Oligo(ethylene glycol)-incorporated hole transporting polymers for efficient and stable inverted perovskite solar cells

Triarylamine (TAA)-based conjugated polymers have been extensively used as hole-transporting layers (HTLs) for inverted perovskite solar cells (PSCs), but their hydrophobic nature often causes insufficient wetting of the perovskite precursor solution on the HTL. This feature not only results in the deposition of a nonuniform perovskite layer on the HTL, but also generates detrimental defects at the interface, limiting the performance and stability of the PSCs. In this study, we develop a series of poly(triarylamine) (PTAA)-based hole transporting materials (HTMs) (MEG-PTAA, DEG-PTAA, and TEG-PTAA) with hydrophilic oligo(ethylene glycol) (OEG) side chains of different lengths to realize efficient and stable inverted PSCs. Incorporating prolonged OEG side chains progressively increases the wettability of the HTLs by perovskite precursor solution, enabling the deposition of a uniform perovskite layer. Moreover, additional oxygen atoms in the longer OEG side chain reinforce the passivation effects of the HTLs on interfacial Pb-based defects, effectively suppressing trap-assisted recombination of charge carriers. Among the series, the DEG-PTAA-based HTL demonstrates the most efficient and stable inverted PSCs, achieving a maximum power conversion efficiency (PCEmax) of 22.26%. Importantly, the DEG-PTAA-based PSC, which retains 80% of its initial PCE after 970 h under 1 sun illumination, is significantly more stable than the reference PTAA-based PSC, which retains only 57% of its initial PCE after the same period.