Ligand--free CdS quantum dots were produced by a reactive ligand stripping procedure and employed for photocatalytic H 2 evolution in pH neutral solution. The rate of H 2 generation of the 'bare' quantum dots was 175 times higher than that of the equivalent mercaptopropionic acid--capped quantum dots in the presence of a cobalt co--catalyst and Na 2 SO 3 as sacrificial electron donor. Under optimised conditions, a turnover number of 58,000 mol H 2 per mol Co and 29,000 mol H 2 per mol CdS quantum dots was achieved after 88 h of continuous solar light irradiation (λ > 420 nm, 1 sun intensity). Ligand removal is therefore a potent method to substantially enhance the photocatalytic performance of quantum dot systems.

We report here the first solid-state, NIR-selective electrochromic devices. Critical to device performance is the arrangement of nanocrystal-derived electrodes into heteromaterial frameworks, where hierarchically porous ITO nanocrystal active layers are infiltrated by an ion-conducting polymer electrolyte with mesoscale periodicity. Enhanced coloration efficiency and transport are realized over unarchitectured electrodes in devices, paving the way towards new smart windows technologies.

Photovoltaic devices require p-type layers with high optical transparency and electrical conductivity. One promising material is cuprous iodide, CuI, thin films of which have hole mobilities in the 1−12 cm 2 /V•s range. However, despite adequate electrical properties in many CuI thin films, most deposition processes afford only rough films that have poor continuity and low optical transparency, hampering the final device performance. We now report an all-vapor method, amenable to large-scale processing, for preparation of CuI thin films with near record optical and electrical properties. In this process, thin films of Cu (2−x) S (x = 0− 0.1) or Cu 2 O grown by chemical vapor deposition from bis(N,N′-di-sec-butylacetamidinato)dicopper(I) in combination with hydrogen sulfide or water, respectively, were converted to γ-CuI upon exposure to dilute hydrogen iodide vapor. The rate of this iodide-for-chalcogenide anion exchange reaction is controlled by the concentration and delivery rate of HI. The nucleation rate of the nascent CuI may be modified by dosing with iodine vapor (for Cu (2−x) S) or with vapors of thiodiglycol or ethylene glycol (for Cu 2 O). By balancing the rates of nucleation and conversion, we are able to prepare smooth, continuous thin films possessing optical and electrical properties approaching those of the best native p-type CuI films. We believe that the underlying chemical and materials science reasoning leading to these high-quality films will prove instructive in other thin-film systems. Furthermore, based on the measured band positions and carrier mobilities we anticipate high utility for these smooth CuI films as hole-transport layers in Earth-abundant, inexpensive thin-film photovoltaics.

Thin films of Cu 2 S grown by pulsed-chemical vapor deposition of bis(N,N'-di-secbutylacetamidinato)dicopper(I) and hydrogen sulfide were converted to CuBr upon exposure to anhydrous hydrogen bromide. X-ray diffraction shows that the as-deposited films have a polycrystalline Cu 2 S structure. After exposure to HBr gas, the surface of the films is transformed to a γ-CuBr polycrystalline structure. Scanning electron microscopy and X-ray photoelectron spectroscopy reveal complete conversion of up to 100 nm of film. However, when the conversion to CuBr approaches the interface between as-2 deposited Cu 2 S and the SiO 2 substrate, the morphology of the film changes from continuous and nanocrystalline to sparse and microcrystalline.

The semiconductors CuX (X = Cl, Br, or I) are high-mobility p-type transparent conductors, promising for use in thin film optoelectronic devices such as perovskite photovoltaics. These devices require smooth, pinhole free films that are tens of nanometers thick but uniform across tens of centimeters. Chemical vapor deposition (CVD), an established and scalable process, can provide excellent throughput, conformality, and uniformity on such large areas. However, no prior CVD method could produce continuous thin films of any cuprous halide. We have established such a method, preparing CuBr thin films by reaction between HBr gas and vinyltrimethylsilane­(hexafluoroacetylacetonato)­copper­(I). Our method not only provides the desired device-quality films but also opens up the possibility of a general route to CVD of other metal halides.

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired. With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5]. The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6]. Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV. [1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020). [2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017). [3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019). [4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997). [5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020). [6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018). [7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017). [8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).