In 2012, Kanatzidis and Chang reported the new tin perovskite solar cell with promises of higher efficiency and lower fabrication costs while being environmentally safe. “Solar energy is free and is the only energy that is sustainable forever,” Kanatzidis said. “If we know how to harvest this energy in an efficient way we can raise our standard of living and help preserve the environment.”
The solid-state tin solar cell is a sandwich of five layers, with each layer contributing something important. Being inorganic chemists, Kanatzidis and his postdoctoral fellows Feng Hao and Constantinos Stoumpos knew how to handle troublesome tin, specifically methylammonium tin iodide, which oxidizes when in contact with air. The first layer is electrically conducting glass, which allows sunlight to enter the cell.
Titanium dioxide is the next layer, deposited onto the glass. Together the two act as the electric front contact of the solar cell. Next, the tin perovskite — the light absorbing layer — is deposited. This is done in a nitrogen glove box — the bench chemistry is done in this protected environment to avoid oxidation. On top of that is the hole transport layer, which is essential to close the electrical circuit and obtain a functional cell.
This required Kanatzidis and his colleagues to find the right chemicals so as not to destroy the tin underneath. They determined what the best chemicals were — a substituted pyridine molecule — by understanding the reactivity of the perovskite structure. This layer also is deposited in the glove box.
The solar cell is then sealed and can be taken out into the air. A thin layer of gold caps off the solar-cell sandwich. This layer is the back contact electrode of the solar cell. The entire device, with all five layers, is about one to two microns thick. The researchers then tested the device under simulated full sunlight and recorded a power conversion efficiency of 5.73 percent.
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