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.     

Influence of Al doping on microstructure,morphology, optical and photoluminescence properties of pyrolytic ZnO thin films prepared in an ambient atmosphere

Zinc oxide (ZnO) and aluminium (Al) doped zinc oxide (AZO) thin films have been fabricated by spray pyrolysis technique in normal atmospheric condition. Samples of different Al-concentrations (0–5% Al) were deposited at 350 °C onto glass substrate to study the structural, morphological, optical and photoluminescence properties. X-ray diffraction study confirms that the films are polycrystalline having hexagonal structure. SEM images show that the films have rope and tube like morphology. Optical properties, such as transmittance, optical band gap, extinction coefficient, refractive index, optical conductivity, dielectric constants and electron energy loss functions were analyzed and discussed. Results show that the optical parameters have been changed significantly with Al-doping concentration. The photoluminescence spectra indicate that the PL peaks originated from deep level emissions (DLE) with different intensities for ZnO and Al-doped ZnO films.     

Effects of substrate temperature on the efficiency of hydrogen incorporation on the properties of Al-doped ZnO films

Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by RF magnetron sputtering at different substrate temperatures in Ar and H₂ + Ar sputtering ambient. The effects of substrate temperature on the effectiveness of hydrogen incorporation in Al-doped ZnO films were investigated. The microstructural, electrical and optical properties of AZO films were systematically analyzed by surface profiler, X-ray diffractometry, scanning electron microscope, four-point probe measurement and UV/vis spectrophotometer. The XRD patterns and SEM pictures indicate that the crystallinity of AZO thin films was markedly improved with hydrogen incorporation at low substrate temperature, while the improvement of crystallinity was not an obvious change at high substrate temperature. The results also indicate that hydrogen incorporation has the stronger effectiveness on the transparent conductive properties of AZO films with the substrate temperature decreasing. The resistivity of the films decreases, especially for lower substrate temperatures, due to the incorporation of hydrogen atoms. These results suggest that substrate temperature should be controlled to the lower level to effectively reduce resistivity without detriment to transmittance of AZO thin films when hydrogen is incorporated.     

用粉末靶在玻璃和PI衬底上制备AZO/Ag/AZO薄膜

室温下在玻璃和聚酰亚胺两种不同衬底上, 采用射频磁控溅射法溅射掺铝氧化锌(AZO)粉末靶和固体Ag靶, 制备了两组AZO/Ag/AZO 3层透明导电薄膜, 研究了AZO层厚度对不同衬底3层膜结构和光电性能的影响.结果表明:不同衬底的两组AZO/Ag/AZO薄膜均为多晶膜.当Ag层厚度不变时, 随着AZO层厚度的增加, 两组薄膜电学性能变化不大, 透射峰向长波方向移动.玻璃和PI衬底上制备的AZO(30 nm)/Ag(14 nm)/AZO(30 nm)薄膜, 在550 nm处的透光率分别为85%和70%, 方块电阻分别为2.6 Ω/□和4.6 Ω/□.     

粉末靶制备的AZO/Ag/AZO透明导电薄膜的光电性能

室温下,采用射频磁控溅射AZO粉末靶和Ag靶在玻璃基底上制备Ag层厚度分别为12 nm和15 nm两组对称结构掺铝氧化锌/银/掺铝氧化锌(AZO/Ag/AZO)透明导电薄膜,研究了Ag层和AZO层厚度对薄膜光电性能的影响。结果表明:3层薄膜的可见光区平均透光率达到了80%,550 nm处的最高透过率达到了88%,方块电阻小于5 Ω/□。Ag层厚度是影响AZO/Ag/AZO薄膜光电性能的主要因素,AZO层的厚度对薄膜光学性能影响较大。     

Effects of deposition temperature and hydrogen flow rate on the properties of the Al-doped ZnO thin films and amorphous silicon thin-film solar cells

A compound of 98 mol% ZnO and 1 mol% Al₂O₃ (AZO, Al:Zn = 98:2) was sintered at 1350 °C as a target and the AZO thin films were deposited on glass using a radio frequency magnetron sputtering system. The effects of deposition temperature (from room temperature to ～300 °C) on the optical transmission spectrum of the AZO thin films were studied. The Burstein–Moss shift was observed and used to prove that defects in the AZO thin films decreased with increasing deposition temperature. The variations in the optical band gap (E _g) values of the AZO thin films were evaluated from plots of (αhv)²=c(hν?E _g), revealing that the measured E _g values increased with increasing deposition temperature. The effects of the H₂ flow rate during deposition (0 %～11.76 %, deposition temperature of 200 °C) on the crystallization, morphology, resistivity, carrier concentration, carrier mobility, and optical transmission spectrum of the AZO thin films were measured. The chemical structures of the Ar-deposited and 2 % H₂-flow rate-deposited AZO thin films (both were deposited at 200 °C) were investigated by XPS to clarify the mechanism of improvement in resistivity. The prepared AZO thin films were also used as transparent electrodes to fabricate amorphous silicon thin-film solar cells, and their properties were also measured.     

