Seeking advantages and avoiding disadvantages: two dimensional chemical bond of unsaturated halogen at the edge of perovskite promotes exciton dissociation and inhibits charge recombination

Compared with the traditional three-dimensional organic-inorganic hybrid perovskite, the two-dimensional (2D) ruddlesden Popper (RP) perovskite has good stability and low lead content The photoelectric conversion efficiency of solar cell based on this kind of material is more than 17%, which has a potential application prospect Due to the quantum confinement effect, the binding energy of the two-dimensional perovskite exciton is large, and the photogenerated electrons and hole pairs are not easy to separate In addition, perovskite prepared by low temperature solution method has many defects, which are generally considered to accelerate the loss of charge and energy, limiting the further improvement of photoelectric conversion efficiency However, it is reported that the edge state formed by 2d-rp perovskite (BA) 2 (MA) n − 1 Pb n I 3N + 1 (n > = 2) is conducive to accelerating exciton dissociation, prolonging excited state lifetime and improving device performance However, the mechanism behind this phenomenon is unclear Using the combination of time-dependent density functional theory and non adiabatic molecular dynamics simulation, the research group of Professor long leap and Fang Weihai from the school of chemistry, Beijing Normal University designed a variety of edge structures of perovskite with Pb, I and Pb / I seals on both sides, and calculated the non radiative electron hole recombination of various geometric structures The simulation results show that the unsaturated non-metallic iodine chemical bond at the edge of perovskite enhances the hole localization, while the lead related defects can self heal by adjusting their oxidation state, so the metal lead unsaturated chemical bond plays a weak role in enhancing the electron localization In addition, the thermal motion accelerates the distortion of the edge geometry, further enhances the charge localization, especially the hole localization becomes more significant, and the charge separation state is strengthened, which is conducive to the exciton dissociation The synergistic effect of the edge geometry and the thermal effect makes the intensity of nonadiabatic electroacoustic coupling less than 1 MeV, and the quantum coherence time shorter than 10 fs These two factors reduce the recombination rate of non radiative electron hole and prolong the life of excited state It can be seen that the edge state can improve the performance of 2D RP perovskite optoelectronic devices The research results were published in J am Chem SOC (DOI: 10.1021 / JACS 9b06046) under the title of "exception disassociation and satisfied charge recommendation at 2D perovskite edits: key roles of unsaturated halide bonds and thermal disorder" The mechanism of 2D perovskite edge state accelerating exciton dissociation and inhibiting charge recombination is established, which provides a new idea for the design of cheap and efficient perovskite solar cell materials.