Roadmap on established and emerging photovoltaics for sustainable energy conversion
, JPhys Energy, Vol: 6, ISSN: 2515-7655Photovoltaics (PVs) are a critical technology for curbing growing levels of anthropogenic greenhouse gas emissions, and meeting increases in future demand for low-carbon electricity. In order to fulfill ambitions for net-zero carbon dioxide equivalent (CO2eq) emissions worldwide, the global cumulative capacity of solar PVs must increase by an order of magnitude from 0.9 TWp in 2021 to 8.5 TWp by 2050 according to the International Renewable Energy Agency, which is considered to be a highly conservative estimate. In 2020, the Henry Royce Institute brought together the UK PV community to discuss the critical technological and infrastructure challenges that need to be overcome to address the vast challenges in accelerating PV deployment. Herein, we examine the key developments in the global community, especially the progress made in the field since this earlier roadmap, bringing together experts primarily from the UK across the breadth of the PVs community. The focus is both on the challenges in improving the efficiency, stability and levelized cost of electricity of current technologies for utility-scale PVs, as well as the fundamental questions in novel technologies that can have a significant impact on emerging markets, such as indoor PVs, space PVs, and agrivoltaics. We discuss challenges in advanced metrology and computational tools, as well as the growing synergies between PVs and solar fuels, and offer a perspective on the environmental sustainability of the PV industry. Through this roadmap, we emphasize promising pathways forward in both the short- and long-term, and for communities working on technologies across a range of maturity levels to learn from each other.
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Journal articlePagano K, Kim JG, Luke J, et al., 2024,
Slow vibrational relaxation drives ultrafast formation of photoexcited polaron pair states in glycolated conjugated polymers
, Nature Communications, Vol: 15, ISSN: 2041-1723Glycol sidechains are often used to enhance the performance of organic photoconversion and electrochemical devices. Herein, we study their effects on electronic states and electronic properties. We find that polymer glycolation not only induces more disordered packing, but also results in a higher reorganisation energy due to more localised π-electron density. Transient absorption spectroscopy and femtosecond stimulated Raman spectroscopy are utilised to monitor the structural relaxation dynamics coupled to the excited state formation upon photoexcitation. Singlet excitons are initially formed, followed by polaron pair formation. The associated structural relaxation slows down in glycolated polymers (5 ps vs. 1.25 ps for alkylated), consistent with larger reorganisation energy. This slower vibrational relaxation is found to drive ultrafast formation of the polaron pair state (5 ps vs. 10 ps for alkylated). These results provide key experimental evidence demonstrating the impact of molecular structure on electronic state formation driven by strong vibrational coupling.
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Journal articleRana A, Park SY, Labanti C, et al., 2024,
Octupole moment driven free charge generation in partially chlorinated subphthalocyanine for planar heterojunction organic photodetectors
, Nature Communications, Vol: 15, ISSN: 2041-1723In this study, high-performance organic photodetectors are presented which utilize a pristine chlorinated subphthalocyanine photoactive layer. Optical and optoelectronic analyses indicate that the device photocurrent is primarily generated through direct charge generation within the chlorinated subphthalocyanine layer, rather than exciton separation at layer interfaces. Molecular modelling suggests that this direct charge generation is facilitated by chlorinated subphthalocyanine high octupole moment (−80 DÅ2), which generates a 200 meV shift in molecular energetics. Increasing the thickness of chlorinated subphthalocyanine leads to faster response time, correlated with a decrease in trap density. Notably, photodetectors with a 50 nm thick chlorinated subphthalocyanine photoactive layer exhibit detectivities approaching 1013 Jones, with a dark current below 10−7 A cm−2 up to −5 V. Based on these findings, we conclude that high octupole moment molecular semiconductors are promising materials for high-performance organic photodetectors employing single-component photoactive layer.
