Properties of ITO–AZO bilayer thin films prepared by magnetron sputtering for applications in thin-film silicon solar cells

In this paper we study the electro-optical behavior and the application of indium–tin oxide (ITO) and aluminum-doped zinc oxide (AZO) bilayer thin films for silicon solar cells. ITO–AZO bilayer thin films were deposited on glass substrates using radio-frequency magnetron sputtering. The experimental results show that a decrease in the electrical resistivity of the ITO–AZO bilayer thin films has been achieved without significant degradation of optical properties. In the best case the resistivity of the bilayer films reached a minimum of 5.075×10^?4 Ω?cm when the thickness of the AZO buffer layer was 12 nm. The ITO–AZO bilayer films were applied as the front electrodes of amorphous silicon solar cells and the short-circuit current density of the solar cells was considerably increased.     

Electrical and optical properties of ITO and ITO/Cr-doped ITO films

In this paper we report on the effects of the insertion of Cr atoms on the electrical and optical properties of indium tin oxide (ITO) films to be used as electrodes in spin-polarized light-emitting devices. ITO films and ITO(80 nm)/Cr-doped ITO(20 nm) bilayers and Cr-doped ITO films with a thickness of 20 nm were grown by pulsed ArF excimer laser deposition. The optical, structural, morphological and electrical properties of ITO films and ITO/Cr-doped structures were characterized by UV–Visible transmission and reflection spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Hall-effect analysis. For the different investigations, the samples were deposited on different substrates like silica and carbon coated Cu grids. ITO films with a thickness of 100 nm, a resistivity as low as ～4×10^?4 Ω?cm, an energy gap of ～4.3 eV and an atomic scale roughness were deposited at room temperature without any post-deposition process. The insertion of Cr into the ITO matrix in the upper 20 nm of the ITO matrix induced variations in the physical properties of the structure like an increase of average roughness (～0.4–0.5 nm) and resistivity (up to ～8×10^?4 Ω?cm). These variations were correlated to the microstructure of the Cr-doped ITO films with particular attention to the upper 20 nm.     

Influence of germanium incorporation on the structural and electrical properties of boron-doped ultrathin poly-Si1−x Ge x films deposited by chemical vapour deposition

A few properties of polycrystalline silicon germanium (poly-Si_1?x Ge _x ) films can be tailored by modulating the germanium incorporation. In this paper, the structural, mechanical and electrical properties of heavily doped ultrathin (~100 nm) poly-Si_1?x Ge _x films (0.84 ≤ x ≤ 0.88) fabricated by low-pressure chemical vapour deposition were investigated. For a boron concentration of ~2.2 × 10²¹ atoms/cm³, a slight increase of germanium fraction significantly enhances the deposition rate, crystallinity and Hall mobility while having negligible influence on the Young’s modulus and hardness. The grain size increases from ~6 to ~12 nm while the grain structure becomes more columnar. In addition, the resistivity decreases from 7.4 to 1.1 m Ω cm with a corresponding increase in the Hall mobility from ~0.9 to ~4.2 cm² V^?1 s^?1. However, the Young’s modulus (~101 GPa) and hardness (~8.8 GPa) are virtually unaffected within the range of germanium fraction explored. In practice, poly-SiGe layer having low resistivity, high modulus, high mobility and low surface roughness can be successfully applied for resonators, biosensors and nanoswitches among others.     

Effects of hydrogen flow on properties of hydrogen doped ZnO thin films prepared by RF magnetron sputtering

