Exploring photoexcited spin states for fullerene-derivatives based organic bulk heterojunction solar cells using magneto-photocurrent

Fullerene-derivatives based bulk heterojunctions hold an exceptionally important role on the roadmap of highly efficient organic solar cells (OSCs). In recent years, the utilization of the non-fused ring acceptors based OSCs has further improved photovoltaic power conversion efficiencies. Among these, one of the fundamental issues is to explore and to understand the spin-related polaron dissociation at charge transfer states because they act as the central unit for the photovoltaic action. It is also eagerly important to quantify some internal fields, such as hyperfine fields and the spin-orbit coupling. The aim of the work is to develop a method for unraveling the photoexcited spin states, particularly for the fullerene-derivative based OSC. Furthermore, it helps to elucidate a long-standing issue regarding the relatively high production of photocurrent for the P3HT:PC71BM system, which is indeed contrary to its counterpart the P3HT:PC61BM system. Their corresponding Jablonski diagrams have been determined in order to understand interior spin dynamics. The method of the study offers an alternative route for an understanding of device performance from the spin-related aspect.