Carrier Recombination and Diffusion Dynamics in LiBr Passivated CsPbBr₃ Perovskite Film with Poly(9-vinylcarbazole) Film Underneath

The performance of cesium lead halide perovskite devices is seriously affected by grain boundaries and other charge traps in the polycrystalline perovskite thin films. LiBr doping could effectively passivate defects in CsPbBr₃ perovskite thin films, but it is still unclear that whether the passivation can help the carriers to diffuse across the grain boundaries. Here we have studied the carrier recombination and diffusion dynamics in LiBr passivated CsPbBr₃ perovskite film with poly(9-vinylcarbazole) (PVK) film underneath by using ultrafast transient absorption spectroscopy and transient absorption microscopy. The photoluminescence imaging and transient absorption morphological imaging show that LiBr passivating has made the grain size larger and reduced grain boundaries in CsPbBr₃ film. The transient absorption spectroscopy and time-resolved photoluminescence data indicate that LiBr passivating has slowed down the bimolecular recombination rate and extended the carrier lifetime. The photoexcited hot holes in the perovskite layer would transfer to the PVK layer in the initial 2 ps. And the transient absorption microscopy measurements reveal 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.