We report all-inorganic solar cells based on solution-processed BiI3. Two-electron donor solvents such as tetrahydrofuran and dimethylformamide were found to form adducts with BiI3, which make them highly soluble in these solvents. BiI3 thin films were deposited by spin-coating. Solvent annealing BiI3 thin films at relatively low temperatures (≤100 °C) resulted in increased grain size and crystallographic reorientation of grains within the films. The BiI3 films were stable against oxidation for several months and could withstand several hours of annealing in air at temperatures below 150 °C without degradation. Surface oxidation was found to improve photovoltaic device performance due to the formation of a BiOI layer at the BiI3 surface which facilitated hole extraction. Nonoptimized BiI3 solar cells achieved the highest power conversion efficiencies of 1.0%, demonstrating the potential of BiI3 as a nontoxic, air-stable metal-halide absorber material for photovoltaic applications.

Si-nanosheets (Si-NSs) have recently attracted considerable attention due to their potential as nextgeneration materials for electronic, optoelectronic, spintronic, and catalytic applications. Even though monolayer Si-NSs were first synthesized over 150 years ago via topotactic deintercalation of CaSi2, there is a lack of consensus within the literature regarding the structure and optical properties of this material. Herein, we provide conclusive evidence of the structural and chemical properties of Si-NSs produced by the deintercalation of CaSi2 with cold (~-30 °C) aqueous HCl, and characterize their optical properties. We use a wide range of techniques, including XRD, FTIR, Raman, solid-state NMR, SEM, TEM, EDS, XPS, diffuse reflectance absorbance, steady-state photoluminescence, time-resolved photoluminescence, and thermal decomposition; combined together, these techniques enable unique insight into the structural and optical properties of the Si-NSs. Additionally, we support the experimental findings with density functional theory (DFT) calculations to simulate FTIR, Raman, NMR, interband electronic transitions, and band structures. We determined that the Si-NSs consist of buckled Si monolayers that are primarily monohydride terminated. We characterize the nanosheets' optical properties, finding they have a band gap of ~2.5 eV with direct-like behavior and an estimated quantum yield of ~9%. Given the technological importance of Si, these results are encouraging for a variety of optoelectronic technologies, such as phosphors, light-emitting diodes, and CMOS-compatible photonics. Our results provide critical structural and optical properties to help guide the research community in integrating Si-NSs into optoelectronic and quantum devices. Disciplines Disciplines Materials Chemistry Comments Comments

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The remarkable performance of Pb halide perovskites in optoelectronic devices is complicated by concerns over their toxicity, which has motivated a search for Pb-free alternatives that have similar performance. Bi halides and halide perovskites have been predicted to be among the most promising Pb-free alternatives; however, their performance in devices has fallen short of expectations. One of the major challenges in fabricating efficient devices based on these Bi-based alternatives has been poor control over the morphology of thin films. Using BiI 3 as a model system, we demonstrate that the film morphology and surface coverage are strongly dependent on the Lewis basicity of solvents that are used during deposition. We demonstrate that coordinating BiI 3 with strong Lewis bases in tetrahydrofuran results in conformal films that have been difficult to achieve using conventional deposition techniques.

Metavanadates MV 2 O 6−δ (M = Zn and Cu) are synthesized by using a deep eutectic solvent (DES), a mixture of hydrogen bond donor and acceptor, as a reaction medium. Dissolution of stable binary metal oxides in a DES followed by a heat treatment yields phase-pure vanadates. According to in situ powder X-ray diffraction, ternary phases (α-Zn 2 V 2 O 7 and β-Cu 2−x V 2 O 7 , x ∼ 0.27) are intermediates in the reaction pathway taken. Identifying a polymorphic phase transformation temperature for CuV 2 O 6 as well as the narrow temperature range between formation and decomposition for both metavanadates allows for tackling the challenge of the synthesis of these materials. The oxygen vacancy introduced by the DES route is accompanied by the formation of reduced V 4+ and Cu + in the oxide matrix, based on X-ray photoelectron spectroscopy. These oxygen vacancies modify the vibrational modes in the corresponding Raman spectra and are also responsible for broad optical absorptions in the 1.8−1.1 eV range. The optical band gaps of the materials are found at 1.8 eV (CuV 2 O 6 ) and 2.2 eV (ZnV 2 O 6 ), approximately 0.1−0.3 eV below the values reported in the literature. The reduced band gaps and sub-band gap photon absorption are key features of the oxygendeficient metavanadates. Surface photovoltage spectroscopy reveals that all the synthesized vanadates are n-type materials with electrons as the majority charge carriers, and photoelectrochemical measurements confirm photoanodic currents for methanol oxidation. These results provide insight into the synthesis and structure−property relationship of the metavanadates for their potential use as photoanodes.