The innovation of photovoltaic materials, [1][2][3][4][5] specially nonfullerene acceptors (NFAs), has pioneered many research hot spots of organic solar cells (OSCs) for in-depth exploration in the past decades. With combinational efforts devoted to molecule evolution and device engineering, the power conversion efficiency (PCE) of single-junction solar cells has approached up to 19%. [6][7][8] Various NFAs have been developed in recent years, such as diketopyrrolopyrrole (DPP) or perylene diimide (PDI) contained molecules, [9][10][11] A-D-A-type acceptors, i.e., ITIC, [12,13] M series [14] and Y series molecules, [15][16][17][18] typically Y6. [19] Core engineering has been demonstrated effective to achieve highperformance NFAs, as molecular conjugation and intramolecular charge transfer (ICT) can be readily realized through introducing or removing the aromatic rings on the backbone of NFAs. Additionally, the asymmetric strategy was adopted for molecule modification, which could precisely regulate the intrinsic optoelectronic properties of NFAs. Derived from symmetric NFAs, i.e., ITIC [12] and IT-4F, [20] various A-D-A-type asymmetric NFAs have been designed and synthesized. [21,22] Sun's group designed asymmetric TPTT-2F and TPTTT-2F through extending molecular conjugation of the IDT core. [23] Along with the enhanced conjugation, redshifted
Incorporating ITIC derivatives as guest acceptors into binary host systems is an effective strategy for constructing high-performance ternary organic solar cells (TOSCs). In this work, we introduced A−D−A type ITIC derivatives PTBTT-4F (asymmetric) and PTBTP-4F (symmetric) into the PM6:BTP-BO-4F (Y6-BO) binary blend and investigated the impacts of two guest acceptors on the performance of TOSCs. Differentiated device performance was observed, although PTBTT-4F and PTBTP-4F presented similar chemical structures and comparable absorptions. The PTBTT-4F ternary devices exhibited an improved power conversion efficiency (PCE) of 17.67% with increased open circuit (V OC ) and current density (J SC ), whereas the PTBTP-4F-based ternary devices yielded a relatively lower PCE of 16.34%. PTBTT-4F showed much better compatibility with the host acceptor BTP-BO-4F, so that they formed a well-mixed alloy phase state; more precise phase separation and increased crystallinity were thus induced in the ternary blends, leading to reduced molecular recombination and improved charge mobilities, which contributed to improved fill factors of the ternary devices. In addition, the optimized PTBTT-4F devices exhibited good performance tolerance of the photoactive layer thickness, as they even delivered a PCE of 15.25% when the active layer was as thick as up to ∼300 nm.
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