Novel symmetric squaraine chromophore containing triphenylamine for solution processed small molecule bulk heterojunction solar cells

New symmetrical low band-gap small molecule materials, SQ-bis[HP-HT2-TPA] and SQ-bis[HP-HT2-BT] incorporating as novel derivative of squaraine-pyrrole framework and π-extended thiophene with triphenyamine (TPA) and benzothiophene (BT) end group, have been synthesized and characterized. The effects of TPA moiety were investigated. Compared to SQ-bis[HP-HT2-BT], SQ-bis[HP-HT2-TPA] exhibited three times improved transporting property of hole carrier and four times enhanced absorptivity by more efficient intermolecular π−π interaction for high-efficiency bulk heterojunction (BHJ) device, suggesting that TPA contributes to a better hole mobility. The bulk-heterojunction photovoltaic devices fabricated with SQ-bis[HP-HT2-TPA]/C71-PCBM BHJ film had an average power-conversion efficiency of 1.83%(±0.12) under 100 mW/cm2, with a short-circuit current (Jsc) of 9.32 mA/cm2, fill factor (FF) of 0.30, and open-circuit voltage (Voc) of 0.65 V, which has ∼42% higher efficiency compared to SQ-bis[HP-HT2-BT]/C71-PCBM BHJ films.