Low cost CuInSe2 thin films production by stacked elemental layers process for large area fabrication of solar cell application

Low cost deposition of large area CuInSe₂ (CIS) thin films have been grown on Mo-coated glass substrate by simple and economic stacked elemental layer deposition technique in vacuum. The grown parameters such as concentration of Cu, In and Se elements have been optimized to achieve uniform thin film in vacuum chamber. The as-grown Cu/In/Se stacked layers have been annealed at 200 °C and 350 °C for 1 h in air ambient. The as-grown and annealed films have been further subjected to characterization by X-ray diffraction (XRD), optical absorption, atomic force microscopy (AFM) and I-V measurement techniques. XRD patterns revealed that as-grown Cu/In/Se stacked layers represent amorphous nature while annealed CIS film reproduces nano-polycrystalline nature with chalcopyrite structure. The optical band gap of annealed films increases with respect to air annealing which confirms the reduction of crystallite size. Surface morphology of as-grown Cu/In/Se stacked layers and annealed CIS thin films have been confirmed by AFM images. The electrical measurements show enhancement of conductivity which is useful for solar cell application.     

The influence of annealing temperature on the structural, electrical and optical properties of ion beam sputtered CuInSe2 thin films

CuInSe₂ (CIS) thin films were prepared by ion beam sputtering deposition of copper layer, indium layer and selenium layer on BK7 glass substrates followed by annealing at different temperatures for 1 h in the same vacuum chamber. The influence of annealing temperature (100-400 °C) on the structural, optical and electrical properties of CIS thin films was investigated. X-ray diffraction (XRD) analysis revealed that CIS thin films exhibit chalcopyrite phase and preferential (112) orientation when the annealing temperature is over 300 °C. Both XRD and Raman show that the crystalline quality of CIS thin film and the grain size increase with increasing annealing temperature. The reduction of the stoichiometry deviation during the deposition of CIS thin films is achieved and the elemental composition of Cu, In and Se in the sample annealed at 400 °C is very near to the stoichiometric ratio of 1:1:2. This sample also has an optical energy band gap of about 1.05 eV, a high absorption coefficient of 10⁵ cm⁻¹ and a resistivity of about 0.01 Ω cm.     

Tribological behavior of radio-frequency sputtering WS2 thin films with vacuum annealing

Thin films of tungsten disulfide (WS₂) were deposited on 3Cr13 martensitic stain less steel substrate by radio-frequency (RF) sputtering. The as-deposited films were annealed at 473, 673 and 873 K respectively for 2 h in 5 × 10^− 4 Pa vacuum. Composition of the films was inspected by energy dispersive spectroscopy. Surface morphology and structure properties were studied by scanning electron microscopy and X-ray diffraction techniques. Tribological behavior was also examined using tribometer. At 473 K, the films exhibited low crystallization structure and no significant improvement in the tribological performance. At 673 K, the tribological performance was improved and a transition from non-crystalline to hexagonal structure took in place. When the annealing temperature rose up to 873 K, the films cracked and fell off from the substrate. The results suggested that with suitable technical parameters vacuum annealing could promote crystallization and improve tribological performance of RF sputtering WS₂ films.     

Study of the properties of CuInSe2 materials prepared from nanoparticle powder

This work studies the properties of CuInSe₂ (CIS) thin films obtained from nanoparticle powder. The samples were prepared by direct thermal evaporation of ball milled powder from a tungsten crucible onto precleaned glass substrates, using a BALZERS coating unit. The as deposited films were annealed in a vacuum at different temperatures. The composition, structure, morphology and optical properties of these samples have been investigated. X-ray diffraction (XRD) results showed that the CuInSe₂ phase may be prepared by mechanical alloying method. The crystallites of the CIS powder were found to be partially copper-rich. The as-deposited film was polycrystalline in nature having chalcopyrite structure as a mainly phase. The surface morphology is homogeneous across the surface. Expected optical properties (E_g = 1.04 eV, α ≈ 10⁴ cm^? 1) and near stoichiometric composition (Cu: 23.62 at.%, In: 24.35 at.% and Se: 52.03 at.%) were determined.     

