Researchers at the Massachusetts Institute of Technology (MIT) have fabricated a perovskite solar cell through the chemical bath deposition method (CBD), which is claimed to have a power conversion efficiency of 25.2%.
CBD is a technique to produce films of solid inorganic, non-metallic materials on substrates by immersing the substrate in a precursor aqueous solution.
The US scientists added a special conductive layer of tin dioxide bonded between the conductive layer and the perovskite material. “If the conductive layer is directly attached to the perovskite itself, the electrons and their counterparts, called holes, simply recombine on the spot and no current flows,” they explained. If the perovskite and the conductive layer are separated by this intermediate layer, the latter lets the electrons through and prevents the recombination.
The special conductive layer was treated with a chemical bath at 90 degrees Celsius, which made the precursor chemicals slowly decompose to form the layer of tin dioxide in place. “The team realized that if we understood the decomposition mechanisms of these precursors, then we’d have a better understanding of how these films form,” the research group explained. “We were able to find the right window in which the electron transport layer with ideal properties can be synthesized.”
Their analysis showed that different mixtures of intermediate compounds form, depending on the acidity of the precursor solution, which enabled to produce more effective films. The positive effect of this special conductive layer was also combined with an improvement of the perovskite layer, which was achieved by adding special additives that do not alter the material’s bandgap.
The achieved conversion efficiency of the solar cell was thus far demonstrated in tiny lab-scale devices. “The kind of insights we provide in this paper, and some of the tricks we provide, could potentially be applied to the methods that people are now developing for large-scale, manufacturable perovskite cells, and therefore boost those efficiencies,” said research author Moungi Bawendi.
“What we’re demonstrating is that even with a single active layer, we can make efficiencies that threaten silicon, and hopefully within punching distance of gallium arsenide,” stated MIT scientist Jason Yoo. “And both of those technologies have been around for much longer than perovskites have.”
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