April 07, 2020

Progress in research on excited-state carrier recombination mechanism of perovskite solar cells

[ Instrument Network Instrument R & D ] Recently, Zhao Jin's team at the School of Physics, University of Science and Technology of China and Hefei National Research Center for Microscale Material Science International Center for Functional Materials Quantum Design (ICQD) is working on the electron hole recombination mechanism of perovskite solar cells New progress has been made. They used the first-principles excited-state dynamics program developed by the team to reveal the important role of low-frequency vibrating phonons in the electron-hole recombination mechanism. The results were explained in terms of Low-frequency lattice phonons in halide perovskites high The subject of defect tolerance toward electron-hole recombination was published in Science Advances. The first author, Chu Weibin, received his Ph.D. from the National Research Center for Microscale Physical Sciences in Hefei, and Zhao Jin and University of Pittsburgh professor Wissam A. Saidi are co-corresponding authors.
How defects and impurities in semiconductor materials affect electron-hole recombination is an important scientific issue in this field. As early as the 1850s, the famous scientists Shockley, Read, and Hall proposed the Shockley-Read-Hall (SRH) model. In this model, they believed that "deep energy levels" with energy in the middle of the energy gap would form electrons- Hole recombination centers. For many years, many scientists in the semiconductor science community have used this simple criterion. However, in the SRH model, the electro-acoustic coupling effect is not taken into account, and electro-acoustic coupling is the decisive factor for the recombination of electrons and holes through non-radiative transitions. In this work, Zhao Jin's team used the self-developed first-principles excited-state dynamics software Hefei-NAMD to study the effect of defects in lead-perovskite battery MAPbI3 on ​​electron-hole recombination, and accurately considered electro-acoustic coupling. , Energy level difference, atomic motion speed, electron decoherence, carrier concentration and other factors, it is found that in this system, defects do not form electron-hole recombination centers, and the SRH model has completely failed. Through quantitative electro-acoustic coupling analysis, it is found that due to the low hardness of the material, phonons that contribute to electron-hole recombination are low-frequency phonons with or without defects. The corresponding non-adiabatic coupling is small, which makes electron-hole recombination slow. This is also the reason why lead halide perovskite batteries still have better solar energy conversion efficiency despite many defects.
In this work, Wissam A. Saidi is responsible for the construction of the system's defect structure and the calculation of the ground state, and Zhao Jin's group is responsible for the calculation of the excited state dynamics. This work is another important application of Hefei-NAMD software. Since 2016, nearly 30 academic papers have been published using this software.
This work was supported by the Funding Committee, the Ministry of Science and Technology, and Anhui Province.

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