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Individual nanostructure optimization in donor and acceptor phases to achieve efficient quaternary organic solar cells
摘要： Fullerene derivative (PC71BM) and high crystallinity molecule (DR3TBDTT) are employed into PTB7-Th:FOIC based organic solar cells (OSCs) to cooperate an individual nanostructure optimized quaternary blend. PC71BM functions as molecular adjuster and phase modifier promoting FOIC forming “head-to-head” molecular packing and neutralizing the excessive FOIC crystallites. A multi-scale modified morphology is present thanks to the mixture of FOIC and PC71BM while DR3TBDTT disperses into PTB7-Th matrix to reinforce donor’s crystallinity and enhance domain purity. Morphology characterization highlights the importance of individually optimizated nanostructures for donor and acceptor, which contributes to efficient hole and electron transport toward improved carrier mobilities and suppressed non-geminated recombination. Therefore, a power conversion efficiency of 13.51% is realized for a quaternary device which is 16% higher than the binary device (PTB7-Th:FOIC). This work demonstrates that utilizing quaternary strategy for simultaneous optimization of donor and acceptor phases is a feasible way to realize high efficient OSCs.
关键词： carrier dynamics,quaternary organic solar cells,hierarchical morphology optimization,fullerene,non-fullerene
更新于2025-09-16 10:30:52
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Orbital-Energy Modulation of Tetrabenzoporphyrin-Derived Non-Fullerene Acceptors for Improved Open-Circuit Voltage in Organic Solar Cells
摘要： Tetrabenzoporphyrin (BP) holds attractive characteristics for optoelectronic applications, such as the large π-conjugated framework and high photoabsorption capability. However, its use in organic solar cells (OSCs) has been limited because of the extremely low solubility that hampers direct solution processing and also the high frontier-orbital energies that lead to low open-circuit voltage (VOC). Herein, we examine BP derivatives equipped with multiple strongly electron-withdrawing groups for photovoltaic applications. The derivatives are generated in thin films through a thermal precursor approach, wherein the corresponding bicyclo[2.2.2]octadiene-fused porphyrin derivatives are solution-cast, and then annealed to carry out the in situ retro-Diels–Alder reaction. The frontier-orbital energies of the resulting derivatives are effectively stabilized as compared to pristine BP to such a degree that they afford high VOC of up to 0.94 V when used as a donor, or can even work as a new class of non-fullerene acceptor in OSCs. Single-crystal X-ray diffraction analyses demonstrate that the conformation of the BP framework largely varies from being near planar to highly curved depending on its substituents. The morphology of polymer:BP-derivative bulk-heterojunction films prepared by the thermal precursor approach also varies between the BP derivatives. These results can greatly extend the scope of both molecular design and morphology control for utilization of the BP chromophore toward achieving viable organic optoelectronic devices.
关键词： Tetrabenzoporphyrin,organic solar cells,thermal precursor approach,frontier-orbital energies,non-fullerene acceptors
更新于2025-09-16 10:30:52
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Assessing the energy offset at the electron donor/acceptor interface in organic solar cells through radiative efficiency measurements
摘要： Energy offsets at the electron donor/acceptor interface play an important role in the operation of organic solar cells (OSCs), because their magnitude strongly affects the efficiency of photo-induced charge separation and hence the short-circuit current of a device under illumination. However, quantitative assessment of energy offsets in operating devices remains an open challenge that is still out of the reach of present techniques. Here we show that the ratio of the radiative efficiency (EQEEL) for a blend device to that for the lower bandgap component device (usually a non-fullerene acceptor), namely the EQEEL ratio, can be a strong indicator of the energy offsets in the blend device. In photovoltaic devices based on donors and acceptors with similar backbone structure but varied energy levels, lowering the highest occupied molecular orbital (HOMO) offset increases the open-circuit voltage (VOC) from 0.95 V to 1.05 V, which is consistent with the EQEEL variation trends in the devices. The blend EQEEL approaches that of the emissive low bandgap acceptor when the HOMO of the donor is sufficiently deepened, which at the same time corresponds to a reduction in VOC loss and inefficient photoinduced charge separation. The results suggest that the intrinsic energy loss associated with charge separation can be minimized in practice by minimizing the energy offsets but at the expense of lowering the charge separation efficiency. Statistics from several state-of-the-art material systems reveal that efficient charge generation occurs when the EQEEL ratio is less than 0.1, corresponding to an additional non-radiative voltage loss due to the energy offset of 60 mV. Based on this finding and a modified Shockley–Queisser theory, we estimate an upper thermodynamic efficiency limit for single-junction organic solar cells of about 31%, which is slightly below the Shockley–Queisser limit.
