Abstract Al-doped ZnO Thin Films Research Articles

Tuning the optoelectronic properties of AZO thin films for silicon thin film solar cell applications

Al-doped ZnO (AZO) thin films are deposited using dc magnetron sputtering and the process conditions are optimized to obtain transparent conducting electrode (TCE) with desirable properties suitable for photovoltaic applications. In the course, the effects of deposition parameters such as growth temperature, deposition time and plasma power density on the structural and optoelectronic properties were investigated using suitable characterization techniques. XRD analysis of the deposited films at different process conditions showed a strong c-axis preferred orientation. The surface roughness of the deposited films was examined using AFM analysis. Elemental analysis was carried out using XPS. The resistivity and sheet resistance of the thin films decreased with increase in temperature, deposition time and power density. The optimized films deposited at 250 °C resulted in electrical resistivity of 6.23 × 10−4 Ωcm, sheet resistance of 9.2 Ω/□ and exhibited an optical transmittance of >85% in the visible range. Figure of merit (FOM) calculations were carried out to analyze the suitability of deposited thin films for thin film amorphous silicon solar cell applications. The photogain of optimized intrinsic a-Si:H layer was in the range of 104, whereas no photogain was observed in doped a-Si:H layers. The thin film solar cell fabricated using the optimized AZO film as TCE exhibited power conversion efficiency of 6.24% when measured at AM 1.5 condition.

Optimizing transparent conductive Al-doped ZnO thin films for SiNx free crystalline Si solar cells

Al-doped ZnO (AZO) thin films with resistivity of 6.6 × 10−4 Ω cm were prepared by introducing H2 in DC magnetron sputtering atmosphere. The Hall Effect measurement demonstrates that a part of the hydrogen atoms act as shallow donors while others act as neutral scattering impurities. Only proper H2 partial pressure decreases the resistivity to the lowest value. The properties of SiNx free crystalline Si (c-Si) solar cells were improved when AZO thin films were applied. The films served as both anti-reflection (AR) coatings and front electrode assistance. Ensuring an outstanding AR effect and a low sheet resistance, the thickness of the films was optimized in order to reduce the optical absorption, and thus effectively increase the short circuit current density (Jsc). The influence of the films versus different Ag fingers and emitter sheet resistance was investigated. The results showed that the Jsc was improved apparently (at least by 0.7 mA/cm2), while the fill factor was enhanced obviously from 62 to 70 % and from 73 to 75 %, respectively, which depended on the initial series resistance.

Effect of oxygen partial pressure on epitaxial growth and properties of laser-ablated AZO thin films

Al-doped ZnO (AZO) thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures (P O2). The effect of PO2 on the crystal structure, preferred orientation as well as the electrical and optical properties of the films was investigated. The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure, showing a significant c-axis orientation. The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P O2. At the optimum oxygen partial pressures of 10 - 15 Pa, the AZO thin films were epitaxially grown on c-sapphire substrates with the (0001) plane parallel to the substrate surface, i e, the epitaxial relationship was AZO (000 1) // Al2O3 (000 1). With increasing P O2, the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly, which led to an enhancement in electrical conductivity of the AZO thin films. All the films were highly transparent with an optical transmittance higher than 85 %.

Investigation of Growth Dynamics of Nanostructured Aluminum Doped Zinc Oxide Thin Films Deposited for the Solar Cell Applications

Al doped ZnO (AZO) is one of the most promising transparent conducting oxide materials, which widely utilizes as a front contact for the cadmium telluride based thin film solar cells and a working electrode for perovskite solar cells. This research presents the optimization process of the AZO thin films deposited by spray pyrolysis technique at room temperature by studying its structural, morphological and electrical properties at different thicknesses (100, 150, 200, 300 and 400 nm). Obtained results from X-ray diffraction revealed that the degree of crystallinity and the average grain size of the AZO deposited thin films enhance with increasing the thickness. Surface topography and growth behavior of AZO thin films have important role in optimization of optical and electrical properties of these films especially in the solar cell applications. In this research, the atomic force microscopy (AFM) has been used to assess the quantitative parameters related to the surface topography of the films. Obtained results from AFM analysis revealed that the surface topography of AZO deposited samples strongly depend on thickness. Also the electrical characteristics indicate that the thin films have an electrical resistivity of the order of 10−4 Ω cm.

