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Amorphous indium oxide (In2O3) and 10-wt% SnO2 doped In2O3 (ITO) thin films were prepared by pulsed-laser deposition. These films were crystallized upon heating in vacuum at an effective heating rate of 0.00847 °C/s, while the evolution of the structure was observed by in situ X-ray diffraction measurements. Fast crystallization of the films is observed in the temperature ranges 165–210 °C and 185–230 °C for the In2O3 and ITO films, respectively. The crystallization kinetics is described by a reaction equation, with activation energies of 2.31 ± 0.06 eV and 2.41 eV and order of reactions of 0.75 ± 0.07 and 0.75 for the In2O3 and ITO films, respectively. The structures of the films observed here during heating are compared with those obtained upon film growth at different temperatures. The resistivity of the films depends on the evolution of the structure, the oxygen content and the activation of tin dopants in the films. A low resistivity of 5.5 × 10−4 Ω cm was obtained for the In2O3 and ITO films at room temperature, after annealing to 250 °C the resistivity of the ITO film reduces to 1.2 × 10−4 Ω cm.

The crystallization process of indium oxide thin films deposited by pulsed laser deposition was studied. X-ray diffraction was performed on amorphous films during real-time in situ annealing in vacuum at temperatures between 100 and 300 °C and a heating rate of 0.00847 °C/s. A fast crystallization was observed in the temperature range 165–210 °C. The crystallization kinetics obtained from the reaction equation shows activation energy of 2.31 eV, reaction order of 0.75 and reaction rate factor of 8.5 × 10 22 Hz. The structures of the in situ annealed films were compared with that of the films grown at different temperatures. The resistivity of the films is related to the structure, oxygen pressure and growth temperature. A low resistivity of 3.5 × 10 − 4 Ω cm, which increased with increasing temperature and oxygen pressure, was obtained at 100 °C and 2 Pa. The increase in the resistivity was due to a depletion of oxygen vacancies. The optical refractive index of the films decreases with changes in the deposition conditions, with an average value being 2.04.

The properties of indium tin oxide (ITO) thin films, deposited at room temperature by simultaneous pulsed laser deposition (PLD), and laser irradiation of the substrate are reported. The films were fabricated from different Sn-doped In2O3 pellets at an oxygen pressure of 10 mTorr. During growth, a laser beam with an energy density of 0, 40 or 70 mJ/cm2 was directed at the middle part of the substrate, covering an area of ∼1 cm2. The non-irradiated (0 mJ/cm2) films were amorphous; films irradiated with 40 mJ/cm2 exhibited microcrystalline phases; and polycrystalline ITO films with a strong 〈111〉> preferred orientation was obtained for a laser irradiation density of 70 mJ/cm2. The resistivity, carrier density, and Hall mobility of the ITO films were strongly dependent on the Sn doping concentration and the laser irradiation energy density. The smallest resistivity of ∼1×10-4 Ω cm was achieved for a 5 wt % Sn doped ITO films grown with a substrate irradiation energy density of 70 mJ/cm2. The carrier mobility diminished with increasing Sn doping concentration. Theoretical models show that the decrease in mobility with increasing Sn concentration is due to the scattering of electrons in the films by ionized centers.

The dependence of structural properties and surface morphology of Cu–In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu–In/In/Glass). This permitted the fabrication of a homogeneous Cu–In alloy layer, which was not possible through the simple co-sputtering.

The atmospheric pressure CSS method has been developed as a reproducible and efficient process. Thin film CdTe grown under atmospheric pressure has a rough surface morphology. The density of carbon black powder in the graphite carbon paste for screen printing is a key factor in reducing the series resistance of the device with rough surface CdTe. Using graphite carbon paste with 7 wt% carbon black powder has resulted in cells with a relatively low back contact resistance. A highly efficient large-area CdS/CdTe solar cell (11.0%, 5327 cm2) sub-module has been fabricated using the new technique.

