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Enabling low voltage losses and high photocurrent in fullerene-free organic photovoltaics
摘要： Despite significant development recently, improving the power conversion efficiency of organic photovoltaics (OPVs) is still an ongoing challenge to overcome. One of the prerequisites to achieving this goal is to enable efficient charge separation and small voltage losses at the same time. In this work, a facile synthetic strategy is reported, where optoelectronic properties are delicately tuned by the introduction of electron-deficient-core-based fused structure into non-fullerene acceptors. Both devices exhibited a low voltage loss of 0.57 V and high short-circuit current density of 22.0 mA cm?2, resulting in high power conversion efficiencies of over 13.4%. These unconventional electron-deficient-core-based non-fullerene acceptors with near-infrared absorption lead to low non-radiative recombination losses in the resulting organic photovoltaics, contributing to a certified high power conversion efficiency of 12.6%.
关键词： non-fullerene acceptors,power conversion efficiency,voltage losses,charge separation,organic photovoltaics
更新于2025-11-14 15:18:02
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The Catalytic Cycle of Water Oxidation in Crystallized Photosystem II Complexes: Performance and Requirements for Formation of Intermediates
摘要： Crystals of Photosystem II (PSII) contain the most homogeneous copies of the water-oxidizing reaction center where O2 is evolved (WOC). However, few functional studies of PSII operation in crystals have been carried out, despite their widespread use in structural studies. Here we apply oximetric methods to determine the quantum efficiency and lifetimes of intermediates of the WOC cycle as a function of added electron acceptors (quinones and ferricyanide), both aerobically and anaerobically. PSII crystals exhibit the highest quantum yield of O2 production yet observed of any native or isolated PSII (61.6%, theoretically 59,000 μmol O2/mg Chl/h). WOC cycling can be sustained for thousands of turnovers using an irreversible electron acceptor (ferricyanide). Simulations of the catalytic cycle identify four distinct photochemical inefficiencies in both PSII crystals and dissolved PSII cores that are nearly the same. The exogenous acceptors equilibrate with the native plastoquinone acceptor at the QB (or QC) site(s), for which two distinct redox couples are observable that regulate flux through PSII. Flux through the catalytic cycle of water oxidation is shown to be kinetically restricted by the QAQB two-electron gate. The lifetimes of the S2 and S3 states are greatly extended (especially S2) by electron acceptors and depend on their redox reversibility. PSII performance can be pushed in vitro far beyond what it is capable of in vivo. With careful use of precautions and monitoring of populations, PSII microcrystals enable the exploration of WOC intermediates and the mechanism of catalysis.
关键词： oxygen-evolving complex,electron acceptors,(micro)crystals,S states,quantum yield,Photosystem II
更新于2025-09-23 15:22:29
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Progress of the key materials for organic solar cells
摘要： Organic solar cells have attracted academic and industrial interests due to the advantages like lightweight, flexibility and roll-to-roll fabrication. Nowadays, 18% power conversion efficiency has been achieved in the state-of-the-art organic solar cells. The recent rapid progress in organic solar cells relies on the continuously emerging new materials and device fabrication technologies, and the deep understanding on film morphology, molecular packing and device physics. Donor and acceptor materials are the key materials for organic solar cells since they determine the device performance. The past 25 years have witnessed an odyssey in developing high-performance donors and acceptors. In this review, we focus on those star materials and milestone work, and introduce the molecular structure evolution of key materials. These key materials include homopolymer donors, D-A copolymer donors, A-D-A small molecular donors, fullerene acceptors and nonfullerene acceptors. At last, we outlook the challenges and very important directions in key materials development.
