Suppressing Voltage Loss and Improving Charge Generation via Fluorinated Molecular Backbone of Low-Cost Polymers for Efficient Organic Solar Cells

Abstract

High efficiency and low cost are indispensable for the industrialization of organic solar cells (OSCs), which urgently needs to be addressed. Herein, three simple-structure terpolymer donors, PTQ13-5, PTQ13-10, and PTQ13-15, are developed by embedding a simple fluorinated unit 3-fluorothiophene (T-F) into the molecular backbone of polymer PTQ10 to pursue low-cost and high-efficiency organic photovoltaic molecules. Three terpolymers show obviously low-cost characteristics due to their short synthesis routes and high total synthetic yields from cheap raw materials. The introduction of the T-F unit leads to the blue-shifted absorption, down-shifted HOMO levels, and more favored molecular aggregation morphology of terpolymers, mainly due to the strong electron-withdrawing property of the F atom, along with the presence of noncovalent F···H interactions. As a result, the PTQ13-5-based OSC achieves enhanced power conversion efficiency (PCE) of 18.42% due to suppressed voltage loss (V_loss) because of low nonradiative loss of 0.189 eV and enhanced charge generation; this is one of the highest PCEs for OSCs based on low-cost organic photovoltaic materials. This work suggests that fluorination of the polymer backbone is an effective strategy to suppress V_loss and improve charge generation of OSCs, and it offers a rational guide in the design of organic photovoltaic molecules with low cost and high performance.