PTB7-Th /Non-fullerene acceptors for organic solar cells

Abstract

The recent advent of non-fullerene acceptors (NFAs), with outstanding advantages such as molecular structure susceptibility, tunable energy levels, broad absorption, and high crystallinity, has restimulated research in the field of organic solar cells (OSCs). Power conversion efficiency (PCE) has reached over 18 % for single-junction non-fullerene organic solar cells (NFOSCs) in 2021. These impressive achievements were strongly driven by the collective efforts of chemists to design novel donor and acceptor organic polymers and small molecules and optimize the active layer morphology. Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)− 3-fluorothieno[3,4-b]thiophene)− 2-carboxylate-2,6-diyl] (PTB7-Th) has been widely used as an excellent low-bandgap polymer donor in highly efficient NFOSCs. Recently, NFOSCs combining PTB7-Th and newly designed NFAs achieved a PCE over 12 %. Thus, a valuable review of NFAs compatible with PTB7-Th is required to direct researchers toward further optimization of PTB7-Th-based NFOSCs. In this perspective, we discuss the progress in molecular design strategies of various NFAs blended with PTB7-Th in single-junction OSCs over the last decade. We also highlight the effects of molecular engineering of NFAs on their optoelectronic properties and review their features on molecular stacking and photovoltaic performance of PTB7-Th-based OSCs. In the last part, the challenges for developing highly efficient NFAs consistent with PTB7-Th are proposed.