Processing temperature control of a diketopyrrolopyrrole-alt-thieno [2,3-b]thiophene polymer for high-mobility thin-film transistors and polymer solar cells with high open-circuit voltages

Abstract

We synthesized a planar pDPPTTi-OD polymer based on diketopyrrolopyrrole (DPP) and thieno [2,3-b] thiophene (TTi) and investigated the electrical properties of the pDPPTTi-OD polymer. pDPPTTi-OD films displayed a low optical bandgap of 1.57 eV, and HOMO and LUMO levels of -5.40 and -3.74 eV, respectively. The 150 degrees C-annealed pDPPTTi-OD films showed a high hole mobility of 0.16 cm(2)V(-1) s(-1) in organic thin-film transistor (OTFT) devices. The photovoltaic properties of polymer solar cells (PSCs) incorporating the pDPPTTi-OD were also measured. A pDPPTTi-OD: PC71BM blend film was spin-coated at 25, 70 and 90 degrees C. High-temperature processing significantly improved the power conversion efficiency of PSCs by effectively reducing the PC71BM domain sizes, which improved the miscibility between pDPPTTi-OD and PC71BM. This work demonstrated that the TTi moiety is a useful donor building block for high-performance D-A type polymers in OTFTs and PSCs, and that processing temperatures should be controlled to fully realize the materials' beneficial intrinsic properties.