Researchers at MIT added to the work on perovskite materials by introducing a light-based method that improves their performance.
Perovskites are compounds often produced as thin films that are used in solar cell applications. Past research differs in that it has used electrical and chemical treatments to alter perovskite performance.
Although perovskites offer solar cell efficiency they can also contain defects in its crystalline structure that can complicate the conversion of light into electricity. The MIT researcher Samuel Stranks explains how light can be used to heal defects, “…just under illumination, where no [electric or magnetic] field has been applied, we see this ion migration that helps to clean the film. It reduces the defect density.”
The applied illumination is also referred to as photo-induced cleaning. The illumination caused iodide ions, which are atoms that have lost an electron and carry an electric charge, to move away from the illuminated region and wipe out defects along its path. The defects are referred to as traps, which cause electrons to recombine with other atoms before their motion can be harnessed.
The researchers specifically used organic-inorganic metal halide perovskites, which are valuable for photoluminescence quantum efficiency and therefore receives the maximum efficiency obtainable in solar cells.
Despite the fact that in practice the performance of the materials are variable, fluorescence imaging was able to show how areas that received more illumination became more purified, exemplified by brighter fluorescence in those regions. The advantage of illumination as opposed to past methods is that there is no contact between the perovskite film and a solution of electrical contacts.
The scientists remain hopeful for creating defect-free films, but greater challenges lie ahead. The observed positive effects from illumination decrease over time. For practical use, the effects from illumination must last much longer in the future.