Effect of Sintering Atmosphere on the Electrical and Thermal Properties of Al-Doped ZnO Thin Films Prepared Using Inkjet Printing Method

Al-doped ZnO thin films were prepared by ink-jet printing and their electrical and thermal properties with different amounts of Al doping and sintering atmosphere were investigated. The XRD traces of films show the doped materials did not form additional crystalline phases with increasing amounts of Al doping. Electrical conductivity of film increased from 4.86 S/cm to 120.94 S/cm as the amounts of Al doping increased from 0 wt% to 4 wt%. However, the thermal conductivity decreased from 24 W/mK to 13 W/mK with increasing the Al doping from 0 wt% to 4 wt%. The electrical conductivity of film shows higher values sintered in vacuum (120.94 S/cm) compared to film sintered in air (114.1 S/cm).

Enhanced electrical properties of AZO thin films grown on different substrates by using a facing-target sputtering system with hetero targets

Al-doped ZnO (AZO) films were deposited on glass, polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) at room temperature by using conventional rf-magneton sputtering (CMS) and a facing-target sputtering (FTS) with hetero targets of Al2O3 and ZnO. Their structural, surface morphology, electrical and optical properties were characterized by using X-ray diffractometry (XRD), atomic force microscopy (AFM), Hall-effect measurement and ultravioletvisible spectrophotometry, respectively. The films exhibit highly c-axis preferred orientation and a closely packed nanocrystalline. Structure the FTS-films deposited on plastic substrate are found to receive much less stress due to bombardment of high-energy particles compress to the CMS-films deposited on plastic substrates, during the sputtering process, which can enhance the electrical properties and crystalline quality of the FTS-films compared with those of the CMS-films. The resistivities of the FTS-films are 6.50 × 10−4 Ω·cm on glass, 7.0 × 10−4 Ω·cm on PEN and 7.4 × 10−4 Ω·cm on PET while the values for the CMS-films are 7.6 × 10−4 Ω·cm on glass, 1.20 × 10−3 Ω·cm on PEN and 1.58 × 10−3 Ω·cm on PET.

Effect of oxygen flowrate on optical and electrical properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films were synthesised on quartz glass substrates by pulsed laser deposition (PLD) method at different oxygen flowrates. The structure, composition, optical and electrical properties in the films were investigated. The result of surface profiler shows that with the increase in oxygen flowrate from 10 to 70 sccm, the films’ thickness increases from 526 to 706 nm. X-ray diffraction results show that the crystalline quality of the films is improved with the increase in oxygen flowrate; energy dispersive spectroscopy results exhibit that the Al content in the films increases from 4·32 to 6·45% with the increase in oxygen flowrate. The former leads to the weakening of grain boundary scattering; consequently, Hall mobility will increase, and the latter results in the increase in carrier concentration. As a result, the electrical resistivity in AZO films decreases from 10·92×10−3 to 2·34×10−3 Ω cm with increasing the oxygen flowrate. Moreover, the increase in carrier concentration induces the slight widening of optical band gap due to the Burstein–Moss effect with the increase in oxygen flowrate. For AZO thin films grown by the PLD method, the control of oxygen flowrate is a simple method to obtain adjustable electrical resistivity, optical band gap and ultraviolet emission.