The hydrogen doped ZnO (ZnO:H) thin films were deposited on quartz glass substrates by radio frequency magnetron sputtering. The doping characteristics of ZnO:H thin films with varied hydrogen flow ratio were investigated. At low hydrogen flow ratio (H₂/(H₂+Ar)≤0.02), the ZnO:H thin films exhibited dominant (002) peaks from X-ray diffraction and the lattice constants became smaller. The particles were mainly a columnar structure. The particles’ size became smaller, and the island-like structure appeared on the thin films surface. In addition, the low resistivity properties of ZnO:H thin films was ascribed to the increase of the carriers concentration and carriers mobility; When the hydrogen flow ratio was more than 0.02 (M≥0.02), two absorption bands at 1400–1800 cm^?1 and 3200–3900 cm^?1 were observed from the FT-IR spectra, which indicated that the ZnO:H thin films had typical Zn–H bonding, O–H bonding (hydroxyl), and Zn–H–O bonding (like-hydroxyl). The scanning electron microscope (SEM) results show that a large number of hydroxyl agglomeration formed an island-like structure on the thin films surface. The absorption peak at about 575 cm^?1 in the Raman spectra indicated that oxygen vacancies (V_O) defects were produced in the process of high hydrogen doping. In this condition, the low resistivity properties of ZnO:H thin films were mainly due to the increasing electron concentration resulted from V_O. Meanwhile, the Raman absorption peaks at approximately 98 cm^?1 and 436 cm^?1 became weaker, and the (002) XRD diffraction peak quenched and the lattice constants increased, which shows that the ZnO:H thin films no longer presented a typical ZnO hexagonal wurtzite structure. With the increasing of hydrogen flow ratio, the optical transmittance of ZnO:H thin films in the ultraviolet band show a clear Burstein–Moss shift effect, which further explained that electron concentration was increased due to the increasing V_O with high hydrogen doping concentration. Moreover, the optical reflectance of the thin films decreased, indicating the higher roughness of the films surface. It was noteworthy that etching effect of H plasma was obvious in the process of heavy hydrogen doping.     

Electrical properties of Sb-doped epitaxial SnO2 thin films prepared using excimer-laser-assisted metal–organic deposition

Excimer-laser-assisted metal–organic deposition (ELAMOD) was used to prepare Sb-doped epitaxial (001) SnO₂ thin films on (001) TiO₂ substrates at room temperature. The effects of laser fluence, the number of shots with the laser, and Sb content on the electrical properties such as resistivity, carrier concentration, and carrier mobility of the films were investigated. The resistivity of the Sb-doped epitaxial (001) SnO₂ thin film prepared using an ArF laser was lower than that of the film prepared using a KrF laser. The van der Pauw method was used to measure the resistivity, carrier concentration, and carrier mobility of the Sb-doped epitaxial (001) SnO₂ thin films in order to determine the effect of Sb content on the electrical resistivity of the films. The lowest resistivity obtained for the Sb-doped epitaxial (001) SnO₂ thin films prepared using ELAMOD with the ArF laser and 2 % Sb content was 2.5 × 10^?3 Ω cm. The difference between the optimal Sb concentrations and resistivities of the films produced using either ELAMOD or conventional thermal MOD was discussed.     

Studies of some physical properties of PrFe0.7Ni0.3O3 thin films after 200 MeV Ag15+ irradiation

PrFe_0.7Ni_0.3O₃ thin films (thickness ~ 200 nm) were prepared by pulsed laser ablation technique on LaAlO₃ substrate. These films were irradiated with 200?MeV Ag¹⁵⁺ ions at various fluencies, ranging from 1 × 10¹¹ to 1 × 10¹² ions/cm². These irradiated thin films were characterized by using X-ray diffraction, dc conductivity, dc magnetization and atomic force microscopy. These films exhibit orthorhombic structure and retain it even after irradiations. The crystallite size (110–137?nm), micro strain (1.48 × 10^?2–1.75 × 10^?2 line^?2?m^?4) and dislocation density (79.7 × 10¹⁴–53.2 × 10¹⁴ line/m²) vary with ion fluencies. An enhancement in resistivity at certain fluence and then a decrease in its value (0.22175–0.21813?Ω?cm) are seen. A drastic change in observed magnetism after ion irradiation is seen. With ion irradiation, an increase in surface roughness, due to the formation of hillocks and other factors, is observed. Destruction of magnetic domains after irradiation can also be visualized with magnetic force microscopy and is in close agreement with magnetization data. The impact on various physical properties in these thin films after irradiation indicates a distortion in the lattice structure and consequently on single-particle band width caused by stress-induced defects.     

