  Interfacial engineering has fueled recent development of p-i-n perovskite
solar cells (PSCs), with self-assembled monolayer-based hole-transport layers
(SAM-HTLs) enabling almost lossless contacts for solution-processed PSCs,
resulting in the highest achieved power conversion efficiency (PCE) to date.
Substrate interfaces are particularly crucial for the growth and quality of
co-evaporated PSCs. However, adoption of SAM-HTLs for co-evaporated perovskite
absorbers is complicated by the underexplored interaction of such perovskites
with phosphonic acid functional groups. In this work, we highlight how exposed
phosphonic acid functional groups impact the initial phase and final bulk
crystal structures of co-evaporated perovskites and their resultant PCE. The
explored surface interaction is mediated by hydrogen bonding with interfacial
iodine, leading to increased formamidinium iodide adsorption, persistent
changes in perovskite structure, and stabilization of bulk {\alpha}-FAPbI3,
hypothesized as being due to kinetic trapping. Our results highlight the
potential of exploiting substrates to increase control of co-evaporated
perovskite growth.
