Alkoxyl Side Chain Substituted Thieno[3,4-c]pyrrole-4,6-dione To Enhance Photovoltaic Performance with Low Steric Hindrance and High Dipole Moment.

A series of N-OR substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) and benzo[1,2-b:4,5-b′]dithiophene (BDT) based copolymers are systematically investigated. The replacing CH2 with smaller size oxygen atom not only reduces the steric hindrance but also enhances the dipole moment (Δμge), which is in favor of charge separation. while the optical and electrochemical properties almost remain unchanged due to the alkoxyl chain on TPD unit not conjugated with the backbone. Consequently, the PBT-O8 based solar cell devices yield a remarkable short-circuit current density (JSC) of up to 14.3 mA/cm² and power conversion efficiency (PCE) of 8.22%, which exhibits an increase of 10% in comparison with that of PBT-C8 (PCE 7.50%). Furthermore, the PCEs increase almost linearly with decreasing side chain length from O12 to O10 to O8. Apart from the novel TPD analogues reported here, this work also provides a new insight into the ingenious use of alkoxyl side chain to improve the photovoltaic performance. [ABSTRACT FROM AUTHOR]