Halide perovskites (HPs) are now leading materials pioneering photovoltaic (PV) technologies, owing to their simple solution processibility and excellent optoelectronic functionality. Among them, inorganic Cs-based HPs, where volatile methylammonium is excluded, are anticipated to be advantageous to thermal stability. Also, it offers a relatively wide bandgap of ~1.7-1.8 eV that is desired for front cell in tandem PV applications , while excluding substantial bromine incorporation that compromises bandgap stability via halide segregation . However, thermodynamically, the synthesis of photoactive α-CsPbI3 phase requires high temperatures over 325 o C . Such high temperature is incompatible with the organic-based hole-transport materials (HTMs), thereby realizing p-i-n type PVs -chemically more stable and a conventional architecture for tandem PV application -difficult.