One-step electrodeposition of CuGaSe2 thin films

CuGaSe₂ thin films have been prepared by one-step electrodeposition and rapid thermal annealing process. According to composition and morphology analysis, deposition potential of − 0.6 V vs. SCE is considered to be optimum for electrodeposition. From the X-ray diffraction and Raman studies, the as-deposited film exhibits poor crystallinity without the evidence of CuGaSe₂ or other Ga-containing phases, while the rapid thermal annealing-treated film shows chalcopyrite structure CuGaSe₂ phase containing MoSe₂ phase between the Mo substrate and the absorber and minor second phase Cu_2 − xSe. The obtained CuGaSe₂ thin film has a band gap of about 1.68 eV and p-type conductivity.     

Characterization of stepwise flash-evaporated CuInSe2 films

CuInSe₂ (CIS) films were deposited by stepwise flash evaporation from polycrystalline powder source onto glass substrates held at various temperatures ranging from 100 to 560 K. The phase purity and microstructure were analyzed by transmission electron microscopy. The investigations show that films grown at 300 K and below were amorphous, whereas those grown at 370 K and above were polycrystalline in nature. The grain size in polycrystalline films were found to improve with increase in substrate temperature and during post-deposition annealing. The films had near stoichiometric composition as revealed by Rutherford backscattering spectrometry. Analysis of the optical transmittance spectra of CIS films deposited at 520 K yielded a value of ∼0.97 eV for the fundamental band gap.     

Effect of H2S treatment on properties of CuInS2 thin films deposited by chemical spray pyrolysis at low temperature

CuInS₂ thin films were deposited by chemical spray of aqueous solutions containing CuCl₂, InCl₃ and thiourea at substrate temperature of 250 °C in air and subjected to annealing at 530 °C in H₂S atmosphere. Structure and composition before and after annealing were studied by XRD, EDS, XPS and Raman spectroscopy. As-sprayed films were low-crystalline, showed uniform distribution of elements in film thickness and no oxygen content. For the CuInS₂ films deposited from the solutions with [Cu²⁺] / [In³⁺] = 1.0 and 1.1, H₂S treatment for 30 min increased the chalcopyrite content up to 73% and 51%, respectively. Cu_XS phase in sprayed CIS films promotes the crystallite growth but retards the formation of chalcopyrite phase during H₂S treatment.     

Growth of single-phase CuInGaSe2 photo-absorbing alloy films by the selenization method using diethylselenide as a less-hazardous Se source

Selenization growth of purely single-phase, polycrystalline CuIn_1 − xGa_xSe₂ (0 ≤ x ≤ 1) alloy films was demonstrated using a less-hazardous metalorganic selenide, diethylselenide [(C₂H₅)₂Se: DESe], without additional thermal annealing. Approximately 2.0-μm-thick films of the alloys exhibited X-ray diffraction peaks originating exclusively from the chalcopyrite structure. Low temperature photoluminescence spectra of the alloy films were dominated by a couple of characteristic donor-acceptor pair emissions that are particular to the state-of-the-art CuInGaSe₂ photo-absorbing layers.     

Tin oxide thin layers obtained by vacuum evaporation of tin and annealing under oxygen flow

Tin dioxide layers have been prepared by vacuum evaporation of tin on ordinary glass substrates. Thickness of the deposited tin layers was 500 or 1000 Å. Enrichment in oxygen was ensured by a thermal annealing at temperatures between 300 and 500 °C, for 1, 2, 4, 6, 8 and 10 h. The layers were characterized using X-ray diffraction, environmental scanning electron microscopy and EDX analysis and conductivity by the 4 point method. Oxygen enrichment of these films during annealing at high temperature induces the formation of the nanocrystalline tin oxide.     

