Correlation between growth orientation and growth temperature for bismuth tri-iodide films

Evaluation of Relationship between Grain Morphology and Growth Temperature of HgI2 Poly-Films for Direct Conversion X-ray Imaging Detectors

The relationship between depositing temperature and crystallinity of grain for HgI2 polycrystalline film with 170 cm2 in area deposited by Physical Vapor Deposition (PVD) was investigated, considering the matches with readout matrix pixelation for female breast examination. The different depositing temperatures, 35, 40 and 45 °C, were carried out with the same source temperature, 100 °C, corresponding to 2–2.5 h of the growth period. The films deposited were investigated by XRD, SEM, and I–V. The results show that the grain size of the films grown increases with the depositing temperature from 35 to 45 °C. At 45 °C, the polycrystalline film has a preferred microcrystal orientation with 97.2% of [001]/[hkl] and grain size is about 180–220 μm. A 256 × 256 pixels X-ray image of a bolt, key, and wiring displacement was present distinctly with 50 keV with 6 mA current of X-ray generator. Our discussions on the relationship between depositing temperature and crystallinity of grain of film suggest that the higher growth temperature, the better crystallinity and excellent preferred microcrystal orientation of grain, however, with complementary bigger grain size. For matching readout matrix pixelation, the growth period of poly-films would be reduced appropriately for reasonable grain size and preventing the crack of films deposited.

Solution-Processed BiI3 Films with 1.1 eV Quasi-Fermi Level Splitting: The Role of Water, Temperature, and Solvent during Processing

We present a mechanistic explanation of the BiI3 film formation process and an analysis of the critical factors in preparing high-quality solution-processed BiI3 films. We find that complexation with Lewis bases, relative humidity, and temperature are important factors during solvent vapor annealing (SVA) of films. During SVA, water vapor and higher temperatures limit the formation of the BiI3-dimethylformamide coordination complex. SVA with an optimized water content and temperature produces films with 300-500 nm grains. Films that formed solvent coordination compounds at lower temperatures showed preferential crystal orientation after solvent removal, and we elucidate its implications for carrier transport. Addition of dimethyl sulfoxide to highly concentrated tetrahydrofuran-BiI3 inks prevents film cracking after spin-coating. We have measured a quasi-Fermi level splitting of 1.1 eV and a diffusion length of 70 nm from films processed with optimal temperature and humidity. The best device produced by optimized SVA has a power conversion efficiency of 0.5%, I sc of ∼4 mA/cm2, and V OC of ∼400 mV. The low photocurrent and voltage we attribute to the low diffusion length and the unfavorable band alignment between the absorber and the adjacent transport layers. The deep understanding of the relationship between morphology/crystal structure and optoelectronic properties gained from this work paves the way for future optimization of BiI3-based solar cells.

Single Walled BiI3 Nanotubes Encapsulated within Carbon Nanotubes

Inorganic nanotubes are morphological counterparts of carbon nanotubes (CNTs). Yet, only graphene-like BN layer has been readily organized into single walled nanotubes so far. In this study, we present a simple route to obtain inorganic single walled nanotubes - a novel ultrathin morphology for bismuth iodide (BiI₃), embedded within CNTs. The synthesis involves the capillary filling of BiI₃ into CNT, which acts as a nanotemplate, by annealing the BiI₃-CNT mixture above the melting point of BiI₃. Aberration corrected scanning/transmission electron microscopy is used in characterizing the novel morphology of BiI₃. A critical diameter which enables the formation of BiI₃ nanotubes, against BiI₃ nanorods is identified. The relative stability of these phases is investigated with the density functional theory calculations. Remarkably, the calculations reveal that the single walled BiI₃ nanotubes are semiconductors with a direct band gap, which remain stable even without the host CNTs.

Synthesis of 2D Layered BiI3 Nanoplates, BiI3 /WSe2 van der Waals Heterostructures and Their Electronic, Optoelectronic Properties

Two-dimensional layered materials (2DLMs) have attracted considerable recent interest as a new material platform for fundamental materials science and potential new technologies. Here we report the growth of layered metal halide materials and their optoelectronic properties. BiI₃ nanoplates can be readily grown on SiO₂ /Si substrates with a hexagonal geometry, with a thickness in the range of 10-120 nm and a lateral dimension of 3-10 µm. Transmission electron microscopy and electron diffraction studies demonstrate that the individual nanoplates are high quality single crystals. Micro-Raman studies show characteristic A_g band at ≈115 cm^-1 with slight red-shift with decreasing thickness, and micro-photoluminescence studies show uniform emission around 690 nm with blue-shift with decreasing thickness. Electrical transport studies of individual nanoplates show n-type semiconductor characteristics with clear photoresponse. Further, the BiI₃ can be readily grown on other 2DLMs (e.g., WSe₂ ) to form van der Waals heterostructures. Electrical transport measurements of BiI₃ /WSe₂ vertical heterojunctions demonstrate p-n diode characteristics with gate-tunable rectification behavior and distinct photovoltaic effect. The synthesis of the BiI₃ nanoplates can expand the library of 2DLMs and enable a wider range of van der Waals heterostructures.

Extended Photo-Conversion Spectrum in Low-Toxic Bismuth Halide Perovskite Solar Cells

Lead-based perovskites show very promising properties for use in solar cells; however, the toxicity of lead is a potential inhibitor for large-scale application of these solar cells. Here, a low-toxic bismuth halide, CsBi3I10, is synthesized from solution and the optical properties and crystal structure are compared with previously reported Cs3Bi2I9 perovskite, and the photovoltaic properties are also investigated. The XRD pattern suggests that the CsBi3I10 film has a layered structure with a different dominating crystal growth direction than the Cs3Bi2I9 perovskite. A band gap of 1.77 eV is obtained for the CsBi3I10 film, which is smaller than the band gap of Cs3Bi2I9 at 2.03 eV, and an extended visible light absorption spectrum is therefore obtained. The solar cell device with CsBi3I10 shows a photocurrent up to 700 nm, and this work shows therefore the possibility for increased light absorption and higher photocurrents in solar cells based on bismuth halide perovskites.

Synthesis of PbI2 nanowires for high sensitivity photodetectors

A simple catalyst-free physical vapor transport method was used to synthesize lead iodide (PbI₂) nanowires of high crystalline quality.

Investigation of Bismuth Triiodide (BiI3) for Photovoltaic Applications

Guided by predictive discovery framework, we investigate bismuth triiodide (BiI3) as a candidate thin-film photovoltaic (PV) absorber. BiI3 was chosen for its optical properties and the potential for "defect-tolerant" charge transport properties, which we test experimentally by measuring optical absorption and recombination lifetimes. We synthesize phase-pure BiI3 thin films by physical vapor transport and solution processing and single-crystals by an electrodynamic gradient vertical Bridgman method. The bandgap of these materials is ∼1.8 eV, and they demonstrate room-temperature band-edge photoluminescence. We measure monoexponential recombination lifetimes in the range of 180-240 ps for thin films, and longer, multiexponential dynamics for single crystals, with time constants up to 1.3 to 1.5 ns. We discuss the outstanding challenges to developing BiI3 PVs, including mechanical and electrical properties, which can also inform future selection of candidate PV absorbers.

Crystal structures and photocatalytic properties of two novel iodoplumbate hybrids templated by multivalent organic cations

Two novel multivalent organic cation-templated iodoplumbate hybrids with trinuclear or 1D anionic structures and good photocatalytic performances are reported.