关键词： D-A copolymer donors,nonfullerene acceptors,key materials,organic solar cells,fullerene acceptors
更新于2025-09-23 15:21:01
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Asymmetric Electron Acceptors for Higha??Efficiency and Lowa??Energya??Loss Organic Photovoltaics
摘要： Low energy loss and efficient charge separation under small driving forces are the prerequisites for realizing high power conversion efficiency (PCE) in organic photovoltaics (OPVs). Here, a new molecular design of nonfullerene acceptors (NFAs) is proposed to address above two issues simultaneously by introducing asymmetric terminals. Two NFAs, BTP-S1 and BTP-S2, are constructed by introducing halogenated indandione (A1) and 3-dicyanomethylene-1-indanone (A2) as two different conjugated terminals on the central fused core (D), wherein they share the same backbone as well-known NFA Y6, but at different terminals. Such asymmetric NFAs with A1-D-A2 structure exhibit superior photovoltaic properties when blended with polymer donor PM6. Energy loss analysis reveals that asymmetric molecule BTP-S2 with six chlorine atoms attached at the terminals enables the corresponding devices to give an outstanding electroluminescence quantum efficiency of 2.3 × 10?2%, one order of magnitude higher than devices based on symmetric Y6 (4.4 × 10?3%), thus significantly lowering the nonradiative loss and energy loss of the corresponding devices. Besides, asymmetric BTP-S1 and BTP-S2 with multiple halogen atoms at the terminals exhibit fast hole transfer to the donor PM6. As a result, OPVs based on the PM6:BTP-S2 blend realize a PCE of 16.37%, higher than that (15.79%) of PM6:Y6-based OPVs. A further optimization of the ternary blend (PM6:Y6:BTP-S2) results in a best PCE of 17.43%, which is among the highest efficiencies for single-junction OPVs. This work provides an effective approach to simultaneously lower the energy loss and promote the charge separation of OPVs by molecular design strategy.
关键词： asymmetric acceptors,molecular design strategies,nonfullerene acceptors,charge separation,organic photovoltaics
更新于2025-09-23 15:21:01
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Small bandgap non-fullerene acceptor enables efficient PTB7-Th solar cell with near 0 eV HOMO offset
摘要： Three small bandgap non-fullerene (SBG NFAs) acceptors, BDTI, BDTI-2F and BDTI-4F, based on a carbon-oxygen bridged central core and thieno[3,4-b]thiophene linker, end-capped with varied electron-withdrawing terminal groups, were designed and synthesized. The acceptors exhibit strong absorption from 600 nm to 1000 nm. The optimal device incorporating designed NFA and PTB7-Th polymer donor achieves a power conversion efficiency of 9.11% with near 0 eV HOMO offset. The work presents a case study of efficient non-fullerene solar cells with small HOMO offsets, which is achieved by blending PTB7-Th with fine-tuned SBG acceptor.
关键词： Organic solar cells,Driving force,HOMO offset,Non-fullerene acceptors,Small bandgap
更新于2025-09-23 15:21:01
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Ternary Organic Solar Cells Based on two Non-fullerene Acceptors with Complimentary Absorption and Balanced Crystallinity
摘要： The ternary blend structure has been demonstrated as an effective approach to increase the power conversion efficiency of organic solar cells. An effective approach to enhance the power conversion efficiency of ternary solar cells is based on two non-fullerene acceptors with complimentary absorption range and balanced crystalinity. In this work, by introducing a high crystallinity small-molecule acceptor, named C8IDTT-4Cl with appropriate alkyl side chains into a low crystalline blend of conjugated polymer donor PBDT-TPD and fused-ring electron acceptor ITIC-4F. A ternary device based on the blend PBDT-TPD:ITIC-4F:C8IDTT-4Cl exhibits a best power conversion efficiency of 9.51% with a simultaneous improvement of the short-circuit current density to 18.76 mA cm-2 and the fill factor up to 67.53%. The absorption onset for C8IDTT-4Cl is located at 900 nm, so that the well complementary light absorption is beneficial to the photocurrent. In addition, the existence of high crystallinity C8IDTT-4Cl in the ternary device is found helpful to modulate crystallinity, improve heterojunction morphologies and stacking structure, therefore to realize higher charge mobility and better performance.
关键词： Non-fullerene Acceptors,Ternary Organic Solar Cells,Power Conversion Efficiency,Complimentary Absorption,Balanced Crystallinity
更新于2025-09-23 15:21:01
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Single-Junction Organic Photovoltaic Cells with Approaching 18% Efficiency
摘要： Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP-4Cl-BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n-undecyl is shortened at the edge of BTP-eC11 to n-nonyl and n-heptyl. As a result, the NFAs of BTP-eC9 and BTP-eC7 are synthesized. The BTP-eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP-eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP-eC11. Significantly, due to the simultaneously enhanced short-circuit current density and fill factor, the BTP-eC9-based single-junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.
