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Nitride perovskites ABN3 are an emerging and highly underexplored class of materials that are of interest due to their intriguing calculated ferroelectric, optoelectronic, and other functional properties. Incorporating novel A-site cations is one strategy to tune and expand such properties; for example, Gd3+ is compelling due to its large magnetic moment, potentially leading to multiferroic behavior. However, the theoretically predicted ground state of GdWN3 was a non-perovskite monoclinic structure. Here, we experimentally show that GdWN3−y crystallizes in a perovskite structure. High-throughput combinatorial sputtering with activated nitrogen is employed to synthesize thin films of Gd2−xWxN3−yOy with oxygen content y < 0.05. Ex situ annealing crystallizes a polycrystalline perovskite phase in a narrow composition window near x = 1. LeBail fits of synchrotron grazing incidence wide angle x-ray scattering data are consistent with a perovskite ground-state structure. Refined density functional theory calculations that included antiferromagnetic configurations confirm that the ground-state structure of GdWN3 is a distorted Pnma perovskite with antiferromagnetic ordering, in contrast to prior predictions. Initial property measurements find that GdWN3−y is paramagnetic down to T = 2 K with antiferromagnetic correlations and that the absorption onset depends on cation stoichiometry. This work provides an important path toward both the rapid expansion of the emerging family of nitride perovskites and understanding their potential multiferroic properties. [ABSTRACT FROM AUTHOR]

Sustainable production of liquid fuels from abundant resources, such as carbon dioxide and water, may be possible through photoelectrochemical processes. Zinc titanium nitride (ZnTiN2) has been recently demonstrated as a potential photoelectrode semiconductor for photoelectrochemical fuel generation due to its ideal bandgap induced by cation disorder, shared crystal structure with established semiconductors, and self-passivating surface oxides under carbon dioxide reduction operating conditions. However, substantial improvements in crystalline quality and optoelectronic properties of ZnTiN2 are needed to enable such applications. In this work, we investigate the heteroepitaxial growth of ZnTiN2 on c-plane (001) sapphire substrates. Growth on sapphire improves crystal quality, while growth on sapphire at elevated temperatures (300 °C) yields highly-oriented, single-crystal-like ZnTiN2 films. When Sn is incorporated during these epitaxial growth conditions, notable improvements in ZnTiN2 film surface roughness and optoelectronic properties are observed. These improvements are attributed to Sn acting as a surfactant during growth and mitigating unintentional impurities such as O and C. The single-crystal-like, 12% Sn-containing ZnTiN2 films exhibit a steep optical absorption onset at the band gap energy around 2 eV, electrical resistivity of 0.7 Ω cm, and a carrier mobility of 0.046 cm2 V−1 s−1 with n-type carrier concentration of 2 × 1020 cm−3. Density functional theory calculations reveal that moderate substitution of Sn (12.5% of the cation sites) on energetically-preferred cation sites has negligible impact on the optoelectronic properties of cation-disordered ZnTiN2. These results are important steps toward achieving high performance PEC devices based on ZnTiN2 photoelectrodes with efficient photon absorption and photoexcited carrier extraction. [ABSTRACT FROM AUTHOR]

Thin‐film solar cells such as CdTe are a major commercial photovoltaic technology, with more than 25 GW installed worldwide and levelized costs of electricity competitive with fossil fuels. Further progress may result from integrating CdSeyTe1−y absorbers with MgxZn1−xO contacts, but the device efficiency is difficult to maximize due to coupled dependence on chemical composition of both alloys. Herein, a high‐throughput approach is demonstrated to codesign chemical compositions in alloyed MgxZn1−xO/CdSeyTe1−y thin‐film solar cells, using combinatorial libraries of PV devices with orthogonal composition gradients in CdSeyTe1−y absorbers and MgxZn1−xO contacts. It is found that the solar cell performance is a strong and coupled function of both elemental compositions, with efficiency up to 17.7% (VOC = 836 mV, fill factor = 69%, JSC = 30.6 mA cm−2) at atomic compositions of Mg/(Mg + Zn) ≈18% and average Se/(Se + Te) ≈4%. These performance trends among >100 devices are explained by >100 ns lifetime of photoexcited charge carriers at the MgxZn1−xO/CdSeyTe1−y interface where strong Se accumulation is also observed. This study reports the optimal compositions of the commercially relevant MgxZn1−xO/CdSeyTe1−y solar cells and demonstrates a general approach to codesigning performance of alloyed thin‐film solar cells and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

The 1.24 eV bandgap, 18.8% power conversion efficiency Ag‐alloyed chalcopyrite (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells are characterized to relate voltage and efficiency improvements to electro‐optical (EO) characteristics. Shockley–Read–Hall recombination center defect density, identified and characterized through deep level transient spectroscopy and time‐resolved photoluminescence (TRPL), is reduced through potassium and copper treatment optimization. Concomitantly, longer minority carrier lifetimes are achieved, which increases open‐circuit voltage (VOC). Near‐conduction band defects associated in earlier studies with light‐induced current instability are also mitigated. Analysis of charge‐carrier dynamics after single‐ and two‐photon excitation is used to separate recombination at the front interface and in the absorber bulk. From TRPL decay simulations, the authors estimate ranges of key solar cell material characteristics: bulk carrier lifetime τbulk = 110–210 ns, charge‐carrier mobility μ = 110–160 cm2 V−1 s−1, and front interface recombination velocity Sfront = 700–1050 cm s−1. This lowest‐reported Sfront for ACIGS absorbers originates from the notched conduction band grading, which also makes the impact of the back interface recombination negligible. It is suggested in the results that solar cell performance enhancements can be made most readily with two distinct strategies: improving device architecture and reducing semiconductor defect densities. Using these approaches, power conversion efficiency in large‐area solar cells is improved by 1.1% absolute. [ABSTRACT FROM AUTHOR]

The study shows that molecular oxygen reacts with bridging OH (OH(sub br)) groups formed as a result of water dissociation on the surface of rutile TiO2(110). The results suggest the negative influence of high water concentrations in gas-phase.

The simulation of TiO(sub 2) solution interface shows that oxygen adsorbed on TiO(sub 2)(110) at 115 K is not completely removed by prolonged exposure to 4.1 eV radiation. This explains why high photodesorption cross sections do not prevent photooxidation reactions from occurring.

Oxide materials with the perovskite structure have been used in sensors and actuators for half a century, and halide perovskites transformed photovoltaics research in the past decade. Nitride perovskites have been computationally predicted to be stable, but few have been synthesized, and their properties remain largely unknown. We synthesized and characterized a nitride perovskite lanthanum tungsten nitride (LaWN3) in the form of oxygen-free sputtered thin films, according to spectroscopy, scattering, and microscopy techniques. We report a large piezoelectric response measured with scanning probe microscopy that together with synchrotron diffraction confirm polar symmetry of the perovskite LaWN3. Our LaWN3 synthesis should inspire growth of other predicted nitride perovskites, and measurements of their properties could lead to functional integration with nitride semiconductors for microelectromechanical devices. [ABSTRACT FROM AUTHOR]