Donor–acceptor–π–acceptor based charge transfer chromophore as electron donors for solution processed small molecule organic bulk heterojunction solar cells

• Two donor–acceptor–π–acceptor (D–A–π–A) based on benzothiazole BT3 and BT4 were used as donors along with PC71BM as acceptor.
• BT3:PC71BM and BT4:PC71BM showed PCE of 2.56% and 3.68%, respectively.
• Solar cells with BT3:PC71BM and BT4:PC71BM active layers processed with DIO/DCM showed PCE of 3.77% and 5.27%, respectively.

Two benzothiazole (BT) based donor–acceptor–π–acceptor (D–A–π–A) molecular system denoted as BT3 and BT4 have been designed, synthesized and their optical and electrochemical properties were investigated. The BT4 show wider absorption profile and lower bandgap as compared to BT3 due to the strong electron withdrawing ability of dicyanoquinodimethane (DCNQ) as compared to tetracyanobutadiene (TCBD). The solution processed bulk heterojunction solar cells were fabricated using BT3 and BT4 as electron donor and PC71BM as electron acceptor. The organic solar cells optimized dichloromethane (DCM) processed BT3:PC71BM (1:1) and BT4:PC71BM (1:1) showed PCE of 2.56% and 3.68%, respectively. The higher PCE of BT4:PC71BM is related to the wider absorption of the blend and better ordered domain sizes in the blend as compared to BT3:PC71BM. The devices processed with 1,8-diiodoctane (DIO) additives showed PCE of 3.77% and 5.27%, for BT3:PC71BM and BT4:PC71BM blends, respectively.

DIO solvent additive enhances the hole mobility of the active layer leading to an improvement in the overall PCE.Figure optionsDownload as PowerPoint slide