Effects of doping with Na, K, Rb, and formamidinium cations on (CH3NH3)0.99Rb0.01Pb0.99Cu0.01I3−x(Cl, Br)x perovskite photovoltaic cells

Abstract

The effects of doping with alkali metals and formamidinium cations on CH3NH3(Rb)Pb(Cu)I3(Cl,Br) perovskite photovoltaic cells were investigated. Lattice constants were slightly decreased and increased by K and Na doping, respectively. This indicated that Na atoms occupied interstitial sites in the perovskite crystal. The conversion efficiencies for most of the devices decreased after one year. However, the conversion efficiency for the CH3NH3(Na,Rb)Pb(Cu)I3(Cl,Br) photovoltaic cell was unchanged after one year. The Na-doped perovskite provided the smallest carrier trap density, which suggested that lattice defects were suppressed by Na doping. First principles calculations supported these experimental results.