Photovoltaic Properties of a Porphyrin-Containing Polymer as Donor in Bulk Heterojunction Solar Cells With Low Energy Loss

A low bandgap D-pi-A polymer (PPDPP; D = Zn-porphyrin, A = diketopyrrolopyrrole, pi = ethynyle linker) has been synthesized and used as an electron donor for the fabrication of solution processed bulk heterojunction polymer solar cells (PSCs). PC71BM is used as the electron acceptor. After the optimization of the PPDPP: PC71BM weight ratio in 2-methyltetrahydrofuran (2-MeTHF), the PSC based on PPDPP: PC71BM (1: 2) showed an overall power conversion efficiency (PCE) of 4.18% with J(sc) = 9.75 mA cm(-2), V-oc = 0.78 V, and FF = 0.54. After the thermal annealing (TA) and subsequent solvent vapor annealing (SVA) of the active layer, the resulting device showed an overall PCE of 6.44% (J(sc) = 13.18 mA cm(-2), V-oc = 0.74 V, and FF = 0.66) with a small voltage loss of 0.51 eV. The improvement in PCE after the TA and SVA treatment of the active layer is attributed to an enhancement of J(sc) and FF related to a more favorable nanoscale morphology for the exciton dissociation and charge transport as evidenced by the increased hole mobility.