  Inverted perovskite solar cells (PSCs) using a Cu:NiOx hole transporting
layer (HTL) often exhibit stability issues and in some cases J/V hysteresis. In
this work, we developed a \b{eta}-alanine surface treatment process on Cu:NiOx
HTL that provides J/V hysteresis-free, highly efficient, and thermally stable
inverted PSCs. The improved device performance due to \b{eta}-alanine-treated
Cu:NiOx HTL is attributed to the formation of an intimate Cu:NiOx/perovskite
interface and reduced charge trap density in the bulk perovskite active layer.
The \b{eta}-alanine surface treatment process on Cu:NiOx HTL eliminates major
thermal degradation mechanisms, providing 40 times increased lifetime
performance under accelerated heat lifetime conditions. By using the proposed
surface treatment, we report optimized devices with high power conversion
efficiency (PCE) (up to 15.51%) and up to 1000 h lifetime under accelerated
heat lifetime conditions (60 C, N2).