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Journal articleStewart K, Pagano K, Tan E, et al., 2024,
Understanding effects of alkyl side-chain density on polaron formation via electrochemical doping in thiophene polymers
, Advanced Materials, Vol: 36, ISSN: 0935-9648Polarons exist when charges are injected into organic semiconductors due to their strong coupling with the lattice phonons, significantly affecting electronic charge-transport properties. Understanding the formation and (de)localization of polarons is therefore critical for further developing organic semiconductors as a future electronics platform. However, there are very few studies reported in this area. In particular, there is no direct in situ monitoring of polaron formation and identification of its dependence on molecular structure and impact on electrical properties, limiting further advancement in organic electronics. Herein, how a minor modification of side-chain density in thiophene-based conjugated polymers affects the polaron formation via electrochemical doping, changing the polymers’ electrical response to the surrounding dielectric environment for gas sensing, is demonstrated. It is found that the reduction in side-chain density results in a multistep polaron formation, leading to an initial formation of localized polarons in thiophene units without side chains. Reduced side-chain density also allows the formation of a high density of polarons with fewer polymer structural changes. More numerous but more localized polarons generate a stronger analyte response but without the selectivity between polar and non-polar solvents, which is different from the more delocalized polarons that show clear selectivity. The results provide important molecular understanding and design rules for the polaron formation and its impact on electrical properties.
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Journal articleWu D-T, Zhu W-X, Dong Y, et al., 2024,
Enhancing the efficiency and stability of tin-lead perovskite solar cells via sodium hydroxide dedoping of PEDOT:PSS
, small methods, ISSN: 2366-9608Tin-lead (Sn-Pb) perovskite solar cells (PSCs) have gained interest as candidates for the bottom cell of all-perovskite tandem solar cells due to their broad absorption of the solar spectrum. A notable challenge arises from the prevalent use of the hole transport layer, PEDOT:PSS, known for its inherently high doping level. This high doping level can lead to interfacial recombination, imposing a significant limitation on efficiency. Herein, NaOH is used to dedope PEDOT:PSS, with the aim of enhancing the efficiency of Sn-Pb PSCs. Secondary ion mass spectrometer profiles indicate that sodium ions diffuse into the perovskite layer, improving its crystallinity and enlarging its grains. Comprehensive evaluations, including photoluminescence and nanosecond transient absorption spectroscopy, confirm that dedoping significantly reduces interfacial recombination, resulting in an open-circuit voltage as high as 0.90 V. Additionally, dedoping PEDOT:PSS leads to increased shunt resistance and high fill factor up to 0.81. As a result of these improvements, the power conversion efficiency is enhanced from 19.7% to 22.6%. Utilizing NaOH to dedope PEDOT:PSS also transitions its nature from acidic to basic, enhancing stability and exhibiting less than a 7% power conversion efficiency loss after 1176 h of storage in N2 atmosphere.
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Journal articleClarke AJ, Yang EJ, Thomas SK, et al., 2024,
Investigating the Photostability of Organic Photovoltaics for Indoor and Outdoor Applications
, ADVANCED ENERGY AND SUSTAINABILITY RESEARCH, ISSN: 2699-9412 -
Journal articlePark SY, Labanti C, Pacalaj RA, et al., 2023,
The state-of-the-art solution-processed single component organic photodetectors achieved by strong quenching of intermolecular emissive state and high quadrupole moment in non-fullerene acceptors
, Advanced Materials, Vol: 35, ISSN: 0935-9648A bulk-heterojunction (BHJ) blend is commonly used as the photoactive layer in organic photodetectors (OPDs) to utilize the donor (D)/acceptor (A) interfacial energetic offset for exciton dissociation. However, this strategy often complicates optimization procedures, raising serious concerns over device processability, reproducibility, and stability. Herein, highly efficient OPDs fabricated with single-component organic semiconductors are demonstrated via solution-processing. The non-fullerene acceptors (NFAs) with strong intrinsic D/A character are used as the photoactive layer, where the emissive intermolecular charge transfer excitonic (CTE) states are formed within <1 ps, and efficient photocurrent generation is achieved via strong quenching of these CTE states by reverse bias. Y6 and IT-4F-based OPDs show excellent OPD performances, low dark current density (≈10-9 A cm-2 ), high responsivity (≥0.15 A W-1 ), high specific detectivity (>1012 Jones), and fast photo-response time (<10 µs), comparable to the state-of-the-art BHJ OPDs. Together with strong CTE state quenching by electric field, these excellent OPD performances are also attributed to the high quadrupole moments of NFA molecules, which can lead to large interfacial energetic offset for efficient CTE dissociation. This work opens a new way to realize efficient OPDs using single-component systems via solution-processing and provides important molecular design rules.
