Fine-Tuning Contact via Complexation for High-Performance Organic Solar Cells

For organic optoelectronic devices, precise tuning of the electrical property of both active layers and interfaces is crucial to achieve enhanced device performance. Herein, we developed a facile method using complexation to modify the work function and energy levels of cathode contact layers in organic solar cells (OSCs) to achieve suitable work function and energy levels while retaining relatively good conductivity. Compared with the control devices with neat (N,Ndimethyl- ammonium N-oxide)propyl perylene diimide (PDINO) contacts, the tris(pentafluorophenyl)borane (BCF)-complexed PDINO cathode contacts showed enhanced power conversion efficiencies (PCEs), which is independent of the composition of the active layer. More specifically, single-junction OSCs employing PDINO cathode contact with 2 wt % BCF-additive achieved an average PCE of 17.7%. Based on experimental data and theoretical modeling, we found that the boron cores of BCF coordinate with the amino N-oxide terminal substituent of PDINO after generating BCF-H2O/methanol complexes. BCF segments with a strong electron-withdrawing property can effectively reduce the energy levels of the PDINO-BCF complex, and thus enhance device PCE when it is used as a cathode contact in OSCs. This strategy can be extended to other types of photovoltaic devices, photodetectors, and light-emitting diodes.