Unveiling structure-performance relationships from multi-scales in non-fullerene organic photovoltaics

Unveiling the correlations among molecular structures, morphological characteristics, macroscopic properties and device performances is crucial for developing better photovoltaic materials and achieving higher efficiencies. To achieve this goal, a comprehensive study is performed based on four state-of-the-art non-fullerene acceptors (NFAs), which allows to systematically examine the above-mentioned correlations from different scales. Its found that extending conjugation of NFA shows positive effects on charge separation promotion and non-radiative loss reduction, while asymmetric terminals can maximize benefits from both terminals. Another molecular optimization is from alkyl chain tuning. The shortened alkyl side chain results in strengthened terminal packing and decreased pi-pi distance, which contribute high carrier mobility and finally the high charge collection efficiency. With the most-acquired benefits from molecular structure and macroscopic factors, PM6:BTP-S9-based organic photovoltaics (OPVs) exhibit the optimal efficiency of 17.56% (certified: 17.4%) with a high fill factor of 78.44%, representing the best among asymmetric acceptor based OPVs. This work provides insight into the structure-performance relationships, and paves the way toward high-performance OPVs via molecular design. Understanding correlations between molecular structures and macroscopic properties is critical in realising highly efficient organic photovoltaics. Here, the authors conduct a comprehensive study based on four non-fullerene acceptors revealing how the extended conjugation, asymmetric terminals and alkyl chain length can affect device performance.Funding Agencies|National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21734008, 21875216, 51803178, 61721005]; National Key Research and Development Program of China [2019YFA0705900, 2017YFA0207700]; China Postdoctoral Science FoundationChina Postdoctoral Science Foundation [2020M671715, 2017M621907, 2019T120501]; Zhejiang University; Swedish Government Strategic Research Area in Material Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [200900971]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2017-04123]; China Scholarship Council (CSC)China Scholarship Council [201708370115]; Research Grant Council of Hong Kong (General Research Fund) [14303519]; CUHK Direct GrantChinese University of Hong Kong [4053415]