Strain engineering and epitaxial stabilization of halide perovskites

Strain engineering is a powerful tool with which to enhance semiconductor device performance.sup.1,2. Halide perovskites have shown great promise in device applications owing to their remarkable electronic and optoelectronic properties.sup.3-5. Although applying strain to halide perovskites has been frequently attempted, including using hydrostatic pressurization.sup.6-8, electrostriction.sup.9, annealing.sup.10-12, van der Waals force.sup.13, thermal expansion mismatch.sup.14, and heat-induced substrate phase transition.sup.15, the controllable and device-compatible strain engineering of halide perovskites by chemical epitaxy remains a challenge, owing to the absence of suitable lattice-mismatched epitaxial substrates. Here we report the strained epitaxial growth of halide perovskite single-crystal thin films on lattice-mismatched halide perovskite substrates. We investigated strain engineering of [alpha]-formamidinium lead iodide ([alpha]-FAPbI.sub.3) using both experimental techniques and theoretical calculations. By tailoring the substrate composition--and therefore its lattice parameter--a compressive strain as high as 2.4 per cent is applied to the epitaxial [alpha]-FAPbI.sub.3 thin film. We demonstrate that this strain effectively changes the crystal structure, reduces the bandgap and increases the hole mobility of [alpha]-FAPbI.sub.3. Strained epitaxy is also shown to have a substantial stabilization effect on the [alpha]-FAPbI.sub.3 phase owing to the synergistic effects of epitaxial stabilization and strain neutralization. As an example, strain engineering is applied to enhance the performance of an [alpha]-FAPbI.sub.3-based photodetector. A method of deposition of mixed-cation hybrid perovskite films as lattice-mismatched substrates for an [alpha]-FAPbI.sub.3 film is described, giving strains of up to 2.4 per cent while also stabilizing the metastable [alpha]-FAPbI.sub.3 phase for several hundred days.
Author(s): Yimu Chen [sup.1] , Yusheng Lei [sup.1] , Yuheng Li [sup.1] , Yugang Yu [sup.2] , Jinze Cai [sup.2] , Ming-Hui Chiu [sup.3] , Rahul Rao [sup.4] , Yue [...]