Annealing effect on structural and electrical properties of thermally evaporated Cd1−xMnxS nanocrystalline films

Thin films of Cd_1−xMn_xS (0 ≤ x ≤ 0.5) were deposited on glass substrates by thermal evaporation. All the films were deposited at 300 K and annealed at 573 K. The as-deposited and the annealed films were characterized for composition, structure and microstructure by using energy-dispersive analysis for X-rays, X-ray diffraction, scanning electron microscopy and atomic force microscopy. Electrical conductivity was studied in the temperature range 190-450 K. All the films exhibited wurtzite structure of the host material with the grain size varying in the range between 36 and 82 nm. Resistivity of all the films is strongly dependent on Mn content and annealing temperature and lies in the range 13-160 Ω cm.     

Growth and vacuum post-annealing effect on the properties of the new absorber CuSbS2 thin films

Post-growth treatments in vacuum atmosphere were performed on CuSbS₂ films prepared by the single-source thermal evaporation method on glass substrates. The films were annealed in vacuum atmosphere for 2 h in temperature range 130-200 °C. The effect of this thermal treatment on the structural, optical and electrical properties of the films was studied. X-ray diffraction (XRD) patterns indicated that the films exhibited an amorphous structure for annealing temperature below 200 °C and a polycrystalline structure with CuSbS₂ principal phase. For the films annealed at temperatures below 200 °C one direct optical transition in range 1.8-2 eV was found. For the films annealed at 200 °C, two optical direct transitions emerged at 1.3 and 1.79 eV corresponding to the CuSbS₂ and Sb₂S₃ values respectively. The electrical measurements showed a conversion from low resistivities (3.10^− 2-9.10^− 2) Ω cm for the samples annealed at temperatures below 200 °C to relatively high resistivities (2 Ω cm) for the samples annealed at 200 °C. In all cases the samples exhibited p-Ztype conductivity.     

Structure and optical properties of Zr1−xSixN thin films on sapphire

A series of zirconium silicon nitride (Zr_1−xSi_xN) thin films were grown on r-plane sapphire substrates using reactive RF magnetron co-sputtering of Zr and Si targets in a N₂/Ar plasma. X-ray diffraction pole figure analysis, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), optical microscopy, and optical absorption spectroscopy were used to characterize the film stoichiometries and structures after growth at 200 °C and post-deposition annealing up to 1000 °C in ultra-high vacuum. The atomically clean r-plane sapphire substrates induce high quality (100) heteroepitaxy of ZrN films rather than the (111) orientation observed on steel and silicon substrates, but the addition of Si yields amorphous films at the 200 °C growth temperature. After the annealing treatment, films with Si content x < 0.15 have compressive stress and crystallize into a polycrystalline structure with (100) fiber texture. For x > 0.15, the films are amorphous and remain so even after ultra-high vacuum annealing at 1000 °C. XPS spectra indicate that the bonding changes from covalent to more ionic in character as Si―N bonds form instead of Zr―N bonds. X-ray reflectivity, atomic force microscopy (AFM) and optical microscopy data reveal that after post-deposition annealing the 100 nm thick films have an average roughness < 2 nm, except for Si content near x = 0.15 corresponding to where the film becomes amorphous rather than being polycrystalline. At this stoichiometry, evidence was found for regions of film delamination and hillock formation, which is presumably driven by strain at the interface between the film and sapphire substrate. UV-visible absorption spectra also were found to depend on the film stoichiometry. For the amorphous Si-rich films (x > 0.15), the optical band gap increases with Si content, whereas for Zr-rich films (x < 0.15), there is no band gap and the films are highly conductive.     

