Improving power conversion efficiency (PCE) is important for broadening the applications of organic photovoltaic (OPV) cells. Here, a maximum PCE of 19.0% (certified value of 18.7%) is achieved in single-junction OPV cells by combining material design with a ternary blending strategy. An active layer comprising a new wide-bandgap polymer donor named PBQx-TF and a new low-bandgap non-fullerene acceptor (NFA) named eC9-2Cl is rationally designed. With optimized light utilization, the resulting binary cell exhibits a good PCE of 17.7%. An NFA F-BTA3 is then added to the active layer as a third component to simultaneously improve the photovoltaic parameters. The improved light unitization, cascaded energy level alignment, and enhanced intermolecular packing result in open-circuit voltage of 0.879 V, short-circuit current density of 26.7 mA cm-2 , and fill factor of 0.809. This study demonstrates that further improvement of PCEs of high-performance OPV cells requires fine tuning of the electronic structures and morphologies of the active layers.

Single-Junction Organic Photovoltaic Cell with 19% Efficiency

Symmetric conjugated molecules can be broken through suitable synthetic strategies to construct novel asymmetric molecules, which can largely broaden the material library. In the field of organic solar cells, fused‐ring electron acceptors (FREAs) with the A‐DA'D‐A type backbone structure have attracted much attention and enabled power conversion efficiencies (PCE) exceeding 18%. Among them, Y6 is one of the most classic FREAs that can derive many symmetric and asymmetric molecules and exhibit unique optoelectronic properties. Thus, in this review, the focus is on the recent progress of Y6‐derived asymmetric FREAs containing a dipyrrolobenzothiadiazole segment, which can be classified as the following three categories: asymmetric end group, asymmetric central core and asymmetric side chain. The relationship of the molecular structure, optoelectronic properties, and device performance is discussed in detail. Finally, the future design directions and challenges faced by this kind of photovoltaic materials are given.

Recent Progress of Y6‐Derived Asymmetric Fused Ring Electron Acceptors

Quantum chemical analysis and molecular dynamics simulations to study the impact of electron-deficient substituents on electronic behavior of small molecule acceptors

Quantum Chemical Approach of Donor−π–Acceptor Based Arylborane–Arylamine Macrocycles with Outstanding Photovoltaic Properties Toward High-Performance Organic Solar Cells

Non-halogenated polymers have great potential in commercialization of organic photovoltaic (OPV) cells due to their advantage in low-cost preparation. However, non-halogenated polymers usually have high HOMO energy levels and inferior self-aggregation properties in solution, thus resulting in low power conversion efficiencies (PCEs). Herein, two non-halogenated polymers, PB1 and PB2, are prepared. When the polymers were used to fabricate OPV cells with the BTP-eC9, the PB1-based device only gave a PCE of 5.3%, while the PB2-based device showed an outstanding PCE of 17.7%. After the introduction of PBDB-TF as the third component, the PB2:PBDB-TF:BTP-eC9-based device with an optimal weight ratio of 0.5:0.5:1 achieved a PCE up to 18.4%. More importantly, PB2 exhibited good compatibility with various non-fullerene acceptors to achieve better PCEs than those of classical polymer (PBDB-T and PBDB-TF)-based devices. When PB2 was combined with wide bandgap electron acceptor (F-BTA3), this device showed the excellent PCE of 27.1% and 24.6% for 1 and 10 cm2 devices, respectively, under light intensity of 1000 lux light-emitting diode illumination. These results provide new insight in the rational design of novel non-halogenated polymer donors for further developing low-cost materials and broadening the application of OPV cells. This article is protected by copyright. All rights reserved.

A Universal Nonhalogenated Polymer Donor for High-Performance Organic Photovoltaic Cells.

Benzothiadiazole-based non-fullerene acceptors

Non-fullerene acceptors (NFAs) can be simply divided into three categories: A-D-A, A-DA'D-A, and A2-A1-D-A1-A2 according to their chemical structures. Benefiting from the easily modified 1,1-dicyanomethylene-3-indanone end groups, the halogenation on the first two types of materials has been proved to be very effective to modulate their optoelectronic properties and improve their photovoltaic performance. Hence, in this work, we systematically investigate the effect of halogenation on the classic NFA molecule of BTA3, which has the linear A2-A1-D-A1-A2-type backbone. After fluorination and chlorination, F-BTA3 and Cl-BTA3 have similar optical band gaps but lower energy levels than BTA3. When blending with a linear copolymer PE25 composed of benzodifuran and chlorinated benzotriazole (BTA) according to "Same-A-Strategy", the corresponding VOC of the halogenated NFAs gradually decreases (1.13 V for F-BTA3 and 1.09 V for Cl-BTA3), compared with that of the BTA3-based device (VOC = 1.22 V). This tendency mainly comes from the lower lowest unoccupied molecular orbital energy levels due to the strong electron-withdrawing ability of halogen atoms and the larger nonradiative energy loss. However, the power conversion efficiencies of the halogenated materials are slightly improved, from 9.08% for PE25: BTA3 to 10.45% for PE25: F-BTA3 and 10.75% for PE25: Cl-BTA, with the nonhalogenated solvent tetrahydrofuran as the processing solvent. The improved photovoltaic performance of F-BTA3 and Cl-BTA3 should come from the higher carrier mobility, weaker bimolecular recombination, and higher fluorescence quenching rate. This study illustrates that halogenation on the A1 unit is a promising strategy for developing novel and effective A2-A1-D-A1-A2-type NFAs.

Effects of Halogenation on the Benzotriazole Unit of Non-Fullerene Acceptors in Organic Solar Cells with High Voltages.

Pyrrolo[3,4-f]benzotriazole-5,7-dione (TzBI) is an effective electron-accepting (A) unit to construct photovoltaic polymers. Though TzBI-based polymers have realized promising photovoltaic performa...

Qingling Nie

Papers

Benzothiadiazole-based non-fullerene acceptors

Effects of Halogenation on the Benzotriazole Unit of Non-Fullerene Acceptors in Organic Solar Cells with High Voltages.

Wide Band Gap Photovoltaic Polymer Based on Pyrrolo[3,4-f]benzotriazole-5,7-dione (TzBI) with Ultrahigh VOC Beyond 1.25 V

Study on the side chain effect of A2-A1-D-A1-A2 type non-fullerene acceptors matched with P3HT