Improved power conversion efficiency of bulk-heterojunction organic solar cells using a benzothiadiazole–triphenylamine polymer

A comparative study of the properties of bulk-heterojunction organic photovoltaic cells (OPVs) using a benzothiadiazole (BTD)–triphenylamine (TPA) small molecule and its polymerized molecule (poly(BTD-TPA)) is presented. OPVs using BTD-TPA or poly(BTD-TPA):PC60BM at a 1 : 2 mixing weight ratio were fabricated. The power conversion efficiency (PCE) of the poly(BTD-TPA)-based OPV was twice that of the BTD–TPA-based OPV. The field-effect hole mobility of poly(BTD-TPA) is two orders of magnitude higher than that of BTD–TPA and the absorption peak of poly(BTD-TPA) is at a longer wavelength than that of BTD–TPA. Accordingly, the improved hole mobility and enhanced absorption of AM1.5 solar-simulated light led to a high short-circuit current (Jsc) and PCE in OPVs based on poly(BTD-TPA). Using OPVs with poly(BTD-TPA):PC70BM (1 : 4), the device performance exhibited a Jsc value of 7.45 mA cm−2, an open-circuit voltage of 0.92 V, a PCE of 2.65%, and incident photon to current conversion efficiencies of around 50% at wavelengths ranging from 360 to 560 nm. The experimental results for the OPVs with BTD–TPA-based materials indicate that the polymer is effective for obtaining high-performance OPVs.