CuInTe2 Films Research Articles

Phases and morphology of CuInTe2 films and their electric properties

The chalcopyrite structure of CuInTe2 is a p-type semiconductor with about 1.1 eV band gap and can be used as the absorber layer material. In this work CuInTe2 film samples were synthesized by chemical co-reduction method. The phases of the product samples were analyzed by X-ray diffraction (XRD) and the morphology was observed using field emission scanning electron microscopy (FESEM). The electrical properties of the product films were measured by the four probe resistance instrument. Experimental results show that, CuInTe2 films can be obtained at the reaction temperatures of 180 °C, 200 °C and 220 °C. For preparing CuInTe2 films, the nitrate raw materials are superior to chloride raw materials. Adding the number of reaction can increase the probability of preparing CuInTe2 films and also effectively improve the crystallinity. While adding the subsequent heat treatment process does not achieve better results. The obtained films are relatively continuous and all contain three elements of Cu, In and Te. The measured resistivities are between 0.152 KΩ·cm and 0.187 KΩ·cm.

Transport Properties of CuInTe2 Thin Films Obtained by the Electrochemical Route

CuInTe2 (CIT) thin films were potentiostatically electrodeposited onto cadmium sulfide thin films coated on fluorine doped tin oxide (FTO) glass in an aqueous bath at 75°C by the standard three-electrode system at − 0.7 V and − 0.8 V, with respect to an Ag/AgCl reference electrode. The electrodeposited layers were heat treated at ∼ 80°C in air ambient for 60 min. X-ray diffraction pattern and Raman analysis confirmed the formation of chalcopyrite CIT thin films upon heat treatment. The optical band gap of heat treated CIT films was found to be ∼ 1.0 eV and 0.95 eV deposited at − 0.7 V and − 0.8 V, respectively. Compact and good adhesive growth of CIT layers onto CdS coated FTO substrates is confirmed by field emission scanning electron microscopy. The current density–voltage (J–V) and capacitance–voltage (C–V) measurement was studied to understand the electronic quality of material for development of CIT layers for solar cell applications. The current density was found to be increased by two orders of magnitude upon low-temperature heat treatment. The capacitance–voltage measurement showed sharp depletion and accumulation region. The built in potential was found to be ∼ 60 mV and 145 mV in the as-deposited samples, deposited at − 0.7 V and − 0.8 V, respectively, whereas upon heat treatment it shifted to 159 mV and 210 mV. The capacitance of the CIT films was found to be a function of applied bias and increased with increasing the bias voltage. The depletion width of the heat treated sample was found to be ∼ 20 nm and 200 nm for the sample deposited at − 0.7 V and − 0.8 V, respectively. Thus, the sample deposited at − 0.8 V shows optimum electronic properties and is found to be suitable for opto-electronic applications.

CuInTe2 thin films synthesis using one-step electrodeposition process: structural, optical, and electrical characterization

Polycrystalline CuInTe2 (CIT) films were grown onto ITO substrate by one-step electrodeposition technique using acidic aqueous solutions. In this study, the influence of the deposition time on CIT films properties was examined using six techniques, the X-ray diffraction, the scanning electron microscopy, the energy dispersive X-ray analysis, the optical transmittance, the Raman spectroscopy and the electrical properties measurements. The thickness of CuInTe2 films increases as the deposition time increases. The X-ray diffraction investigation of the films deposited during 5 and 10 min shows up only a tetragonal CuInTe2 chalcopyrite structure, with a preferred orientation along [112] direction. However, the films deposited during 15 and 20 min exhibits the CuInTe2 chalcopyrite structure as a main phase with In4Te3 as additional secondary phase. We have noticed a change in the preferred orientation axis of the prepared films as function of deposition time. The films show the direct allowed band gap and their energy band gap decreased from 1.06 to 0.99 eV as the deposition time increased from 5 to 20 min. Hall effect measurements show that the deposition time changes the conductivity type and films carrier concentration. The electrical conductivity is affected by the variation in the carrier mobility rather than by their concentration. The observed Raman modes in the films match well with those reported for single crystal CuInTe2 in the literature. All Raman spectra show the A1 mode at 127 cm−1 confirming the chalcopyrite crystalline quality of these films.

