Dynamics Study Of Photoelectric Processes In Functional Materials Of Perovskite Optoelectronic Devices

In the forefront of optoelectronic devices,metal halide perovskite exhibits promising applications due to its excellent optoelectronic performance,which has attracted constant attention from researchers and the optoelectronic industry.The performance of perovskite optoelectronic devices is closely related to the photoelectric processes in functional materials.However,the dynamic analysis of the photoelectric processes in functional materials is not yet perfect,and further in-depth research is needed.For CH₃NH₃Pb I₃ and CH₃NH₃Pb Br₃ single crystals,the ultra-long photocarrier lifetime has been reported many times,but the dynamic process of carriers inside the crystal is not fully understood.For CH₃NH₃Pb Cl₃ single crystal,its spectral characteristics also exhibit significant diversity,making it difficult to form a unified understanding of its optoelectronic properties.On the other hand,Spiro-OMe TAD,as a common hole functional material in perovskite optoelectronic devices,its intramolecular and intermolecular charge transfer properties have a significant impact on the transport process of charge carriers.However,for amorphous thin films,precise photophysical parameters and internal carrier dynamics are difficult to be characterized.In response to the above issues,spectral measurements and theoretical analysis of metal halide perovskites and undoped Spiro-OMe TAD are carried out in this dissertation.The main works are as follows:（1）High-quality CH₃NH₃Pb I₃ and CH₃NH₃Pb Br₃ single crystals were grown by the anti-solvent diffusion method,and corresponding perovskite films were prepared by the one-step spin-coating method.During the spectral testing process,it was found that its photoluminescence output consists of two parts,namely high-energy luminescence attributed to the surface state of the crystal and low-energy luminescence attributed to the interior of the crystal.The law that the relative intensity of dual emission peak changes with the surface roughness of crystals is summarized,that is,the proportion of high-energy luminescence component increases with the increase of crystal surface roughness.By utilizing the curing effect of component ions in the saturated growth mother liquor on the surface hanging bonds of perovskite lattice,the photoluminescence spectrum curve containing only a low-energy luminescence component was characterized.The steady-state photoluminescence spectrum measurement revealed the asymmetric characteristics of bulk-specific luminescence in metal halide perovskite single crystals,and the classical van Roosbroeck-Shockley relationship was used to correctly explain this asymmetric feature,achieving the unity of theoretical and experimental results.（2）In the process of in-depth research on the physical mechanism of the dual luminescence phenomenon of metal halide perovskites,it was found that the charge carriers inside the crystal have an ultra-long photoluminescence lifetime,which is significantly different from the basic spectral characteristics of direct bandgap semiconductors.For high-quality CH₃NH₃Pb I₃ and CH₃NH₃Pb Br₃ single crystals whose luminescence is dominated by bulk-specific photoluminescence,excitation intensity-dependent photoluminescence spectra measurements were conducted.It was found that there is a certain threshold of excitation intensity for the detected bulk-specific photoluminescence,and obvious hysteresis is observed in the forward and reverse scan tests by increasing and decreasing excitation intensity,indicating that there is a phase transition process of the excited state in CH₃NH₃Pb I₃ and CH₃NH₃Pb Br₃ single crystals.By analogy with the evolution law of the traditional semiconductor excited state,it can be inferred that the excited perovskite single crystal contains the gas-to-liquid phase conversion of electron-hole plasmas,the dynamic process of internal carriers is also described according to the time-resolved photoluminescence spectrum.（3）In addition to spontaneous emission or non-radiation quenching,photocarriers in metal halide perovskite single crystals may also be bound by trap states generated by surface impurities or lattice defects.Here,the absorption spectrum of CH₃NH₃Pb Cl₃single crystal was obtained through reflection method testing.It was found that there is a sharp absorption peak at the edge of the absorption band,which corresponds to the absorption of trap states whose energy level is slightly lower than the conduction band bottom.Through steady-state photoluminescence spectrum testing,it can be observed that there are two luminescence components in the spectrum,corresponding to the luminescence of bulk and trap states,respectively.It is worth noting that compared to bulk-specific luminescence,the luminescence of trap states exhibits a significant redshift and spectral broadening,which means that its electronic energy level distribution also undergoes corresponding shift and broadening.In this study,the spectral signals of trap states in CH₃NH₃Pb Cl₃ crystal were observed from both absorption and photoluminescence levels,and carrier dynamic characteristics of trap states were also explored.（4）Spiro-OMe TAD is the most commonly used hole functional material in perovskite optoelectronic devices.By characterizing the low-concentration Spiro-OMe TAD chlorobenzene solution,spectral characteristics of the Spiro-OMe TAD monomolecular solution can be obtained.It was found that light soaking can change the color and spectrum of Spiro-OMe TAD 1,2-dichloroethane solution,which is related to the formation of molecular aggregates.By analyzing the spectral changes of Spiro-OMe TAD 1,2-dichloroethane solution under light conditions,a novel oxidation mechanism is described,the oxidation of Spiro-OMe TAD is caused by the charge transfer between molecules in the aggregate.In addition,it was found that due to the special stacking mode between molecules in the aggregate,Spiro-OMe TAD thin films prepared through the aggregate solution have better conductivity and charge extraction ability.