Undoped CdS Films Research Articles

Influence of deposition temperature and fluorine doping on CdS properties: Exploring applications in CdTe solar cells

CdS and CdS:F thin films were synthesized at 75 °C and 90 °C by CBD with NH4F as the fluorine dopant. The structural, morphological, optical, and electrical properties were investigated with varying F wt.%. XRD analysis revealed a coexistence of cubic and hexagonal phases with small crystallite sizes. Raman spectroscopy exhibited characteristic peaks of 1LO and 2LO, corresponding to longitudinal optical phonons. Scanning electron microscopy (SEM) images displayed dense films with excellent substrate adhesion and crystalline morphology. Optical analyses unveiled noticeable alterations in optical transmittance due to F doping, with bandgap values ranging between 2.3 to 2.4 eV. Electrical resistivity, typically in the order of kΩcm, was influenced by incorporating F atoms within the CdS lattice. Notably, the fabrication of CdS/CdTe solar cells yielded efficiencies of 5.53 % for undoped CdS films and 7.47 % when utilizing films doped with 0.00455 wt% fluoride, highlighting the beneficial impact of F incorporation on solar cell performance.

Role of Cu dilute on microstructures, optical, photoluminescence, magnetic and electrical properties of CdS film

Thin films of CdS1-xCux (with 0 ≤ x ≤ 0.10) were deposited using electron beam evaporation. Using XRD, EDX, SEM and UV–Vis–NIR spectroscopy, the impact of [Cu]/[S] on the film properties was examined. The influences of various concentrations of Cu are also elucidated on the optical parameters of the films. The XRD analysis shows that the thin films of CdS1-xCux have been improved and have hexagonal polycrystalline structure with the increase of Cu doping ratio. Additionally, the crystallite size is reduced while the micro-strain ε increases with enhancement of the incorporation of Cu in CdS lattice. The envelope method was used to extract the optical parameters of the undoped and Cu-doped CdS films. With the increase of Cu concentration, the energy optical bandgap decreased, and the variation values of band gap could play an important role in solar cell applications. Another optical parameters such as, dissipation factor and real/imaginary dielectric constant parts were evaluated and demonstrated a strong Cu doping dependence. The shift observed in the photoluminescence spectra emission band confirmed Cu's substitution to CdS lattice. The measurements of magnetization using vibrating sample magnetometer illustrated a hysteresis loop in Cu-doped CdS films, and confirmed the room temperature ferromagnetism. Finally, the Hall effect results show that the pure CdS film corresponds to an n-type semiconductor with a resistivity of 8.11 × 10-2 Ω cm and a carrier concentration of 29.6 × 1019 cm-3, and the CdS:Cu film is a p-type semiconductor and the resistivity is reduced from 6.8 × 10-2 to 3.7 × 10-2 Ωcm, and the carrier concentration is reduced from 26.4 × 1019 to 4.1 × 1019 cm-3, which has potential application prospects in solar cells.

CdS/CdSe HETEROSTRUCTURES GROWN BY CHEMICAL TECHNIQUES ON FLEXIBLE PET/ITO SUBSTRATES

Undoped and Mn-doped CdS films, CdSe films and CdS:Mn/CdSe heterostructures were deposited by chemical techniques. Undoped and Mn-doped CdS films were grown onto flexible PET/ITO substrates by chemical bath deposition at different temperatures. CdSe thin films were synthesized following a two stages process. In the first stage, CdO2 precursor films, were synthesized by chemical bath deposition at different deposition time. In the second stage, the CdO2 precursor films were transformed into CdSe films by immersion in a Se ionic solution. CdS, CdS:Mn, CdSe and CdS/CdSe samples were characterized by high-resolution transmission electron microscopy, UV-vis, Raman and room temperature photoluminescence spectroscopies. The structural characterization indicates that CdS and CdSe films with hexagonal phase were obtained. CdSe films showed the LO Raman mode with three order phonon replicas, an indication of the excellent crystalline quality of the samples.

