At present, the intense concern about global climate change will affect and is already affecting all living things on earth. To prevent the creation of so-called "hot lands" and meet the requirements of the Paris Agreement, clean energy use and development should exceed current levels. Therefore, high hopes are placed on the development of low-cost solar cell modules.
At present, crystalline silicon (Si) is the representative solar cell material, accounting for more than 90% of all types of solar panels. However, as the conversion efficiency of silicon solar panels reaches its theoretical limit, their cost reduction is becoming slower and slower. In order to achieve a significant reduction in the cost of renewable solar power generation, research is looking for new solar cell materials.
In recent years, great breakthroughs have been made in solar cell research - high conversion efficiency has been achieved in hybrid perovskite solar cells. Perovskite is a crystal structure with simple cubic symmetry, while hybrid perovskite is composed of organic cations and inorganic cage structures.
Quite remarkably, silicon-based solar cells take half a century to achieve a conversion efficiency of 26.7%, but just a decade is enough to develop a perovskite hybrid solar cell with similar efficiency. However, hybrid perovskites are inherently unstable and exhibit rapid phase transitions when exposed to light, heat (~100°C), and air. In addition, the presence of toxic lead atoms in hybrid perovskites is very unfavorable for large area applications.
In an effort to find alternatives to perovskite, professor Hiroyuki Fujiwara of Gifu University and his team, along with Professors Hidenori Hiramatsu and Hideo Hosono of Tokyo Institute of Technology, conducted a new study on sulfur-based perovskite. Sulfur compounds represent VI atoms, such as sulfur and selenium, and the chemical formula for sulfur perovskites is simply ABS3 (A for alkaline earth metals, B for early transition metals).
In the paper published today in Solar RRL, the manufacture of a sulfur-based perovskite alloy containing BaZrTiS3 is reported to adjust the band gap to the appropriate value (~ 1.6eV). This material has great potential, with a theoretical maximum conversion efficiency of 38% in a perovskite/silicon tandem solar cell structure, which is impressive.
Prior to this manufacture, several sulfur perovskites, such as BaZrS3, SrZrS3, BaHfS3 and SrHfS3, have been found to exhibit very strong light absorption properties, with light absorption intensity (absorption coefficient) exceeding 10^5/cm, much higher than all existing solar cell materials.
Such remarkable light-absorption properties allow ultra-thin solar cells to easily collect photocarriers (that is, electrons and holes) and improve conversion efficiency. Theoretical calculations have successfully explained the considerable light absorption observed in sulfur perovskites due to the unique sulfur orbit formed by the perovskite structure.
These sulfur-based perovskite materials, composed of only non-toxic elements, are very stable, and the excellent optical properties of these materials discovered by Professor Hiroyuki Fujiwara's team will have a significant impact on the future research of solar cell devices. It is very important to develop suitable thin-film forming technology for the realization of thioid-perovskite solar devices. Using this processing technology, it is possible to achieve mass production of solar panels.