Structural modification of thieno[3,4-c]pyrrole-4,6-dione: structure–property relationships and application in solution-processed small-molecule organic solar cells

Abstract

We present a method for the modification of the structure of thieno[3,4-c]pyrrole-4,6-dione (TPD) to gain two novel acceptors TPN and TIN. And a series of donor–acceptor–donor-type oligomers 3TTPD3T, 3TTPN3T, and 3TTIN3T, based on TPD, TPN and TIN, have been designed and synthesized for solution-processed small-molecule bulk-heterojunction (BHJ) solar cells. The impact of these different central acceptor moieties on their optical, electrochemical properties, morphology, and solar cell performance were studied. Optical and electrochemical data showed that structural modification of TPD exhibited a slight impact on the band gap and HOMO/LUMO energy levels. Atomic force microscopy and grazing incidence wide-angle X-ray scattering studies revealed that the central acceptors of these oligomers played an important role in determine the morphology of solid-state packing. Oligomer 3TTPD3T showed weak crystallinity in a thin film. The larger conjugation plane counterpart 3TTPN3T showed an improved structure order. Surprisingly, the structurally twisted compound 3TTIN3T showed a strong crystalline nature with large crystalline domains of several hundred nanometers. The photovoltaic properties of these oligomers were evaluated by fabricating BHJ devices with PC₇₁BM. 3TTPD3T/PC₇₁BM blends with a weight ratio of 2 : 1 showed a best power conversion efficiency of 1.87%, with a J_sc of 4.93 mA cm⁻², a V_oc of 0.87 V, and a fill factor of 44%.