P-type CdS Research Articles

Controlled synthesis of SnSxSe2-x thin films for solar energy water splitting

Earth-abundant and ecofriendly minerals SnSxSe2–x can be promising candidates for photoelectrochemical (PEC) cells because of their tunable band gaps and high absorption efficiency in the visible light range. In this paper, p type SnS thin films with sheet-like morphologies were successfully prepared by CBD method and then n-type SnSxSe2-x thin films were achieved by selenization annealing of SnS thin films. The physical properties and PEC performances of SnSxSe2-x thin films influenced by the annealing process were detailed studied. The photocurrent densities and stability of SnSxSe2-x films were further improved by the deposition of p-type CdS:Cu buffer layer. And the fabrication of FTO/SnSxSe2-x/CdS:Cu/TiO2/Pt photocathode improved the PEC performance further and the photocurrent as high as 10.5 mA/cm2 had been achieved. IPCE tests indicated that the FTO/SnSxSe2-x/CdS:Cu/TiO2/Pt structure achieved a power conversion efficiency of 31.3 %.

Multipoint-bridging structure with a piezoelectricity-induced S-scheme junction for piezoelectricity-enhanced photoelectrochemical H2O2 production

A novel photoanode is prepared by bridging a vertical p-type CdS nanowire array by transverse Au nanorods for piezoelectricity (PE)-enhanced photoelectrochemical H2O2 production, and a new concept of PE-induced S-scheme junctions is proposed.

Pristine hexagonal CdS assembled with NiV LDH nanosheet formed p-n heterojunction for efficient photocatalytic hydrogen evolution

Efficient charge utilization in photocatalysis are of great importance not only for improving photocatalytic hydrogen evolution, but also for achieving excellent performance of semiconductors applying for actual operation. Herein, it is demonstrated that by the way of providing an additional electric field, the migration efficiency of electron-hole pairs can be improved apparently. Specifically, for the first time, hexagonal CdS and NiV-layered double hydroxide (NiV LDH), both of them are reported to be one of the most promising materials in photocatalytic water splitting, is assembled with the mass ratio of ten to one to constract a novel p-n heterojunction photocatalyst named as CNV-2. The combination of p-type CdS and n-type NiV LDH can facilitate electrons and holes transfer and separation ultimately enhance photocatalytic hydrogen-production efficiency by providing an additional electric field. Furthermore, the delicate architecture and the excellent property in the absence of sacrificial agents is certified various characterization studies, which are in good consistent with each other, thereby confirming its potential of CNV-2p-n junction for the water-splitting reaction and energy storage.

Synthesis and characteristics of p-type CdS nanobelts

We report, for the first time, the synthesis of single crystalline p-type CdS nanobelts using a simple thermal evaporation of mixture of CdS and trace tin (Sn) powder. Single-crystal Sn doped CdS nanobelts are grown along the direction. The Raman spectrum of Sn-doped CdS nanobelts has a ~2 cm−1 red-shift in comparison with that of undoped CdS nanobelts. The neutral-acceptor bound exciton (AOX) and donor–acceptor pair (DAP) emissions in the low temperature photoluminescence spectroscopy of Sn doped CdS nanobelts studies support the p-type conduction in Sn doped CdS. Electrical transport measurements reveal that the tin-doped CdS nanobelts show p-type conductivity. The synthesis of p-type CdS nanobelts is expected to shed light on p-type doping difficulty of II–VI wide semiconductor.

Can a benignj-Vcharacteristic with current saturation be the beginning of a new area of semiconductor physics? The vanishing space charge cleans up the defect-level spectrum

The measurement of the current as a function of the applied voltage is a primary tool to investigate the electrical properties and much attention was given to its deviation from ohmicity. Only recently we have learned that even the most simple characteristics with saturation current can be full of surprises. In this paper, we will emphasize how important it is to employ immediately other tools, such as the Franz–Keldysh effect to make the field distribution visible. We will very briefly review the electrode-adjacent high-field domain and their ability to render a CdS crystal thermodynamically stable as being n- or p-type, i.e., being ambipolar depending on whether the domain is attached to the cathode or anode, respectively. We will now also point to the differences for junction-adjacent high-field domains. We will focus on the small slab between a blocking contact and a high-field domain that permits a precise spread of the quasi-Fermi levels within the domains. Within the domains, the crystal is space-charge-free and permits to investigate the electronic transitions to defect levels around the quasi-Fermi levels. The defect levels are free from distortion caused by electric field variation in their neighborhood caused by space charges. A very steep electron quenching minimum is shown in the p-type CdS with anode-adjacent domain. The domains are stabilized by the electron density at blocking cathodes and by hole densities at blocking anodes.

