Osman M. Bakr's group in the KAUST Catalysis Facility has designed a low-temperature method that can be useful for making improved single crystal perovskites. The team said that novel perovskites have positive and negative ions in the same plan as the natural perovskite calcium titanate (CaTiO3). Lead halide perovskites, having lead ions as well as halide ions, such as chlorine and iodine in the perovskite mix, are drawing attention for optoelectronic applications.
The crystals have previously been created using high temperatures, however these have created many challenges. Now, the KAUST team has developed a new approach, enabling better crystals to form.
Their "solvent engineering" approach modifies the liquid solvent in which the components of the perovskite are originally liquified, and in which they combine to build the perovskite crystals.
The researchers are developing a particular perovskite known as methylammonium lead iodide, including large methylammonium ions (CH6N+), combined with iodide (I−) and lead (Pb2+) ions.
Earlier, it was essential to maintain the solutions used to make the crystals at 120 °C, but such a high temperature hindered with the maximum integration of iodide and methylammonium ions into the structure.
"We investigated a variety of different solvents to carry the perovskite components and allow them to crystallize. Eventually, we found a solution that could work at less than 90 degrees Celsius and produce single crystals that were of significantly higher quality", said Bekir Turedi, Study Co-First Author, KAUST.
The improvement in the formation of crystals corresponded to enhanced performance when using the crystals as the light-absorbing layers in solar cells.
"We obtained markedly higher photovoltages, and power conversion efficiencies approaching 22 percent, among the highest ever reported for these perovskites", stated Osman M. Bakr, KAUST.
The team confirmed that the new single crystals are, at present, too small to be used for commercial applications—an issue that now impedes several other efforts to improve the complete potential of perovskites in solar cells.
However, this new study is a vital first step toward addressing the problem of size as well as further enhancements.