Indium tin oxide (ITO) thin films 60–100 nm thick have been grown on SiO 2 glass by laser irradiation of the substrate during pulsed laser deposition. A laser beam with an energy density of 0.07 J cm −2 (size ∼1 cm 2 ) was directed on to the middle part of the substrates during film growths. Films were deposited from a 95 wt% In 2 O 3 –5 wt% SnO 2 sintered ceramic target at a room temperature and oxygen pressures ( P O 2 ) ranging from 0.13 to 5.99 Pa. The structural, electrical, and optical properties of the laser-irradiated and the nonirradiated parts of the films were studied as a function of P O 2 . Crystalline ITO films with 〈1 1 1〉 preferred orientation were observed at all P O 2 , except 0.13 Pa. Under P O 2 around 1.33 Pa, minimal resistivities of 1.2×10 −4 and 2.3×10 −4 Ω cm were obtained on the laser irradiated and the nonirradiated parts of the deposited films. The observed low resistivity for the laser-irradiated part of the films was a consequence of both the high carrier concentration and Hall mobility of the films. High optical transmittance (>85%) to visible light was obtained.

The relation between electrical and structural properties of indium tin oxide (ITO) films prepared by pulsed laser deposition with and without in situ laser irradiation is examined. The residual stresses of the films were estimated from x-ray diffraction patterns measured by grazing-incidence asymmetric Bragg and grazing-incidence x-ray diffraction geometries. For the films prepared without in situ irradiation, the residual stress depended on oxygen pressure (PO2) during deposition and had minimum around PO2 of 1.3 Pa, which coincided with the optimum PO2 for growing the lowest resistivity films. The resistivity was only slightly improved with an increase of substrate temperature (Ts) because a large residual stress was introduced. In contrast, the ITO films prepared with in situ laser irradiation showed very low resistivity (ρ

The electrical and optical properties of pulsed laser deposited amorphous indium tin oxide films at room temperature are discussed. The films were grown from indium oxide (In 2 O 3 ) targets of different tin (Sn) doping content (0, 5 and 10 wt%) at different oxygen pressures ( P O 2 ) ranging from 1×10 −3 to 5×10 −2 Torr. The electrical and optical properties of the films were examined by Hall measurements and optical spectrophotometry. It was found that high conductivity amorphous films could be prepared at room temperature irrespective of the Sn doping content. The properties of these films deposited from 0, 5, 10 wt% Sn-doped In 2 O 3 targets show a similar response to changes in P O 2 . The maximal conductivity of (4.0, 2.1 and 1.8)×10 3 S/cm and optical transmittance (visible) higher than 90% were obtained at P O 2 region of (1–1.5)×10 −2 Torr. An undoped In 2 O 3 film produced the highest conductivity of 4×10 3 S/cm in these studies.

High quality indium tin oxide (ITO) films of thickness 80±20 nm grown by laser irradiation of the glass substrates during pulsed laser deposition are reported. Films were deposited from a 5 wt.% SnO 2 -doped In 2 O 3 target at substrate temperatures ( T s ) ranging from room temperature (RT) to 400°C and oxygen pressure (PO 2 ) of 1.3 Pa. The energy of the laser beam focused unto the middle of the glass substrate during coatings was about 70 mJ cm −2 . The structural, electrical and optical properties of the laser-irradiated and the nonirradiated parts of the ITO films were studied as a function of T s . Crystalline films with 〈1 1 1〉 preferred orientation and crystal sizes⪢200 nm were obtained at all T s . At RT, the resistivity of the laser-irradiated part of one film was 1.2×10 −4 Ω cm compared with 2.3×10 −4 Ω cm for a nonirradiated part. At 300°C, a low resistivity value of 8.5×10 −5 Ω cm was achieved for both the laser-irradiated and the nonirradiated parts of the ITO film. The achievement of low resistivity resulted from the high carrier concentration ∼1.2×10 21 cm −3 and the high Hall mobility (40–57) cm 2 V −1 s −1 . The films also exhibited high optical transmittance (∼90%) to visible light.