Influence of hydrogen introduction on structure and properties of ZnO thin films during sputtering and post-annealing

ZnO thin films were prepared in Ar and Ar + H₂ atmospheres by rf magnetron sputtering, and then they were annealed in vacuum and Ar + H₂ atmosphere, respectively. The structure and optical-electrical properties of the films were investigated by X-ray diffraction, transmittance spectra, and resistivity measurement, and their dependences on deposition atmosphere, annealing treatment, and aging were studied. The results showed that adding H₂ in deposition atmosphere improved the crystallinity of the films, decreased lattice constant, increased band gap, decreased the resistivity by the order of 10⁴ Ω cm, but exhibited poor conductive stability with aging. After Ar + H₂ and vacuum annealing, crystallinity of the films deposited in Ar and Ar + H₂ was further improved; their resistivity was decreased by the order of 10⁵ and 10¹ Ω cm, respectively, and exhibited high conductive stability with aging. We suggest that the formed main defect is V_O and H_i when H₂ is introduced during deposition, which decreases the resistivity but cannot improve the conductive stability; hydrogen would remove negatively charged oxygen species near grain boundaries during Ar + H₂ annealing to decrease the resistivity, and grain boundaries are passivated by formation of a number of V_O-H complex (H_O) to improve the conductive stability at the same time. Under vacuum annealing, the hydrogen that is introduced non-intentionally from deposition chamber maybe plays an important role; it exists as H_O in the films to improve the conductive stability of the films.     

Adjustment of the selenium amount during ion beam sputtering deposition of CIS thin films

CuInSe₂ (CIS) films were prepared by ion beam sputtering depositing Cu, In and Se layers sequentially on BK7 glass substrates and annealing the 3-layer film in the same vacuum chamber. The adjustment of the Se amount in the film was achieved by controlling the sputtering time of the Se target. X-ray diffraction pattern shows CIS films have chalcopyrite structure and preferential (112) orientation when the sputtering of the Se layer is between 60 and 180 min. It also can be seen that the most intense and narrow peak indicates the highest crystallinity for the sample with sputtering Se of 60 min, which is in agreement with the Raman measurement. The content of Cu, In and Se in the film deviates from 1, 1 and 2 with increasing the sputtering time of the Se target. Direct band gap energy between 0.96 and 1.05 eV, depending on the Se amount, and a high absorption coefficient of 10⁵ cm⁻¹ are found. The measured film resistivities vary from 0.01 to 0.05 Ω cm. Thus, the structural, optical and electrical characteristics of the CIS thin films were dependent on the Se amount during the fabrication of films and after fitting the sputtering time of Se, an optimization of the properties and a saving of Se consumption were achieved.     

Rapid thermal annealed Al-doped ZnO film for a UV detector

A low-resistive Al-doped ZnO (AZO) film was achieved by rapid thermal annealing. A co-sputtering method was used in the initial growth of AZO films and a rapid annealing process was performed on the as-deposited AZO film under N₂ atmosphere for 3 min. An as-deposited AZO film had an optical transmittance of 84.78% at 550 nm and a resistivity of 7.8 × 10^− 3 Ω cm. A rapid annealing process significantly improved the optical transmittance and electrical resistivity of the AZO film to 99.67% and 1 × 10^− 3 Ω cm, respectively. The structural changes of the AZO films were investigated by X-ray diffraction and transmission electron microscopy. The high quality AZO film was used to fabricate a metal-semiconductor-metal (MSM) structure for a UV detector. The MSM device provided a stable current of 25 μA at a bias of 2 V in a dark condition. Under UV illumination, the MSM device was highly responsive to UV light uniformly and repeatedly, and it enhanced the current by 80% at 45 μA. This rapid thermal annealing process may provide a useful method to fabricate quality AZO films for photoelectric applications with a low thermal budget.     

