P-nitrophenol-terminated alkyl side chain substituted polymer as high dielectric constant polymer additive enables efficient organic solar cells

Abstract

Herein, we introduced p-nitrophenol-terminated alkyl side chain into the benzotriazole unit and synthesized a high dielectric constant polymer PBTA-NO2 (εr = 7.1). The properties as absorption spectra, energy levels, aggregation, dielectric constant, photovoltaic performance, etc. of PBTA-NO2 were analyzed and compared with its controlled polymer PBTA-C10H21. It is found that the PBTA-NO2 exhibits a similar absorption spectrum, lower highest occupied molecular orbital (HOMO) energy level, stronger aggregation characteristic and higher dielectric constant at 1 kHz in contrast to that of PBTA-C10H21. Beyond that, the PBTA-NO2 was adopted as a high dielectric constant polymer additive into the active layer of the PM6:Y6 based polymer solar cells (PSCs). The incorporation of 5 wt% PBTA-NO2 slightly increased the relative dielectric constant (εr) of the blend film from 4.4 to 4.8 and simultaneously improved the morphology of the active layer, which promoted the exciton dissociation and carrier transport, inhibited bimolecular recombination, and eventually increased the power conversion efficiency (PCE) by 6% as compared to the original device.