New Avenues for Organic Solar Cells Using Intrinsically Charge-Generating Materials

Abstract

The molecular electron acceptor material Y6 has been a key part of the most recent surge in organic solar cell sunlight-to-electricity power conversion efficiency, which is now approaching 20%. Numerous studies have sought to understand the fundamental photophysical reasons for the exceptional performance of Y6 and its growing family of structural derivatives. Though significant uncertainty about several details remains, many have concluded that initially photogenerated excited states rapidly convert into electron–hole charge pairs in the neat material. These charge pairs are characterized by location of the electron and hole on different Y6 molecules, in contrast to the Frenkel excitons that dominate the behavior of most organic semiconductor materials. Here, we summarize the current state of knowledge regarding Y6 photophysics and the key observations that have led to it. We then link this understanding to other advances, such as the role of quadrupolar fields in donor–acceptor blends, and the importance of molecular interactions and organization in providing the structural basis for Y6′s properties. Finally, we turn our attention to ways of making use of the new photophysics of Y6, and suggest molecular doping, crystal structure tuning, and electric field engineering as promising avenues for future exploration.

Towards high-throughput exciton diffusion rate prediction in molecular organic semiconductors

“…However, these interactions involve Y6, which is already problematic to model because it is not a purely excitonic material. 21,71,72 Properly correcting for these effects would require the use of partially delocalised rate theories. 73–76 This may ultimately prove tractable, 77 but at present such an approach would conflict with our goal of minimising computational demand.…”