Preparation of CuInSe2 thin films by selenization of co-sputtered Cu-In precursors using rapid thermal processing

CuInSe₂ thin films have been synthesized by selenization of co-sputtered Cu-In precursors using rapid thermal processing (RTP). Heat treatments from 400 to 450 °C for periods between 1 min and 10 min were carried out on (Cu-In)/Se precursors. Phase evolution as function of reaction temperature and holding time was analyzed according to XRD and SEM results. Severe Se loss during RTP was proved in our experiments and has been reported by many other researchers. To solve the problem, a new effective way of reducing Se loss was presented, which is based on low temperature heat treatment at 250 °C before high temperature annealing. Nearly single-phase CuInSe₂ thin films have been achieved by annealing precursors at 250 °C for 5 min then 450 °C for 1 min. Se loss can be significantly reduced via low temperature heat treatment by the fact that under 250 °C, Se is evaporated mildly and largely consumed as Cu-Se and In-Se binary selenides.     

CuInSe2 thin films formed by selenization of Cu–In precursors

CuInSe2 (CIS) thin films were grown by selenization of electro-deposited or electroless-deposited Cu–In precursors. Cu–In precursors were formed by layer-by-layer electro-deposition of Cu and In as well as by electroless co-deposition of Cu and In. The major phases in the precursors were found to be Cu11In9 and elemental In. It was found that the stoichiometric CIS phase (CuInSe2) may be formed by selenization of the precursors at temperatures higher than 500°C. The Cu–In precursors as well as CIS films were characterized by X-ray diffraction and scanning electron microscopy. The cubic CIS phase was formed when electroless-deposited Cu–In precursor was selenized, whereas the chalcopyrite CIS or the In-rich phase (CuIn2Se3.5) was formed when the layered precursors were selenized at a high temperature.     

Production of CuInSe2 thin films by a sequential processes of evaporations and selenization

Thin films of copper indium diselenide (CuInSe₂) were prepared by selenization of CuInSe₂-Cu-In multilayered structure on glass substrate. The selenization procedure was carried out in a vapour of elemental selenium in a vacuum chamber. The obtained films were characterised by XRD and SEM measurements. The effects of substrate temperature on the structural, electrical and optical properties were studied. It was found that single phase CuInSe₂ thin films with significant adhesion to substrate can be produced by selenization of CuInSe₂-Cu-In multilayered structure at 450°C, when the first non single phase CuInSe₂ layer was deposited at substrate temperature of 400°C. The thin films were found to be direct band gap semiconductors with a band gap of 0.97 eV.     

Flash-evaporated thin films of CuInSe2

Flash-evaporated technique has been developed for deposition of CuInSe₂ thin films. A control over the stoichiometry and chemical composition of the films has been obtained by varying the deposition parameters. Single phase chalcopyrite structure films with optical gap ∼ 1·15 eV have been obtained. The electronic properties of the films have been tailored for solar cell applications.     

Structural analysis of Ti-Fe thin films prepared by pulsed laser deposition

Titanium iron oxide (Ti-Fe-O) thin films have been successfully deposited by pulsed laser deposition (PLD). Experiments were carried out by using some targets. One was a Ti-50 at.% Fe-sintered target, while the others were Ti and Fe plates with various surface area ratio [S_R=S_Fe/(S_Fe+S_Ti)] from 30 to 70%. The thin films were analyzed by X-ray diffractometry, Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). From XRD analysis, the main phase in the thin films deposited at S_R=30 and 50% was β-Ti (Fe). By increasing S_R to 70%, the main phase of the thin film changed to TiFe. By phase diagram, composition of TiFe must be between Ti-47.5-50.3 at.% Fe at a temperature of 1085 °C. However, the composition of the thin film deposited at S_R=70% was found to be Ti_0.15Fe_0.62O_0.23. Thus, the composition of Fe in the thin film was much greater than the solubility limit. This fact suggests two possibilities. One is that the thin films, which we have deposited, were in a metastable state. The other is that metal oxides of amorphous state could be contained in the thin film.     

