A team of scientists at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia has developed a method for growing single-crystal perovskites and achieved record setting efficiency for this technology at 21.09%.

While certain configurations of perovskite are far down the road to commercialization, the technology’s broader potential for high efficiency solar cells is well known, and universities and research institutes the world over are working on a plethora of different configurations and processes for getting the most out of this crystalline structure.

This latest breakthrough from KAUST concerns single crystal perovskites. Though the benefits of switching from multi to single crystal growth in silicon are well known, in perovskites this has so far proved challenging. The stability issues that have plagued the technology’s development primarily stem from the tendency of crystals to grow in a disordered manner, with a high number of defects, many of which appear at the grain boundary between two individual crystals.

Worthwhile challenge

Growing a single crystal perovskite could be a way to eliminate many of these defects; and is therefore seen by KAUST and several other research institutes as a worthwhile challenge to overcome. “We reasoned that these single crystals offer a chance for perovskite solar-cell technology to overcome these limitations and get as close as possible to the theoretical efficiency limit,” says Omar Mohammed, assistant professor of chemical science at KAUST and co lead author of the research paper.

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Mohammed and his team produced single crystals of methylammonium lead triiodide (MAPbI 3 ) using a method where the crystallization process was started in between two polymer coated substrates which physically restrict the crystal growth to one dimension. Their method and the devices produced are described in the paper Single-Crystal MAPbI 3 Perovskite Solar Cells Exceeding 21% Power Conversion Efficiency, published in the journal ACS Energy Letters.

The crystals produced were 20 micrometers thick. These were then processed with copper to create solar cells measuring 1mm², which achieved the maximum efficiency of 21.09%. The team says they were surprised by the results, and expected to have to tackle the problem of growing crystalline films much thinner than 20 micrometers, which they describe as “extremely challenging.”

While perovskite single crystals would have to be grown many times larger than the 3-6mm achieved here to be of any commercial interest, the researchers say that the high efficiency reached highlights the potential of single crystals in the development of perovskite based solar devices.