Synthesis and photovoltaic properties of D–A–D type small molecules containing diketopyrrolopyrrole (DPP) acceptor central unit with different donor terminal units

•DPP based small molecules have been successfully synthesized and applied for organic photovoltaics.•The energy levels of both CSDDPs well match with the PC70BM.•Dibutyloxy phenyl (BuP) group acts as better electron donor compared to difluoro phenyl (FP).•CSDDP4 exhibited higher PCE than CSDPP2 due to the presence of dibutyloxy phenyl.•The devices showed higher PCE in CN/CF solvent compared to CF solvent.

Two D–A–D small molecules TDPP (FP)2 and TDPP (BuP)2 coded as CSDPP2 and CSDPP4 respectively were synthesized having same diketopyrrolopyrrole (DPP) as core acceptor and difluoro-phenyl (FP) and dibutyloxy phenyl (BuP) as different end donor units with broad absorption and suitable energy levels. We have used these small molecules as donor components along with the PC70BM as electron acceptor for the preparation of bulk heterojunction (BHJ) active layer in small molecule (SM) organic photovoltaics (OPV) test cells. The optimal power conversion efficiencies obtained with CSDPP2 and CSDPP4 are 2.26% and 3.23% when the BHJ active layer was cast from CF solvent. The PCE has been further enhanced up to 3.03% and 4.65% for CSDPP2 and CSDPP4 when the BHJ active layer was cast from CN/CF solvent. The enhancement in PCE has been explained in terms of change in crystallinity and nanoscale morphology and more balanced charge transport resulting from increased hole mobility.

Graphical abstractTwo D–A–D small molecules CSDPP2 and CSDPP4 with diketopyrrolopyrrole (DPP) as core acceptor modified with difluoro-phenyl (FP) and dibutyloxy phenyl (BuP) produced PCE of 3.03% and 4.65% respectively when the BHJ active layer was cast from CN/CF solvent.Figure optionsDownload full-size imageDownload as PowerPoint slide