Surface charge transfer induced p-CdS nanoribbon/n-Si heterojunctions as fast-speed self-driven photodetectors

Heterojunctions composed of single p-type CdS nanoribbons (NRs) and n-type silicon (Si) were successfully fabricated and can be applied as fast-speed self-driven visible photodetectors.

Hydrogen Evolution from Pt Nanoparticles Covered p-Type CdS:Cu Photocathode in Scavenger-Free Electrolyte

The photoelectrolysis of water to generate hydrogen by semiconductor photoelectrodes has been known to be a promising approach to utilize clean and sustainable solar energy. In this study, photocathode based on p-type CdS:Cu was successfully fabricated by the thermal evaporation process and photoelectrochemical investigations were carried out to determine its water photoelectrolysis potential. Cu doping concentration at 5.4% was found to be the optimal doping level and the bare CdS:Cu photocathode showed a large transient photocurrent as a result of the slow water reduction kinetics of the photoinduced electrons at the photoelectrode/electrolyte interface. The electrons accumulated at the interface and caused the photocathode to suffer from photodegradation during the stability test. After modifying the photocathode surface with the Pt nanoparticles to reduce the hydrogen evolving reaction overpotential, both the photocurrent and stability were enhanced. Hydrogen evolution from the CdS:Cu/Pt surface in the near neutral and scavenger-free electrolyte demonstrated for the first time the CdS with p-type conductivity was a feasible candidate for solar water splitting.

Structural and Photoelectrochemical Properties of Cu-Doped CdS Thin Films Prepared by Ultrasonic Spray Pyrolysis

Cu-doped CdS thin films of variable doping levels have been deposited on indium tin oxide-coated glass substrate by simple and cost-effective ultrasonic spray pyrolysis. The influences of doping concentration and annealing treatment on the structure and photoelectrochemical properties of the films were investigated. The deposited films were characterized by XRD, SEM, and UV-Vis spectra. Moreover, the films were investigated by electrochemical and photoelectrochemical measurements with regard to splitting water for solar energy conversion. The results showed that the Cu impurity can cause a structural change and red shift of absorption edge. It was found that the photocurrent can be improved by the Cu-doping process for the unannealed films under the weak illumination. The unannealed 5 at.% Cu-doped sample obtained the maximum IPCE, which achieved about 45% at 0.3 V versus SCE potential under 420 nm wavelength photoirradiation. In addition, the p-type CdS was formed with a doping of 4 at.%~10 at.% Cu after 450°C 2 h annealed in vacuum.

Ultrahigh Mobility of p‐Type CdS Nanowires: Surface Charge Transfer Doping and Photovoltaic Devices

Unique p-type CdS nanowires with ultrahigh mobility for photovoltaic devices: p-type CdS nanowires can be prepared by surface charge transfer doping with a thin MoO3 layer, which shows excellent rectifying characteristics with a high on/off current ratio of ∼1.6 × 102 and a low forward turn-on voltage of about 1.0 V at room temperature, and obvious photovoltaic behavior with a power conversion efficiency (η) up to 1.65%.

CdTe Solar Cell from Sputtering Method

ABSTRACTWe report CdTe/CdS solar cell with CdTe layer grown by sputtering method. A controlled etch and anneal process on the sputter-grown CdTe films was performed to increase the average grain size of the film. The process involved dipping the CdTe films in a saturated solution of cadmium chloride (CdCl2) in methanol (2.08 gram in 100 ml) followed by a 30 minute annealing at 400 °C. We performed various experiments on this process by varying the dipping times, drying process and annealing times and analyzed the resultant films using Scanning Electron Microscopy (SEM). We could see a clear increase in grain size from 200 nm to 5 μm after CdCl2 treatment. The process also increased the overall roughness of the sample so that more light is absorbed than reflected. We prepared solar cells using CdTe as p-type layer and CdS as n-type layer. The efficiency of the cell improved from 1.1% to 4.2% after air annealing. The effect of air-annealing is studied by means of quantum efficiency measurement.

