Oligo(Ethylene Glycol) Functionalization of a Dopant-Free Hole Transport Material for Perovskite Photovoltaics

Advancing the performance of perovskite photovoltaics (PPVs) complementarily necessitates the utilization of charge transport layers. The development of functionalized hole transport materials (HTMs) through the precise tuning of conjugated core structures and side groups is crucial for realizing the efficient transport and extraction of photogenerated charge carriers in PPVs. Here, we prepared a series of polymeric HTMs functionalized with various amounts and lengths of oligo(ethylene glycol) (OEG) side groups to identify the effect of the latter on the performance of the HTM in PPVs. Subsequent analysis revealed that the polymeric HTM with the longest OEG side groups improved the number of hole transport carriers and passivated traps at the perovskite/HTM interface. This is attributed to the effective interaction with the perovskite layer and the formation of face-on-oriented crystallites. Consequently, a PPV with the optimized dopant-free OEG-substituted polymer HTM showed high efficiency of about 22% along with excellent device stability in air.