Designing a thiophene-fused DPP unit to build an A–D–A molecule for solution-processed solar cells

Abstract

A novel thiophene-fused diketopyrrolopyrrole unit (7H-pyrrolo[3,4-a]thieno[3,2-g]indolizine-7,10(9H)-dione, PTI) has been designed as an electron acceptor with the 4,4′-bis-(2-ethylhexyl)-dithieno[3,2-b:2′,3′-d]silole (DTS) unit as a donor to construct a new kind of A–D–A molecule (DTS–2TPTI) for solution-processed solar cells. DTS–2TPTI exhibits excellent thermal stability with the decomposition temperature over 400 °C and shows strong absorption from 550 to 750 nm with a high molar extinction coefficient. The optical band gap (E_g) estimated from the absorption edge of the thin film is about 1.44 eV. The highest occupied molecular orbital energy level of DTS–2TPTI determined from CV is about −4.99 eV. Through optimizing the photovoltaic performances of devices, the DTS–2TPTI/PC₇₁BM-based solution processed bulk-heterojunction solar cell with 0.5% DIO as a solvent additive exhibits the best photovoltaic performance with a J_SC of 11.28 mA cm⁻², V_OC of 0.64 V, FF of 59.5% and power conversion efficiency (PCE) of 4.28%, indicating that the PTI unit can act as an efficient acceptor moiety to construct D–A small molecules for OPVs.