Synthesis, optical and electrochemical properties of small molecules DMM-TPA[DTS(FBTTh3)(3)] and TPA[DTS(FBTTh3)(3)], and their application as donors for bulk heterojunction solar cells

Abstract

Two symmetrical planar star-shaped organic small molecules, i.e., DMM-TPA[DTS(FBTTh3)(3)] (1) and TPA [DTS(FBTTh3)(3)] (2), with fused TPA and TPA core donors, respectively, and three branched DTS(FBTTh3) units were synthesized and characterized. These small molecules were used donor materials along with a PC71BM acceptor for solution-processed bulk heterojunction solar cells. The power conversion efficiency (PCE) of the solar cells based on 1 and 2 is about 2.87% and 2.51%, respectively, when the active layers were processed from a CB solvent. The higher PCE of the solar cell based on 1 may be attributed to its low bandgap and broad absorption profile as compared to 2. The PCE of the solution-processed SMBHJ solar cells was improved up to 5.16% and 4.70% for 1 and 2, respectively, when the active layers were processed with 4 v% DIO as an additive in the CB solvent. The enhancement in the PCE was mainly due to the increase in J(sc) and FF, which is attributed to the balanced charge transport between the electron and hole transport and reduction in the bimolecular recombination, leading to an increase in the PCE.