Effective Control of Chlorine Contents in MAPbI_3–<i>x</i>Cl<i>_x</i> Perovskite Solar Cells Using a Single-Source Vapor Deposition and Anion-Exchange Technique

Abstract

In this study, a new method is developed to control the Cl-to-I ratio in MAPbI_{3- x}Cl _x perovskite solar cells (PSCs) more easily and precisely using single-source vapor deposition of MAPbCl₃ thin films and a subsequent anion exchange by repeated spin-coatings of methylammonium iodide (MAI) solution. This method can overcome the problems of previous vapor-deposition techniques for PSCs such as the occurrence of morphological defects in the films and difficulty in controlling the stoichiometry of the elements. The repetitive MAI treatments gradually fill the interstitial voids in the perovskite film and increase the average grain size up to 1.2 μm, which improves the charge-transfer property of the cells. The atomic Cl content, i.e., the x value, of the MAPbI_{3- x}Cl _x film can also be simply controlled by changing the number of MAI treatments. The energy levels and resistive elements of the cells are strongly dependent on the x value of the MAPbI_{3- x}Cl _x film. A maximum power conversion efficiency of 19.1% is achieved at x = 0.005.