A-D-A small molecule donors based on pyrene and diketopyrrolopyrrole for organic solar cells

Abstract

Three new electron donating small molecules (SMs), Pyr(EH-DPP)2, Pyr(HD-DPP)2 and PyrA(EH-DPP)2, are designed and synthesized through coupling electron rich pyrene core with electron deficient diketopyrrolopyrrole (DPP) terminals, of which the derived organic solar cells (OSCs) exhibit interesting structure-performance correlation. It shows that the tune of their solubilizing side chains and π-bridge for the acceptor-donor-acceptor (A-D-A) SMs can significantly alter the resultant short-circuit current density and power conversion efficiency (PCE) in OSCs. The Pyr(EH-DPP)2 with short side chains displays broader absorption and higher hole mobility than the Pyr(HD-DPP)2 with long side chains. Although showing planar structure, the acetylene bridge-incorporated PyrA(EH-DPP)2 adapts an undesired edge-on packing and strong aggregation in film, leading to non-ideal morphology and poor miscibility with fullerene acceptors. As a result, the PCE of the solar cell based on Pyr(EH-DPP)2 is several times higher than those based on Pyr(HD-DPP)2 and PyrA(EH-DPP)2, indicating the A-D-A combination of polyaromatics with DPP would be the promising skeleton for developing photovoltaic semiconductors.