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Journal articleYan H, Cong S, Daboczi M, et al., 2023,
Ionic density control of conjugated polyelectrolytes via postpolymerization modification to enhance hole-blocking property for highly efficient PLEDs with fast response times
, Advanced Optical Materials, Vol: 11, ISSN: 2195-1071For an ideal electron interlayer, both electron injection and hole-blocking properties are important to achieve better polymer light-emitting devices (PLEDs) performance. Conjugated polyelectrolytes (CPEs) are applied widely in PLEDs to enhance charge injection. Understanding the role of backbone structures and energetic matching between the CPEs and emitters can benefit charge injection and balance. Herein, a postpolymerization approach to introduce varying amounts of alkyl sulfonate groups onto the backbone of a copolymer of 5-fluoro-2,1,3-benzothiadiazole and 9,9′-dioctylfluorene is utilized. This study finds that device performance is dependent on the percentage of sulfonate groups incorporated, with the optimal copolymer (CPE-50%) maintaining efficient ohmic electron injection and gaining enhanced hole-blocking properties, thereby achieving the most balanced hole/electron current. Therefore, the PLED with CPE-50% interlayer exhibits the highest efficiency (20.3 cd A−1, 20.2 lm W−1) and the fastest response time (4.3 µs), which is the highest efficiency among conventional thin (70 nm) F8BT PLEDs with CPEs. These results highlight the importance of balanced charge carrier density in CPEs and highlight that postpolymerization modification is a useful method for fine-tuning ionic content.
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Journal articleHenderson C, Luke J, Bicalho I, et al., 2023,
Charge transfer complex formation between organic interlayers drives light-soaking in large area perovskite solar cells
, Energy and Environmental Science, Vol: 16, Pages: 5891-5903, ISSN: 1754-5692Light soaking (LS) is a well-known but poorly understood phenomenon in perovskite solar cells (PSCs) which significantly affects device efficiency and stability. LS is greatly reduced in large-area inverted PSCs when a PC61BM electron transport layer (ETL) is replaced with C60, where the ETL is commonly in contact with a thin bathocuproine (BCP) interlayer. Herein, we identify the key molecular origins of this LS effect using a combination of surface photovoltage, ambient photoemission spectroscopy, Raman spectroscopy, integrated with density functional theory simulations. We find that BCP forms a photoinduced charge-transfer (CT) complex with both C60 and PC61BM. The C60/BCP complex accelerates C60 dimer formation, leading to a favourable cascading energetic landscape for electron extraction and reduced recombination loss. In contrast, the PC61BM/BCP complex suppresses PC61BM dimer formation, meaning that PC61BM dimerisation is not the cause of LS. Instead, it is the slow light-induced formation of the PC61BM/BCP CT complex itself, and the new energetic transport levels associated with it, which cause the much slower and stronger LS effect of PC61BM based PSCs. These findings provide key understanding of photoinduced ETL/BCP interactions and their impact on the LS effect in PSCs.
