Asymmetric thiophene/pyridine flanked diketopyrrolopyrrole polymers for high performance polymer ambipolar field-effect transistors and solar cells

Abstract

Two novel asymmetric thiophene/pyridine flanked diketopyrrolopyrrole (DPP) based polymers, named PPyTDPP-TT and PPyTDPP-BT were designed, synthesized and applied in organic field-effect transistors (OFETs) and polymer solar cells (PSCs). In contrast to the reported bipyridine flanked DPP, the asymmetric DPP polymers incorporating thiophene/pyridine flankers exhibited narrower bandgaps of ∼1.5 eV and deeper HOMO energy levels, thus leading to a broadened absorption from 500 to 850 nm and were potentially beneficial for low-energy photon harvesting. Both polymers displayed promising ambipolar semiconducting properties. The hole and electron mobilities of PPyTDPP-TT reach 0.48 cm² V⁻¹ s⁻¹ and 0.18 cm² V⁻¹ s⁻¹; and PPyTDPP-BT reach 0.55 cm² V⁻¹ s⁻¹ and 0.08 cm² V⁻¹ s⁻¹, respectively. Intriguingly, due to their ambipolar properties, two polymers can play an ambipolar role, both as electron donors and acceptors with PC₇₁BM and P3HT in PSCs. Photovoltaic devices based on PPyTDPP-BT as the donor material reach PCEs of 7.56% and achieve 0.59% as the acceptor material, while those based on PPyTDPP-TT reach 5.48% with PC₇₁BM and 0.82% with P3HT, respectively. These results suggest that the adoption of asymmetric flanker DPP polymers can effectively tune the absorption properties of polymers as excellent ambipolar transporting polymers towards high performance in both OFETs and PSCs.