D(A-A′)2 architecture: An efficient strategy to improve photovoltaic performance of small molecules for solution-processed organic solar cells

Abstract

Two novel small molecules (SMs) of BDT(TPD-DPP)2 and BDTT(TPD-DPP)2 with a D(A-A′)2 framework were designed and synthesized, in which the electron-rich benzodithiophene (BDT) and thiophenyl-substituted benzodithiophene (BDTT) are used as a central donor (D) core, as well as the electron-deficient diketopyrrolopyrrole (DPP) and thieno [3,4-c]pyrrole-4,6-dione (TPD) as dual acceptor (A and A′) units, respectively. Their optical, electrochemical, and photovoltaic properties were investigated together with their counterparts, which bearing an accepter-donor-accepter (A-D-A) architecture. Wider and stronger solar photon responses and decreasing the lowest unoccupied orbital (LUMO) levels are observed in the D(A-A′)2 rather than A-D-A type SMs. The significantly increasing power conversion efficiency of 4.25% with a short-circuit current density of 10.08 mA cm−2 were obtained in the BDTT(TPD-DPP)2 based solar cells. This work demonstrates that using D(A-A′)2 architecture with dual acceptor units is an effective method to improve photovoltaic performance of SMs for solution-processed organic solar cells.