Low band gap diketopyrrolopyrrole-based small molecule bulk heterojunction solar cells: influence of terminal side chain on morphology and photovoltaic performance†
Abstract
Two new low band gap small molecules BDT(DPP-TTHex)2 and BDT(DPP-TT)2 with different terminal side chain are designed and synthesized for bulk heterojunction solar cells. BDT(DPP-TTHex)2 is flanked by hexyl at head and tail of backbone while BDT(DPP-TT)2 is free attachment. Both small molecules exhibit similar optical, electrochemical properties and charge carrier mobilities. Nevertheless, BDT(DPP-TT)2 performs optimal film morphology leading to higher short circuit current (JSC) comparing with BDT(DPP-TTHex)2, thus 5.12% power conversion efficiencies (PCE) of BDT(DPP-TT)2 is achieved, higher than 2.36% PCE of BDT(DPP-TTHex)2 under AM1.5G illumination (100 mW cm−2).