Elucidating the Roles of Hole Transport Layers in p‐i‐n Perovskite Solar Cells

The hole-transport layer (HTL) is critical to high performance of perovskite solar cells (PSCs) in terms of hole extraction, transportation, and mediation of the following film formation. Here, the interplay between HTLs and open-circuit voltage (V-OC) in PSCs is directly targeted. The results suggest that there is no evident relation between the obtained V-OC and the work function of HTLs and it is directly controlled by the recombination losses inside the perovskite material (grain boundaries and trap states) as well as at the interfacial contacts. Additionally, an insight understanding about the charge transfer behavior in PSCs is provided and it is pointed out that the nature of interfacial contacts is a critical factor in defining charge accumulation and recombination at the interfaces. Analysis of the electroluminescence efficiency and transient absorption spectroscopy confirms the better interfacial contact of HTL/perovskite, and larger grain size of perovskite films mediated by the hydrophobic nature of HTLs can collectively and efficiently eliminate nonradiative recombination, resulting in faster charge transfer and lower resistance at the interfaces. This work provides a profound understanding of how the surface hydrophobicity and the interface contact are correlated in terms of nonradiative losses and J-V characters in real devices.