Cu-In多层膜后硒化法制备CuInSe2多晶薄膜及性能的研究

CuInSe2是优异的薄膜太阳能电池吸收层材料.本文在玻璃衬底上真空蒸镀Cu-In多层膜后,硒化制得了CuInSea多晶薄膜.通过SEM和XRD微观形貌结构分析发现,薄膜的晶粒分布比较均匀,在相同的实验条件下,元素原子比在化学计量比的附近能够获得比较大的晶粒.测量了薄膜的厚度和方块电阻,并由此计算了薄膜的电阻率,发现了薄膜的电阻率随着Se含量的增加呈增大趋势.对薄膜的光透过率测量显示,在可见光的范围内,1.8 μm厚的薄膜的光透过率小于0.7%.XRD物相分析显示,元素比例在化学计量比(CuInSe=112)附近能够制得单一相的CuInSe2多晶薄膜.     

基底温度对四元叠层硒化法制备铜铟镓硒(CIGS)薄膜的影响

利用四元叠层硒化法制备了铜铟镓硒(缩写为CIGS)薄膜,重点分析了在叠层法制备CIGS薄膜过程中,基底温度对CIGS薄膜的晶体结构,表面形貌以及各种元素沿深度分布的影响.实验结果表明,在叠层法制备CIGS薄膜时,发现在550℃的基底温度时,不经过退火便可以生成CIGS晶体,表面Ga的含量处于比较合适的范围.而基底温度为500℃,450℃时,只能生成铜铟硒(CIS)晶体,Ga元素表面的含量较少,主要分布在薄膜底部.     

Electrical and optical properties of thin p-type films prepared by vacuum evaporation from the chalcopyrite CuInSe2

The electrical and optical properties of thin films prepared by vacuum evaporation from the chalcopyrite CuInSe₂ are discussed in relation to their structure and deposition parameters. It is shown that p-type films may contain CuSe or Cu_{2 ? x}Se as a second phase and that the presence of Cu_{2 ? x}Se is particularly difficult to identify by X-ray diffraction.     

Some physical properties of CuInSe2 thin films

Semiconducting thin films of CuInSe₂ have been grown by thermal annealing in air of evaporated layers of Cu, In and Se on glass substrates. The structure of the films has been studied using the X-ray diffraction (XRD). The films were polycrystalline and showed mixture phases (binary and ternary) depending on the annealing temperature. The electrical properties revealed resistivity range of 10¹–10⁴Ωcm, respectively. The resistivity influenced with the annealing temperature and decreased with increasing temperature. The films have been analyzed for optical band gap.     

Growth and characterization of CuInSe2 thin films

Films of CulnSe₂ have been grown using a technique similar to close-spaced vapour transport. The effect of substrate temperature and the distance of the substrate from the source have been optimised to grow well-oriented chalcopyrite phase of CuInSe₂. D.c. conductivity and Hall coefficient studies have been made in the temperature range 77–300 K. The films grown at a substrate temperature of 350 °C have an electron mobility of 3.4×10³ cm²V^–1 s^–1 at 77 K.     

Study of trap levels by electrical techniques in p-type CuInSe2 thin films prepared using chemical bath deposition

CuInSe₂ thin films, prepared using the Chemical Bath Deposition (CBD) technique, were analysed using Thermally Stimulated Current (TSC) measurements in order to get a clear picture of the different trap levels present in it. As-prepared samples showed two trap levels: the prominent one was due to the presence of a Se vacancy, while the weak one was due to the presence of a Cu vacancy. After annealing in air, the Se vacancy disappeared and a new level appeared which is suspected to be due to adsorbed oxygen. But annealing in air does not affect the Cu vacancy. On the other hand, annealing in vacuum does not affect Se vacancy, but the presence of an Fe impurity was detected in this case. A possible explanation for this phenomenon is also discussed. The dark conductivity measurements were also conducted on as-prepared as well as annealed CuInSe₂ samples. These results are found to be in good agreement with the results obtained from TSC measurements.     