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Journal articleChanda RC, Vafaei-Zadeh A, Syafrizal S, et al., 2023,
Charge transfer complex formation between organic interlayers drives light-soaking in large area perovskite solar cells
, ENERGY & ENVIRONMENTAL SCIENCE, ISSN: 1754-5692 -
Journal articleLuke J, Yang EJ, Labanti C, et al., 2023,
Key molecular perspectives for high stability in organic photovoltaics
, Nature Reviews Materials, ISSN: 2058-8437Organic photovoltaics (OPVs) have rapidly improved in efficiency, with single-junction cells now exceeding 18% efficiency. These improvements have been driven by the adoption of new non-fullerene acceptors and the fine tuning of their molecular structures. Although OPVs are highly efficient, they often show extremely poor operational stability, primarily owing to the complex interplay between the morphological instability of the blended bulk heterojunction photoactive layers and the intrinsically poor photostability of the organic semiconductor materials themselves. To realize commercialization, it is vital to understand the degradation mechanisms of these organic materials to improve their stability. Efficiency increases have, in part, been driven by the rational molecular design of materials. In this Perspective, we examine how a similar bottom-up molecular design can be applied to OPV stability. Specifically, we highlight key molecular design parameters and demonstrate how each parameter impacts different degradation pathways. Looking forward, we propose that fundamental understanding of the molecular origin of OPV stability is a key research theme for next-generation OPVs. Additionally, we discuss the tools required, across length scales, to implement these design rules, particularly the use of in situ Raman spectroscopy as a critical bridge linking the molecular scale to the nanoscale and beyond.
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Journal articleWang Y, Daboczi M, Zhang M, et al., 2023,
Origin of the switchable photocurrent direction in BiFeO<sub>3</sub> thin films
, MATERIALS HORIZONS, ISSN: 2051-6347 -
Journal articleYang M, Cui J, Daboczi M, et al., 2023,
Interplay between Collective and Localized Effects of Point Defects on Photoelectrochemical Performance of TiO<sub>2</sub> Photoanodes for Oxygen Evolution
, ADVANCED MATERIALS INTERFACES, ISSN: 2196-7350 -
Journal articleHart LJF, Gruene J, Liu W, et al., 2023,
Understanding the Role of Triplet-Triplet Annihilation in Non-Fullerene Acceptor Organic Solar Cells
, ADVANCED ENERGY MATERIALS, Vol: 13, ISSN: 1614-6832 -
Journal articleJiang Z, Du T, Lin C, et al., 2023,
Deciphering the role of hole transport layer HOMO level on the open circuit voltage of perovskite Solar cells
, Advanced Materials Interfaces, Vol: 10, ISSN: 2196-7350With the rapid development of perovskite solar cells, reducing losses in open-circuit voltage (Voc) is a key issue in efforts to further improve device performance. Here it is focused on investigating the correlation between the highest occupied molecular orbital (HOMO) of device hole transport layers (HTLs) and device Voc. To achieve this, structurally similar HTL materials with comparable optical band gaps and doping levels, but distinctly different HOMO levels are employed. Using light-intensity dependent Voc and photoluminescence measurements significant differences in the behavior of devices employing the two HTLs are highlighted. Light-induced increase of quasi-Fermi level splitting (ΔEF) in the perovskite layer results in interfacial quasi-Fermi level bending required to align with the HOMO level of the HTL, resulting in the Voc measured at the contacts being smaller than the ΔEF in the perovskite. It is concluded that minimizing the energetic offset between HTLs and the perovskite active layer is of great importance to reduce non-radiative recombination losses in perovskite solar cells with high Voc values that approach the radiative limit.
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Journal articleJeong S, Rana A, Kim J-H, et al., 2023,
New ternary blend strategy based on a vertically self-assembled passivation layer enabling efficient and photostable inverted organic solar cells
, Advanced Science, Vol: 10, Pages: 1-9, ISSN: 2198-3844Herein, a new ternary strategy to fabricate efficient and photostable inverted organic photovoltaics (OPVs) is introduced by combining a bulk heterojunction (BHJ) blend and a fullerene self-assembled monolayer (C60 -SAM). Time-of-flight secondary-ion mass spectrometry - analysis reveals that the ternary blend is vertically phase separated with the C60 -SAM at the bottom and the BHJ on top. The average power conversion efficiency - of OPVs based on the ternary system is improved from 14.9% to 15.6% by C60 -SAM addition, mostly due to increased current density (Jsc ) and fill factor -. It is found that the C60 -SAM encourages the BHJ to make more face-on molecular orientation because grazing incidence wide-angle X-ray scattering - data show an increased face-on/edge-on orientation ratio in the ternary blend. Light-intensity dependent Jsc data and charge carrier lifetime analysis indicate suppressed bimolecular recombination and a longer charge carrier lifetime in the ternary system, resulting in the enhancement of OPV performance. Moreover, it is demonstrated that device photostability in the ternary blend is enhanced due to the vertically self-assembled C60 -SAM that successfully passivates the ZnO surface and protects BHJ layer from the UV-induced photocatalytic reactions of the ZnO. These results suggest a new perspective to improve both performance and photostability of OPVs using a facial ternary method.
