Benzodi(pyridothiophene): a novel acceptor unit for application in A1–A–A1 type photovoltaic small molecules

Abstract

A series of novel A₁–A–A₁ type small molecules (SMs) of BDPT-2BT, BDPT-2FBT and BDPT-2DPP were designed and synthesized, in which benzodi(pyridothiophene) (BDPT) was used as a novel weak central acceptor (A) unit, and benzothiadiazole (BT), fluorinated benzothiadiazole (FBT) and diketopyrrolopyrrole (DPP) were used as terminal acceptor (A₁) units, respectively. The pentacyclic BDPT aromatic unit can form big conjugated and planar SMs with the A₁ unit, resulting in enhanced π–π stacking and crystallinity. The effect of the A₁ unit on the optical, electrochemical and photovoltaic properties of three SMs was observed. The broader absorption spectrum, lower HOMO energy level, higher photo-response efficiency and better photovoltaic properties were exhibited for BDPT-2DPP. A maximum PCE of 3.97% with a V_oc of 0.84 V, a J_sc of 9.0 mA cm⁻² and a FF of 52.37% was obtained in the BDPT-2DPP/PC₇₁BM-based solar cells, which is 1.8 and 1.5 times the values of the BDPT-2BT and BDPT-2FBT-based cells, respectively.