Highly Efficient Solar Cell Polymers Developed via Fine-Tuning of Structural and Electronic Properties

TLDR

The study reports the synthesis and photovoltaic evaluation of new semiconducting polymers composed of alternating thieno[3,4‑b]thiophene and benzodithiophene units. Polymers were engineered by substituting alkoxy side chains or adding fluorine to lower HOMO levels, thereby fine‑tuning their electronic properties for improved photovoltaic performance. These structural modifications broadened absorption, enhanced hole mobility and fullerene miscibility, raised V_oc, and produced a finely interpenetrated polymer/fulleride network that achieved over 6 % efficiency, demonstrating the bright future of polymer solar cells.

Abstract

This paper describes synthesis and photovoltaic studies of a series of new semiconducting polymers with alternating thieno[3,4-b]thiophene and benzodithiophene units. The physical properties of these polymers were finely tuned to optimize their photovoltaic effect. The substitution of alkoxy side chains to the less electron-donating alkyl chains or introduction of electron-withdrawing fluorine into the polymer backbone reduced the HOMO energy levels of polymers. The structural modifications optimized polymers' spectral coverage of absorption and their hole mobility, as well as miscibility with fulleride, and enhanced polymer solar cell performances. The open circuit voltage, V(oc), for polymer solar cells was increased by adjusting polymer energy levels. It was found that films with finely distributed polymer/fulleride interpenetrating network exhibited improved solar cell conversion efficiency. Efficiency over 6% has been achieved in simple solar cells based on fluorinated PTB4/PC(61)BM films prepared from mixed solvents. The results proved that polymer solar cells have a bright future.