Donor-Acceptor Type Polymers Containing Fused-Ring Units as Dopant-Free, Hole-Transporting Materials for High-Performance Perovskite Solar Cells

Hole-transporting layer (HTL) plays a key role in most high-efficiency perovskite solar cells (PVSCs). Especially in the n-i-p conventional PVSCs, HTL promotes device performances through multiple ways, including hole injection and transport, interface optimization, inhibition of charges recombination, and protection of the perovskite active layer from oxygen, water, and metal electrode. Although spiro-based small-molecular hole-transporting materials (HTMs) brought PCE records of PVSCs one by one, the poor film quality and requirement of additives brought some negative effects on the long-term stability of the devices. Therefore, dopant-free, compact polymeric HTLs attract intensive attention as potential alternatives to doped spiro-based ones. Among polymeric HTMs, electron donor (D)-acceptor (A)-type polymers become promising HTMs owing to the superior hole-transporting properties. In this work, two D-A polymers containing fused rings perform as dopant-free HTMs. The fused-ring ladder-type units can facilitate carrier transport, electron donation, and p-p stacking interactions. Polymers PDT-T and PDTT-T employ the same A unit of BDD and p-bridge of thiophene and different D units of IDT and IDTT. Both polymers exhibit favorable properties as HTMs including high hole mobility, well-matched energy levels, and excellent film-formation ability. Along with a peak PCE of 19.02%, the superior device stabilities of the PVSCs employing dopant-free PDT-T and PDTT-T over the reference devices confirm the significance of precise molecular design on fused-ring polymeric HTMs for the long-life PVSCs.