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Lead‐free ternary bismuth halide perovskites A3Bi2X9 have gained much attention as a solution for toxic and unstable lead halide perovskites due to their facile solution processability, high optical absorption coefficient, and high stability. However, their photovoltaic performance remains poor due to their wide bandgap (∼2 eV), and poor charge transport properties stem from their low‐dimensional crystal structure. To promote the 3D structure and reduce the bandgap of ternary Bi‐halide perovskites, we replace the alkali elements at the A‐site with the transition element Ag+ to obtain a new class of perovskite‐like materials named rudorffites AgaBibIa+3b. We investigated the photophysical properties of AgBiI4 by a combined theoretical and experimental approach. Our DFT‐PBE‐SOC predicted band gap for cubic defect spinel AgBiI4 is 2.01 eV, while that obtained for spin‐coated AgBiI4 film is 1.67 eV. Furthermore, the strong p‐p band edge transition leads to high optical absorption in this material. Finally, a photodetector device fabricated using AgBiI4 shows excellent photoresponsivity (183 μA/W) and detectivity (20.93×108 Jones) with a fast rise/decay time of 0.27 s/0.29 s. This newly explored semiconductor class can be a promising and stable choice for advanced optoelectronic devices. [ABSTRACT FROM AUTHOR]

A promising method for producing hydrogen from solar energy and transforming it into chemical fuel is photoelectrochemical (PEC) water splitting. This ecologically friendly process can also avoid energy crises. Herein, we present the electrodeposition and chemical bath deposition methods used to create ZnO-nanorod/CdS nanoparticle (ZnO/CdS) heterostructures. The structural, optical, morphological, and PEC properties are investigated. UV–Visible spectroscopy analysis reveals the ZnO/CdS films have absorption edges in the visible and ultraviolet regions. The CdS loading directly impacts the PEC result of ZnO/CdS photoanodes. The M-S plots show a positive slope, indicating the n-type nature of ZnO and CdS. Under illumination intensity of 100 mW cm−2, the ideal photocurrent density reaches 4.90 mA/cm2 at a bias of 1.35 V versus reversible hydrogen electrode (vs. RHE) and is five times greater than the pristine ZnO nanorods. The maximum applied bias photon to the current conversion efficiency of 0.23 % at 0.26 V vs. RHE is observed in the pristine ZnO photoanodes. In contrast, the ZnO/CdS photoanode has achieved 3.02 % at 0.26 V vs. RHE, almost 13 times greater than the pristine ZnO photoanode. Finally, the hydrogen evolution process and the mechanism of charge transfer in ZnO/CdS heterostructure are discussed. • ZnO/CdS fabrication by electrodeposition and chemical bath deposition. • Efficient photoelectrochemical water splitting by ZnO/CdS. • The Mott-Schottky analysis revealed p-n junction formation. • Photocurrent density up to 4.90 mA/cm2 at 1.35 V vs. RHE under 100 mW/cm2 illumination. • Applied bias photon to current conversion efficiency of 3.02 % at 0.26 V vs. RHE. [ABSTRACT FROM AUTHOR]

In this paper, we synthesized lead-free cesium bismuth iodide (Cs 3 Bi 2 I 9) perovskite films by solution process using one-step spin-coating technique. Formation of Cs 3 Bi 2 I 9 perovskite was confirmed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy analysis. The XRD analysis showed that all Cs 3 Bi 2 I 9 perovskite films were polycrystalline in nature, with hexagonal crystal structure and preferred-orientation along (006) direction. The environmental stability of Cs 3 Bi 2 I 9 perovskite was confirmed by XRD analysis and UV–visible spectroscopy. Multiple XRD and UV–Vis spectra taken after long time spans revealed the stable nature of Cs 3 Bi 2 I 9 perovskite films. The UV–visible spectroscopy and photoluminescence analysis showed that the perovskite films absorbed strongly in the visible region and had an optical band gap of ~2.1 eV. Surface morphology of Cs 3 Bi 2 I 9 perovskite over the entire substrate surface was investigated using scanning electron microscopy. Thermo-gravimetric analysis showed that Cs 3 Bi 2 I 9 perovskite was thermally stable up to ∼ 420 °C. Finally, solar cells fabricated using Cs 3 Bi 2 I 9 perovskite material showed maximum power conversion efficiency (PCE) of 0.17%, with short circuit current density of 1.43 mA/cm2, open circuit voltage of 0.37 V and fill factor of 32%. Applying compositional engineering and optimizing the device structure should further improve the PCE. These results are a significant step toward fabrication of Cs 3 Bi 2 I 9 perovskite-based solar cells. • Synthesis of lead-free Cs 3 Bi 2 I 9 perovskite films by spin coating. • Films have hexagonal crystal structure with (006) preferred orientation. • Cs 3 Bi 2 I 9 perovskite is thermally stable up to ~420 °C. • Maximum power conversion efficiency is 0.17%. • A significant step toward fabricating Cs 3 Bi 2 I 9 perovskite based solar cells. [ABSTRACT FROM AUTHOR]