Charge Localization Induced by Reorientation of FA Cations Greatly Suppresses Nonradiative Electron-Hole Recombination in FAPbI3 Perovskites:a Time-Domain Ab Initio Study

Recent experiments report the rotation of FA(FA=HC[NH2]2+)cations significantly influence the excited-state lifetime of FAPbI3.However,the underlying mechanism remains unclear.Using ab initio nonadiabatic(NA)molecular dynamics combined with time-domain density functional simulations,we have demonstrated that reorientation of partial FA cations significantly inhibits nonradiative electron-hole recombination with respect to the pristine FAPbI3 due to the decreased NA coupling by localizing electron and hole in different positions and the suppressed atomic motions.Slow nuclear motions simultaneously increase the decoherence time,which is overcome by the reduced NA coupling,extending electron-hole recombination time scales to several nanoseconds and being about 3.9 times longer than that in pristine FAPbI3,which occurs within sub-nanosecond and agrees with experiment.Our study established the mechanism for the experimentally reported prolonged excited-state lifetime,providing a rational strategy for design of high performance of perovskite solar cells and optoelectronic devices.

Numerical analysis of non-Newtonian rheology effect on hydrocyclone flow field

In view of the limitations of the existing Newton fluid effects on the vortex flow mechanism study,numerical analysis of non Newton fluid effects was presented.Using Reynolds stress turbulence model(RSM)and mixed multiphase flow model(Mixture)of FLUENT(fluid calculation software)and combined with the constitutive equation of apparent viscosity of non-Newtonian fluid,the typical non-Newtonian fluid(drilling fluid,polymer flooding sewage and crude oil as medium)and Newton flow field(water as medium)were compared by quantitative analysis.Based on the research results of water,the effects of non-Newtonian rheology on the key parameters including the combined vortex motion index n and tangential velocity were analyzed.The study shows that:non-Newtonian rheology has a great effect on tangential velocity and n value,and tangential velocity decreases with non-Newtonian increasing.The three kinds of n values(constant segment)are:0.564(water),0.769(polymer flooding sewage),0.708(drilling fluid)and their variation amplitudes are larger than Newtonian fluid.The same time,non-Newtonian rheology will lead to the phenomenon of turbulent drag reduction in the vortex flow field.Compared with the existing formula calculation results shown,the calculation result of non-Newtonian rheology is most consistent with the simulation result,and the original theory has large deviations.The study provides reference for theory research of non-Newtonian cyclone separation flow field.