Ga doping of nanocrystalline CdS thin films by electrodeposition method for solar cell application: the influence of dopant precursor concentration

Ga doping of CdS thin films has been achieved using a simplified cathodic electrodeposition method and with glass/indium tin oxide (glass/ITO) as a substrate. CdCl2, Na2S2O3 and GaCl3 were used as precursors. The Ga-doped and un-doped CdS films obtained were characterized for their structural, optical, luminescence, compositional and morphological properties using state-of-the-art X-ray diffraction (XRD), spectrophotometry, room-temperature photoluminescence (PL), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM), respectively. XRD results show that the presence of Ga ions in the deposition electrolyte and post-deposition annealing promote crystallinity of deposited CdS films, with estimated crystallite sizes of the films in the range (5–22) nm after annealing. Optical characterization results show that incorporation of Ga atoms into the crystal lattice of CdS results in increase in energy bandgap of the films, which makes them advantageous for application as window/buffer layers in solar cells. PL results show a single green emission peak whose intensity increases as Ga-content of the films increases. EDX results show a direct relationship between the percentage atomic Ga composition of the CdS:Ga films and the molar concentration of GaCl3 in the deposition electrolyte. SEM images reveal smooth surfaces of doped and un-doped CdS films. However, after annealing, cracks begin to develop in the films grown with electrolytic GaCl3 concentration in excess of 0.004 M, thus indicating a possible threshold in GaCl3 concentration for obtaining device-grade CdS:Ga films. The entire work presents one of the strengths of electrodeposition as a reliable semiconductor growth technique for device application.

Effect of the sulfur and fluorine concentration on physical properties of CdS films grown by chemical bath deposition

Undoped and F-doped CdS thin films were grown on glass slides by chemical bath deposition using thiourea, cadmium acetate and ammonium fluoride as sulfur, cadmium, and fluorine sources, respectively. Undoped CdS films were deposited varying the concentration of thiourea. Once the optimal thiourea concentration was determined, based on the crystalline quality of the samples, this concentration was maintained and ammonium fluoride was added at different concentrations in order to explore the effect of the F nominal concentration on properties of CdS films. Undoped and F-doped CdS films were characterized by X-ray diffraction, UV–Vis, room temperature photoluminescence, and four probe resistivity measurements. Results showed highly transparent F-doped CdS films with strong PL and low resistivity were obtained.

Effect of magnesium incorporation on the structural, morphological, optical and electrical properties of CdS thin films

Undoped CdS and nanostructured Mg-doped CdS (CdS:Mg) thin films were deposited on suitably cleaned glass substrates maintained at 400°C by a spray pyrolysis technique using perfume atomizer. The magnesium content in the films is varied from 0 to 8at% in steps of 2at%. The effect of Mg doping on the structural, morphological, optical and electrical properties of CdS thin films has been studied. The crystal structures of the films were determined by X-ray diffraction studies. All the films exhibit hexagonal structure with a preferential orientation along the (002) plane irrespective of the Mg doping level. Film surface modifies from porous nature to needle shaped nanorods with Mg doping. The optical band gap energy exhibits a decreasing trend and is shifted from 2.48 to 2.29eV with increasing Mg content. Film coated with 6at% Mg doping concentration exhibits a minimum resistivity of 1.87×102Ωm.

Chemical bath deposition of CdS thin films doped with Zn and Cu

Zn- and Cu-doped CdS thin films were deposited onto glass substrates by the chemical bath technique. ZnCl2 and CuCl2 were incorporated as dopant agents into the conventional CdS chemical bath in order to promote the CdS doping process. The effect of the deposition time and the doping concentration on the physical properties of CdS films were investigated. The morphology, thickness, bandgap energy, crystalline structure and elemental composition of Zn- and Cu-doped CdS films were investigated and compared to the undoped CdS films properties. Both Zn- and Cu-doped CdS films presented a cubic crystalline structure with (1 1 1) as the preferential orientation. Lower values of the bandgap energy were observed for the doped CdS films as compared to those of the undoped CdS films. Zn-doped CdS films presented higher thickness and roughness values than those of Cu-doped CdS films. From the photoluminescence results, it is suggested that the inclusion of Zn and Cu into CdS crystalline structure promotes the formation of acceptor levels above CdS valence band, resulting in lower bandgap energy values for the doped CdS films.