Deposition of quasi-crystal Al-doped ZnO thin films for photovoltaic device applications

Quasi-crystal aluminum-doped zinc oxide (AZO) films were prepared by in situ radio frequency (RF) magnetron sputtering (sputtering without annealing) on glass substrates. The influence of deposition parameters on the optoelectronic and structural properties of the in situ deposited quasi-crystal AZO films was investigated in order to compare resulting samples. X-ray diffraction (XRD) patterns show that the quasi-crystal AZO thin films have excellent crystallization improved with increase of the RF power and substrate temperature, with an extremely preferential c-axis orientation exhibit sharp and narrow XRD pattern similar to that of single-crystal. Field emission scanning electron microscopy (FESEM) images show that quasi-crystal AZO thin films have uniform grains and the grain size increase with the increase of RF power and substrate temperature. Craters of irregular size with the columnar structure are observed in the quasi-crystal AZO thin films at a lower substrate temperature while many spherical shaped grains appeared at a higher substrate temperature. The average optical transmittance of all the quasi-crystal AZO films was over 85% in the 400-800 nm wavelength range. The resistivity of 4.176 × 10⁻⁴ Ω cm with the grain size of 76.4891 nm was obtained in the quasi-crystal AZO thin film deposited at 300 °C, under sputtering power of 140 W.     

Temperature-dependent luminescence dynamics for ZnO thin films

The paper presents the photoluminescence investigation of zinc oxide thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz wafers. The films with different thickness (number of layers) were annealed at different temperatures after the preparation process. It was found that high quality, transparent ZnO thin films could be produced on quartz substrates at relatively low annealing temperature (450–550  $^{\circ }\mathrm{C}$ ). The dependence of the ZnO thin film quality was studied by X-ray diffraction and atomic force microscopy techniques. Optical properties were investigated by classic and time-resolved photoluminescence (TRPL) measurements. Photoluminescence spectra allowed us to estimate energy of the free excitons, bond excitons and their longitudinal optical (LO) phonon replicas as a function of the annealing temperature. An innovative TRPL technique let us precisely measure the decay time of the free- and bond excitons’ in the real time. TRPL measurements as a function of temperature reveal a biexponential decay behavior with typical free/bound exciton decay constants of 970/5310 ps for the as-grown sample and 1380/5980 ps after annealing process. Presented spectra confirm high structural and optical quality of investigated films. We proved that the thermal treatment improve both optical and structural quality and extend the photoluminescence’s lifetimes. The obtained experimental results are important for identification of exciton’s peaks and their LO phonon replicas for the investigated ZnO films.     

Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150 nm to 750 nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12 mTorr to 25 mTorr, and from room temperature to 450 °C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.     

Investigation of the crystallinity,structural, and optical properties in hydrotreating of Li–W co-doped ZnO thin films

The hydrotreated Li–W co-doped ZnO (LWZO:H) thin films was prepared on quartz glass substrates by RF magnetron sputtering at substrate temperature 100 °C with varied hydrogen flow ratios. The X-ray diffraction spectra indicated that the hydrotreating Li–W co-doped ZnO films showed a preferred orientation toward the c-axis. The chemical compositions of all samples were confirmed by X-ray photoelectron spectroscopy, which clearly showed the existence of W as a doping element into ZnO crystal lattice. The surface morphology of LWZO:H thin films changed with the increasing R value can clearly be seen. The average transmittance of the films was found to be almost 85 % for the wavelength range of 400–1,200 nm. Meanwhile, the optical band gap increase of the films may be attributed to the band Burstein–Moss effect.     

