Brown University reported on Monday, March 16th that a graduate student has discovered a new method to produce light-absorbing perovskite films for solar cells.
The new method, developed by PhD. candidate Yuanyuan Zhou, uses a room-temperature solvent bath to create perovskite crystals, instead of the high-temperature process used in current crystallization methods. A research was published in the Journal of Materials Chemistry A, and proves that the technique can create high-quality crystalline films with exact control across large areas, and has been hailed as a possible breakthrough toward mass production methods for perovskite solar cells.
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Details on the new solar cell technology
Perovskites are a type of crystal that have a great potential for energy storage and as a solar cell technology. Perovskite films are very efficient light absorbers and much cheaper to make than the silicon wafers in typical solar cells. Moreover, the efficiency of perovskite cells has increased dramatically over the last few years. Standard silicon cells today offer around a 25% efficiency, but the newest perovskite cells can offer an efficiency above 20% (from under 5% a few years back). Given these improvements, researchers are working hard to develop perovskite cells in commercial products.
All of the current methods to produce perovskite films require heat. In the process, perovskite precursor chemicals are dissolved into a solution, which is then coated onto a substrate. Heat is then used to evaporate the solvent, and the perovskite crystals form a film across the substrate.
However, the crystals often form unevenly when heat-treated, creating pinholes in the film. These pinholes decrease efficiency in a solar cell. High temperatures also mean inexpensive, flexible plastic substrates cannot be used because they are damaged by the heat.
Zhou’s new approach has been dubbed the solvent-solvent extraction (SSE) method.
In his method, perovskite precursors are dissolved in anNMP solvent and coated onto a substrate. Then, instead of heating, the substrate is bathed in diethyl ether , a second solvent that selectively absorbs the NMP solvent. The final result is a smooth film of perovskite crystals.
Statement from director of Brown University’s Institute for Molecular and Nanoscale Innovation
“People have made good films over relatively small areas — a fraction of a centimeter or so square. But they’ve had to go to temperatures from 100 to 150 degrees Celsius, and that heating process causes a number of problems,” explains Nitin Padture, a professor of engineering and director of the Institute for Molecular and Nanoscale Innovation at Brown.