Effect of indium diffusion on characteristics of CdS films and nCdS/pSi heterojunctions

Diffusion of indium in In/nCdS/glass and In/nCdS/pSi structures at 350–550 °C in vacuum 1.33 × 10 −1 Pa and its effect on structural, electrical, optical and photovoltaic characteristics of nCdS films, fabricated by spray pyrolysis technique and nCdS/pSi heterojunctions have been investigated. The indium-doped and undoped CdS films were characterized by X-ray diffraction (XRD), electrical and optical measurements. The concentration profiles of indium and the components of CdS films (Cd and S) in In/nCdS/pSi structures were studied using the energy dispersive X-ray fluorescence (EDXRF) analysis. The thermal annealing of In/nCdS/pSi structures is accompanied by the diffusion penetration of In through CdS film into Si substrate. At the same time, the Cd and S atoms from CdS film diffuse into Si substrate. The diffusion doping of CdS film by indium did not change the polycrystalline hexagonal structure and the energy band gap of CdS films and increased the electron concentration from 1.4 × 10 13 to 1.3 × 10 16 cm −3. The photovoltaic parameters and spectral responsivity of In-doped nCdS(In)/pSi(In) cells were higher than those for nCdS/pSi cells and reached the maximum values after the thermal annealing at 450 °C. The improvement of the photovoltaic parameters of nCdS(In)/pSi(In) photocells was discussed on the base of the changes introduced in the energy band diagram of nCdS/pSi heterojunction due to the indium diffusion.

Luminescence and photoconductivity of alkali-metal-doped cadmium sulfide films

Data are presented on the luminescence and photosensitivity of cadmium sulfide films doped with an alkali metal (Na or K) in the presence of chlorine. The doping is shown to increase the luminescence quantum yield by more than one order of magnitude in comparison with undoped CdS films. The doped films are resistant to high-intensity UV radiation, which usually initiates photochemical reactions.

Structural and optical characterization of undoped and indium-doped CdS films grown by pulsed laser deposition

Three types of CdS thin films, one undoped and two n-doped, have been grown on the quartz substrates by pulsed laser deposition technique. The two n-doped films have been deposited by laser ablating a home-made target obtained by mixing CdS and metallic Indium powders with two different concentrations of In powder weight (1 and 5%). The films were grown highly oriented along the (002) direction of the hexagonal phase. Raman spectra show that the LO peak broadens as the Indium doping increases, due to the increase of compositional disorder. Band filling effects characterize the absorption spectra of the heavily doped films: in particular, the band gap of the doped films presents an evident blue-shift with respect to the undoped film, due to Burstein-Moss effect. Photoluminescence spectra show the intrinsic radiative recombinations persisting up to room temperature.

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.

Undoped and indium-doped CdS films prepared by chemical vapour deposition

Undoped and In-doped films of CdS were deposited at different temperatures by the chemical vapour deposition technique on glass and In-coated (30 nm) glass, respectively. Both kinds of film present a columnar microstructure, low porosity and good adherence to the substrate. The doped films have higher electron mobility values compared with the undoped ones. Shifts in the transmission spectra (Moss-Burstein effect) were observed with increased doping. Small crystals grew over the doped films during the deposition stage, mainly at the higher substrate temperatures.

High orientation CdS thin films grown by pulsed laser and thermal evaporation

Undoped CdS films have been grown by pulsed laser evaporation (PLE) and thermal evaporation (TE) techniques on Corning’s 7059 glass at a substrate temperature between room temperature and 250 °C. The deposition rates are 0.07 Å/s for PLE and 60 Å/s for the TE technique. These as-deposited films have high (002) preferred orientation by both techniques even without preheating the substrate. However, films deposited by PLE have more preferred orientation and larger grain size. These features make the PLE films have sharper Raman peaks, smaller Raman shift of surface mode and more overtones of longitudinal optical phonon mode observed than those in TE films. The transparency of PLE or TE films for wavelengths which are larger than that of absorption edge is around 90% on average.

