Efficient Bulk Heterojunction Solar Cells Based on a Broadly Absorbing Phenylenevinylene Copolymer Containing Thiophene and Pyrrole Rings

摘要

A novel low band gap alternating phenylenevinylene copolymer, P, containing thiophene and pyrrole rings was synthesized by Heck polycondensation. It was soluble in common organic solvents and showed a long-wavelength absorption maximum at 596—635 nm and an optical band gap of 1.65 eV. The electrochemical properties and electronic energy levels of P were studied by cyclic voltammetry. The highest occupied molecular orbital (HOMO) level of P is deeper than that of poly(3-hexylthiophene) (P3HT). The polymer solar cells (PSCs) based on P with a modified l-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]-C-61 (PCBM) (i.e., E) as an electron acceptor shows higher open circuit voltage (V_(oc)) than that for the device based on P3HT. The power conversion efficiency (PCE) for the devices P—F and P—PCBM processed from tetrahydrofuran (THF) solvent is approximately 2.42% and 1.50%, respectively. The enhanced PCE is attributed to the higher value of both V_(oc) and short circuit current (J_(SC)). The PCE of the devices based on P—F processed from mixed solvents has been further improved. The P—F blend film cast from mixed solvents shows higher absorption and incident photons to current efficiency (IPCE) with respect to the THF-cast film. The overall PCE for the PSC processed from 1-chloronaphthalene (CN)/THF (thermally annealed) is 4.14%. The improved PCE has been attributed to the increased crystallite size and hole mobility in the blend, resulting in balanced charge transport.