Electrical and optical properties of Si-doped indium tin oxides as transparent electrode and anti-reflection coating for solar cells

We have studied the electrical and optical properties of Si-doped indium tin oxides (ITSOs) as transparent electrodes and anti-reflection coatings for Si-based solar cells. The ITSO thin films were obtained by co-sputtering of ITO and SiO₂ targets under target power control. The resistivity of the ITSO thin films deposited at 0.625 in terms of power ratio (ITO/SiO₂) were 391 Ωcm. In this condition, the ITSO thin films showed very high resistivity compared to sputted pure ITO thin films (1.08 × 10⁻³ Ωcm). However, refractive index of ITSO thin films deposited at the same condition at 500 nm is somewhat lowered to 1.97 compared to ITO thin films (2.06). The fabricated graded refractive index AR coatings using ITO, ITSO, and SiO₂ thin films kept over 80% of transmittance regardless of their thickness varing from 97 nm to 1196 nm because of their low extinction coefficient. As the AR coating with graded refractive indices using ITO, ITSO, and SiO₂ layers was applied to general silicon-based solar cell, the current level increased nearly twice more than that of bare silicon solar cell without AR coating.     

ITO: Zr bi-layers deposited by reactive O2 and Ar plasma with high work function for silicon heterojunction solar cells

We report the influence of reactive oxygen (O₂) and argon (Ar) plasma based ITO:Zr bi-layers for silicon heterojunction (SHJ) solar cells. The purpose of reactive O₂ sputtered ITO:Zr was to improve the Hall mobility and work function while the Ar based ITO:Zr films play an important role to maintain good electrical characteristics. The thickness of reactive O₂ based ITO:Zr films was fixed at 15 nm while Ar based films was varied from 65 to 125 nm, respectively. ITO:Zr bi-layers with the thickness of 15/105 nm deposited by O₂ and Ar plasma, respectively, showed lowest resistivity of 2.358 × 10⁻⁴ Ω cm and high Hall mobility of 39.3 cm²/V · s. All ITO:Zr bi-layers showed an average transmittance of above 80% in the visible wavelength (380–800 nm) region. Work function of ITO:Zr bi-layers was calculated from the X-ray photoelectron spectroscopic (XPS) data. The ITO:Zr work function was enhanced from 5.3 eV to 5.16 eV with the variation of ITO:Zr bi-layers from 15/65 to 15/125 nm, respectively. Front barrier height in SHJ solar cells can be modified by using TCO films with high work function. The SHJ solar cells were fabricated by employing the ITO:Zr bi-layer as front anti-reflection coating. The SHJ solar cells fabricated on ITO:Zr bi-layer with the thickness of 15/105 nm showed the best photo-voltage parameters as; V_oc = 739 mV, J_sc = 39.12 mA/cm², FF = 75.97%, η = 21.96%.     

Growth of high-quality ZnO thin films on (11\bar{2}0) a-plane sapphire substrates by plasma-assisted molecular beam epitaxy

High-quality ZnO thin films were grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Al₂O₃ interface. The full width at half maximum values of the 0002 and $30\bar{3}2$ ZnO ω-rocking curves are 467.8 and 813.5 arc sec for a 600 nm thick ZnO film. A screw dislocation density of 4.35×10⁸ cm^?2 and an edge dislocation density of 3.38×10⁹ cm^?2 are estimated by X-ray diffraction. The surface of the ZnO epilayers contains hexagonal pits, which can be observed in the Zn-polar ZnO. The films have a resistivity of 0.119 Ω?cm, an electron concentration of 6.85×10¹⁷ cm^?3, and a mobility of 76.5 cm²?V^?1?s^?1 at room temperature. Low temperature photoluminescence measurements show good optical properties comparable to ZnO single crystals.     

Ion beam deposition of a-Si:H

The ion beam deposition (IBD) of hydrogenated amorphous silicon is described. Hydrogen incorporation and bonding with the silicon network is evident from SIMS and infrared spectra; the latter show absorption bands centered at 2000cm^?1 and 630cm^?1 typical of monosilicon hydride bonding. IBD a-Si:H thin films are found to be free of microvoids and trace metallic impurities. Four probe conductivity measurements show that the ion beam deposition process yields high resistivity, hydrogenated amorphous silicon (?≥10⁹Ωcm). All of these measurements suggest a low density of defects states in the band gap.     

