All-polymer solar cells with efficiency approaching 16% enabled using a dithieno[3′,2′:3,4;2′′,3′′:5,6]benzo[1,2-c][1,2,5]thiadiazole (fDTBT)-based polymer donor

Abstract

In this study, a series of large-bandgap polymer donors comprising dithieno[3′,2′:3,4;2′′,3′′:5,6]benzo[1,2-c][1,2,5]thiadiazole (fDTBT) and benzo[1,2-b:4,5-b′]dithiophene units with or without sulfur/fluorine substitution in the side-chains are designed. It is found that the energy levels of these polymer donors can be linearly tuned due to the π-accepting properties of the sulfur atom and strong electron-withdrawing ability of the fluorine atom, while the absorption spectra keep nearly unchanged, which offers us the opportunity to balance the open-circuit voltage and charge separation driving force in all-polymer solar cells (all-PSCs). The device performances of these polymer donors are validated by combining them with the polymer acceptor PJ1. The device results indicate that as the energy-level offsets are increased, these systems exhibit a more efficient charge transfer and lesser charge recombination, which afford remarkably improved short-circuit current density, fill factors, and power conversion efficiency (PCE). Eventually, high-efficiency binary all-PSCs with a maximum efficiency of 15.8% are obtained, which is the highest value reported so far for all-PSCs. Moreover, this system demonstrates superior performance for 1 cm² all-PSC devices with a PCE of 14.4% and semitransparent all-PSC devices with a PCE of 10.3% (with average visible-light transmittance of 21.5%). Our study manifests that these fDTBT-based polymers are promising donor candidates for high-performance all-PSCs toward practical applications.