Researchers at University of Tsukuba have used electron spin resonance technology to observe the state and movement of the charge inside Ruddlesden-Popper tin -based perovskite solar cells, an emerging technology for next-generation solar cells. They have discovered a mechanism that improves the performance of these cells compared with conventional three-dimensional tin-based perovskite solar cells. Their findings signal a great leap forward in the development of high-efficiency, long-lasting solar cells.

Tsukuba, Japan—Perovskite solar cells are attracting attention as next-generation solar cells. These cells have high efficiency, are flexible, and can be printed, among other features. However, lead was initially used in their manufacture, and its toxicity has become an environmental issue. Therefore, a method for replacing lead with tin, which has a low environmental impact, has been proposed. Nevertheless, tin is easily oxidized; consequently, the efficiency and durability of tin perovskite solar cells are lower than those of lead perovskite solar cells.

To improve the durability of tin perovskite by suppressing tin oxidation, a method that introduces large organic cations into tin perovskite crystals to form a two-dimensional layered structure called Ruddlesden-Popper (RP) tin-based perovskites has been proposed. However, the internal state of this structure and the mechanism by which it improves performance have not been fully elucidated.

In this study, researchers used electron spin resonance to investigate an RP perovskite solar cell's internal state during operation from a microscopic perspective.

Perovskite solar cells have a structure in which hole and electron transport layers surround a perovskite crystal. First, when no light was irradiated on the RP perovskite solar cell, holes diffused from the hole transport layer to the RP perovskite. This led to the formation of an energy barrier at the hole transport layer-RP tin perovskite interface, which suppressed the backflow of electrons and hence improved the performance. Second, under sunlight irradiation, electrons moved from the RP tin-based perovskite to the hole transport layer, attributable to the high-energy electrons produced by short-wavelength light, such as ultraviolet rays. Further, they found that this electron transfer increased the energy barrier at the hole transport layer-RP tin perovskite interface, further improving the device's efficiency.

Understanding the mechanism behind the performance improvements during device operation is crucial for developing highly efficient, long-lasting solar cells and will contribute to future research developments

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This work was supported by the Japan Science and Technology Agency MIRAI (Grants No. JPMJMI20C5, JPMJMI22C1, and JPMJMI22E2), Japan; by the New Energy and Technology Development Organization, Green Innovation, Japan; by the Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research (KAKENHI) (Grant No. 24K01325), Japan; by the University of Tsukuba, Organization for the Promotion of Strategic Research Initiatives, Japan; and by the JST SPRING (Grant No. JPMJSP2124), Japan.

Original Paper

Title of original paper:

Operando spin observation elucidating performance-improvement mechanisms during operation of Ruddlesden-Popper Sn-based perovskite solar cells.

Journal:

npj Flexible Electronics

DOI:

10.1038/s41528-024-00376-2

Correspondence

Professor MARUMOTO Kazuhiro
Institute of Pure and Applied Sciences, University of Tsukuba

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Institute of Pure and Applied Sciences