High-Performance Polymer Solar Cells Realized by Regulating the Surface Properties of PEDOT:PSS Interlayer from Ionic Liquids.

Significant efforts have been dedicated to the interface engineering of organic photovoltaic device, suggesting that the performance and aging of the device are not only dependent on the active layer, but also governed by the interface with electrodes. In this work, controllable interfacial dipole and conductivity have been achieved in ionic liquids (ILs) modified poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). We conclude that an appropriate interfacial conductivity is as essential as the suitable work function for an efficient buffer layer. Through forming favorable dipoles for hole transportation and reducing the film resistance by [HOEMIm][HSO4] treatment, an averaged performance of 8.64% is obtained for OPVs based on PTB7:PC71BM bulk heterojunction with improved stability. However, the improvement of performance is inconspicuous for OPVs based on PTB7-Th:PC71BM bulk heterojunction due to the incompetent energy level of high concentration ILs-modified PEDOT:PSS. The enhanced in-plane conductivity will reduce shunt resistance, and produce a fake high short-circuit current density (Jsc) with a lower fill factor. We point out that the Jsc can be improved by decreasing series resistance; meanwhile, the accompanying reduced shunt resistance has an unfavorable effect on device performance.