High photo-current in solution processed organic solar cells based on a porphyrin core A-π-D-π-A as electron donor material

Abstract Two new conjugated acceptor-donor-acceptor (A-π-D-π-A) molecules with a porphyrin core linked by ethynylene bridges to two thiophene ( 1a ) or thienylenevinylenethiophene ( 1b ) units and both capped by N -ethylrhodanine have been synthesized. These compounds were used as the main electron donor moieties for bulk heterojunction small molecule organic solar cells (BHJ-SMOSC). The optimized devices, with PC71BM as the main electron acceptor molecule, show remarkable short circuit currents, up to 13.2 mA/cm 2 , an open circuit voltage of around 0.85 V, and power conversion efficiencies up to 4.3% under 100 W/cm 2 . The External Quantum Efficiency (EQE), Atomic Force Microscopy (AFM), hole mobility, Photo-Induced Charge Extraction (PICE) and Photo-Induced Transient Photo-Voltage (PIT-PV) were analyzed in devices based on 1a and 1b in order to account for differences in the final performance of the two molecules. The PIT-PV decays showed slower recombination kinetics for devices fabricated with 1b . Moreover, the EQE was greater for 1b and this is ascribed to the better nanomorphology, which allows better charge collection before carrier recombination takes place.