A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H(2) production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm(-2) at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

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Light emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago. A barrier to the widespread utilization of luminescent silicon nanocrystals in such diverse application areas as optoelectronics, solid-state lighting for general illumination, or fluorescent agents for biological applications has been the lack of a simple, high-yield synthesis approach. Here we report a scaleable single-step synthesis process for luminescent silicon nanocrystals based on a low-pressure nonthermal plasma.

An experimental study of the influence of gold nanoparticles on α-Fe(2)O(3) photoanodes for photoelectrochemical water splitting is described. A relative enhancement in the water splitting efficiency at photon frequencies corresponding to the plasmon resonance in gold was observed. This relative enhancement was observed only for electrode geometries with metal particles that were localized at the semiconductor-electrolyte interface, consistent with the observation that minority carrier transport to the electrolyte is the most significant impediment to achieving high efficiencies in this system.

We present a systematic study on the effects of electrodeposition parameters on the photoelectrochemical properties of Cu 2 O. The influence of deposition variables (temperature, pH, and deposition current density) on conductivity has been widely explored in the past for this semiconductor, but the optimization of the electrodeposition process for the photoelectrochemical response in aqueous solutions under AM 1.5 illumination has received far less attention. In this work, we analyze the photoactivity of Cu 2 O films deposited at different conditions and correlate the photoresponse to morphology, film orientation, and electrical properties. The photoelectrochemical response was measured by linear sweep voltammetry under chopped simulated AM 1.5 illumination. The highest photocurrent obtained was −2.4 mA cm −2 at 0.25 V vs RHE for a film thickness of 1.3 μm. This is the highest reported value reached so far for this material in an aqueous electrolyte under AM 1.5 illumination. The optical and electrical properties of the most photoactive electrode were investigated by UV−vis spectroscopy and electrochemical impedance, while the minority carrier lifetime and diffusion length were measured by optical-pump THz-probe spectroscopy.

Nanostructured titanium dioxide (TiO2) films were synthesized with controlled morphology and thickness in an ambient pressure single-step flame aerosol reactor (FLAR) for use in water splitting photocells and dye-sensitized solar cells. Two different morphologies were studied:  a granular morphology and a highly crystalline columnar morphology. The granular morphology consisted of nanoparticles, approximately 10 nm in diameter, aggregated into fractal structures on the substrate. The granular morphology contained a large number of grain boundaries and other interfacial defects. The columnar morphology consisted of single-crystal structures, approximately 85 nm in width, oriented normal to the substrate. The well controlled deposition process was used to deposit films with thicknesses in the range from 98 nm to 12 μm to establish the relationship to water splitting and dye-sensitized solar cell performance. It was found that for watersplitting there was an optimum thickness (∼1.5 μm), which was a tradeoff between light absorption and electron transport losses, where the conversion efficiency was maximized. Due to differences in electron transport and lifetime in the TiO2 film, for both applications the columnar morphology outperformed the granular morphology, achieving a uv-light to hydrogen conversion efficiency of 11% for water splitting and a visible light to electricity conversion efficiency of 6.0% for the dye-sensitized solar cell.

Thin films comprising semiconductor nanocrystals are emerging for applications in electronic and optoelectronic devices including light emitting diodes and solar cells. Achieving high charge carrier mobility in these films requires the identification and elimination of electronic traps on the nanocrystal surfaces. Herein, we show that in films comprising ZnO nanocrystals, an electron acceptor trap related to the presence of OH on the surface limits the conductivity. ZnO nanocrystal films were synthesized using a nonthermal plasma from diethyl zinc and oxygen and deposited by inertial impaction onto a variety of substrates. Surprisingly, coating the ZnO nanocrystals with a few nanometres of Al 2 O 3 using atomic layer deposition decreased the film resistivity by seven orders of magnitude to values as low as 0.12 O cm. Electron mobility as high as 3 cm 2 V À 1 s À 1 was observed in films comprising annealed ZnO nanocrystals coated with Al 2 O 3 .

The highest efficiency solar cells based on copper zinc tin sulfide (CZTS), a promising photovoltaic material comprised of earth abundant elements, are built on soda lime glass (SLG), a substrate which contains many impurities, including Na and K. These impurities may diffuse into CZTS films during processing and affect film structure and properties. We have investigated the effects of these impurities on the microstructure of CZTS films synthesized by ex situ sulfidation of Cu-Zn-Sn alloy films co-sputtered on SLG, Pyrex, and quartz.CZTS films synthesized on SLG were found to have significantly larger grains than films grown on the other substrates. Furthermore, we show that by including a bare additional piece of SLG in the sulfidation ampoule, the grain size of films grown on nominally impurity-free quartz increases from 100's of nm to greater than 1 mm. This demonstrates conclusively that impurities in SLG volatilize in S-containing atmospheres and incorporate into nearby CZTS films synthesized on other substrates. Impurity concentrations in these CZTS films were examined using depth profiling with time-of-flight secondary ion mass spectrometry (TOF-SIMS). Of all the impurities present in SLG, the TOF-SIMS experiments implicated Na, K, and Ca as possible elements responsible for the enhanced grain growth. To investigate the effects of these impurities individually, we introduced very small and controllable amounts of Na, K, or Ca into the sulfidation ampoule during CZTS synthesis. Impurity amounts as low as 10 À6 moles of Na or 10 À7 moles of K resulted in a dramatic increase in grain size, from 100's of nm to several microns, for films deposited on quartz, while Ca loading had no visible effect on the final microstructure. Based on this vapor transport mechanism, we thus demonstrate an approach for delivering precisely controlled amounts of specific impurities into CZTS films on arbitrary substrates to facilitate large-grain growth. Broader contextState-of-the-art thin-lm solar cells use cadmium telluride or copper indium gallium selenide as the light absorbing material. However, the production of these solar cells may be limited to less than 1 terawatt by the scarcity of tellurium and indium, and possibly by the toxicity of cadmium. These sustainability concerns provide a strong motivation to search for new photovoltaic materials comprised of nontoxic and abundant elements. The rapid rise in power conversion efficiencies of solar cells based on copper zinc tin sulde and selenide (CZTS and CZTSe) attests to their potential as low-cost, earth-abundant solar absorber materials. One of the properties that affects the CZTS solar cell performance is the lm's microstructure. Ideally, a monolayer of single crystal grains with sizes on the order of the lm thickness (1-3 micrometers) is required. The present study shows the remarkable effects of the presence of very small amounts of alkali metal atom impurities in enhancing grain growth in CZTS thin lms. The article also presents an approach for delivering preci...