The effects of stress in pulsed laser deposited (PLD) indium-tin-oxide (ITO) films formed on glass substrate at 200 °C and oxygen pressures (Po2) ranging from 0.1 to 2.7 Pa are discussed. Grazing incidence X-ray diffraction (GIXRD) investigations of the ITO films show splitting of the diffraction peaks and significant changes in the lattice constants for films deposited at low Po2 and when the thickness of the films is larger than 150 nm. These features were due to intrinsic stress caused by the incidence of energetic particles on the substrate during growth. The splitting of the peaks only occurred in the bulk of the films, while near the surface, single peaks were evidenced, indicating the existence of two layers. No apparent splitting of the diffraction peaks or shifts in peak positions occurred in the ITO layers with thickness less than 100 nm. In spite of the presence of stress in the ITO films, resistivity less than 3 10, -4 Ωcm was obtained. © 2001 Kluwer Academic Publishers

Pure indium oxide (In2O3) and SnO2-doped In2O3 (5 and 10 wt %) films were deposited on glass at different substrate temperatures (Ts) ranging from room temperature (RT=25 °C) to 350 °C using pulsed laser deposition. At low Ts (RT to 100 °C), pure In2O3 films yielded the lowest resistivity of (1.8–2.5)×10−4 Ω cm and the resistivity increased sharply with an increase in Ts, and the rise in the resistivity of pure In2O3 films resulted mainly from a decrease in carrier concentration and Hall mobility. For SnO2-doped In2O3 films, the resistivity decreased from 3.5×10−4 to 1.3×10−4 Ω cm with increasing Ts from RT to 350 °C and the reduction in the resistivity is associated with thermal activation of Sn leading to an increase in carrier concentration. Amorphous films were obtained at RT, but from Ts of 100 °C, the films appeared polycrystalline with orientation in the 〈111〉 plane. From atomic force microscopy, minimum surface roughness (Ra)⩽1.3 nm was obtained at RT and Ts>200 °C. Between 100 and 150 °C, Ra was maximum (2.5–4.9 nm). The films also exhibited high optical transmittance (>85%) to visible light.

Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO2 glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In2O3-10 wt.% SnO2 sintered ceramic target. The growths of ITO films under different oxygen pressures (PO2) ranging from 1×10 −4 –5×10 −2 Torr at low substrate temperatures (Ts) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the PO2 during the film deposition. Under a PO2 of 1×10 −2 Torr, ITO films with low resistivity of 5.35×10 −4 and 1.75×10 −4 Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal PO2 region of 1×10 −2 to 1.5×10 −2 Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at P o 2 ≥1×10 −2 Torr and it was significantly reduced as the PO2 decreases.

The formation of CuIn(S,Se)2 thin films by thermal diffusion of sulfur (S) and selenium (Se) vapours into co-sputtered Cu–In alloy within a closed-space graphite container is reported. All films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Four-point-probe and hot-probe measurements. Cu–In alloy films with composition varying from Cu-rich to In-rich were deposited. The synthesized In-rich films yielded CuIn5(S,Se)8 spinel compound which gradually transformed into a single phase CuIn(S,Se)2 as the film composition approached the Cu-rich region. The morphology of the CuIn5(S,Se)8 was found to differ from the stoichiometric and Cu-rich CuIn(S,Se)2 as observed from SEM. EDX composition analysis of the films showed a Cu/In ratio varying from 0.36 to 1.54 and a (S+Se)/(Cu+In) varying from 0.97 to 1.32. The amount of S incorporated in the films was found to differ with changes in the composition. The resistivity of the films ranged between 10−1 and 107 Ω cm and it strongly followed the change in the alloy film composition.

