Employing symmetry-breaking strategy to reduce self-aggregation of donor in blend films to control morphology for all-small-molecule organic solar cells

Abstract

In this work, we employed symmetry-breaking strategy to construct A-π-D-π-A typed small molecule donors SMD1, SMD2 and SMD3 to reduce the self-aggregation in blends and form ideal phase separation morphology. The effect of different side chains and terminal groups on the photovoltaic properties of these asymmetric small molecule donors were investigated in detail. SMD3 shows more red-shifted absorption and weaker self-aggregation than SMD1 and SMD2. Consequently, SMD3:PC71BM blend films show homogenous morphology, which is beneficial for exciton dissociation and charge transport. As a result, SMD3:PC71BM based devices exhibit the highest power conversion efficiency (PCE) of 4.67%. Our investigation proved that the benzene-alkoxyl and thiophene-alkylthiol are ideal candidates for side chains on BDT and 3-isooctyl rhodanine is an ideal terminal group for asymmetric small molecular donors.