A rational design of an electrocatalyst presents a promising avenue for solar fuels synthesis from carbon dioxide (CO2) fixation but is extremely challenging. Herein, we use density functional theory calculations to study an inexpensive binary copper−iron catalyst for photoelectrochemical CO2 reduction toward methane. The calculations of reaction energetics suggest that Cu and Fe in the binary system can work in synergy to significantly deform the linear configuration of CO2 and reduce the high energy barrier by stabilizing the reaction intermediates, thus spontaneously favoring CO2 activation and conversion for methane synthesis. Experimentally, the designed CuFe catalyst exhibits a high current density of −38.3 mA⋅cm−2 using industry-ready silicon photoelectrodes with an impressive methane Faradaic efficiency of up to 51%, leading to a distinct turnover frequency of 2,176 h−1 under air mass 1.5 global (AM 1.5G) one-sun illumination.

Self-organized AlGaN nanowires by molecular beam epitaxy have attracted significant attention for deep ultraviolet optoelectronics. However, due to the strong compositional modulations under conventional nitrogen rich growth conditions, emission wavelengths less than 250 nm have remained inaccessible. Here we show that Al-rich AlGaN nanowires with much improved compositional uniformity can be achieved in a new growth paradigm, wherein a precise control on the optical bandgap of ternary AlGaN nanowires can be achieved by varying the substrate temperature. AlGaN nanowire LEDs, with emission wavelengths spanning from 236 to 280 nm, are also demonstrated.

Ultrasmall semiconductor lasers can improve the efficiency and resolution of next-generation displays by 10 to 100 times.

We report AlGaN nanowire light emitting diodes (LEDs) operating in the ultraviolet-C band. The LED structures are grown by molecular beam epitaxy on Si substrate. It is found that with the use of the n+-GaN/Al/p+-AlGaN tunnel junction (TJ), the device resistance is reduced by one order of magnitude, and the light output power is increased by two orders of magnitude, compared to AlGaN nanowire LEDs without TJ. For unpackaged TJ ultraviolet LEDs emitting at 242 nm, a maximum output power of 0.37 mW is measured, with a peak external quantum efficiency up to 0.012%.

A photo-driven direct methanol-to-ethanol conversion is reported with a robust gallium nitride catalyst under ambient conditions. This conversion is achieved with no solvent, ligand, additive, heating, atmosphere, or pressurization-just with light irradiation. A methyl carbene reaction intermediate is observed during the conversion, and the method enables access to the more useful (as both fuel and starting material) renewable resource ethanol.

To date, there have been no efficient semiconductor light emitters operating in the green and amber wavelengths. This study reports on the synthesis of InGaN nanowire photonic crystals, including dot-in-nanowires, nanotriangles, and nanorectangles with precisely controlled size, spacing, and morphology, and further demonstrates that bottom-up InGaN photonic crystals can exhibit highly efficient and stable emission. The formation of stable and scalable band edge modes in defect-free InGaN nanowire photonic crystals is directly measured by cathodoluminescence studies. The luminescence emission, in terms of both the peak position (λ ≈ 505 nm) and spectral linewidths (full-width-half-maximum ≈ 12 nm), remains virtually invariant in the temperature range of 5-300 K and under excitation densities of 29 W cm −2 to 17.5 kW cm −2 . To the best of our knowledge, this is the first demonstration of the absence of Varshni and quantum-confined Stark effects in wurtzite InGaN light emitters-factors that contribute significantly to the efficiency droop and device instability under high-power operation. Such distinct emission properties of InGaN photonic crystals stem directly from the strong Purcell effect, due to efficient coupling of the spontaneous emission to the highly stable and scalable band-edge modes of InGaN photonic crystals, and are ideally suited for uncooled, high-efficiency light-emitting-diode operation.

Compared to the extensive studies on the efficiency droop of InGaN visible light emitting diodes (LEDs), the efficiency droop of AlGaN deep ultraviolet (UV) LEDs is much less studied. In this context, we discuss the efficiency droop of AlGaN ternary nanowire deep UV LEDs. The device active region consisted of AlGaN double heterojunctions, which were grown by molecular beam epitaxy on silicon substrates. Through detailed analysis of the device optical characteristics under both continuous-wave and pulsed operations, as well as of the electrical characteristics from 293 K to 77 K, it is suggested that the efficiency droop is largely rooted in the low hole mobility, due to the dominant Mg impurity band conduction at room temperature in highly p-doped AlGaN alloys.

Summary Photoelectrochemical CO 2 reduction into syngas (a mixture of CO and H 2 ) provides a promising route to mitigate greenhouse gas emissions and store intermittent solar energy into value-added chemicals. Design of photoelectrode with high energy conversion efficiency and controllable syngas composition is of central importance but remains challenging. Herein, we report a decoupling strategy using dual cocatalysts to tackle the challenge based on joint computational and experimental investigations. Density functional theory calculations indicate the optimization of syngas generation using a combination of fundamentally distinctive catalytic sites. Experimentally, by integrating spatially separated dual cocatalysts of a CO-generating catalyst and a H 2 -generating catalyst with GaN nanowires on planar Si photocathode, we report a record high applied bias photon-to-current efficiency of 1.88% and controllable syngas products with tunable CO/H 2 ratios (0–10) under one-sun illumination. Moreover, unassisted solar CO 2 reduction with a solar-to-syngas efficiency of 0.63% is demonstrated in a tandem photoelectrochemical cell.