Charge-carrier Dynamics In Perovskite Multiple Quantum Wells

Halide perovskite materials have drawn great attention in optoelectronic applications,which is contributed to their large photon absorption coefficient,widely tunable direct bandgap,and large carrier mobility.As the charge-carriers confined in the inorganic layers,perovskite multiple quantum wells have fast electron-hole bimolecular radiative recombination and long-term stability.The charge-carrier mobility and dynamics are very important for optoelectronic device efficiency.In order to optimize the perovskite multiple quantum wells photoelectric device and improve the device efficiency,we have synthesized perovskite multiple quantum well thin films with different electron band structures and investigated the charge-carrier dynamics of these thin films by time-resolved terahertz spectroscopy.Frist,we have determined the charge-carrier mobility of these thin films.We have synthesized seven kinds of perovskite multiple quantum well thin films by changing the cations of the organic layer and the thickness of the inorganic layer,and taken the terahertz time-domain spectroscopy measurement at different pump-probe delays.We have extracted the complex photoconductivity of these thin films,and fitted with the Drude-smith model and determined the carrier mobility of each thin film sample.The carrier mobility of three-dimensional bulk perovskite(MAPbI3,n=infinity)is about 395 cm2V-1s-1,and the carrier mobility of BA(n=1)thin films is about 126 cm2V-1s-1.The charge-carrier mobility and the carrier density are larger with the thin film with the thicker inorganic layer,and the kind of cations of organic layer has an impact on it.Similar to other low-dimensional materials,perovskite multiple quantum wells also have quantum confinement effect.With increased the quantum confinement,thin films exhibit enhanced excitonic and weakened electronic properties which means a decrease of charge-carrier mobility.Then we have investigated the charge-carrier recombination process of these thin films.We performed time-resolved optical pumping terahertz probe measurement with perovskite multiple quantum wells thin films,and obtained the charge-carrier recombination process.The effective bimolecular and effective auger recombination rates of photoinduced charge-carriers were extracted with rate equation fitting.For example,the monomolecular recombination rate of the PEA(n=3)thin film is about 0.5 × 109 s-1,the effective bimolecular recombination rates is 2.1 x 10-9 cm3s-1,and the effective auger recombination rates is 0.06×10-27 cm6 s-1.The effective bimolecular and Auger recombination rate constants both exhibit similar trends.The higher of the thickness of inorganic layer is,the larger the effective bimolecular recombination rate and the effective auger recombination rate are,and the effective bimolecular recombination rate and the effective auger recombination rate also had a similar trend when the cations of the organic layer were changed.We attributed this effect to the quantum confinement effect and exciton binding energy in the thin films.The stronger the quantum confinement effect is,the faster the recombination rates are.In perovskite multiple quantum wells,the monomolecular recombination is dominated by charge-carrier trapping at impurities,which is independence with the structure of the multiple quantum wells.To further improve the performance of perovskite multiple quantum wells optoelectronic devices,it is necessary to have a bright understanding of the charge-carrier mobility and recombination processes.In this thesis,we have investigated the charge-carrier properties,and explored the relationship between charge-carrier dynamics and the structure of perovskite multiple quantum wells.This paper offered implications for future theoretical works and provided a direction for further optimization of the perovskite multiple quantum wells optoelectronic devices.