Method of making a perovskite layer at high speed

A method of making a perovskite layer comprising:

• providing a flexible substrate;
• providing a perovskite solution comprising an initial amount of solvent and perovskite precursor materials and having a provided solution temperature and a total solids concentration by weight between 30 percent and 70 percent of its saturation concentration at the provided solution temperature;
• depositing the perovskite solution on the flexible substrate at a first location;
• removing a first portion of the initial amount of solvent from the deposited perovskite solution with a first drying step having a first drying step dwell time at a second location wherein the first drying step heats the deposited perovskite solution to a coated layer temperature and increases the total solids concentration of the perovskite solution to at least 75 percent of its saturation concentration at the coated layer temperature;
• and removing a second portion of the initial amount of solvent from the deposited perovskite solution with a second drying step having a higher rate of solvent evaporation than the first drying step during a second drying step dwell time at a third location that causes saturation and a conversion reaction in the deposited perovskite solution resulting in perovskite crystal formation or formation of a perovskite intermediate phase, wherein the first drying step dwell time is at least 5 times longer than the second drying step dwell time, wherein the flexible multilayer substrate is moving at a constant speed from the first location to the second location, the flexible multilayer substrate is moving at the constant speed from the second location to the third location, and the constant speed is greater than 5 meters per minute, and the perovskite solution has at least 50 weight percent of the total initial amount of solvent that has a boiling point less than 150 degrees Celsius.