Controllable Growth of Centimeter-Sized 2D Perovskite Heterostructures for Highly Narrow Dual-Band Photodetectors

Abstract

Heterostructures consisting of 2D layered perovskites are expected to exhibit interesting physical phenomena inaccessible to the single 2D perovskites and can greatly extend their functionalities for electronic and optoelectronic applications. Herein, we develop a solution method to synthesize (C₄H₉NH₃)₂PbI₄/(C₄H₉NH₃)₂(CH₃NH₃)Pb₂I₇ heterostructures with centimeter size, high phase purity, controllable thickness and junction depth, high crystalline quality, and great stability for highly narrow dual-band photodetectors. On the basis of the different lattice constant, solubility, and growth rate between (C₄H₉NH₃)₂PbI₄ and (C₄H₉NH₃)₂(CH₃NH₃)Pb₂I₇, the designed synthetic method allows to first grow the (C₄H₉NH₃)₂PbI₄ at the water-air interface and subsequently the (C₄H₉NH₃)₂(CH₃NH₃)Pb₂I₇ layer is formed via a diffusion process. Such a growth process provides an efficient way for us to readily obtain heterostructures with various thickness and junction depth by controlling the concentration, reaction temperature, and time. The formation of heterostructures has been verified by X-ray diffraction, cross-section photoluminescence, and reflection spectroscopy with the estimated junction width below 100 nm. Photodetectors based on such heterostructures exhibit low dark current (∼10^-12 A), high on-off current ratio (∼10³), and highly narrow dual-band spectral response with a full-width at half-maximum (fwhm) of 20 nm at 540 nm and 34 nm at 610 nm. The high performance can be attributed to the high crystalline quality of the heterostructures and the extremely large resistance in the out-of-plane direction. The synthetic strategy is versatile for other 2D perovskites, and the narrow dual-band spectral response with all fwhm < 40 nm can be continuously tuned from red to blue by properly changing the halide compositions.