关键词： energy offsets,charge separation,organic solar cells,non-fullerene acceptors,radiative efficiency
更新于2025-09-16 10:30:52
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Introducing an identical benzodithiophene donor unit for polymer donors and small-molecule acceptors to unveil the relationship between the molecular structure and photovoltaic performance of non-fullerene organic solar cells
摘要： The side-chain conjugation strategy is adopted in the synthesis of heptacyclic non-fullerene electron acceptors, ITIC2, ITIC-S, and ITIC-SF, for application in organic solar cells (OSCs). The new ITIC-SF molecule features a BDT-SF building block which is the electron-donating component in the widely used donor PBDB-T-SF. Compared with ITIC-S without fluorine substituents, fluorination weakens the crystallinity of ITIC-SF, while the intermolecular interaction between the PBDB-T-SF donor and ITIC-SF acceptor, containing the same BDT-SF building block, results in the increased crystallinity of the corresponding blend films. The OSC based on PBDB-T-SF:ITIC-SF exhibits a champion power conversion efficiency (PCE) of 12.1%, higher than the PCE of 10.1% for the device based on PBDB-T-SF:ITIC2 and the PCE of 11.6% for the device based on PBDB-T-SF:ITIC-S. The better photovoltaic performance of the OSC based on PBDB-T-SF:ITIC-SF is benefitted from the weaker bimolecular recombination and more efficient charge transfer and extraction of the device. The structure–property relationship of the non-fullerene acceptors revealed in this work will play an important role in instructing the molecular structure design of high performance photovoltaic materials for the development of OSCs.
关键词： organic solar cells,non-fullerene acceptors,side-chain conjugation,photovoltaic performance,fluorination
更新于2025-09-16 10:30:52
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Suppressing photo-oxidation of non-fullerene acceptors and their blends in organic solar cells by exploring material design and employing friendly stabilizers
摘要： In addition to a high power conversion efficiency, ambient stability is another impact factor for the successful commercialization of organic solar cells (OSCs). Understanding the role of photovoltaic materials is the key to address this challenge, but no such studies have been systematically performed on non-fullerene acceptors (NFAs). In this work, we firstly investigate the role of NFA photo-oxidation in device degradation. Relevant investigation of physical dynamics underlines the effects on the device performance for NFA photo-oxidation acting as trap states in exposed blends. In addition, taking ITIC as an example, we shed some light on the possible mechanisms of NFA photo-oxidation, which cannot be eliminated by relevant strategies and principles of material design. These results drive us to further investigate the photobleaching rates of thirty-three NFAs, including fused-ring electron acceptors and perylene diimide acceptor derivatives. Surprisingly, most of them show a higher optical density loss as compared to their fullerene-based counterparts. In view of relevant comparative analysis in the Discussion section, we further propose some design strategies to improve the photo-oxidation stability of NFAs. More importantly, we also find a stabilizer (namely nickel chelate S6) that can effectively suppress the photo-oxidation of NFAs and their blends and thus improve the ambient stability of OSCs.
关键词： stability,organic solar cells,non-fullerene acceptors,stabilizers,photo-oxidation
更新于2025-09-16 10:30:52
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How Does Polymorphism Affect the Interfacial Charge-Transfer States in Organic Photovoltaics?
摘要： The bulk heterojunction in organic photovoltaic (OPV) devices is a mixture of polymer (electron donor) and an electron acceptor material (typically functionalized fullerenes), and it is crucial for the device operation, as this is where excitons are split into electrons and holes to produce current. Non-fullerene acceptors (NFAs) are promising new materials for improving the device efficiency, and their solid-state arrangement with respect to the electron donor polymer is critical for the charge mobility and the performance of OPV devices. Although there have been numerous studies on NFAs, most of the current understanding comes from empirical considerations, with little atomistic-level interpretation of why and how the packing influences the charge transport properties of these materials. In this work we describe large-scale (with up to 3462 atoms) DFT simulations for ground and excited states on a number of polymer-NFA interfaces of realistic size, whose NFA domains consist of polymorphs of the same materials. Hence, we bridged the gap between experimental evidence and the intuitive expectation on the importance of intermolecular π-π stacking interactions in the NFA phase. We show that low connectivity leads to highly localized excitons, whereas in phases with a higher connectivity excitons are able to delocalize over multiple directions. Remarkably, excitons with a three-dimensional delocalization were also observed, leading to isotropic mobilities, similarly to fullerenes. Furthermore, a lower charge-transfer exciton binding energy and a lower energy loss between the lowest excitation of the polymer and the first charge-transfer state in the interface were both observed in systems characterized by a highly interconnected NFA phase. This suggests a higher probability of exciton splitting for these interfaces, which could potentially lead to higher device efficiencies.
