Overcoming Nanoscale Inhomogeneities in Thin-Film Perovskites via Exceptional Post-annealing Grain Growth for Enhanced Photodetection

Abstract

Antisolvent-assisted spin coating has been widely used for fabricating metal halide perovskite films with smooth and compact morphology. However, localized nanoscale inhomogeneities exist in these films owing to rapid crystallization, undermining their overall optoelectronic performance. Here, we show that by relaxing the requirement for film smoothness, outstanding film quality can be obtained simply through a post-annealing grain growth process without passivation agents. The morphological changes, driven by a vaporized methylammonium chloride (MACl)–dimethylformamide (DMF) solution, lead to comprehensive defect elimination. Our nanoscale characterization visualizes the local defective clusters in the as-deposited film and their elimination following treatment, which couples with the observation of emissive grain boundaries and excellent inter- and intragrain optoelectronic uniformity in the polycrystalline film. Overcoming these performance-limiting inhomogeneities results in the enhancement of the photoresponse to low-light (<0.1 mW cm –2 ) illumination by up to 40-fold, yielding high-performance photodiodes with superior low-light detection.

Elucidating the Factors Limiting the Photovoltaic Performance of Mixed Sb–Bi Halide Elpasolite Absorbers

“…From Figure 4c, it can be seen that there was an overall reduction in FWHM with an increase in the aerosol annealing temperature. This may be due to an increase in grain size (as previously found from aerosol‐annealed lead–halide perovskite films), [ 33,35 ] or a decrease in strain in the films. To decouple the effects of grain size and strain, we constructed Williamson–Hall plots for films annealed at each temperature (Figure S7, Supporting Information).…”

“…[ 34 ] Aerosol annealing with lead–halide perovskites has been demonstrated to give rise to reduced nonradiative recombination, improved optoelectronic uniformity between grains, as well as improved performance in PVs and photodetectors. [ 33,35 ]…”

“…[34] Aerosol annealing with lead-halide perovskites has been demonstrated to give rise to reduced nonradiative recombination, improved optoelectronic uniformity between grains, as well as improved performance in PVs and photodetectors. [33,35] To investigate the effect of aerosol annealing on the bulk optical and structural properties of the halide elpasolites, we again prepared films without antisolvent treatment. We used a 50:50 mixture of N,N-dimethylformamide (DMF) and DMSO for the aerosol, and annealed the films at temperatures from 100 to 150 °C for 5 min during the treatment.…”

Tuning Halide Composition Allows Low Dark Current Perovskite Photodetectors With High Specific Detectivity

“…[28][29][30] Some of the highest performing perovskite solar cells are based on mixed-cation, mixed-halide materials with power conversion efficiencies currently > 25 %. [27,31,32] Incorporating increasing quantities of Br into MAPb(I 1−x Br x ) 3 allows effective tuning of the optical bandgap, [33][34][35][36][37] which is critical to improve the efficiency of both single and multi-junction solar cells. [38,39] Moreover, altering halide composition can also have positive effects on film crystallization, morphology, and stability.…”

“…They are based on the use of charge-blocking layers to minimize charge injection. [22,23] Other strategies are related to inclusion of additives [24,25] or controlling film crystallization [26,27] to minimize backward charge injection at the electrodes. However, there is a deficit of efforts focused on understanding the role of perovskite composition and its correlation to device J d .…”