Sequentially Fluorinated Polythiophene Donors for High-Performance Organic Solar Cells with 16.4% Efficiency

Abstract

Polythiophenes (PTs) have attracted considerable interest for application in organic solar cells (OSCs) owing to their simple molecular structures and low-cost synthesis. However, the power conversion efficiencies (PCEs) of PT-based OSCs are lower than those of state-of-the-art OSCs. Herein, the development of two sequentially fluorinated PT donors (PT-2F and PT-4F) is reported for realizing highly efficient OSCs. PT-2F and PT-4F are designed to contain two and four fluorine atoms, respectively, per repeating unit to decrease their highest occupied molecular orbital energy levels and increase the open-circuit voltages of the OSCs. Importantly, the PT-4F polymers exhibit high backbone rigidity and the desired temperature-dependent aggregation behavior, affording well-developed crystalline structures in thin films for efficient charge transport. These beneficial features promote the construction of an optimal blend morphology of PT-4F:small-molecule acceptor with a suitable energy offset and low energetic disorder. Thus, the PT-4F-based binary and ternary OSCs achieve high PCEs of 15.6% and 16.4%, respectively.