Preparation of p-type CdS thin films and in situ dark conductivity in vacuum deposited CdS:Cu films

CdS:Cu thin films were prepared using a vacuum co-evaporation technique. The Hall measurements indicate that the conductivity characteristic of CdS thin films transformed from highly compensated in as-grown or weakly annealed materials to p-type conductive in strongly annealed materials. X-ray diffraction spectra show that as-deposited thin films were the hexagonal phase of CdS except the presence of copper for high Cu doping and the diffraction peaks of Cu disappeared after annealing. From the X-ray photoelectron spectroscopy we found the ionization of Cu atoms and the formation of an acceptor level. In situ dark conductivity in vacuum as-deposited CdS:Cu was performed in the temperature range between 27 and 250 °C. An abnormal temperature dependence of conductivity was observed in medium and heavily Cu-doped films. The formation of a p-type material at a certain temperature was also studied by the hot probe measurements, which indicates a complex compensation process in the Cu-doped CdS films.

Photoluminescence of p‐type CdS:Cu thin films

Cu-doped p-type CdS (CdS:Cu) and non-doped n-type CdS films were fabricated by the vacuum deposition process. Photoluminescence (PL) spectra of CdS:Cu and CdS films were measured between 8.7 K and room temperature. Free excitonic emission (FX), neutral acceptor-bound excitonic emission (I1), and donor–acceptor pair emission (DAP) were observed from CdS:Cu films. These results suggest that crystallinity of CdS films was improved by Cu doping and that Cu atoms in CdS behave as acceptors and form shallow levels (about 80 meV above the valence band edge) in CdS. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Improvement in the efficiency of Cu-doped CdS/non-doped CdS photovoltaic cells fabricated by an all-vacuum process

Thin-film photovoltaic cells composed of p-type Cu-doped CdS (CdS(Cu)) and n-type CdS layers (CdS(Cu)/CdS system) were fabricated by an all-vacuum deposition process. The cells showed a higher response in the longer-wavelength side than at the absorption edge of CdS with an increase in the thickness of the CdS(Cu) layer. High efficiency (over 8.5%) was obtained by improvement in CdS(Cu) layer fabrication. It is thought that the photovoltic effect of the cells is caused by a p-CdS(Cu)/n-CdS homojunction.

X-Ray diffraction studies of p-CdS:Cu thin films

X-Ray diffraction (XRD) was performed in order to detect p-type Cu–S compounds such as Cu 2S in p-type Cu-doped CdS (CdS:Cu) films fabricated by the vacuum deposition of CdS on thin Cu films on a glass substrate. The diffraction angles of CdS:Cu films and the powder corresponded to those of hexagonal CdS, and their relative peak intensities were also similar to those of the CdS. Lattice constants of the CdS:Cu corresponded to those of hexagonal CdS within 0.06% of difference. However, some XRD lines of CdS:Cu were close to a few lines of each Cu–S compound. Detailed examination of d-spacings and the relative peak intensities of the diffraction patterns of the CdS:Cu and each Cu–S compound was carried out. However, XRD traces of Cu–S compounds could not be detected in the CdS:Cu films. Therefore, it is thought that crystalline Cu–S compounds were not formed in p-type Cu-doped CdS films.

Light Emission of a CdS(Cu)/CdS Thin-Film Diode

Thin-film diodes composed of Cu-doped p-type CdS (CdS(Cu)) and non-doped n-type CdS films (CdS(Cu)/CdS diode) were fabricated by an all-vacuum deposition process. The diodes showed good rectification characteristics and light emission of blue-green, green and red colors under a forward current at 77 K. The colors of light were changed by the Cu concentration, thickness of the Cu-diffused CdS layer and current density. It is thought that light emission of the diode was generated by a p-CdS(Cu)/n-CdS homojunction.

