Science & Technology

Bright outlook for solar

Hybrid organic-inorganic perovskite has already demonstrated very high photovoltaic efficiencies of over 25%. Widely known in this field, organic (carbon and hydrogen-containing) molecules in the material are thought to suppress defect-supporting carrier recombination and are therefore important for achieving this impressive performance. It means that there is.

New research in the materials department at the University of California, Santa Barbara shows that not only is this assumption incorrect, but all inorganic materials may be superior to hybrid perovskite.The survey results are published in the article “All-inorganic halide perovskite as a candidate for efficient solar cells(The link is external)Appears on the cover of the October 20th issue of the journal Cell Reports Physical Science.

“We performed a comprehensive simulation of the recombination mechanism to compare the materials,” explained Xie Zhang, the lead researcher for this study. “When the solar cell material is exposed to light, the photogenerated carriers generate current. Recombination at the defects destroys some of those carriers and therefore reduces efficiency. Therefore, the defects It acts as a factor that reduces efficiency. “

To compare inorganic perovskite with hybrid perovskite, researchers studied two prototype materials. Both materials contain lead and iodine atoms, one of which has a crystalline structure completed by the inorganic element cesium and the other of which has an organic methylammonium molecule.

Experimental classification of these processes is very difficult, but thanks to a new methodology developed by the UCSB Materials Professor’s group, state-of-the-art quantum mechanical calculations can accurately predict recombination rates. Chris van de Wall(The link is external), Admitted that Mark Turiansky, a senior graduate student in the group, helped write the code to calculate the recombination rate.

“Our method is very powerful in determining which defects cause carrier loss,” Turiansky said. “It’s exciting to see this approach applied to one of the key issues of our time: the efficient generation of renewable energy.”

Simulations have shown that defects common to both materials cause similar (and relatively benign) levels of recombination. However, the organic molecules of hybrid perovskite can be degraded. When a hydrogen atom is lost, the resulting “vacancy” significantly reduces efficiency. Therefore, the presence of molecules is a disadvantage, not an asset, to the overall efficiency of the material.

So why was this not noticed experimentally? The main reason is that it is more difficult to grow a high quality layer of all inorganic materials. They tend to adopt other crystal structures and promoting the formation of the desired structure requires greater experimental effort. However, recent studies have shown that achieving a favorable structure is undoubtedly feasible. Still, this difficulty explains why all-inorganic perovskite has never received so much attention.

“We hope that our findings on the expected efficiency will stimulate more activity towards the production of inorganic perovskite,” Vandeware concludes.

Funding for this research was provided by the Department of Science, Department of Energy, Department of Basic Energy Science. The calculation was performed at the National Center for Energy Research and Science.

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