Replacing thiophene with selenophene in PCDTBT to lower LUMO for efficient polymer solar cells

Abstract

We have synthesized a selenophene analogue of PCDTBT, namely, PCDSeBT, in which diselenienylbenzothiadiazole (DSeBT) monomer alternately flanks with 2,7-carbazole unit. The intrinsic properties of PCDSeBT are not only characterized by UV-vis absorption, cyclic voltammetry (CV), and organic field-effect transistors (OFETs) but also the surface morphology, mobilities of space charge-limited current (SCLC) model, and polymer solar cells (PSCs) in its bulk-heterojunction (BHJ) active layer with PC71BM are evaluated in detail. It is found that PCDSeBT has a low-lying HOMO energy level at -5.4 eV and a low bandgap of 1.70 eV as required by the ideal polymers for BHJ PSCs. The high current of 11.7 mA/cm2 is obtained for PCDSeBT-based PSCs. The high JSC value, along with a moderate fill factor (FF) of 45% and a high open-circuit voltage (VOC) of 0.79 V, yields a power conversion efficiency (PCE) of 4.12%, which is about 37% increase in PCE from a PCDTBT-based reference device.