Studies on interface between In2O3 and CuInTe2 thin films

Interface between dc sputtered In2O3 and stepwise flash evaporated CuInTe2 films were studied by probing Si/In2O3/CuInTe2 and Si/CuInTe2/In2O3 structures with the help of glancing angle X-ray diffraction, Rutherford backscattering spectrometry and micro-Raman spectroscopy. The results showed that in Si/In2O3/CuInTe2 structure, a ∼20nm thick interface consisting of In, Cu and O had formed between In2O3 and CuInTe2 and was attributed to the diffusion of Cu from CuInTe2 into In2O3 film. On the other hand, in Si/CuInTe2/In2O3 structure, homogeneity of the underlying CuInTe2 film was found lost completely. An estimate of the masses of the constituent elements showed that the damage was caused by loss of Te from CuInTe2 film during the growth of In2O3 film on Si/CuInTe2.

Illumination-induced changes on the optical functions and valence band splitting parameters of flash evaporated CuInTe2 films

Chalcopyrite CuInTe2 thin films have been deposited by flash evaporation technique on optically flat quartz substrates. The influence of light illumination on the structural and optical properties of CuInTe2 thin films has been reported. The structural properties of the films are investigated by energy dispersive X-ray, grazing incident in-plane X-ray diffraction and transmission electron microscope. The transmittance and reflectance spectra of the films are measured at normal incidence of light, from which, the refractive and absorption indices of the films are determined. The optical absorption process of as-deposited and illuminated CuInTe2 films is found to be characterized by three direct transitions. The triplet transitions are explained in terms of the valence band splitting under the influence of the tetragonal crystalline field and spin-orbit interaction. Below the lowest optical band gap, the absorption coefficient exhibits exponential behavior, in which Urbach's energy of as-deposited and illuminated films is determined as 0.45 and 0.41eV, respectively. Single oscillator and Drude models are employed to determine the optical dispersion parameters for as-deposited and illuminated films.

Characterization of electrochemically deposited CuInTe2 thin films for solar cell applications

CuInTe2 (CIT) thin films have been electrochemically deposited from aqueous electrolyte onto fluorine doped tin oxide (FTO) coated glass substrates. A conventional three-electrode geometry consisting working, counter and reference electrodes was used to perform the electrochemical studies. The deposition potential, −0.75V with respect to Ag/AgCl was optimized by cyclic voltammetry (CV). The as-deposited as well as annealed films were characterized using range of characterization techniques to study the structural, morphological, compositional and optoelectronic properties. Amorphous CIT films have been deposited for all reported potentials, however after heat treatment the polycrystalline films with (112), (220)/(204) and (312)/(116) planes corresponds to tetragonal CIT are observed. After heat treatment the secondary peaks of Indium oxide and Indium telluride with planes (012), (222) and (311) were also observed. Identification of secondary microcrystalline phases and vibration modes of chalcopyrite were studied by using Raman spectroscopy. The most intense line observed in Raman spectra at 123cm−1 is due to the A1 mode, which is generally observed in Raman spectra of I–III–VI2 chalcopyrite structure. Densely packed, adherent and relatively uniform thin films of CIT are deposited for all used growth potentials. The grain size has been improved with heat treatment. Elemental compositional analysis was performed using Energy Dispersive X-ray Analysis (EDAX). Tellurium rich films are deposited for all reported potentials. The final solar cell devices fabricated at optimum deposition potential are tested using solar simulator with 1.5 AM, (100mWcm−2). The cell parameters obtained from J–V characteristics are, Voc=480mV, Jsc=20mA/cm2, FF=43% and η=4.13%. The calculated values of series resistance Rs and Ideality factor A under dark and illuminated conditions are 334/27Ω and 1.43/1.63, respectively.

Electrochemical Growth and Studies of Indium-Rich CuInTe2 Thin Films

CuInTe2 thin films were electrochemically deposited on fluorine-doped tin oxide (<10 Ω/□) coated glass. The electrochemical bath used for the electrodeposition of CuInTe2 thin films consisted of aqueous solution mixture of 0.025 M CuCl2, 0.1 M InCl3 and pre-reacted 0.01M tellurium with HNO3.Linear and cyclic sweep voltammograms were analysed to find out the suitable deposition potentials and growth parameters. Acetronitrile was added as a supporting electrolyte and growth was carried out at the constant deposition potentials of -350 mV and - 450 mV with and without stirring. X-ray diffraction (XRD) results obtained in this work show films that were grown under stirring conditions are more oriented in the (112) direction. CuInTe2 were also analyzed by scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX). SEM study revealed the formation of uniformly covered nanoflakes of 40-50 nanometers in width and compositional analysis show that CuInTe2 film grown had an excess of indium content, but (Cu %+In%):Te% is close to stoichiometry.