Hydrophilic properties of nano-TiO2 thin films deposited by RF magnetron sputtering

Microstructure and hydrophilicity of nano-titanium dioxide (TiO₂) thin films, deposited by radio frequency magnetron sputtering, annealed at different temperatures, were studied by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and water contact angle methods. It is found that the crystal phase transforms from amorphous to rutile structure with increase of annealing temperature from room temperature to 800 °C. It is also indicated that the organic contaminants on the surface of the films can be removed and the oxygen vacancies can be reduced by the annealing treatment. Annealed at the temperature below 300 °C, amorphous TiO₂ thin films show rather poor hydrophilicity, and annealed at the temperature range from 400 to 650 °C, the super hydrophilicity anatase of TiO₂ thin films can be observed. However, when the annealing temperature reaches 800 °C, the hydrophilicity of the films declines mainly derived from the appearance of rutile.     

CuInS2 thin films obtained by spray pyrolysis for photovoltaic applications

Copper indium disulphide, CuInS₂, is a promising absorber material for thin film photovoltaic which has recently attracted considerable attention due to its suitability to reach high efficiency solar cells by using low-cost techniques. In this work CuInS₂ thin films have been deposited by chemical spray pyrolysis onto glass substrates at ambient atmosphere, using different composition solutions at various substrate temperatures. Structural, chemical composition and optical properties of CIS films were analysed by X-ray diffraction, energy dispersive X-ray spectroscopy and optical spectroscopy. Sprayed CIS films are polycrystalline with a chalcopyrite structure with a preferential orientation along the <112> direction and no remains of oxides were found after spraying in suitable conditions. X-ray microanalysis shows that a chemical composition near to stochiometry can be obtained. An optical gap of about 1.51 eV was found for sprayed CIS thin films.     

Characterization of copper oxide thin films deposited by the thermal evaporation of cuprous oxide (Cu2O)

Thin films of copper oxide were deposited by thermal evaporation of cuprous oxide (Cu₂O) powder. The substrates were either unheated or heated to a temperature of 300 °C. The films were also annealed in air at a temperature of 500 °C for 3 h. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and UV-visible spectrophotometry. The effects of the substrate temperature and post-deposition annealing on the chemical, structural and optical properties of the films were investigated. As-deposited films on unheated substrates consisted of mixed cupric oxide (CuO) and Cu₂O phases, with a higher concentration of the Cu₂O phase. However, the films deposited on heated substrates and the annealed films were predominantly of the CuO phase.     

Effect of thermal treatments on the structure of MoNxOy thin films

MoN_xO_y films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure molybdenum target, varying the flow rate of reactive gases. X-ray diffraction (XRD) results revealed the occurrence of cubic MoN_x and hexagonal (δ-MoN) phases for the films with high nitrogen flow rates. The increase of oxygen content induces the decrease of the grain size of the molybdenum nitride crystallites. The thermal stability of a set of samples was studied in vacuum, for an annealing time of 1 h, for temperatures ranging from 500 to 800 °C in 100 °C steps. The results showed that pure molybdenum nitride films changed their structure from a meta-stable cubic MoN to hexagonal δ-MoN and cubic γ-Mo₂N-type structures with increasing annealing temperatures. The samples with molybdenum nitride films evidenced a good thermal stability, but those with molybdenum oxynitride coatings showed a tendency to detach with the increase of the annealing temperature.     

Growth of single-phase Cu(In,Al)Se2 photoabsorbing films by selenization using diethylselenide

Selenization growth of purely single-phase, polycrystalline CuIn_1 − xAl_xSe₂ (0 ≤ x ≤ 0.26) alloy films was demonstrated using a less-hazardous metal-organic selenide, diethylselenide [(C₂H₅)₂Se: DESe], by simple thermal annealing of metal precursor. Approximately 2.0 µm thick alloy films exhibited X-ray diffraction peaks originating exclusively from the chalcopyrite structure. Transitions seen in the low temperature photoluminescence spectra were attributed to characteristic donor-acceptor pair emissions of the state-of-the-art CuIn_1 − xAl_xSe₂ photoabsorbing layers.