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Journal articleMotai K, Koishihara N, Narimatsu T, et al., 2023,
Bifurcated Hydrogen Bonds in a Peptide Crystal Unveiled by X-ray Diffraction and Polarized Raman Spectroscopy (vol 23, pg 4556, 2023)
, CRYSTAL GROWTH & DESIGN, Vol: 23, ISSN: 1528-7483 -
Journal articleMohapatra AA, Pranav M, Yadav S, et al., 2023,
Interface engineering in perylene diimide-based organic photovoltaics with enhanced photovoltage
, ACS Applied Materials and Interfaces, Vol: 15, Pages: 25224-25231, ISSN: 1944-8244The introduction of nonfullerene acceptors (NFA) facilitated the realization of high-efficiency organic solar cells (OSCs); however, OSCs suffer from relatively large losses in open-circuit voltage (VOC) as compared to inorganic or perovskite solar cells. Further enhancement in power conversion efficiency requires an increase in VOC. In this work, we take advantage of the high dipole moment of twisted perylene-diimide (TPDI) as a nonfullerene acceptor (NFA) to enhance the VOC of OSCs. In multiple bulk heterojunction solar cells incorporating TPDI with three polymer donors (PTB7-Th, PM6 and PBDB-T), we observed a VOC enhancement by modifying the cathode with a polyethylenimine (PEIE) interlayer. We show that the dipolar interaction between the TPDI NFA and PEIE─enhanced by the general tendency of TPDI to form J-aggregates─plays a crucial role in reducing nonradiative voltage losses under a constant radiative limit of VOC. This is aided by comparative studies with PM6:Y6 bulk heterojunction solar cells. We hypothesize that incorporating NFAs with significant dipole moments is a feasible approach to improving the VOC of OSCs.
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Journal articleMotai K, Koishihara N, Narimatsu T, et al., 2023,
Bifurcated Hydrogen Bonds in a Peptide Crystal Unveiled by X-ray Diffraction and Polarized Raman Spectroscopy
, CRYSTAL GROWTH & DESIGN, Vol: 23, Pages: 4556-4561, ISSN: 1528-7483 -
Journal articleBellchambers P, Henderson C, Abrahamczyk S, et al., 2023,
High Performance Transparent Silver Grid Electrodes for Organic Photovoltaics Fabricated by Selective Metal Condensation
, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648 -
Journal articleLee TH, Fu Y, Chin Y-C, et al., 2023,
Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance
, Nature Communications, Vol: 14, Pages: 1-12, ISSN: 2041-1723The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs.
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Journal articleWang Y, Luke J, Privitera A, et al., 2023,
The critical role of the donor polymer in the stability of high-performance non-fullerene acceptor organic solar cells
, Joule, Vol: 7, Pages: 810-829, ISSN: 2542-4351The poor operational stability of non-fullerene electron acceptor (NFA) organic solar cells (OSCs) currently limits their commercial application. While previous studies have primarily focused on the degradation of the NFA component, we also consider here the electron donor material. We examine the stability of three representative donor polymers, PM6, D18, and PTQ10, paired with the benchmark NFA, Y6. After light soaking PM6 and D18 in air, we find an enhanced conversion of singlet excitons into trapped interchain polaron pairs on sub-100 femtosecond timescales. This process outcompetes electron transfer to Y6, significantly reducing the charge generation yield. However, this pathway is absent in PTQ10. We identify twisting in the benzo[1,2-b:4,5-b′]dithiophene (BDT)-thiophene motif shared by PM6 and D18 as the cause. By contrast, PTQ10 does not contain this structural motif and has improved stability. Thus, we show that the donor polymer can be a weak link for OSC stability, which must be addressed collectively with the NFA.