Effect of O2 partial pressure on optical and electrical properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films were synthesised on single crystal silicon and quartz glass substrates by pulsed laser deposition method at different O2 partial pressure. The structure, composition, optical and electrical properties in AZO thin films were investigated. With the increase in O2 partial pressure, the crystalline quality of AZO thin films becomes poor, and the Al content in the films decreases from 6·3 to 4·3%. The former leads to the enhancement of grain boundary scattering, consequently Hall mobility will decrease. While the latter results in the decrease of carrier concentration. As a result, the electrical resistivity in AZO thin films increases from 2·18×10−4 to 13·40×10−4 Ω cm with increasing the O2 partial pressure. The increase of carrier concentration induces the widening of optical band gap due to the Burstein-Moss effect with the increase of O2 partial pressure. For AZO thin films grown by PLD method, the control of O2 partial pressure is a simple method to adjust the electrical resistivity, optical band gap and UV emission in the films.

Influence of hydrogen annealing on structure and optoelectronic properties in Al doped ZnO thin films

Al doped ZnO (AZO) thin films are of significant interest for flat panel displays, solar cells, etc. In this regard, AZO films were prepared in Ar atmosphere by radio frequency magnetron sputtering with an AZO (2 wt-%Al2O3) ceramic target at room temperature. To investigate the influence of hydrogen related defects on the structure and optoelectronic properties in AZO films, the prepared films were annealed in Ar+H2 ambient at different temperatures (100–500°C). The results show that the films’ crystallinity becomes better and the resistivity decreases with the increase in annealing temperature. The lowest resistivity of 2·79×10−3 Ω cm is obtained after 500°C hydrogen annealing, which decreases by about four orders of magnitude compared to the resistivity of as deposited film. The improvement of electrical properties is attributed to the formation of H related defects and desorption of weakly bonded oxygen species near grain boundaries in AZO films after H2 annealing treatment, and the corresponding physical mechanism was discussed. It is proved that hydrogen annealing is an effective method for the improvement of electrical properties in AZO thin films. The optical bandgap energy of the films obviously increases with the increase in annealing temperature due to Burstein–Moss effect.

Study on Micro-Structure of Al-Doped ZnO Thin Films

Al-doped ZnO thin films（ZnO:Al）were prepared by sol-gel process, the influence of preparation parameters on micro-structure was studied by XRD. The results showed that the solution concentration of 0.65mol/L was multi-axis orientation and when the concentration reached 0.8mol/L the film showed c-axis preferred growth; when film was too thin, showing amorphous, with the film thickness increased, ZnO:Al film turned multi-axis orientation to (002) plane preferential growth; the grain could not get enough energy to move to the right place for crystal when annealing temperature was too low, with the annealing temperature increased, ZnO:Al turned from multi-axis orientation to c-axis preferred orientation.

Preparation and Properties of Al-Doped ZnO Thin Films for Solar Cells

Al-doped ZnO thin films were prepared by sol-gel process. Structural features and surface morphology were studied by XRD and AFM. The influence of Al-doped concentration and aging time to microstructure and electric resistivity were investigated. It was demonstrated that the best condition was Al/Zn ratios of 4.0at% and aging time of 48h.

Electrical and Optical Properties of Al-doped Zinc-oxide Thin Films Deposited at Room Temperature by Using the Continuous Composition Spread Method

Al-doped ZnO (AZO) thin films were deposited on glass substrates at room temperature by using the continuous composition spread (CCS) method. CCS is a thin-film growth method for various AlxZn1−xO thin film compositions with a binary or ternary composition spread, and the critical properties can be evaluated as functions of position, which is directly related to material composition, by using an automated probe station. Various compositions of Al-doped ZnO thin films deposited at room temperature were explored to find excellent electrical and optical properties. The lowest resistivity of the AZO thin films deposited at room temperature was 2.8 × 10−3 Ω·cm, and the average transmittance in the 400-to-900-nm wavelength region was 93%. The optimized composition of the AZO thin film, which had the lowest resistivity and highest transmittance was Al0.05Zn1O1.05 (about 3.13-wt% Al2O3).