No abstract

Lead‐free perovskite‐inspired materials (PIMs) are gaining attention in optoelectronics due to their low toxicity and inherent air stability. Their wide bandgaps (≈2 eV) make them ideal for indoor light harvesting. However, the investigation of PIMs for indoor photovoltaics (IPVs) is still in its infancy. Herein, the IPV potential of a quaternary PIM, Cu2AgBiI6 (CABI), is demonstrated upon controlling the film crystallization dynamics via additive engineering. The addition of 1.5 vol% hydroiodic acid (HI) leads to films with improved surface coverage and large crystalline domains. The morphologically‐enhanced CABI+HI absorber leads to photovoltaic cells with a power conversion efficiency of 1.3% under 1 sun illumination—the highest efficiency ever reported for CABI cells and of 4.7% under indoor white light‐emitting diode lighting—that is, within the same range of commercial IPVs. This work highlights the great potential of CABI for IPVs and paves the way for future performance improvements through effective passivation strategies.

Amorphous titanium dioxide (a-TiO2) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO2 without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO2 induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO2 is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO2. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O– species within a-TiO2 that are essentially electronic defects in the anionic framework.

Surface oxidation of Cu(100) has been investigated by variable temperature scanning tunneling microscopy and quantitative x-ray photoelectron spectroscopy as a function of O2 pressure (8.0×10−7 and 3.7×10−2mbar) at 373K. Three distinct phases in the initial oxidation of Cu(100) have been observed: (1) the formation of the mixed oxygen chemisorption layer consisting of Cu(100)-c(2×2)-O and Cu(100)-(22×2)R45°-O domains, (2) the growth of well-ordered (22×2)R45°-O islands, and (3) the onset of subsurface oxide formation leading to the growth of disordered Cu2O. We demonstrate that the (22×2)R45°-O reconstruction is relatively inert in the low pressure regime. The nucleation and growth of well-ordered two-dimensional Cu–O islands between two (22×2)R45°-O domains is revealed by time-resolved scanning tunneling microscopy experiments up to 0.5 ML of oxygen. The formation of these islands and their nanostructure appear to be critical to the onset of further migration of oxygen atoms deeper into copper and subsequent Cu2O formation in the high pressure regime. The reactivity of each phase is correlated with the surface morphology and the role of the various island structures in the oxide growth is discussed.

Visually black, electrically leaky, amorphous titania (am-TiO 2 ) thin films were grown by atomic layer deposition (ALD) for photocatalytic applications. Broad spectral absorbance in the visible range and exceptional conductivity are attributed to trapped Ti 3+ in the film. Oxidation of Ti 3+ upon heat treatment leads to a drop in conductivity, a color change from black to white, and crystallization of am-TiO 2 . ALD-grown black TiO 2 , without any heat treatment, is subject to dissolution in alkaline photoelectrochemical conditions. The best photocatalytic activity for solar water splitting is obtained for completely crystalline white TiO 2 .