Spin-coating thermal-pressed strategy for the preparation of inorganic perovskite quasi-single-crystal thin films with giant single-/two-photon responses

All-inorganic mixed-halide perovskite thin films exhibit intriguing one- and two-photon absorption properties and optical stabilities. However, perovskite polycrystalline thin films prepared via conventional methods generally possess high trap densities, which reduces the efficiency of carrier transport. Thus, highly sensitive dual-mode photodetection in both the visible and near-infrared (NIR) regions is seemingly difficult to achieve. To overcome these issues, we utilized a spin-coating thermal-pressed (SCTP) strategy to grow CsPbI1.5Br1.5 QSC films with high crystallinity and a uniform orientation. The SCTP-grown films were found to be densely stacked with large single-crystal grains that vertically spanned the entire film thickness. The crystals were determined to be approximately 40 µm in diameter, which resulted from the removal of a significant number of grain boundaries and surface defects. The trap density of the SCTP-grown film was markedly decreased (ntrap: (8.55 ± 0.96) × 1011 cm–3), and it demonstrated a long carrier lifetime (τ2: 132.53 ± 9.45 ns) and a large two-photon absorption coefficient (β: 0.94 ± 0.04 cm·GW–1), all of which made the SCTP-grown CsPbI1.5Br1.5 QSC film superior to other reported CsPbI3−xBrx quantum dots and films. The visible and NIR dual-mode photodetection of the film at 532 and 1030 nm, respectively, was demonstrated with giant single-/two-photon responses. In addition, the surface nonlinear optics of the SCTP-grown QSC films were innovatively studied. This endowed the high-quality all-inorganic perovskite QSC films with optical properties beneficial for high-contrast photodetection necessary in application such as encryption imaging and high-efficiency solar cells.