Phase-Pure Layered Perovskite Films for Photodetectors with Enhanced Performance and Stability

Organic-inorganic hybrid perovskites have attracted intense interest in solution-processable optoelectronic devices, while reduced dimensional perovskites with layered structures show a widely tunable band gap and superior environmental stability. Controlled synthesis of phase-pure layered perovskites, especially in the form of polycrystalline films, is crucial to improve the overall performance of perovskite-based devices. Here, we report a facile method to fabricate phase-pure layered perovskite films by the addition of a poor solvent during the spin-casting process. The use of these perovskites as active layers in photodetectors shows enhanced detection capability and stability. It is found that the kinetics of nucleation and crystallization processes is the key factor in controlling the phase purity of layered perovskites, and the introduction of the poor solvent elevates the supersaturation level of the precursor solution to form kinetic-controlled products. Moreover, the high phase purity significantly reduces the pinholes in polycrystalline films, which is beneficial for the efficient charge separation of photogenerated electron-hole pairs. As a result, the photodetectors based on phase-pure perovskites show a superior responsivity of 12.7 mA W-1 excited at the corresponding absorption band, which is enhanced by 1 order of magnitude compared with those based on as-cast perovskites. Meanwhile, the stability of photodetectors is significantly improved, in which the photocurrent shows only similar to 20% decrease after exposure to excitation light or ambient environment for a long period of time.