Interface engineering on phenanthrocarbazole/thienopyrroledione-based conjugated polymer for efficient organic photovoltaic devices with ideal nano-morphology and improved charge carrier dynamics

Abstract

We synthesized PP-TPD, based on a phenanthro[1,10,9,8-cdefg]carbazole unit as a donor and a thieno [3,4-c]pyrrole-4,6-dione (TPD) unit as an acceptor for efficient bulk heterojunction photovoltaic cells. The copolymer achieves a relatively low bandgap (1.6 eV) by its internal charge-transfer, which concurs with the results of density functional theory (DFT) calculation for the distribution of HOMO and LUMO levels. In addition, we fabricated the bulk-heterojunction (BHJ) photovoltaic cells as a function of the blend ratio of the donor (PP-TPD) and acceptor (PC70BM), and applied a solvent additive and an interlayer to the device, with the optimized ratio used in this study. To comprehend the relationships between the device performance and the synergetic effects of 1,8-diiodooctane (DIO) and titanium oxide (TiOx) within the PP-TPD: PC70BM blends, we investigated the hole mobility related to the charge carrier transport, the charge generation, and the charge transport resistance using space-charge limited current (SCLC) measurement, photocurrent analysis, and impedance spectroscopy, respectively. Especially, we implemented fluorescence imaging by Raman spectroscopy, which related to the charge generation and recombination dynamics within the surface of photoactive areas.