Influence of copper to indium atomic ratio on the properties of Cu–In–Te based thin-film solar cells prepared by low-temperature co-evaporation

The influence of copper to indium atomic ratio (Cu/In) on the properties of Cu–In–Te based thin films and solar cells was investigated. The films (Cu/In = 0.38–1.17) were grown on both bare and Mo-coated soda-lime glass substrates at 250 °C by single-step co-evaporation using a molecular beam epitaxy system. Highly (112)-oriented CuInTe2 films were obtained at Cu/In ratios of 0.84–0.99. However, stoichiometric and Cu-rich films showed a poor film structure with high surface roughness. The films consist of polyhedron-shaped grains, which are related to the coexistence of a Cu2−xTe phase, and significant evidence for the coexistence of the Cu2−xTe phase in the stoichiometric and Cu-rich films is presented. KCN treatment was performed for the films in order to remove the Cu2−xTe phase. The stoichiometric CuInTe2 thin films exhibited a high mobility above 50 cm2/V s at room temperature after the KCN treatment. A preliminary solar cell fabricated using a 1.4-μm-thick Cu-poor CuInTe2 thin film (Cu/In = 0.84, Eg = 0.988 eV) yielded a total-area efficiency of 2.10%. The photovoltaic performance of the cell was improved after long-term ambient aging in dark conditions.

High‐Mobility p‐Type Transistor Based on a Spin‐Coated Metal Telluride Semiconductor

A crystalline CuInTe2 film is used as the channel layer in a thin-film field-effect transistor (see figure) yielding field-effect mobilities of over 10 cm2 V–1 s–1, which is approximately an order of magnitude better than previous results for spin-coated p-type systems. A novel three-component hydrazine-based solution is employed to achieve spin coating of the CuInTe2 film.

Electrodeposition of CuInTe2 film from an acidic solution

Copper–indium–telluride films were electrochemically deposited from solutions containing CuCl 2 , InCl 3 , TeO 2 and HCl. Although a flat and smooth film with closely stoichiometric composition was deposited at −660 mV vs. Ag/AgCl at 303 K from a solution of 2.5×10 −4 mol dm −3 CuCl 2 , 1.0×10 −2 mol dm −3 InCl 3 , 5.0×10 −4 mol dm −3 TeO 2 and 0.1 mol dm −3 HCl, a polycrystalline CuInTe 2 film was not obtained. Increasing the temperature from 303 to 363 K allowed the deposition at lower overpotential of a polycrystalline CuInTe 2 film with closely stoichiometric composition and increased indium content. The band gap of the polycrystalline CuInTe 2 film electrodeposited at 363 K at −660 mV was 0.98 eV.

Characterization of CuInTe2 thin film synthesized by three source co-evaporation technique

CuInTe2 films were synthesized by co-evaporating Cu, In and Te from three different elemental sources onto glass substrates. The films were polycrystalline in nature and oriented preferentially in the (112) direction. Lattice constants were determined from the X-ray diffraction analysis. The optical band gap, determined from wavelength dependence of optical transmittance, varied within 0.86–0.98eV with variation of Cu/In ratio within 0.68–1.42. The grain size for CuInTe2 film deposited at optimum substrate temperature (∼770K) was ∼0.5μm. The electrical (dark conductivity, photoconductivity and carrier concentration) and optical properties of the films with different Cu/In and Te/(Cu+In) ratios were studied to ascertain the carrier transport mechanism in the films.

00/00916 The kinetic behaviour of ion transport in WO3 based films produced by sputter and sol-gel deposition: Part I. The simulation model

The CuInTe2 thin films is one of the most attractive semiconductors for solar cells applications, since its direct band gap energy (Eg≈1 eV) is suitable as an absorber in photovoltaic conversion. In this letter the CuInTe2 thin films are prepared by flash evaporation technique. X-ray diffraction measurements on the as-deposited CuInTe2 film showed that these films consist mainly of the chalcopyrite phase. The junction formation in the n-CdS/p-CuInTe2 cell has been investigated using current–voltage (I–V) and capacitance-voltage (C–V) measurements.