Understanding polycarbazole-based polymer:CdSe hybrid solar cells

We report for the first time the fabrication and characterization of organic-inorganic bulk heterojunction (BHJ) hybrid solar cells made of poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and pyridine-capped CdSe nanorods. By optimizing both CdSe loading and active layer film thickness, the power conversion efficiencies (PCEs) of PCDTBT:CdSe hybrid solar cells were able to reach 2%, with PCDTBT:CdSe devices displaying an open-circuit voltage (V(OC )) that is 35% higher than P3HT:CdSe devices due to the deeper HOMO level of PCDTBT polymer. The performance of PCDTBT:CdSe devices is limited by its morphology and also its lower LUMO energy offset compared to P3HT:CdSe devices. Hence, the performance of PCDTBT:CdSe solar cells could be further improved by modifying the morphology of the films and also by including an interlayer to generate a built-in voltage to encourage exciton dissociation. Our results suggest that PCDTBT could be a viable alternative to P3HT as an electron donor in hybrid BHJ solar cells for high photovoltage application.