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Conference paperKim JS, 2023,
Key Impact of Molecular Structure and Orientation of Non-Fullerene Acceptors on Organic Photoconversion Devices
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Journal articleLuke J, Jo Y-R, Lin C-T, et al., 2022,
The molecular origin of high performance in ternary organic photovoltaics identified using a combination of in situ structural probes
, Journal of Materials Chemistry A, Vol: 11, Pages: 1281-1289, ISSN: 2050-7488A ternary blend, wherein a tertiary acceptor is incorporated into a donor:non-fullerene acceptor (NFA) binary blend has emerged as a promising strategy for improving power conversion efficiency and stability of organic bulk heterojunction photovoltaics (OPVs). However, the effects of the tertiary component remain elusive due to the complex variation of crystallinity and morphology of donor and acceptor phases during thermal annealing. Herein a combination of in situ transmission electron microscopy and X-ray diffraction spectroscopy utilized during annealing identifies that (1) the addition of the tertiary component (O-IDFBR) delays the glass transition temperature of edge-on-oriented polymer donor (P3HT), prohibits the glass transition of face-on-oriented polymer donor (P3HT), broadens the crystallization temperature of O-IDTBR, and enhances the overall crystallinity of the donor and acceptor phases (P3HT and O-IDTBR), and (2) the ternary component induces homogeneously distributed nanoscale domains rather than a microscale separation between the donor and acceptor as observed in the binary blend. The optimized nanoscale domain morphology, driven by slower crystallization and enhanced overall crystallinity leads to a more stable morphology, resulting in superior device performance and stability.
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Journal articleLee TH, Dong Y, Pacalaj RA, et al., 2022,
Organic Planar Heterojunction Solar Cells and Photodetectors Tailored to the Exciton Diffusion Length Scale of a Non-Fullerene Acceptor
, ADVANCED FUNCTIONAL MATERIALS, Vol: 32, ISSN: 1616-301X- Author Web Link
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Journal articleCui J, Daboczi M, Regue M, et al., 2022,
2D bismuthene as a functional interlayer between BiVO4 and NiFeOOH for enhanced oxygen-evolution photoanodes
, Advanced Functional Materials, Vol: 32, Pages: 1-12, ISSN: 1616-301XBiVO4 has attracted wide attention for oxygen-evolution photoanodes in water-splitting photoelectrochemical devices. However, its performance is hampered by electron-hole recombination at surface states. Herein, partially oxidized two-dimensional (2D) bismuthene is developed as an effective, stable, functional interlayer between BiVO4 and the archetypal NiFeOOH co-catalyst. Comprehensive (photo)electrochemical and surface photovoltage characterizations show that NiFeOOH can effectively increase the lifetime of photogenerated holes by passivating hole trap states of BiVO4; however, it is limited in influencing electron trap states related to oxygen vacancies (VO). Loading bismuthene on BiVO4 photoanodes increases the density of VO that are beneficial for the oxygen evolution reaction via the formation of oxy/hydroxyl-based water oxidation intermediates at the surface. Moreover, bismuthene increases interfacial band bending and fills the VO-related electron traps, leading to more efficient charge extraction. With the synergistic interaction of bismuthene and NiFeOOH on BiVO4, this composite photoanode achieves a 5.8-fold increase in photocurrent compared to bare BiVO4 reaching a stable 3.4 (±0.2) mA cm–2 at a low bias of +0.8 VRHE or 4.7(±0.2) mA cm–2 at +1.23 VRHE. The use of 2D bismuthene as functional interlayer provides a new strategy to enhance the performance of photoanodes.
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