Efficient bulk heterojunction photovoltaic devices based on diketopyrrolopyrrole containing small molecule as donor and modified PCBM derivatives as electron acceptors

摘要

A new solution processable small molecule (DPP-CN) containing electron donor diketopyrrolopyrrole (DPP) core and cyanovinylene 4-nitrophenyl (CN) electron acceptor has synthesized for use as the donor material in the bulk heterojunction organic solar cells along with PCBM, modified PCBM i.e. F and A as electron acceptor. It showed a broad absorption in longer wavelength region having optical band gap around 1.64 eV. We have used PCBM. F and A as electron acceptor for the fabrication of bulk heterojunction photovoltaic devices. The power conversion efficiency (PCE) of the BHJ devices based on DPP-CN:PCBM, DPP-CN:F and DPP-CN:A blends cast from the THF solvent is 1.83%, 2.79% and 2.83%, respectively. The increase in the PCE based on F and A as electron acceptor is mainly due to the increase in both short circuit current (J_(sc)) and open circuit voltage {V_(oc)). The PCE value of the photovoltaic devices based on the blends DPP-CN:PCBM, DPP-CN:F and DDP-CN:A cast from the mixed solvents (DIO/THF) has been further improved up to 2.40%, 3.32% and 3.34%, respectively. This improvement is mainly due to the increased value of J_(sc), which is attributed not only to the increase of crystallinity, but also to the morphological change in the film cast from mixed solvent. Finally, the device ITO/PEDOT:PSS/DPP-CN:A (DIO/THF cast)/TiO_2/ Al device shows a PCE of 3.9%. The improved device performance could be attributed to the electron transporting and hole-blocking capabilities due to the introduced TiO_2 buffer layer.