Two A2-D-A1-D-A2 small molecules with isoindigo as the central core for efficient organic photovoltaics

Abstract Two A 2 -D-A 1 -D-A 2 small molecules ID-IND and ID-RHO have been designed and synthesized, in which isoindigo, thiophene-benzene-thiophene, and 1,3-indenedione or 3-ethylrhodanine are used as the central acceptor unit (A 1 ), the donor units (D) and the end-caped acceptor units (A 2 ), respectively. The effects of the end-caped acceptor units on molecular aggregation, absorption spectra, film morphology, hole mobilities and photovoltaic performance have been fully studied. The results indicate that ID-IND with 1,3-indenedione as the end-caped acceptor units possesses more regular molecular aggregation, red-shifted absorption spectrum, more appropriate microphase separation, higher hole mobility and better photovoltaic performance than ID-RHO with 3-ethylrhodanine as the end-caped acceptor units. Therefore, the ID-IND -based solar cell shows a power conversion efficiency (PCE) of 4.70% with a open-circuit voltage of 1.01 V, which is one of the highest PCE values in organic solar cells based on the small molecules with isoindigo as the central acceptor unit.