The crystallization of CuInSe 2 thin films by high Se vapour selenization of co-sputtered Cu-In alloy precursor within a partially closed graphite container is reported. X-ray diffusion (XRD) analysis of the Cu-In alloy films displayed mainly the CuIn 2 and Cu 11 In 9 phases. A three-fold volume expansion was recorded in all the selenized CuInSe 2 films at 500–550°C. Large and densely packed crystals with sizes of about 5 μm were exhibited by the films irrespective of whether they were Cu-rich or In-rich. Single phase chalcopyrite CuInSe 2 structure with preferential orientation in the (112) direction were obtained. Films with a wide range of compositions (Cu/In of 0.43–1.2 and Se/(Cu+In) of 0.92–1.47) were fabricated. All the films where Se rich, with the exception of samples with very high Cu content. The measured film resistivities varied from 10 −1 to 10 5 Ω-cm in consistence with the increasing Cu content of the alloy precursor during deposition. The alloy films with very high In content yielded the CuIn 2 Se 3.5 or CuIn 3 Se 5 compound as determined from XRD and EDX analyses. A study of the reaction mechanism performed between 250 and 550°C indicated that the crystal growth was assisted by the formation of the CuSe flux agent. The development of a suitable window layer to test the photovoltaic properties of these films is currently in progress.

This paper discusses the viability and readiness of the photovoltaics (PV) market in Nigeria. An opportunity for decentralized sources like PV has been opened up by the finding that it is currently impractical for the centralized grid to meet all of Nigeria's rural electricity demand. PV is identified as the most economical decentralized source to contribute to rural development. The current low level of PV utilisation in the country has been identified as being chiefly due to lack of awareness among potential buyers and energy planners of its large-scale applicability. With increasing awareness, some industrialist and government agencies (as well as some wealthy individuals) have now installed PV systems for home-lighting, water-pumping, and rural electrification, etc. This paper reviews this activity and also suggests some other new uses. Generally the PV installations have been found to be successful, and so PV markets have been springing up to meet the demand. The role the government could play in fully introducing and harnessing PV technology is also discussed in this paper.

Sputtering technique for Cu–In precursor films fabrication using different Cu and In layer sequences have been widely investigated for CuInSe 2 production. But the CuInSe 2 films fabricated from these precursors using H 2 Se or Se vapour selenization mostly exhibited poor microstructural properties. The co-sputtering technique for producing Cu–In alloy films and selenization within a close-spaced graphite box resulting in quality CuInSe 2 films was developed. All films were analysed using SEM, EDX, XRD and four-point probe measurements. Alloy films with a broad range of compositions were fabricated and XRD showed mainly In, CuIn 2 and Cu 11 In 9 phases which were found to vary in intensities as the composition changes. Different morphological properties were displayed as the alloy composition changes. The selenized CuInSe 2 films exhibited different microstructural properties. Very In-rich films yielded the ODC compound with small crystal sizes whilst slightly In-rich or Cu-rich alloys yielded single phase CuInSe 2 films with dense crystals and sizes of about 5 μm. Film resistivities varied from 10 −2 –10 8 Ω cm. The films had compositions with Cu/In of 0.40–2.3 and Se/(Cu+In) of 0.74–1.35. All CuInSe 2 films with the exception of very Cu-rich ones contained high amount of Se (>50%).

CuInSe2 thin films have been prepared by high Se vapor selenization of co-sputtered Cu–In alloy precursors within a partially closed graphite container. Cu–In alloys with different compositions were investigated. X-ray diffraction (XRD) analysis of the films showed mainly CuIn2 and Cu11In9 phases and the Cu11In9 peak intensity was found to increase as the alloy composition tended towards Cu-rich. A linear dependence of the alloy composition on the Cu/In deposition power was observed from energy dispersive analysis by X-rays (EDX). A three-fold volume expansion was exhibited by all the CuInSe2 films after selenization at 500–550 °C. Scanning electron microscopy (SEM) analysis of the films showed large and densely packed crystal structures with sizes above 5 μm. The CuInSe2 films exhibited single phase chalcopyrite structure with preferential orientation in the (1 1 2) direction. The EDX composition analyses of the films showed Cu/In ratio ranging from 0.43 to 1.2, and Se/(Cu+In) ratios from 0.92 to 1.47. The measured film resistivities varied from 10-1 to 105 Ωcm. The Cu–In alloy precursors with Cu/In ratio less than 0.70 were found to form CuIn3Se5 a defect chalcopyrite compound. All films were Se rich, with the exception of samples with very high Cu content.© 1998 Kluwer Academic Publishers

