A Cathode Interface Layer Based on 4,5,9,10-Pyrene Diimide for Highly Efficient Binary Organic Solar Cells.

Efficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7-di-tert-butyl-4,5,9,10-pyrene diimide (t-PyDI) framework. By introducing amino, amino N-oxide and quaternary ammonium bromide as functional groups, three novel self-doped CIMs named t-PyDIN, t-PyDINO and t-PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t-PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.