XPS analysis of p-type Cu-doped CdS thin films

X-ray photoelectron spectroscopy (XPS) was used to examine the chemical states and depth profiles of Cu, Cd and S in p-type Cu-doped CdS (CdS(Cu)) thin films. An Auger parameter was used to examine the chemical states of the elements. Auger parameters of Cu and Cd were similar to those of Cu2S and CdS, respectively. Therefore, it is thought that the doped Cu was Cu+ and Cd was Cd2+ in the CdS(Cu) films. Depth profiles of the elements in the CdS(Cu) films showed that the concentration of S was about 50% and constant, that Cu was diffused throughout the films, but rich at the surface and interface of CdS and the substrate, and that the concentration of Cd decreased with Cu doping, although the sum of the concentrations of Cd and Cu was also about 50%. Since Cu–S compounds such as Cu2S were not detected by XRD and EDX analyses using TEM in CdS(Cu) films. It is thought that the p-type characteristics of CdS(Cu) films are due to a Cu acceptor in which some of the Cd2+ are substituted by Cu+ in unit cells of CdS, not to the formation of p-type Cu–S compounds.

真空蒸着によるＣｄＳ（Ｃｕ）／ＣｄＳ薄膜光電池の作成と効率の基板温度依存性

Thin-film photovoltaic cells composed of Cu-doped CdS and non-doped CdS layers (SnO2/CdS (Cu) /CdS/A1) have been fabricated by an all vacuum deposition process. First, thin Cu film (about 10 nm thick) was deposited on the SnO2 coated glass substrate followed by the deposition of CdSI layer (about 500 nm thick). These layers were annealed in a vacuum at 350°C for 15 min. before the deposition of CdSII layer (about 4 pm thick). The substrate temperature was lowered from 200°C to 130°C and held at 130°C during deposition of CdSII layer. This process was most important to get efficient cells. Finally, Al film was deposited on the CdSII layer as a counter electrode. The conversion efficiency of the best cell was over 7%. Depth profiles measured by SIMS showed that the Cu diffused into CdSII layer through CdSI layer and the diffusion of Cu slowed down drastically at a substrate temperature of about 140°C and stopped at about 130°C. As a result, the boundary between the Cu-doped p-type CdS layer and non-doped CdS layer was formed in the CdSII layer. The spectral responses of the short-circuit current of the cells were mainly dominated by the band gap energy and Cu impurity levels in CdS. Therefore, we concluded that the photovoltaic effect of the cells was caused by the p-i-n or p-n homojunction of CdS.

Luminescence properties pf p-type thin CdS films prepared by laser ablation

Investigations of the luminescence of p-type CdS:Cu thin (less than or equal to 2 μm) films on glass substrate prepared by laser ablation were performed for the first time. The dependences of the luminescence on the Cu content in the thin films were studied at 300 K with argon laser lines at 457.9 nm, 488.0 nm and 514.5 nm. It is demonstrated that the luminescence excited with the 514.5 nm line corresponds to the donor-acceptor transition. Furthermore, it is shown that the intensity of the red emission of CdS:Cu films can be efficiently bleached by Cu doping.

Modification of structural and opto-electronic properties of CdS thin films by Cu doping

The formation of p-type CdS thin films in a chemical bath doped with Cu is reported. Cu-doped films showed an amorphous nature and exhibited high electrical conductivity and quick photoresponse characteristics at high and low levels of Cu doping, respectively. Undoped CdS films were near stoichiometric, crystalline in nature, and exhibited slow photodecay. Cu doping influenced the photoresponse characteristics, structural, electrical, and optical properties of the films. The optical band gap of CdS film changed from 2.35 to 2 eV after Cu doping. These films may be used as a second layer on top of a lower band gap material in thin film solar cell structures and in wide range photo-IR detector structures.

P-Type II-VI Compound Semiconductor Thin Films Grown by Pulsed Laser Deposition

AbstractIn this paper the results on p-type ZnS, ZnSe, CdS and CdSe thin films grown by pulsed laser deposition will be discussed. these films were deposited on GaAs substrates. Li-doping has been shown to be effective in producing p-type II-VI thin films, while in-doping is excellent for n-type CdS and CdSe thin films. No post-annealing process was used. these preliminary results suggest a possible new approach through pulsed laser deposition to solve the doping problem of II-VI compound semiconductors.