近年来，全无机钙钛矿CsPbX₃（X = Cl，Br，I）由于其优异的光电特性和稳定性，在发光二极管（LEDs）、太阳能电池和激光器等领域得到了广泛的研究。例如，CsPbBr₃钙钛矿太阳能电池的认证效率已达到11.08%，全无机钙钛矿绿色LEDs的外量子效率已超过16%。然而，溶液法制备的全无机钙钛矿薄膜会产生许多缺陷和晶界。缺陷会导致载流子捕获过程，过量的晶界会阻碍载流子的传输，从而缩短载流子寿命和扩散长度。因此，通过有效手段钝化缺陷和减少晶界是制备高质量钙钛矿薄膜的主要挑战。通过超快时间分辨光谱研究钙钛矿中的光物理过程可以深入理解其光学性质和钝化机制，有助于设计并制备高效率的光电器件，并为相关领域的应用提供理论基础和技术支持。本文使用一步旋涂法制备了基于CsPbBr₃的四种全无机钙钛矿薄膜，利用飞秒瞬态吸收光谱和瞬态吸收显微镜等超快光谱技术研究了其光生载流子的动力学过程。

本论文的主要研究成果如下：

（1）利用瞬态吸收光谱技术（TA）研究了LiBr钝化前后两种CsPbBr₃钙钛矿薄膜中载流子的动力学过程，发现了热载流子捕获过程的存在。我们发现加入LiBr后，钙钛矿薄膜的XRD谱图、稳态吸收和光致发光（PL）光谱特征峰位置没有移动，表明Li⁺没有进入到钙钛矿晶格中。扫描电镜（SEM）和PL显微镜成像表明经LiBr钝化的钙钛矿薄膜表面更平整，空隙更少。通过在近带边激发的TA光谱发现冷载流子捕获过程并不明显，表明被捕获的冷载流子可能很容易脱离陷阱。而带隙以上激发的TA光谱中，在光致漂白（PB）动力学的初始阶段存在一个快衰减过程，归属于热载流子捕获过程（因为冷载流子不会被捕获）。热载流子冷却过程与热载流子捕获过程同时发生并竞争。LiBr能够有效钝化CsPbBr₃钙钛矿中的缺陷态，减慢热载流子的冷却过程。

（2）利用瞬态吸收显微镜（TAM）研究了CsPbBr₃和LiBr钝化的CsPbBr₃钙钛矿薄膜的载流子扩散过程。在TAM实验中，带隙之上激发测得的扩散常数明显小于近带边激发的。我们建立了CsPbBr₃钙钛矿薄膜中的载流子传输动力学模型，模拟了载流子扩散动力学的实验数据，证明在带隙之上激发时热载流子捕获过程与冷却过程的竞争使得冷载流子的总量减少，从而降低了扩散速率。而且我们发现LiBr钝化能够有效减少薄膜中的缺陷态，减弱热载流子捕获过程，因此提高了载流子的扩散速率。这项工作证明了热载流子捕获过程对CsPbBr₃钙钛矿薄膜中载流子扩散的影响。

（3）利用TA和TAM研究了LiBr钝化前后与聚（9-乙烯基咔唑）（PVK）薄膜复合的CsPbBr₃钙钛矿薄膜中的载流子复合和传输动力学。PL成像和瞬态吸收形貌成像表明钝化后的CsPbBr₃晶粒明显变大。瞬态吸收光谱和时间分辨荧光结果表明LiBr钝化能够减慢载流子的双分子复合速率并延长载流子的寿命。钙钛矿层中的光生热空穴会在2皮秒内转移到PVK层。TAM测量揭示了LiBr钝化可以促使载流子跨越晶界并扩散到周围的晶粒中。当晶粒间距约为0.9 μm时，载流子的扩散时间约为100 ps。

In recent years, the all-inorganic cesium lead halide perovskites (CsPbX₃, X = Cl, Br, I) have been widely studied as materials for light-emitting diodes (LEDs), solar cells and lasers due to their excellent photoelectric characteristics and stability. For example, the authentication efficiency of CsPbBr₃ perovskite solar cell has reached 11.08%, and the external quantum efficiency of all-inorganic perovskite green LEDs has surpassed 16%, in the past few years. However, the solution-processed perovskite film would generate many defects and grain boundaries. Defects could trap the carriers and excess grain boundaries could block the carriers, leading to slow carrier transport and decreased carrier lifetime. Therefore, passivation of defects and reduction of grain boundaries by effective means are the main challenges in preparing efficient perovskite films. The study of photophysical processes in perovskite by ultrafast time-resolved spectroscopy can deeply understand its optical properties and passivation mechanism, which is helpful for the design and preparation of high-efficiency optoelectronic devices, and provide theoretical basis and technical support for applications in related fields. In this paper, four kinds of all-inorganic perovskite films based on CsPbBr₃ were prepared by one-step spin-coating method. The photo-induced carrier dynamics were studied by femtosecond transient absorption spectroscopy and transient absorption microscopy.

The main contents of this paper are as follows:

(1) The carrier dynamics processes in two all-inorganic CsPbBr₃ perovskite films before and after LiBr passivation has been investigated by using transient absorption spectroscopy. The XRD pattern, steady-state absorption and photoluminescence (PL) spectra of the perovskite films did not move after the addition of LiBr, indicating that Li⁺ did not enter the perovskite lattice. Scanning electron microscopy (SEM) and PL microscope imaging showed that the surface of LiBr passivated perovskite films was much flatter and less voids. It is found that the cold carrier trapping process is not obvious in TA spectra under near the band edge excitation, indicating that the trapped cold carriers may easily escape the trap. In the TA spectra under above bandgap excitation, it appears a fast decay in the initial stage of photobleaching (PB) dynamics, which is attributed to the hot carrier capture process (because cold carriers are not trapped). The hot carrier cooling and hot carrier trapping process occurs simultaneously and compete with each other. LiBr can effectively passivate the defects in CsPbBr₃ perovskite and slow down the hot carrier cooling process.

(2) Carrier diffusion processes in CsPbBr₃ and CsPbBr₃ with LiBr passivated perovskite films were studied using transient absorption microscopy (TAM). In TAM experiments, the diffusion constant obtained from high-energy excitation is obviously smaller than that near-band-edge excitation. We established a kinetic model for carrier transport in CsPbBr₃ perovskite films and simulated the experimental data of carrier diffusion dynamics, it indicated that the competition between hot carrier trapping process and cooling process during excitation above the band gap reduces the total number of cold carriers, thus reducing the diffusion rate. Moreover, we found that LiBr passivation can effectively reduce the defects in the film, weaken the hot carrier trapping process, and thus increase the carrier diffusion rate. This work demonstrates the effect of hot carrier trapping process on carrier diffusion in CsPbBr₃ perovskite films.

(3) The carrier recombination and transport kinetics of CsPbBr3 perovskite films combined with poly (9-vinylcarbazole) (PVK) films before and after LiBr passivation were studied by TA and TAM. PL imaging and transient absorption morphology imaging showed that LiBr passivating has made the grain size larger and reduced grain boundaries. Transient absorption spectra and time-resolved fluorescence results show that LiBr passivating has slowed down the bimolecular recombination rate and extended the carrier lifetime. The photoexcitation hot holes in the perovskite layer would transfer to the PVK layer in the initial 2 ps. And we found that the LiBr passivation can help the carriers to diffuse across the grain boundaries to the surrounding grains in the CsPbBr₃ perovskite films. The carrier diffusion time is around 100 ps when the distance between two grains is ~ 0.9 μm.