The Intrinsic Role of the Fusion Mode and Electron-Deficient Core in Fused-Ring Electron Acceptors for Organic Photovoltaics

The A-DA ' D-A fused-ring electron acceptors with an angular fusion mode and electron-deficient core has significantly boosted organic photovoltaic efficiency. Here, the intrinsic role of the peculiar structure is revealed by comparing representative A-DA ' D-A acceptor Y6 with its A-D-A counterparts having different fusion modes. Owing to the more delocalized HOMO and deeper LUMO level, Y6 exhibits stronger and red-shifted absorption relative to the linear and angular fused A-D-A acceptors, respectively. Moreover, the change from linear to angular fusion substantially reduces the electron-vibration couplings, which is responsible for the faster exciton diffusion, exciton dissociation, and electron transport for Y6 than the linear fused A-D-A acceptor. Notably, the electron-vibration coupling for exciton dissociation is further decreased by introducing the electron-deficient core, thus contributing to the efficient charge generation under low driving forces in the Y6-based devices.