A-π-A-π-A small molecules for ternary solar cells

Ternary organic solar cells (OSCs) are very promising because they can further enhance the photons' utilization efficiencies of binary cells. Herein, we design and synthesize three linear A-pi-A-pi-A (A: electron acceptor) small molecules (SMs) BTTR, BT2TR and BT3TR with a 2,1,3-benzothiadiazole (BT) unit as the central core and two 3-octylrhodanine as the end-capping units pi-bridged with different numbers of thiophene units for photovoltaics. Though the binary solar cells based on PTB7/SM and SM/PC71BM show very poor device performance with power conversion efficiencies (PCEs) < 1%, the ternary devices based on PTB7:PC71BM with BT2TR and BT3TR as the third components exhibit PCEs of 9.30% and 9.16%, respectively, which are enhanced by > 15% compared with that of the PTB7:PC71BM binary solar cells (PCE: 7.97%). Especially, the PCEs of the ternary cells are larger than the sums of those of the two related binary solar cells, indicating that A-pi-A-pi-A small molecules are promising on ternary solar cells.