A comprehensively theoretical and experimental study of carrier generation and transport for achieving high performance ternary blend organic solar cells

Abstract

Ternary blend organic solar cells (OSCs) composed of three components in the active layer shows the potential to achieve higher power conversion efficiency (PCE) as compared to the binary counterpart due to the wider absorption spectrum, higher generation rate, and better morphology. However, the physical understanding of carrier generation and transport processes in the ternary blend OSCs has been limited explored. In the work, together with experimental studies of the two donors, one acceptor ternary blend OSCs with PCE > 12%, we will theoretically and experimentally describe the roles of the carrier generation (including exciton transfer, delocalization and dissociation), and carrier transport (particularly the hole transport) on the performance of ternary blend OSCs. Through theoretical and experimental investigations, critical design rules for improving the device performance are concluded: (1) improving the exciton delocalization ratio via donor ratio optimization with physical understanding, (2) selecting the donors with well overlap of emission and absorption spectra to promote a beneficial exciton transfer, (3) engineering the energy level of donors to form the blocking barrier for reducing hole transfer into the donor with high recombination loss. The work unveils the device physics which is fundamentally important for designing and optimizing high-performance ternary blend OSCs.