Shaping Perovskites: In Situ Crystallization Mechanism of Rapid Thermally Annealed, Prepatterned Perovskite Films

Abstract

Understanding and controlling the crystallization of organic–inorganic perovskite materials is important for their function in optoelectronic applications. This control is particularly delicate in scalable single-step thermal annealing methods. In this work, the crystallization mechanisms of flash infrared-annealed perovskite films, grown on substrates with lithographically patterned Au nucleation seeds, are investigated. The patterning enables the in situ observation to study the crystallization kinetics and the precise control of the perovskite nucleation and domain growth, while retaining the characteristic polycrystalline micromorphology with larger crystallites at the boundaries of the crystal domains, as shown by electron backscattering diffraction. Time-resolved photoluminescence measurements reveal longer charge carrier lifetimes in regions with large crystallites on the domain boundaries, relative to the domain interior. By increasing the nucleation site density, the proportion of larger crystallites is increased. This study shows that the combination of rapid thermal annealing with nucleation control is a promising approach to improve perovskite crystallinity and thereby ultimately the performance of optoelectronic devices.

Physical Passivation of Grain Boundaries and Defects in Perovskite Solar Cells by an Isolating Thin Polymer

“…Only the fast crystallization prevents the dewetting of the film, because solvent evaporation outpaces the material diffusion. 27 Despite parameter optimization, the perovskite films exhibit small uncovered areas and regions with low film thickness at the domain boundaries. These valleys can reach several micrometers in width (Figure 1d).…”

“…During FIRA annealing, a good wetting of the substrate by the precursor solution is crucial, since the crystallization typically forms isolated islands. Only the fast crystallization prevents the dewetting of the film, because solvent evaporation outpaces the material diffusion . Despite parameter optimization, the perovskite films exhibit small uncovered areas and regions with low film thickness at the domain boundaries.…”

Switched‐On: Progress, Challenges, and Opportunities in Metal Halide Perovskite Transistors

“…[253][254][255] Importantly, one has to consider that crystallization on pre-patterned electrodes in bottom contact FETs, for example, will be starkly different to that on flat smooth surfaces such as extraction layers in solar cells. A structured metal contact surface could provide nucleation sites that will trigger crystallization and the growth of perovskite domains, [256] so the exact geometry of these contacts will be instrumental in influencing the final perovskite active layer microstructure. This opens the opportunity for the development of novel strategies for the design of FET device structures with contacts that actively guide the perovskite crystallization to form the desired microstructure.…”

Annealing Engineering in the Growth of Perovskite Grains

“…In the fabrication of perovskite films, infrared light can effectively promote precursor reactions and drive grain growth [72,[80][81][82][83][84][85][86][87][88][89][90]. Infrared light is an electromagnetic wave with a frequency between microwave and visible light.…”

“…Pulsed flash infrared annealing provided precise control of the kinetic process of perovskite nucleation [87,89]. The crystal growth rate and solute concentration determines the grain size of the grain boundaries in flash annealing [85], and the carriers at the grain boundary edges exhibited longer electronic lifetimes. Gradient flash annealing has also been confirmed to provide a significant improvement on crystalline quality [75].…”