Enhancing the photovoltaic properties of terpolymers containing benzo[1,2-b:4,5-b′]dithiophene, phenanthro[4,5-abc]phenazine and benzo[c][1,2,5]thiadiazole by changing the substituents

Abstract

In this study, three novel donor–acceptor (D–A)-type random conjugated terpolymers of PBDTT–PPzBT–H, PBDTT–PPzBT–F and PBDTT–PPzBT–O were synthesized by copolymerizing electron-rich 5,8-dialkylthienyl substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT) and two electron-deficient phenanthro[4,5-abc]phenazine (PPz) and benzo[c][1,2,5]thiadiazole (BT) units. By changing the substituents at the 5,6-positions of BT, the optoelectronic properties of the terpolymers could be rationally adjusted for application as donor materials in polymer solar cells (PSCs). As a result, these terpolymers exhibited different light absorption properties, HOMO energy levels and hole mobilities, which contributed to the optimization of short-circuit current (J_sc), open-circuit voltage (V_oc) and fill factor (FF) properties, respectively. Interestingly, a maximum power conversion efficiency (PCE) of 6.3% was obtained with an V_oc of 0.75 V, a J_sc of 13.0 mA cm⁻² and a FF of 64.8% in the PBDTT–PPzBT–O based PSCs using [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as an acceptor, while PBDTT–PPzBT–H and PBDTT–PPzBT–F based devices also demonstrated a PCE of more than 4.5%. To the best of our knowledge, these are the highest recorded maximum PCE, J_sc and FF values obtained to date compared with previously reported phenazine copolymeric derivatives in BHJ-PSCs. This study illustrates the potential of these random conjugated terpolymers as promising donor materials in the application of PSCs.