In this Letter, we report the effects of ammonium sulfide [(NH4)2S] surface treatment on electrical and optical characteristics of the electrodeposited n‐type Cu2O thin films on Ti substrates. Films characterized structurally and morphologically before and after the surface treatment were compared using conductivity, spectral photoresponse and current–voltage (I–V) measurements. The ammonium sulfide surface treatment time showed an impact on optical and electrical characteristics of the films. Treated Cu2O films exhibited enhanced conductivity giving rise to a 50‐fold increase in the photocurrent and improved I–V characteristics. It was found that the sulfur passivation resulted in a nearly ohmic behaviour for Au or Ni contacts made with n‐type Cu2O whereas Ag or Cu contacts showed nearly Schottky behaviour. The results showed that ammonium sulfide treatments were very effective to passivate defects and improve the optical and electrical properties of polycrystalline n‐type Cu2O thin films that may provide a solid platform for Cu2O based devices of enhanced quality. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Grain size of polycrystalline semiconductor thin films in solar cells is optimized to enhance the efficiency of solar cells. This paper reports results on an investigation carried out on electrodeposited n-type cuprous oxide (Cu 2 O) thin films on Ti substrates with small crystallites and sulfidation of them to produce a thin-film solar cell. During electrodeposition of Cu 2 O films, pH of an aqueous acetate bath was optimized to obtain films of grain size of about 100 nm, that were then used as templates to grow thicker n-type nanocrystalline Cu 2 O films. XRD and SEM analysis revealed that the films were of single phase and the substrates were well covered by the films. A junction of Cu 2 O/Cu x S was formed by partially sulfiding the Cu 2 O films using an aqueous sodium sulfide solution. It was observed that the photovoltaic properties of nano Cu 2 O/Cu x S heterojunction structures are better than micro Cu 2 O/Cu x S heterojunction solar cells. Resulting Ti/nano Cu 2 O/Cu x S/Au solar cell structure produced an energy conversion efficiency of 0.54%, V oc = 610 mV and J sc = 3.4 mA cm −2 , under AM 1.5 illumination. This is a significant improvement compared to the use of microcrystalline thin film Cu 2 O in the solar cell structure where the efficiency of the cell was limited to 0.11%. This improvement is attributed mainly to the increased film surface area associated with nanocrystalline Cu 2 O films.

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We report electrodeposition of n-type cuprous oxide (Cu 2 O) films on p-type CuO films electrodeposited on Ti substrates for forming p-CuO/n-Cu 2 O heterostructures. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis revealed that the films had good structural quality, with substrates being well-covered by the films. The p-CuO/n-Cu 2 O heterojunctions exhibited good photovoltaic properties and diode characteristics. The surfaces of Cu 2 O films subject to ammonium sulfide treatment exhibited enhanced photocurrents. Under AM 1.5 illumniation, the obtained sulfur-treated and annealed Ti/p-CuO/n-Cu 2 O/Au solar cell structure yielded energy conversion efficiency of 0.64%, with V oc = 220 mV and J sc = 6.8 mA cm %2 .

Highly photoactive Cl-doped Cu 2 O films were electrodeposited potentiostatically on Ti substrates. Optimum deposition potential was determined by Linear-Sweep Voltammetry measurements. The influence of chlorine doping on grain size, crystallite shape and orientation was examined using scanning electron microscopy and X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of Cl due to doping. Mott-Schottky electrochemical impedance analysis showed the p-type conductivity for undoped Cu 2 O films and ntype conductivity for Cl-doped Cu 2 O films. Analysis also showed that the carrier concentration of Cu 2 O thin films varied with Cl concentration of the deposition bath. Spectral responses of the resulting films were investigated in a photo-electrochemical cell to optimize the CuCl 2 concentration of the deposition bath to obtain highly photoactive films. Photocurrent measurements further confirmed that the conductivity of these Cl-doped Cu 2 O films was n-type while undoped films showed p-type conductivity at a bath pH 9.3. The resistivity of Cu 2 O films decreased with the Cl concentration and the resistivity obtained for the Cl-doped Cu 2 O films with the highest photoactivity was about 10 2 Vcm at 30 8C. The low resistance and high photoactivity of Cldoped cuprous oxide thin films make them more suitable for solar cell and other applications.

As one of the most widely used domestic fuels, the detection of possible leakages of Liquefied Petroleum (LP) gas from production plants, from cylinders during their storage, transport and usage is of utmost importance. This article discusses a study of the response of undoped and chlorine doped electrodeposited n-type Cuprous Oxide (Cu 2 O) films to of LP gas. Undoped n-type Cu 2 O films were fabricated in an electrolyte bath containing a solution of sodium acetate and cupric acetate whereas n-type chlorine doped Cu 2 O thin films were prepared by adding a 0.02 M cuprous chloride (CuCl 2) into an electrolyte solution containing lactic acid, cupric sulfate and sodium hydroxide. The n-type conductivity of the deposited films was determined using spectral response measurements. The structural and morphological properties of the fabricated films were monitored using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Due to doping, the overall conductivity of the chlorine doped n-type Cu 2 O films increased by several orders of magnitude. The temperature dependent gas responses of both the undoped and chlorine doped n-type Cu 2 O thin films to the LP gas was monitored by measuring the electrical resistance (R), and using the contact probe method at a constant gas flow rate of 0.005 ml/s. Upon exposure to gases, both doped and undoped films showed a good response to the gas by increasing/decreasing the electrical resistance by ΔR. The undoped n-type Cu 2 O thin films showed a negative response (ΔR < 0) at all temperatures resulting in a maximum response around 85˚C. However, the chlorine doped n-type Cu 2 O thin films initially showed a positive response (ΔR > 0) to the LP gas which then reversed its sign to give a negative response which peaked at 52˚C. The positive response shown by the chlorine doped Cu 2 O films vanished completely at 42˚C. N. Bandara et al.

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The surface of electrodeposited n-Cu2O thin films were modified by sulphidation using aqueous Na2S followed by (NH4)2S vapor treatment. Compared to untreated thin films, the resultant films showed an enhanced response to liquefied petroleum (LP) gas at a relatively low operating temperature (~45 °C), one of the lowest reported for a cuprous oxide based material. X-ray diffraction spectra confirmed that the films were of single phase. Observed by contact angle measurements and energy dispersive x-ray spectroscopy, (NH4)2S vapor treatment converted the highly wetting sulphided films containing both Na and S to a partially wetting surface by forming sulphur on the film surface. This modification on the film surface, enabled the sensor response to recover to an ambient level after stoppage of LP gas flow, which sulphidation alone was inapt. Scanning electron micrographs complemented roughness measurements made by atomic force microscopy and showed a transformation of polycrystalline morphology of bare n-Cu2O film to one having highly porous structures, which thereby increased the surface area of the surface modified films. Therefore, this work demonstrates that the surface of the n-type Cu2O thin films modified by (NH4)2S vapor treatment and sulphidation can alter the surface wetting nature and increase the surface area to enhance LP gas sensing at a relatively low temperature.