Precision perovskite layer spraying method opens up new avenues for perovskite solar cell research and development

Perovskites are of great interest for their potential material properties as solar cells, but for them to be widely used in practice, researchers must develop efficient fabrication processes to handle them. Scientists in Thailand have devised a spray coating method to coat a sophisticated layer of perovskite on a substrate to create a stable, high-performance photovoltaic structure.

There are many chemical formulas for perovskites, usually with two distinct cations and three anions. The scientific team from Mahidol University’s School of Materials Science and Innovation focused their research on hybrid halide perovskites, which include a combination of some bromine or iodine atoms as anions. This semiconducting compound varies in color from brown to orange and has some transparency to light.

On the scale of a few hundred nanometers, the shape and layering of the semiconductor determines the functionality of the device. Using different types of perovskites to create light absorbers in three or more layers enables many complex designs that were previously unattainable, the researchers say.

Since perovskites can be processed in liquid solutions, spray deposition appears to be a better fabrication method, but the technique is difficult to predict and control. Previously, scientists had only been able to coat a second perovskite layer on top of the base layer by quickly exposing the base layer to some chemicals. These processes lead to surface passivation—water droplets from the upper layer partially redissolve the previously dried lower layer. The researchers say previous scientists could not precisely control the thickness of the overlay and its effect on the underlying layers.

  

The researchers call their technique “sequential spray deposition.” They used two nozzles to spray the perovskite solution onto the substrate heated to 100°C at a 45-degree angle, while maintaining the air humidity in the experimental space at 45% to 50% relative humidity — to make the perovskite layer more stable .

Some halide perovskites — containing three iodine atoms per molecule — have better electrical properties, but are relatively less stable. The research team first identified the type, then sprayed a 90-nm-thick cap layer after the next 400-nm-thick layer had dried. While the researchers say they only made two layers, they say that by precisely controlling the thickness and deposition rate of each layer, many more layers can be built up.

The researchers say this new technique opens new avenues not only for perovskite solar cells, but also for the entire spectrum of perovskite Electronic devices, such as perovskite LEDs, photodetectors, lasers, and more.

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