A New Electron Acceptor with meta-Alkoxyphenyl Side Chain for Fullerene-Free Polymer Solar Cells with 9.3% Efficiency

A new small molecule acceptor, m-ITIC-OR, based on indacenodithieno[3,2-b]thiophene core with meta-alkoxyphenyl side chains, is designed and synthesized. The m-ITIC-OR film shows broader and redshift absorption compared to its solution and matched energy levels with a hexafluoroquinoxaline-based polymer donor-HFQx-T. Here, polymer solar cells (PSCs) by blending an HFQx-T donor and an m-ITIC-OR acceptor as an active layer deliver the power conversion efficiency (PCE) of 6.36% without any posttreatment. The investigations demonstrate that the HFQx-T:m-ITIC-OR blend films possess higher and more balanced charge mobility, negligible bimolecular recombination, and nanoscale interpenetrating morphology after thermal annealing (TA) treatment. Through a simple TA treatment at 150 °C for 5 min, an impressive PCE of 9.3% is obtained. This efficiency is among one of the highest PCEs for additive free PSCs. This is the first time alkoxyphenyl side chain is introduced into nonfullerene electron acceptor; more interestingly, the new electron acceptor (m-ITIC-OR) in this work shows a great potential for highly efficient photovoltaic properties.