Structural and optical properties of the Cu2ZnSnSe4 thin films grown by nano-ink coating and selenization

Quaternary semiconductor Cu₂ZnSnSe₄ (CZTSe) is a very promising alternative to semiconductors based on indium (In) and gallium (Ga) as solar absorber material due to its direct band gap, inherent high absorption coefficient (>10⁴ cm^?1) and abundance of cheap elements zinc (Zn) and tin (Sn). In this study, high quality CZTSe thin films were successfully synthesized by a green and low-cost solution based non-vacuum method, which involves spin coating non-toxic solvent-based CZTSe nano-inks onto Mo coated soda lime glass substrates followed by selenization with elemental Se vapor. The effect of selenization temperature on structural, morphological, compositional and optical properties of CZTSe films are investigated using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and photoluminescence spectroscopy. XRD and Raman analysis indicates that a tetragonal stannite-type structured CZTSe is formed. Depend on the selenization temperature, the dense and compact films with grain sizes from 200 nm (500 °C) up to about 1 μm (580 °C) are obtained. EDS measurement indicates that the composition ratios of the prepared CZTSe films are copper-poor and zinc-rich nature. The CZTSe films are p-type conductivity confirmed by a hot point probe method. Photoluminescence spectrum shows slightly asymmetric narrow bands with a maximum of intensity at 0.92 eV. The dependence of the photoluminescence on the excitation temperature reveals a decrease in the intensity of the photoluminescence bands. An absorption coefficient exceeding 10⁴ cm^?1 and the band gap energy about 0.87 eV of the studied films are determined by an absorption spectroscopy.     

Preparation and characterization of flash-evaporated CuInSe2 thin films

Thin films of CuInSe₂ have been evaporated onto glass substrates by flash evaporation. The as-deposited films are amorphous and annealing in selenium atmosphere produces polycrystalline films. The films were characterized bytem and x-ray diffraction techniques. The optical absorption of the films shows three energy gaps of 1·03, 1·07 and 1·22 eV. The crystal field and spin-orbit splitting are thus found to be 0·04 eV and 0·16 eV respectively. The percentaged-character of the valence band states is ∼35%. The Arrhenius plot of electrical conductivity of films showed impurity ionization ofE _A = 75 meV.     

Formation of CuInSe2 by the selenization of sputtered Cu/In layers

Single layers of Cu and In were deposited onto Mo coated glass substrates by radio frequency sputtering. The Cu11In9 phase has been found to be the majority phase in these precursors. The selenization of the sputtered layers has been achieved by depositing a 1 μm Se layer onto the precursor by thermal evaporation followed by an annealing in vacuum. Samples were annealed at different temperatures varying between 100–600°C at intervals of 50°C. The chalcopyrite structured ternary phase of CuInSe2 with a significant amount of preferential orientation in the (112) direction was obtained in samples annealed at 400°C or above. Morphological, compositional and structural analyses of the samples annealed at different temperatures were performed using a variety of complementary techniques. The results were analysed to explain the growth of CuInSe2 on the selenization of sputtered Cu-In precursors. The occurrence of various binary phases of Cu-In, Cu-Se and In-Se in different annealing temperature ranges has also been investigated. The phenomenon of volume expansion in CuInSe2 on selenization has been found to manifest itself as a shift in the characteristic (110) X-ray diffraction peak of Mo. This revised version was published online in November 2006 with corrections to the Cover Date.     

CuInSe2 thin films by d.c. and pulse-plated electrodeposition

CuInSe₂ thin films were prepared by electrodeposition from aqueous solution, containing CuSO₄, InCl₃ and SeO₂ under d.c. step pulse-voltage on d.c., and pulse-plating conditions. The films were characterized by scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. The influence of deposition technique on film composition, morphology and structure were studied. Heat treatment of pulse-plated films under vacuum resulted in the formation of CuInSe₂ with single-phase chalcopyrite structure.