New n-Type Copolymers Based on Pentafluorobenzene-Substituted Thieno [3,4-c] Pyrrole-4,6-dione for All-Polymer Solar Cells

Abstract

New n-type copolymers (PBDT-FTPD, PBDT(T)-FTPD) based on pentafluorobenzene-substituted thieno[3,4-c] pyrrole-4,6-dione and benzo[1,2-b:4,5-b/]dithiophene (BDT) were designed and synthesized. Ethyl-hexylthiophenyl and branched octyl-decyloxyl side chains were introduced into BDT unit to explore the effects of side chain on the thermal, photo-physical and electrochemical properties of copolymers. All-polymer solar cells based on these copolymers as the acceptors and classical P3HT as the donor were fabricated to investigate the relationship between photovoltaic performance and copolymer structure. The results show that these copolymers exhibit deep HOMO energy levels and relative high open-circuit voltage (Voc) (0.86–0.90 V) used as acceptors in all-polymer solar cells (PSCs). When the ethyl-hexylthiophenyl group was introduced into the BDT unit, two-dimensional conjugated (2D-conjugated) copolymer PBDT(T)-FTPD had a higher Td (428°C) and relative molecular weight (Mn = 48875 g·mol−1), better photovoltaic performance than copolymer PBDT-FTPD with branched octyl-decyloxyl side chain. As a result, PBDT(T)-FTPD film exhibited electron-mobility of 5.03 × 10−6cm2V−1S−1and P3HT/PBDT(T)-FTPD solar cells had a Voc of 0.90 V, a Jsc and FF of 1.06 mA/cm2 and 30.0%, respectively, giving a PCE of 0.29%.