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Retarding the Crystallization of a Nonfullerene Electron Acceptor for High‐Performance Polymer Solar Cells

2018; Wiley; Volume: 29; Issue: 5 Linguagem: Inglês

10.1002/adfm.201807662

1616-3028

Wei Li, Mengxue Chen, Zhuohan Zhang, Jinlong Cai, Huijun Zhang, Robert S. Gurney, Dan Liu, Jiangsheng Yu, Weihua Tang, Tao Wang,

Perovskite Materials and Applications

Abstract Developing a fundamental understanding of the molecular order within the photoactive layer, and the influence therein of solution casting conditions, is a key factor in obtaining high power conversation efficiency (PCE) polymer solar cells. Herein, the molecular order in PBDB‐T:INPIC‐4F nonfullerene solar cells is tuned by control of the molecular organization time during film casting, and the crucial role of retarding the crystallization of INPIC‐4F in achieving high performance is demonstrated. When PBDB‐T:INPIC‐4F is cast with the presence of solvent vapor to prolong the organization time, INPIC‐4F molecules form spherulites with a polycrystalline structure, resulting in large phase separation and device efficiency below 10%. On the contrary, casting the film on a hot substrate is effective in suppressing the formation of the polycrystalline structure, and encourages face‐on π−π stacking of INPIC‐4F. This molecular transformation of INPIC‐4F significantly enhances the absorption ability of INPIC‐4F at long wavelengths and facilitates a fine phase separation to support efficient exciton dissociation and balanced charge transport, leading to the achievement of a maximum PCE of 13.1%. This work provides a rational guide for optimizing nonfullerene polymer solar cells consisting of highly crystallizable small molecular electron acceptors.