Photovoltaic cells based on arrays of semiconductor nanowires promise efficiencies comparable or even better than their planar counterparts with much less material. One reason for the high efficiencies is their large absorption cross section, but until recently the photocurrent has been limited to less than 70% of the theoretical maximum. Here we enhance the absorption in indium phosphide (InP) nanowire solar cells by employing broadband forward scattering of self-aligned nanoparticles on top of the transparent top contact layer. This results in a nanowire solar cell with a photovoltaic conversion efficiency of 17.8% and a short-circuit current of 29.3 mA/cm under 1 sun illumination, which is the highest reported so far for nanowire solar cells and among the highest reported for III-V solar cells. We also measure the angle-dependent photocurrent, using time-reversed Fourier microscopy, and demonstrate a broadband and omnidirectional absorption enhancement for unpolarized light up to 60° with a wavelength average of 12% due to Mie scattering. These results unambiguously demonstrate the potential of semiconductor nanowires as nanostructures for the next generation of photovoltaic devices.

We demonstrate an efficiency enhancement of an InP nanowire (NW) axial p-n junction solar cell by cleaning the NW surface. NW arrays were grown with in situ HCl etching on an InP substrate patterned by nanoimprint lithography, and the NWs surfaces were cleaned after growth by piranha etching. We find that the postgrowth piranha etching is critical for obtaining a good solar cell performance. With this procedure, a high diode rectification factor of 10(7) is obtained at ±1 V. The resulting NW solar cell exhibits an open-circuit voltage (Voc) of 0.73 V, a short-circuit current density (Jsc) of 21 mA/cm(2), and a fill factor (FF) of 0.73 at 1 sun. This yields a power conversion efficiency of up to 11.1% at 1 sun and 10.3% at 12 suns.

Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. Planar III/V material systems have shown the highest efficiencies, but are expensive. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap. This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Here we report the photoelectrochemical reduction of water, on a p-type wurtzite gallium phosphide nanowire photocathode. By modifying geometry to reduce electrical resistance and enhance optical absorption, and modifying the surface with a multistep platinum deposition, high current densities and open circuit potentials were achieved. Our results demonstrate the capabilities of this material, even when used in such low quantities, as in nanowires.

Semiconductor nanowire arrays are expected to be advantageous for photoelectrochemical energy conversion due to their reduced materials consumption. In addition, with the nanowire geometry the length scales for light absorption and carrier separation are decoupled, which should suppress bulk recombination. Here, we use vertically aligned p-type InP nanowire arrays, coated with noble-metal-free MoS3 nanoparticles, as the cathode for photoelectrochemical hydrogen production from water. We demonstrate a photocathode efficiency of 6.4% under Air Mass 1.5G illumination with only 3% of the surface area covered by nanowires.

The solar energy conversion efficiency of photoelectrochemical (PEC) devices is usually limited by poor interface energetics, limiting the onset potential, and light reflection losses. Here, a three‐pronged approach to obtain excellent performance of an InP‐based photoelectrode for water reduction is presented. First, a buried p–n+ junction is fabricated, which shifts the valence band edge favorably with respect to the hydrogen redox potential. Photoelectron spectroscopy substantiates that the shift of the surface photovoltage is mainly determined by the buried junction. Second, a periodic array of InP nanopillars is created at the surface of the photoelectrode to substantially reduce the optical reflection losses. This device displays an unprecedented photocathodic power‐saved efficiency of 15.8% for single junction water reduction. Third, a thin TiO2 protection layer significantly increases the stability of the InP‐based photoelectrode. Careful design of the interface energetics based on surface photovoltage spectroscopy allows obtaining a PEC cell with stable record performance in water reduction.