High mobility In2O3:H transparent conductive oxides prepared by atomic layer deposition and solid phase crystallization

The preparation of high‐quality In₂O₃:H, as transparent conductive oxide (TCO), is demonstrated at low temperatures. Amorphous In₂O₃:H films were deposited by atomic layer deposition at 100 °C, after which they underwent solid phase crystallization by a short anneal at 200 °C. TEM analysis has shown that this approach can yield films with a lateral grain size of a few hundred nm, resulting in electron mobility values as high as 138 cm²/V s at a device‐relevant carrier density of 1.8 × 10²⁰ cm^–3. Due to the extremely high electron mobility, the crystallized films simultaneously exhibit a very low resistivity (0.27 mΩ cm) and a negligible free carrier absorption. In conjunction with the low temperature processing, this renders these films ideal candidates for front TCO layers in for example silicon heterojunction solar cells and other sensitive optoelectronic applications. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Plasma-based sputtering of indium tin oxide for the application of photovoltaic cells

Transparent and conducting indium tin oxide (ITO) thin films were deposited on soda lime glass substrates by RF plasma magnetron sputtering at room temperature. The effect of thickness (100, 200 and 300?nm) on the physical (structural, optical, electrical) properties of ITO thin films was investigated systematically. It is observed that with an increase in thickness, the X-ray diffraction data indicate polycrystalline films with grain orientations predominantly along (222) and (400) directions; the average grain size increases from 10 to 30?nm; the optical band gap increases from 3.68 to 3.73?eV and the transmission decrease from 80% to 70% . Four-point probes show a low resistivity (2.4×10^?5?Ω?cm) values for film with a thickness 300?nm. Present work shows that the ITO is a promising transparent conductive oxide material for the solar cell application.     

Volume of precursor solution effect on the properties of SnO<Subscript>2</Subscript> thin films prepared by nebulized spray pyrolysis technique

Undoped SnO₂ thin films have been deposited on amorphous glass substrates with different precursor solution volume (10, 15, 20 and 25 ml) using simple and cost-effective nebulized spray pyrolysis technique. The influence of precursor solution on structural, optical, photoluminescence and electrical properties had been studied. The X-ray diffraction spectra prove the polycrystalline nature of SnO₂ with tetragonal structure. All the films show a preferred growth orientation along (110) diffraction plane. The average transmittance of SnO₂ thin films varied between 82 and 75% in the visible as well as IR region. The band gap energy decreases from 3.74 to 3.64 eV corresponding to direct transitions with the precursor solution volume had increased from 10 to 20 ml and then increased as 3.72 eV for 25 ml. SEM pictures demonstrated polyhedrons like grains. EDX confirmed the existence of Sn and O elements in all the prepared SnO₂ thin films. Photoluminescence spectra at room temperature revealed that the four emission bands in all the samples such as sharp dominant peak at 361 nm with shoulder peak at 377 nm (UV region), a broad and low intensity peak at 492 nm (blue region) and 519 nm (green region). The electrical parameters were examined by Hall effect measurements, which demonstrated that the film prepared at 20 ml precursor solution volume possess minimum resistivity 2.76?×?10^?3 Ω-cm with activation energy 0.10 eV and maximum figure of merit 1.54?×?10^?2 (Ω/sq)^?1.     

透光导电ITO膜的制备及其光电特性的研究

采用溶胶-凝胶方法制备ITO膜,并从制备工艺上研究了各种因素对ITO膜光电特性的影响.最后制出的ITO膜厚度约为50nm,在可见光区平均透射比达97%,最高达99.55%,电阻率在2.0Ω·cm左右,最低达到0.31Ω·cm.     

Spin-coating deposition of PbS and CdS thin films for solar cell application

In this work, we describe a simple spin-coating deposition technique for lead sulphide (PbS) and cadmium sulphide (CdS) films from a methanolic metal–thiourea complex. The characterization of the films by X-ray diffraction and X-ray photoelectron spectroscopy techniques revealed that pure cubic phase PbS and CdS layers were formed via this method. As shown by atomic force microscopy and scanning electron microscopy results, both films were homogeneous and presented a smooth surface. Optical properties showed that the energy band gap of PbS and CdS films were around 1.65 and 2.5 eV, respectively. The PbS film is p-type in nature with an electrical conductivity of around 0.8 S/cm. The hole concentration and mobility were 2.35 × 10¹⁸ cm^?3 and 2.16 × 10^?3 cm²/V/s, respectively, as determined from Hall measurement. Both films were used to develop a thin film solar cell device of graphite/PbS/CdS/ITO/glass. Device characterization showed the power conversion efficiency of around 0.24 %. The corresponding open circuit voltage, short circuit current and fill factor were 0.570 V, 1.32 mA/cm² and 0.32, respectively.     

