Supporting Information Materials and MethodsChemicals and reagents. Lead bromide (≥ 98%), lead iodide (99.999% trace metal basis), DMF (anhydrous, 99.8%) and GBL (≥ 99%) were purchased from Sigma Aldrich. MABr, FABr and FAI were purchased from Dyesol Limited (Australia). All salts and solvents were used as received without any further purification. MAPbBr 3 , FAPbBr 3 and FAPbI 3 single crystals were grown by Inverse Temperature Crystallization (ITC) technique from 1 M solution of PbBr 2 /MABr in DMF, 1 M solution PbBr 2 /FABr in DMF:GBL (1:1 v/v) and 0.8 M solution of PbI 2 /FAI in GBL, respectively, as it was previously reported by Saidaminov et al. 1,2Powder X-ray diffraction was performed on a Bruker AXS D8 diffractometer using Cu-Kα radiation.

Single crystals of hybrid perovskites have shown remarkably improved physical properties compared to their polycrystalline film counterparts, underscoring their importance in the further development of advanced semiconductor devices. Here we present a new method of growing sizable CH3NH3PbCl3 single crystals based on the retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy band structure, charge recombination, and transport properties of CH3NH3PbCl3 single crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility, and diffusion length comparable with the best quality crystals of methylammonium lead iodide or bromide perovskites reported so far. The high quality of the crystal along with its suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector, demonstrating its potential in optoelectronic applications.

A rapid, low‐temperature, and solution‐based route is developed for growing large‐sized cesium lead halide perovskite single crystals under ambient conditions. An ultralow minority carrier concentration was measured in CsPbBr3 (≈108 holes per cm3, much lower than in any other lead halide perovskite and crystalline silicon), which enables to realize self‐powered photodetectors with a high ON/OFF ratio (105).

Photodetectors are designed, which operate in the broadband regime upon bottom illumination (from the indium tin oxide (ITO) side) and in the narrowband regime upon top illumination (from the air/perovskite side). The narrowband photodetectors show high external quantum efficiency of above 10 %. The operational spectrum of the photodetectors can also be tuned by adjusting the halide composition in the active material.

Hybrid Perovskites have emerged as a class of highly versatile functional materials with applications in solar cells, photodetectors, transistors, and lasers. Recently, there have also been reports on perovskite-based resistive switching (RS) memories, but there remain open questions regarding device stability and switching mechanism. Here, an RS memory based on a highquality capacitor structure made of an MAPbBr 3 (CH 3 NH 3 PbBr 3 ) perovskite layer sandwiched between Au and indium tin oxide (ITO) electrodes is reported. Such perovskite devices exhibit reliable RS with an ON/OFF ratio greater than 10 3 , endurance over 10 3 cycles, and a retention time of 10 4 s. The analysis suggests that the RS operation hinges on the migration of charged ions, most likely MA vacancies, which reversibly modifies the perovskite bulk transport and the Schottky barrier at the MAPbBr 3 /ITO interface. Such perovskite memory devices can also be fabricated on flexible polyethylene terephthalate substrates with high bendability and reliability. Furthermore, it is found that reference devices made of another hybrid perovskite MAPbI 3 consistently exhibit filament-type switching behavior. This work elucidates the important role of processing-dependent defects in the charge transport of hybrid perovskites and provides insights on the ion-redistribution-based RS in perovskite memory devices.