Indacenodithiophene core-based small molecules with tunable side chains for solution-processed bulk heterojunction solar cells

Two indacenodithiophene (IDT) core-based small molecules with different side chains of bulky 4-hexylphenyl and flexible n-dodecyl with the same number of carbon atom, namely SM1 and SM2, respectively, were designed and synthesized as the donor materials in organic solar cells (OSCs). The impacts of the different side chains combined with the IDT core on the optical absorption, electrochemical property, hole mobility, film morphology, and solar cell performance were studied thoroughly. The two compounds possess a broad absorption covering the wavelength range of 450-700 nm and relatively low HOMO energy levels of -5.46 and -5.52 eV. The power conversion efficiency (PCE) of the OSCs based on SM2 as the donor material and PC61BM as the acceptor material (1 : 2, w/w) is 2.33%. In contrast, a PCE of 4.72% was achieved for the device based on SM1 as the donor and PC71BM as the acceptor (1 : 2, w/w) without any treatment such as thermal annealing or the utilization of a solvent additive.