关键词： nonfullerene acceptors,organic photovoltaic cells,molecular modification,power conversion efficiency
更新于2025-09-23 15:21:01
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Non-fullerene small molecule acceptors with three-dimensional thiophene/selenophene-annulated perylene diimides for efficient organic solar cells
摘要： Three-dimensional non-fullerene acceptors with a spiro core linked with S/Se fused perylene diimides possess appropriate energy levels, twisted molecular configuration and high carrier mobility, leading to a power conversion efficiency of 6.95% for the organic solar cells.
关键词： perylene diimides,organic solar cells,carrier mobility,non-fullerene acceptors,spiro core
更新于2025-09-23 15:21:01
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Suppressing the Photocatalytic Activity of Zinc Oxide Electron-Transport Layer in Nonfullerene Organic Solar Cells with a Pyrene-Bodipy Interlayer
摘要： Organic solar cells based on nonfullerene acceptors have recently witnessed a significant rise in their power conversion efficiency values. However, they still suffer from severe instability issues, especially in an inverted device architecture based on the zinc oxide bottom electron transport layers. In this work, we insert a pyrene-bodipy donor?acceptor dye as a thin interlayer at the photoactive layer/zinc oxide interface to suppress the degradation reaction of the nonfullerene acceptor caused by the photocatalytic activity of zinc oxide. In particular, the pyrene-bodipy-based interlayer inhibits the direct contact between the nonfullerene acceptor and zinc oxide hence preventing the decomposition of the former by zinc oxide under illumination with UV light. As a result, the device photostability was significantly improved. The π?π interaction between the nonfullerene acceptor and the bodipy part of the interlayer facilitates charge transfer from the nonfullerene acceptor toward pyrene, which is followed by intramolecular charge transfer to bodipy part and then to zinc oxide. The bodipy-pyrene modified zinc oxide also increased the degree of crystallization of the photoactive blend and the face-on stacking of the polymer donor molecules within the blend hence contributing to both enhanced charge transport and increased absorption of the incident light. Furthermore, it decreased the surface work function as well as surface energy of the zinc oxide film all impacting in improved power conversion efficiency values of the fabricated cells with champion devices reaching values up to 9.86 and 11.80% for the fullerene and nonfullerene-based devices, respectively.
关键词： bodipy,zinc oxide,photocatalytic activity,pyrene,organic solar cells,photostability,nonfullerene acceptors
更新于2025-09-23 15:21:01
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Effects of the Isomerized Thiophene-Fused Ending Groups on the Performances of Twisted Non-Fullerene Acceptor-Based Polymer Solar Cells.
摘要： Recently, benefiting from the merits of small molecule acceptors (NFAs), polymer solar cells (PSCs) have achieved tremendous advances. From the perspective of the structural characteristics of the π-conjugated acceptor-donor-acceptor (A-D-A)-type of organic molecules, the backbone’s planarity, as well as the terminal groups and their substituents, have strong influences on the performances of the constructed NFAs. Through enlarging the dihedral angle of the conjugated main-chain of NFAs, a certain degree of enhanced photovoltaic parameters have been achieved. To further probe the influences of ending groups on the performances of nonplanar NFAs, we synthesized two new NFAs of i-cc23 and i-cc34 with isomerized thiophene-fused ending groups and twisted π-conjugated main-chain. Compared to the i-cc23 containing 2-(6-oxo-5,6-dihydro-4H-cyclopenta[b]thiophen-4-ylidene)malononitrile ending group, the 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile contained acceptor i-cc34 has a relatively higher molar extinction coefficient, bathochromic-shifted absorption spectrum, and deepened energy levels. When mixed with PBDB-T in solar cells, the i-cc23-based device achieved an excellent open-circuit voltage (VOC) of 1.10 V and a moderated power conversion efficiency of 7.34%. Although the VOC of i-cc34 related device was decreased to 0.96 V, the short-circuit current density and fill factor were improved, giving rise to enhanced efficiency of 9.51%. Apart from the distinct photovoltaic performances, the two isomers-based devices exhibit high radiative efficiency of 8×10-4, leading to a very small non-radiative loss of 0.19 V. Our results emphasize the importance of the isomerized thiophene-fused ending groups on the performances of nonplanar NFAs-based PSCs.
关键词： Twisted small molecular electron-acceptors,Thiophene-fused ending groups,Polymer solar cells,Isomerized end-groups,Non-radiative energy loss
更新于2025-09-23 15:21:01