Determining cost-effective semiconductors exhibiting desirable properties for commercial photoelectrochemical water splitting remains a challenge. Herein, we report a Sb₂Se₃ semiconductor that satisfies most requirements for an ideal high-performance photoelectrode, including a small band gap and favourable cost, optoelectronic properties, processability, and photocorrosion stability. Strong anisotropy, a major issue for Sb₂Se₃, is resolved by suppressing growth kinetics via close space sublimation to obtain high-quality compact thin films with favourable crystallographic orientation. The Sb₂Se₃ photocathode exhibits a high photocurrent density of almost 30 mA cm⁻² at 0 V against the reversible hydrogen electrode, the highest value so far. We demonstrate unassisted solar overall water splitting by combining the optimised Sb₂Se₃ photocathode with a BiVO₄ photoanode, achieving a solar-to-hydrogen efficiency of 1.5% with stability over 10 h under simulated 1 sun conditions employing a broad range of solar fluxes. Low-cost Sb₂Se₃ can thus be an attractive breakthrough material for commercial solar fuel production.

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (V_Pb) defects in MAPbI₃ (MA = CH₃NH₃⁺) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 10¹⁵ cm⁻³ was determined. There was also evidence of trapping at the vacancy complex $$({{{{{\rm{V}}}}}}_{{{{{\rm{Pb}}}}}}{{{{{\rm{V}}}}}}_{{{{{\rm{I}}}}}})^{-}$$( V Pb V I ) − in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, $${{{{{{\rm{V}}}}}}}_{{{{{{\rm{Pb}}}}}}}^{2-}$$V Pb 2 − , point defects are one of the most stable defects in MAPbI₃. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.

We examine ZnSnN₂, a member of the class of materials contemporarily termed “earth-abundant element semiconductors,” with an emphasis on evaluating its suitability for photovoltaic applications. It is predicted to crystallize in an orthorhombic lattice with an energy gap of 2 eV. Instead, using molecular beam epitaxy to deposit high-purity, single crystal as well as highly textured polycrystalline thin films, only a monoclinic structure is observed experimentally. Far from being detrimental, we demonstrate that the cation sublattice disorder which inhibits the orthorhombic lattice has a profound effect on the energy gap, obviating the need for alloying to match the solar spectrum.

Ellipsometry was used to measure the amplitude ratio and phase difference of light undergoing a phase shift as it interacts with a thin film of organic-inorganic hybrid perovskite CH3NH3PbI3 (MAPI) deposited onto a (100) silicon wafer. The refractive index and extinction coefficient was extracted from a multi-oscillator model fit to the ellipsometry data, as a function of wavelength, from 300 to 1500 nm.

Heteroepitaxial growth of BaSnO₃ and Ba_1−xLa_xSnO₃ (x = 7%) lanthanum doped barium stannate thin films on different perovskite single crystal (SrTiO₃ (001) and SmScO₃ (110)) substrates has been achieved by pulsed laser deposition under optimized deposition conditions. X-ray diffraction measurements indicate that the films on either of these substrates are relaxed due to the large mismatch and present a high degree of crystallinity with narrow rocking curves and smooth surface morphology while analytical quantification by proton induced X-ray emission confirms the stoichiometric La transfer from a polyphasic target, producing films with measured La contents above the bulk solubility limit. The films show degenerate semiconducting behavior on both substrates, with the observed room temperature resistivities, Hall mobilities, and carrier concentrations of 4.4 mΩ cm, 10.11 cm² V⁻¹ s⁻¹, and 1.38 × 10²⁰ cm⁻³ on SmScO₃ and 7.8 mΩ cm, 5.8 cm² V⁻¹ s⁻¹, and 1.36 × 10²⁰ cm⁻³ on SrTiO₃ ruling out any extrinsic contribution from the substrate. The superior electrical properties observed on the SmScO₃ substrate are attributed to reduction in dislocation density from the lower lattice mismatch.