Cubic-Like Bimolecular Crystal Evolution

Abstract

One of the major problems preventing widespread use of organic solar cells (OSCs) is the fact that most high-performance OSCs at present are prepared using hazardous halogenated solvents and/or additives. In this study, we determine the solubility properties of a given ternary blend set, in which two donors (PTB7-Th and DR3TSBDT) and one acceptor (PC71BM) are used, in a series of solvents, and use active material–solvent interactions as an aid for finding suitable non-chlorinated solvents to achieve effective ternary OSCs based on PTB7-Th:DR3TSBDT:PC71BM. A hitherto unrealized power conversion efficiency (PCE) as high as 12.3% (a certified PCE of 11.94%) is obtained using the developed non-halogenated processing system. In-depth investigations (morphology, charge mobility, recombination dynamics, and OSC characteristics) uncover the underlying structure–property relationships as a function of the chosen non-halogenated systems. In addition, another intriguing finding of this study is the formation of a cubic bimolecular crystal structure of PTB7-Th:PC71BM in a non-halogenated system, which is the first such demonstration in blend films. This sheds light upon the fact that the physical properties of a material applied from different solutions may surpass the variation in the properties between two material having totally different molecular structure. Therefore, this work not only offers important scientific insights into developing highly efficient and eco-friendly OSCs but also improves our understanding of achievable bimolecular crystals with an intercalated structure.