Correlation of plume dynamics and oxygen pressure with VO2 stoichiometry during pulsed laser deposition

Vanadium dioxide thin films have been deposited on Corning glass substrates by a KrF laser ablation of V₂O₅ target at the laser fluence of 2 J?cm^?2. The substrate temperature and the target-substrate distance were set to 500 ^°C and 4 cm, respectively. X-ray diffraction analysis showed that pure VO₂ is only obtained at an oxygen pressure range of 4×10^?3–2×10^?2 mbar. A higher optical switching contrast was obtained for the VO₂ films deposited at 4×10^?3–10^?2 mbar. The films properties were correlated to the plume-oxygen gas interaction monitored by fast imaging of the plume.     

Effects of different deposition conditions on the properties of Cu2S thin films

Cu₂S thin films deposited on glass substrate by chemical bath deposition were studied at different deposition temperatures and times. The results of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), the Hall Effect measurement system and UV-Vis absorption spectroscopy indicate that both deposition temperature and time are important to obtain polycrystalline thin films. XRD showed that the polycrystalline Cu₂S thin films have monoclinic structure. Meanwhile, the structural variations were analyzed using SEM. EDX analysis results of the thin film showed that the atomic ratio of Cu/S was close to 2:1. It was found from the Hall Effect measurement that the resistivity varied from 4.59?×?10^?3 to 13.8?×?10^?3 (Ω?cm). The mobility values of the Cu₂S thin films having p-type conductivity varied from 15.16 to 134.6?cm²/V.s. The dark electrical resistivity measurements were studied at temperatures in the range 303–423?K. The electrical activation energies of Cu₂S thin films were calculated by using Arrhenius plots, from which two different activation energy values are estimated for each thin film. Using UV-Vis absorption spectroscopy (Ultraviolet/visible), the direct and indirect allowed optical band gap values were determined to lie between 2.16 and 2.37?eV and 1.79 and 1.99?eV, respectively. In addition, the values of the refractive index (n) and the extinction coefficient (k) were determined.     

Biocompatible film deposition by using Nd:YAG pulsed laser

A Nd:YAG laser operating at the fundamental wavelength (1064 nm) and at the second harmonic (532 nm), with 9 ns pulse duration, 100–900 mJ pulse energy, and 30 Hz repetition rate mode, was employed to ablate in vacuum (10^?6 mbar) biomaterial targets and to deposit thin films on substrate backings. Titanium target was ablated at the fundamental frequency and deposited on near-Si substrates. The ablation yield increases with the laser fluence and at 40 J/cm ² the ablation yield for titanium is 1.2×10¹⁶ atoms/pulse. Thin film of titanium was deposited on silicon substrates placed at different distance and angles with respect to the target and analysed with different surface techniques (optical microscopy, scanning electron spectrosopy (SEM), and surface profile).

Hydroxyapatite (HA) target was ablated to the second harmonic and thin films were deposited on Ti and Si substrates. The ablation yield at a laser fluence of 10 J/cm ² is about 5×10¹⁴ HA molecules/pulse. Thin film of HA, deposited on silicon substrates placed at different distance and angles with respect to the target, was analysed with different surface techniques (optical microscopy, SEM, and Raman spectroscopy).

Metallic films show high uniformity and absence of grains, whereas the bio-ceramic film shows a large grain size distribution. Both films found special application in the field of biomaterial coverage.     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

Double-layer indium doped zinc oxide for silicon thin-film solar cell prepared by ultrasonic spray pyrolysis

Indium doped zinc oxide(ZnO:In) thin films were prepared by ultrasonic spray pyrolysis on corning eagle 2000 glass substrate.1 and 2 at.% indium doped single-layer ZnO:In thin films with different amounts of acetic acid added in the initial solution were fabricated.The 1 at.% indium doped single-layers have triangle grains.The 2 at.% indium doped single-layer with 0.18 acetic acid adding has the resistivity of 6.82×10-3Ω·cm and particle grains.The doublelayers structure is designed to fabricate the ZnO:In thin film with low resistivity(2.58×10-3Ω·cm) and good surface morphology.It is found that the surface morphology of the double-layer ZnO:In film strongly depends on the substratelayer,and the second-layer plays a large part in the resistivity of the double-layer ZnO:In thin film.Both total and direct transmittances of the double-layer ZnO:In film are above 80% in the visible light region.Single junction a-Si:H solar cell based on the double-layer ZnO:In as front electrode is also investigated.