Recently, the team of professor Zhao Jin from the Institute of Physics of the University of Science and Technology of China and the International Research Center for Quantum Design of Functional Materials (ICQD) of the National Research Center for Microscale Material Science of Hefei made new progress in the study of the electron-hole recombination mechanism of perovskite solar cells The first-principles excited state dynamics program independently developed by the team revealed the important role of low-frequency vibratory phonons in the electron-hole recombination mechanism. This result is explained by Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole The topic of recombination was published in Science Advances. The first author, Chu Weibin, obtained a Ph.D. from the National Research Center for Microscale Physical Sciences in Hefei. Zhao Jin and Professor Wissam A. Saidi of the University of Pittsburgh are co-corresponding authors.
How semiconductor defects and impurities 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 the "deep energy level" in the middle of the energy gap would form electrons- The Hole Recombination Center has been used by many scientists in the semiconductor science community for many years. However, in the SRH model, the electroacoustic coupling effect has not been taken into account, and the electroacoustic coupling is the decisive factor for the recombination of electron holes through non-radiative transitions. In this work, the team of Zhao Jin used the self-developed first-principles excited state kinetics software Hefei-NAMD to study the effect of defects in MAPbI3 of lead-halogen perovskite batteries on electron-hole recombination, accurately considering the electroacoustic coupling , Energy level difference, atomic velocity, electron decoherence, carrier concentration and other factors, found that in this system, the defect will not form an electron hole recombination center, and the SRH model has completely failed. Through quantitative electroacoustic 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, and the corresponding amount of non-adiabatic coupling is small, making electron-hole recombination slow. This is why lead-halogen perovskite batteries have many defects, but still have good solar energy conversion efficiency.
In this work, Wissam A. Saidi is responsible for the construction of the defect structure of the system and the calculation of the ground state, and the group of Zhao Jin 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 is supported by the Fund Committee, Ministry of Science and Technology, Anhui Province, etc.
Figure: Defects in lead-halogen perovskite solar cell systems cannot form electron-hole recombination centers. (a) Schematic diagram of recombination of electron holes through defects; (b) Probability of recombination of electron holes in different systems within 2 ns; (c) Probability of direct recombination of electron holes; (d) Probability of recombination of electron holes through defects.
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