Various techniques have been used to produce CuInSe2 but the problem of producing films with the desired properties for efficient device fabrication over large areas has always persisted. The Stacked Elemental Layer (SEL) technique has been demonstrated as a method for producing films over a large area, but the films normally annealed in vacuum or in Se ambient, mostly exhibited poor morphology with small grain sizes which result in poor devices. A method of synthesizing CuInSe2 films by annealing or selenization of the Cu, In and Se elemental layers using a closed graphite box was developed. SEM, EDX, XRD, spectrophotometric and Hall measurements were used to characterize all annealed films. Results have shown single phase chalcopyrite films with improved crystal sizes of about 4 μm The film composition varied from Cu-rich to In-rich with electrical resistivities of 10−3 to 104 Ωcm, cattier concentrations of 5 × 1015 to 1017 cm−3 and mobilities of 0.6 to 7.8 cm2 V−1 s−1 An energy band gap of 0.99 eV and 1.02 eV was obtained for a Cu-rich and near stoichiometric In-rich films respectively. Heterojunction devices using the structure ZnO/CdS/CuInSe2 were fabricated with electrical conversion efficiencies of 6.5%.

The formation of CuInSe2 thin films from CuInSe stacked elemental layers was performed to evaluate the reaction mechanism involved using the Stacked Elemental Layers (SEL) technique. The nature of the deposited single layer of Cu, In and Se, and the reactions involved in the binary compounds of CuSe, InSe, and CuIn after annealing at different temperatures was used to provide evidence for the formation of CuInSe2 from the ternary compound of CuInSe using XRD, EDX and SEM. Studies of the time progressive reaction at a temperature of 450°C showed that CuInSe2 formation starts immediately and a single phase chalcopyrite film was formed after a reaction time of less than 60s. By varying the temperature for a constant annealing time of 60 s, the formation of CuInSe2 was seen to begin at 200°C with a film orientation in the 112 plane. An exothermic reaction was found to take place in the films at this temperature due to the reaction of β-In2Se3 with liquid Se, resulting in a large amount of Se loss from the film. This is the cause of the film delamination which has been a major problem identified in SEL films produced from multistack structures. Film delamination was eliminated by using an alternative processing method involving annealing the initial stack at low temperature of about 200°C before deposition of the next stacks, followed by a final annealing at a higher temperature of 450°C. This initial annealing is important in order to suppress the energetic reaction species and to form thermodynamically stable β-In2Se3 and Cu2Se before forming a homogeneous layer of CuInSe2 suitable for device fabrication.

Low-resistivity (ρ) and highly transparent pure indium oxide (In2O3) thin films grown on glass substrates by pulsed laser deposition at substrate temperature (Ts) between room temperature and 200 °C are reported. As-deposited films with resistivity (ρ) of ∼3×10−4 Ω cm and transmittance (visible), above 87% were obtained within a narrow range of PO2 (1×10−2–1.5×10−2 Torr). Hall effect measurements showed that the low ρ resulted from the high carrier concentration (n)∼7×1020 cm−3, whereas modest Hall mobility (μ

The stacked elemental layer (SEL) technique has been demonstrated as a method for producing films over a large area, but the films normally annealed in vacuum, mostly exhibited poor morphology with small grain sizes

Crystalline tin (Sn)-doped indium oxide (ITO) films grown at room temperature (RT) using pulsed laser deposition (PLD) coupled with laser irradiation of the growing films are discussed. The energy of the laser irradiation beam was ∼0.07 J·cm-2. The films were deposited from Sn-doped (0–10 wt%) In2O3 targets under oxygen pressure (P O2 ) of 10-2 Torr. At RT, the laser-irradiated and nonirradiated portions of the films yielded resistivities of ∼1.2×10-4 and ∼2.5×10-4 Ω·cm, respectively. At 200°C, a resistivity of 8.9×10-5 Ω·cm was observed for the laser-irradiated part of the ITO films.

