Solution-processed halide perovskites are photoactive materials that may be used to produce low-cost and/or high-performance optoelectronics. For example, perovskite-based solar cells having efficiencies of at least 20%, and perovskite-based light emitting diodes (PeLEDs) having high brightness and tunable color across the entire visible range have been produced (see, e.g., Yang, W. S. et al., Science 2015, 348, 1234; and Tan, Z. K. et al., Nat. Nanotechnol. 2014, 9, 687). PeLEDs typically include organic-inorganic hybrid perovskites, such as CH3NH3PbBr3, as emitters.
Due to concerns regarding the stability of organic-inorganic hybrid perovskites, all-inorganic halide perovskites, such as cesium lead bromide (CsPbBr3), have been used as alternative emitters in PeLEDs (see, e.g., Brittman, S. et al., MRS Commun. 2015, 5, 7). In addition to a photoluminescence (PL) comparable to that of CH3NH3PbBr3 (Protesescu, L. et al., Nano Lett. 2015, 15, 3692), cesium-based perovskites have exhibited higher thermal and chemical stability (see, e.g., Kulbak, M. et al., J Phys. Chem. Lett. 2015, 6, 2452).
Despite these advantages, the brightness and/or quantum efficiency of cesium-based PeLEDs remains limited. To improve the external quantum efficiency (EQE), CsPbBr3 quantum dots have been created, which have exhibited higher PL efficiency owing to the surface passivation as well as better morphology in close-packed quantum dot films (see, e.g., Li, G. et al., Nano Lett. 2015, 15, 2640). However, organic capping ligands stabilizing the quantum dots typically suppress charge injection into the emitters, which can result in limited brightness, high turn-on voltage, or a combination thereof.
Although some CsPbBr3 films have been attempted, the relatively low solubility of cesium bromide (CsBr) precursor in commonly used solvents typically makes it difficult to produce CsPbBr3 films of suitable quality. Perovskite-based films that include a large amount of polymer as a host matrix for the perovskite crystallites also have been made, but the inclusion of the host matrix has not cured one or more of the foregoing disadvantages (see, e.g., J. Li, et al., Adv. Mater. 2015, 27, 5196). Due, at least in part, to substantial current leakage caused by incomplete surface coverage, the maximum brightness achieved with PeLEDs based on CsPbBr3 films has been only 407 cd m−2 with peak EQE of 0.008% (Yantara, N. et al., J. Phys. Chem. Lett. 2015, 6, 4360).
Therefore, methods and materials that overcome one or more of the foregoing disadvantages associated with all-inorganic perovskites are desirable, including methods that [1] reduce or eliminate the substantial current leakage that can occur when films of all-inorganic perovskites, such as CsPbBr3, are used, [2] produce all-inorganic perovskite-based films having favorable physical and/or light emitting characteristics, and/or [3] produce films of all-inorganic perovskites that are stable at a variety of ambient conditions, which may include relatively high humidity.