Monovalent Cation Doping of CH$_{3}$NH$_{3}$PbI$_{3}$ for Efficient Perovskite Solar Cells

M. Abdi-Jalebi thanks Nava Technology Limited for a PhD scholarship. M.I. Dar and M. Gratzel thank the King Abdulaziz City for Science and Technology (KACST) and Swiss National Science Foundation (SNSF) for financial support. The authors would like to thank Dr. Pierre Mettraux in Molecular and Hybrid Materials Characterization Center, EPFL for carrying out XPS measurements. A. Sadhanala gratefully acknowledges financial support from the Indo-UK APEX project. S.P. Senanayak acknowledges Royal Society London for the Newton Fellowship. R.H. Friend, M. Abdi-Jalebi, and A. Sadhanala would like to acknowledge the support from EPSRC.