Low-resistivity indium–tin–oxide (ITO) films (8.9×10−5–2.3×10−4 Ω cm), 80±20 nm thick grown by combining pulsed laser deposition and laser irradiation of the substrate were studied in relation to tin (Sn) doping content. Films with Sn doping content over the range 0–10 wt % were deposited at room temperature (RT) and 200 °C at a fixed oxygen pressure of 1×10−2 Torr. The laser beam with energy density of 70 mJ/cm2 was directed at the middle portion of the substrate during growth. At RT, the laser-irradiated and nonirradiated parts of the films exhibited crystalline and amorphous phase, respectively. The amorphous films indicated a steady resistivity, carrier concentration, and Hall mobility of ∼2.4×10−4 Ω cm, 8×1020 cm−3, and ∼32 cm2/V s, respectively, and showed no significant change over 0–10 wt % Sn doping content. The crystalline films deposited at RT by laser irradiation and 200 °C indicated a strong dependence of the resistivity, carrier concentration, and Hall mobility on Sn doping content over the ...

Indium tin oxide (ITO) thin films were grown on SiO2 glass and silicon (Si) substrates from a 95 wt% In2O3–5 wt% SnO2 sintered ceramic target by pulsed laser deposition (PLD). The films were deposited under different oxygen pressures (P o2) of 5×10-3 to 5×10-2 Torr at room temperature (RT) and 200°C. P o2 was found to have a critical influence on the optical and the electrical properties of the ITO films. Under a P o2 of 1×10-2 Torr, ITO films with resistivity as low as 4.5×10-4 and 1.8×10-4 Ωcm were obtained on glass at RT and 200°C, respectively. Moreover, by increasing the substrate temperature (T s) to 350°C, the resistivity was further reduced to 1.3×10-4 Ωcm. Optical transmittance in visible light greater than 85% was attained in all the films deposited under P o2 above 5× 10-3 Torr. However, a reduction in the transmittance to less than 80% was observed as P o2 decreased. The films deposited at RT were amorphous, whereas those produced at 200°C were polycrystalline.

Cu–In alloy films were prepared on bare or Mo-coated glass by co-sputtering from Cu and In targets at ambient temperature. The formation of CuInS2 films was accomplished by sulfurization within a graphite container under high S vapor pressure. X-ray diffraction (XRD) analysis of the alloy films showed predominant variation of the phases from In→CuIn2→Cu11In9 as the Cu content in the films increased. The sulfurized In-rich films formed the CuIn5S8 phase that steadily transformed into CuInS2 as film composition changed toward the Cu-rich region. SEM analysis showed different morphologies for the CuIn5S8 and CuInS2 films. Cu-rich films exhibited very dense crystal structures. EDX composition measurements on the films showed Cu/(Cu+In) varying from 0.21 to 0.64 and S/(Cu+In) from 0.80 to 1.36. Resistivities in the range of 2.36 to 1.7×108 Ω·cm were obtained. Studies of the growth mechanism indicated formation of CuIn5S8 as the main secondary phase in both Cu-rich and In-rich films at low temperatures before conversion into CuInS2 at temperatures >400°C.

Properties of indium-tin-oxide (ITO) thin films grown on glass and silicon (Si) substrates from a 95 wt% In 2 O 3 –5 wt% SnO 2 sintered ceramic target by pulsed laser deposition (PLD) are compared and discussed. Depositions were performed under different oxygen pressures (PO 2 ) ranging from 0.1–6.7 Pa and substrate temperature ( T s ) from room temperature (RT) to 350°C range. PO 2 was found to affect the properties of the ITO films. At RT under a PO 2 of 1.3 Pa, the resistivity of 4.5×10 −4 and of 4.8×10 −4 Ω cm were obtained on glass and Si substrates, respectively, while at 200°C, the respective resistivity was reduced to 1.7×10 −4 and 1.6×10 −4 Ω cm on glass and Si. No significant difference in the resistivity was observed in the films deposited on both substrates. High carrier density (∼10 21 cm −3 ) and Hall mobility (∼33 cm 2 V −1 s −1 ) were obtained at PO 2 of 0.7–1.3 Pa at RT and 200°C. For PO 2 >0.7 Pa, optical transmittance (visible light) above 80% was displayed by the films deposited on glass. XRD showed that at low T s T s ⩾150°C, crystalline films were obtained on both substrates.