Researchers from the King Abdullah University of Science and Technology (KAUST), in Saudi Arabia, have fabricated a mixed-cation perovskite solar cell based on a microns-thick absorber layer consisting of perovskite single crystals.
The layer contains a mixture of methylammonium and formamidinium organic cations and is claimed to minimize the absorber bandgap. “Formamidinium lead triiodide (FAPbI3) features the smallest bandgap to date, but this bandgap exceeds the optimal range for single-junction devices,” the scientists explained. “One way to reduce the bandgap of perovskites involves forming lead-tin alloys in the absorber, but this introduces crystal defects and instability.”
The layer was embedded in an inverted perovskite cell with a “p-i-n” layout between an electron transport top layer and a hole-transport bottom layer. Through this architecture, the PV device was able to achieve a power conversion efficiency of 22.8%, an open-circuit voltage of 1.1 V, and a short-circuit current of 26 mA/cm−2, which the research team described as the best performance for an inverted perovskite cell based on single-crystal methylammonium lead triiodide. “The rise in performance mainly stemmed from an increase in short-circuit current,” it specified.
“We had known that mixed-cation, single-crystal absorbers could outperform single-cation absorbers due to their lower bandgap and superior optoelectronic qualities,” said researcher Abdullah Alsalloum. “However, this had not been realized before because of challenges in crystal growth and device integration.”
The Saudi group is convinced that this cell design may deliver efficiencies close to that of gallium arsenide solar cells. “Future studies include optimizing device interfaces and exploring more favorable device structures,” Alsalloum added. ” Suggested future efforts include interface engineering and exploration of perovskite cells in more favorable architectures, such as lateral structures.”
The solar cell is presented in the paper 22.8%-Efficient single-crystal mixed-cation inverted perovskite solar cells with a near-optimal bandgap, published in Energy & Environmental Science.
The KAUST Solar Center has been working for years on ways to speed up the flow of charge carriers in perovskite crystals. It made some major investments in research over past years, and produced several steps forward in perovskite research as a result.
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Source: pv magazine