Research has shown that all-inorganic, perovskite solar cell technology is promising for increasing the efficiency of solar cells.

Hybrid organic-inorganic perovskites have already demonstrated more than 25% photovoltaic efficiency. According to the current wisdom, the organic molecules (carbon- and hydrogen-containing) in the material are essential to achieve this remarkable performance. They are believed to suppress defect-assisted carrier recombination.

The UC Santa Barbara materials research department has found that not only is this incorrect but that all-inorganic materials can outperform hybrid perovskites. These findings were published in the article “All -inorganic Halide Perovskites as Candidates for Efficient Solar Cells,” which appears on the cover of the October 20, 2021, issue of the journal Cell Reports Physical Science.

“To compare materials, we performed extensive simulations of the recombination mechanism,” said Xie Zhang (lead researcher). “When sunlight shines on a solar cell material, photo-generated carriers create a current. Recombination at defects destroys some pages and lowers efficiency. Defects are efficiency killers.

The researchers studied two prototype materials to compare inorganic and mixed perovskites. Both materials contain iodine and lead atoms. However, in one of the prototype materials, the crystal structure has been completed by the inorganic element cesium. In the other, however, the organic methylammonium mole is present.

It takes work to sort these processes out experimentally. However, state-of-the-art quantum-mechanical calculations can accurately forecast the recombination rate. Chris Van de Walle, UCSB materials professor, developed this new method. He also credits Mark Turiansky (a senior graduate student) with writing the code that calculates the recombination rs.

Turiansky stated, “our methods are potent in determining which defects cause carrier losses.” It is thrilling to see this approach applied to one of the most pressing issues of our times, the efficient generation and use of renewable energy.

Simulations revealed that both materials have similar (and relatively benign) levels of recombination. The hybrid perovskite’s organic molecule can be broken down. When hydrogen atoms are lost, these “vacancies” significantly decrease efficiency. The presence of this molecule is a disadvantage rather than an asset to the material’s overall efficiency.

This is why it has yet to be observed experimentally. It isn’t easy to grow layers of high-quality all-inorganic material. They are more inclined to adopt other crystal structures, and it takes more experimental work to promote the formation of the desired format. Recent research has demonstrated that it is possible to achieve the desired design. The difficulty explains why all-inorganic perovskites are getting less attention.

Van de Walle concluded, “We hope our findings regarding the expected efficiency will encourage more activities directed towards producing inorganic Perovskites.”