关键词： organic photovoltaics,non-fullerene acceptors,DFT simulations,polymorphism,charge-transfer states
更新于2025-09-16 10:30:52
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Efficient non-fullerene organic solar cells based on thickness-insensitive conjugated small molecule cathode interface
摘要： Interfacial engineering plays an essential role in the enhancement of device performance of organic solar cells (OSCs). Plentiful dopant-free electron- transporting materials have been e?ectively applied to modify ZnO in the inverted OSCs. However, these materials usually work with strict thickness, which observably limits their application in large area device fabrication. In this manuscript, an industrial small-molecule PyM with simply chemical structure solved in methyl alcohol was applied to modify ZnO in non-fullerene OSCs. PyM has good solubility in both methyl alcohol and chlorobenzene. Therefore, there is only a thin PyM layer left and distributed on the ZnO surface after coating the active layer. Meanwhile, a small amount PyM may be blended with the active layer near ZnO layer. The intense interaction between ZnO and PyM layer as well as the potential n-doping between PyM and the electron acceptor could modify the work function of ZnO and reduce the charge carrier recombination. Correspondingly, the inverted PBDB-T:ITIC OSCs with ZnO/PyM serving as electron transport layers achieve device power conversion e?ciency (PCE) of 10.9% and 10.0% with 10 nm and 105 nm thick PyM ?lm, respectively. The device performance is insensitive to the thickness of PyM. This phenomenon indicates that the PyM can be employed in roll-to-roll techniques to fabricate large-area devices at low cost. Similar results also emerged in PBDB-T:IT-M system, and the PCE was improved from 10.4% to 11.5% for ZnO and ZnO/PyM (~10 nm)-based devices.
关键词： Cathode interface,Organic solar cells,Hydrophobic property,Non-fullerene,Hydrogen bond,Thickness-insensitive
更新于2025-09-16 10:30:52
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5H-Fluoreno [3,2- b:6,7- b’] Dithiophene Based Non-fullerene Small Molecular Acceptors for Polymer Solar Cell Application
摘要： Two novel non-fullerene small molecule acceptors were prepared with the conjugated backbone of 5H- fluoreno[3, 2- b:6, 7- b’] dithiophene carrying the electron deficient unit of dicyanomethylene indanone (DICTFDT) and rhodanine (TFDTBR), respectively. The two acceptors exhibited excellent thermal stability and strong absorption in the visible region. The LUMO level is estimated to be at -3.89 eV for DICTFDT and -3.77 eV for TFDTBR. When utilized as the acceptor in bulk heterojunction polymer solar cells with the polymer donor of PBT7-Th, the optimized maximum power conversion efficiency of 5.12% and 3.95% was obtained for the device with DICTFDT and TFDTBR, respectively. The research demonstrates that 5H- fluoreno[3, 2- b:6, 7- b’] dithiophene can be an appealing candidate for constructing small molecular electron acceptor towards efficient polymer:non-fullerene bulk heterojunction solar cells.
关键词： polymer solar cells,non-fullerene acceptor,bulk heterojunction
更新于2025-09-16 10:30:52
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The Crucial Role of Fluorine in Fully Alkylated Ladder Type Carbazole Based Non-fullerene Organic Solar Cells
摘要： Two fused ladder type non‐fullerene acceptors, DTCCIC and DTCCIC‐4F, based on an electron‐donating alkylated dithienocyclopentacarbazole core flanked by electron‐withdrawing non‐fluorinated or fluorinated 1,1‐dicyanomethylene‐3‐indanone (IC or IC‐4F), are prepared and utilized in organic solar cells (OSCs). The two new molecules reveal planar structures and strong aggregation behavior, and fluorination is shown to red shift the optical band gap and down shift energy levels. OSCs based on DTCCIC‐4F exhibit a power conversion efficiency of 12.6 %, much higher than that of DTCCIC based devices (6.2 %). Microstructural studies reveal that while both acceptors are highly crystalline, bulk heterojunction blends based on the non‐fluorinated DTCCIC result in overly coarse domains, while blends based on the fluorinated DTCCIC‐4F exhibit a more optimal nanoscale morphology. These results highlight the importance of end group fluorination in controlling molecular aggregation and miscibility.
关键词： fluorine effect,carbazole,fully alkylated side chains,organic solar cells,non‐fullerene acceptors
更新于2025-09-16 10:30:52
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Efficient and Mechanically Robust Ultraflexible Organic Solar Cells Based on Mixed Acceptors
摘要： A simple strategy to simultaneously improve power conversion efficiency (PCE) and mechanical stability of ultra?exible organic solar cells is reported. By using a fullerene/non-fullerene mixed acceptor, 3-mm-thick ultra?exible organic solar cells achieve a PCE of 13% (a certi?ed value of 12.3%) with 97% PCE retention after 1,000 bending cycles and 89% PCE retention after 1,000 compression-stretching cycles.
关键词： mixed acceptors,fullerene,mechanical stability,non-fullerene,ultra?exible organic solar cells,power conversion efficiency
更新于2025-09-12 10:27:22