Highly reproducible, efficient hysteresis-less CH₃NH₃PbI_3-xCl_x planar hybrid solar cells without requiring heat-treatment

CH₃NH₃PbI_3-xCl_x(MAPbI_3-xCl_x) mixed halide perovskite powder with uniform composition was synthesized via simple solution chemistry, which demonstrates highly reproducible, efficient planar type MAPbI_3-xCl_x mixed halide perovskite solar cells. Pure MAPbI_3-xCl_x mixed halide perovskite powder was synthesized by reacting a 3:1 molar ratio of MAI:PbCl₂ powder mixture in isopropanol (IPA) solution for 30 min at 60 °C with subsequent repeated centrifugation and washing in IPA. IPA functions as both the reaction medium for the formation of MAPbI_3-xCl_x mixed halide and a selective remover of unreacted MAI and MACl byproducts. Accordingly, we could deposit a pinhole-free dense MAPbI_3-xCl_x mixed halide perovskite film on a TiO₂/FTO substrate through a simple one step spin-coating of pure MAPbI_3-xCl_x mixed halide perovskite powder in DMF solution with HI additive, without further long heat-treatment processes. The deposited MAPbI_3-xCl_x mixed halide perovskite film revealed uniform composition throughout the entire area, and the ratio of Cl to I + Cl and I + Cl to Pb was constant at ∼0.03 and ∼1/3, respectively. On the other hand, the conventional MAPbI_3-xCl_x mixed halide perovskite film prepared by the long heat-treatment process had non-uniform composition because the ratio of Cl to I + Cl fluctuated greatly from 0 to 7.2. The average efficiency of planar type MAPbI_3-xCl_x mixed halide perovskite solar cells was 18.65% ± 0.30% and the champion cell had 1.11 V V_oc, 22.1 mA cm^-2J_sc, 77% F.F., and 18.9% η for forward scan conditions and 1.11 V V_oc, 22.1 mA cm^-2J_sc, 78% F.F., and 19.1% η for reverse scan conditions. Although the thickness of the MAPbI_3-xCl_x mixed halide perovskite layer varied from ∼500 nm to ∼900 nm, the efficiency was within the range of 18.3%-19.0%.