Effect of thermal annealing on the cathodoluminescence of evaporated CdS films

Cathodoluminescence (CL) of evaporated undoped CdS films was investigated before and after thermal annealing in air and in vacuum at 300 °C for several hours. Pure CdS single crystals were studied for comparison. CL spectra were obtained at room temperature using the electron microprobe technique. The two well-known (green and red) CL bands of pure CdS were observed for all samples. Annealing of the films in air decreased the green luminescence while vacuum annealing led to its increase. The red luminescence increased under both annealing conditions. The results were explained in terms of radiative transitions attributed mainly to native defects and their complexes. The role of oxygen and residual impurities on the CL of thin films was discussed. A modulation of the CL spectra was obtained in thin films owing to optical interference.

Effect of Bi 3+ doping on the properties of chemically deposited GdS films

CdS films were prepared by a chemical bath deposition technique with different Bi concentrations (0.01 to 5 wt %) on glass substrates. Optical and electrical properties were studied with these films. It was observed that the absorption coefficient of the CdS film increases with Bi-doping up to 2 wt % and then decreases. These results are explained in terms of the crystallanity of the film. The optical band gaps (E g) were determined and found to decrease with Bi-doping. The conductivity and thermoelectric power are higher for doped films than undoped CdS films. These results are explained by considering the existance of Cd 2+ ions as donor centres in Bi-doped CdS films.

Studies on stability of PEC cells formed with CdS:Al films

Aluminum doped and undoped CdS films are deposited on stainless steel substrates by chemical bath deposition technique and are employed in PEC cells. The effects of heat treatment to photoanode and addition of salts like KCl and NaCl in an electrolyte on the stability of the PEC cells are studied. It is found that though the PEC cells formed with CdS films are stable in NaOH-Na 2S-S electrolyte, the stability of PEC cells formed with Al doped CdS films is achieved only after the addition of saturated salts in the electrolyte.

Studies on electrochemical photovoltaic cells formed with as-deposited in-doped CdS films

Indium doped and undoped CdS films have been deposited on conducting substrates by a chemical bath deposition technique. The doping concentration was varied from 0.005 to 1.0 wt. % of indium. Electrochemical photovoltaic (ECPV) cells are formed with these films and their electrical properties are studied. It is observed that the performance of the cell measured in terms of open circuit voltage (Voc), short circuit current (Isc), efficiency (η), and maximum power output (Pm), is optimum for the cells formed with 0.01 wt. % In-doped CdS photoanode.

Low resistivity CdS thin films grown by flash-evaporation at low substrate temperature (150–200 °C)

Undoped and In-doped CdS films have been grown by flash-evaporation at a substrate temperature between 150 and 200 °C. A resistivity of 5 Ω⋅cm has been obtained for undoped CdS films at 150 °C substrate temperature while a resistivity of about 2.5×10−3 Ω⋅cm could be obtained for 1% In-doped CdS films at any substrate temperature between 150 and 200 °C. The transparency of such films for wavelengths larger than that of absorption edge is close to 100% when corrected for the reflection loss. Due to the above characteristics these films are suitable as windows in heterojunction solar cells.

Effect of aluminum doping on the properties of PEC cells formed with CdS:Al films

Aluminum doped and undoped CdS films were prepared by chemical bath deposition technique and the photoelectrochemical (PEC) properties have been studied by forming doped CdS/NaOHNa 2SS/C junction. Better results are obtained with 0.1 wt% Al doped CdS films. These results are discussed with the help of the optical and transport properties of the Al doped CdS films.

Optical and transport properties of chemical bath deposited CdS: Al films

Aluminium doped and undoped CdS films are deposited on the glass substrates by chemical bath deposition technique. Their optical and transport properties are studied and the effect of dopant concentration on these properties is discussed at length.