Controllable Methylamine Vapor Treatment for Improving Performance of Vapor-Processed Perovskite Solar Cells

While the development of methylammonium lead iodide (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{MAPbI}}_{3}$</tex-math></inline-formula>) perovskite in photovoltaic research has matured for solution-based fabrication methods, the growth of high-quality material from vapor processes continues to be difficult due to challenges in vapor chemistry control. Postdeposition methylamine (MA) vapor treatment is an approach to improve the morphology and crystallinity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{MAPbI}}_{3}$</tex-math></inline-formula> films, producing highly oriented, large-grain perovskite films. Herein, experiments to characterize the effects of substrate temperature, MA partial pressure, and MA exhaust flow rate on the liquefaction and recrystallization processes that occur during MA treatments are described. Improved morphology and crystallinity following MA treatment indicate that substrate temperature plays a significant role in both processes during treatment. The enhancement in electronic properties after treatment is confirmed by steady-state and time-resolved photoluminescence spectroscopy. The solar cells made from the films treated at the optimal treatment conditions have shown open circuit voltages over 1 V and fill factors up to 70%. The result of this study is a useful pathway for the fabrication of high-quality <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{MAPbI}}_{3}$</tex-math></inline-formula> films via all-vapor process manufacturing.