Near infrared to UV dielectric functions of Al doped ZnO films deposited on c-plane sapphire substrate using pulsed laser deposition

Transparent conducting polycrystalline Al-doped ZnO (AZO) films were deposited on sapphire substrates at substrate temperatures ranging from 200 to 300 °C by pulsed laser deposition (PLD). X-ray diffraction measurement shows that the crystalline quality of AZO films was improved with increased substrate temperature. The electrical and optical properties of the AZO films have been systematically studied via various experimental tools. The room-temperature micro-photoluminescence (µ-PL) spectra show a strong ultraviolet (UV) excitonic emission and weak deep-level emission, which indicate low structural defects in the films. A Raman shift of about 11 cm⁻¹ is observed for the first-order longitudinal-optical (LO) phonon peak for AZO films when compared to the LO phonon peak of bulk ZnO. The Raman spectra obtained with UV resonant excitation at room temperature show multi-phonon LO modes up to third order. Optical response due to free electrons of the AZO films was characterized in the photon energy range from 0.6 to 6.5 eV by spectroscopic ellipsometry (SE). The free electron response was expressed by a simple Drude model combined with the Cauchy model are reported.     

功率密度对中频磁控溅射制备 AZO薄膜性能的影向

利用中频磁控溅射法在普通玻璃衬底上沉积掺铝氧化锌(ZnO ∶ Al,简称AZO)薄膜,通过调整溅射功率密度参数得到沉积速率与功率密度之间的关系,制备了不同厚度的AZO薄膜.利用台阶仪、XRD、XPS、紫外可见分光光度计和Hall测试系统等方法研究了功率密度与厚度对AZO薄膜结构、组分、光学和电学性能的影响.实验结果表明...     

Photoluminescence of ZnO films prepared by r.f. sputtering on different substrates

Polycrystalline ZnO films with good orientation were deposited on sapphire, quartz, Si and 7059 glass substrates by r.f. magnetron sputtering. A strong UV photoluminescence (PL) peak (located at 356 nm) and a weak blue emission peak (located at 446 nm) were observed at room temperature (RT) for the films deposited on sapphire, quartz and Si substrates when excited with 270 nm light. For the films prepared on Corning 7059 glass, only a strong 446 nm blue emission peak was found, and the PL intensity decreased with increasing oxygen pressure during films deposition. The intensity of the UV emission increased 7 and 14 times, respectively, for the films on sapphire and quartz substrates after high temperature annealing in vacuum. The UV emission originates from the inter-band transition of electrons and the blue emission is due to transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.     

ZnO退火条件对硫化法制备的ZnS薄膜特性的影响

采用反应磁控溅射法在玻璃和石英衬底上沉积了ZnO薄膜, 然后经过不同条件退火和在H22S气氛中硫化最终得到ZnS薄膜. 用x射线粉末衍射仪、扫描电子显微镜和UV—VIS分光光度计 对ZnS薄膜样品进行了分析. 结果表明, ZnO薄膜硫化后的晶体结构和光学性质取决于它的退 火条件. 真空和纯O2₂中退火的ZnO薄膜硫化后只是部分形成六角晶系结构的ZnS . 而在空气 和纯N2₂中退火的ZnO薄膜则全部转变为ZnS, 在可见光范围内的光透过率 关键词： ZnS薄膜 磁控溅射 ZnO硫化 太阳电池     

Effect of oxygen partial pressure on the structural and optical properties of ZnO film deposited by reactive sputtering

Effects of variation of the oxygen partial pressure on the structural and optical properties of zinc oxide (ZnO) thin films prepared by reactive radio-frequency sputtering were investigated. Measurements by X-ray diffraction (XRD) and atomic force microscopy (AFM) indicated that the crystallinity and the surface morphology were sensitive to the oxygen partial pressure. The interfacial and optical properties of the targeted films were investigated by spectroscopic ellipsometry (SE) characterization. Based on Tauc-Lorentz (TL) model, the optical constants of ZnO films were tentatively extracted in the photon energy ranging from 1.5 to 6.0 eV. Analyses by XRD and SE revealed that the oxygen partial pressure had effect on the orientation of the ZnO films, the surface morphology, the packing density, and the interfacial layers. And the relationship between crystallinity and interfacial layer, as well as the relationship between surface roughness and packing density was discussed. All these had a significant impact on the optical properties illustrated by SE analysis.     

Effect of Al doping on microstructure and optical band gap of ZnO thin film synthesized by successive ion layer adsorption and reaction

Thin films of pure and aluminum-doped zinc oxide (AZO) were deposited on glass substrates from ammonium zincate bath following a chemical dipping technique called successive ion layer adsorption and reaction (SILAR). Characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-rays (EDX) were used to investigate the effect of Al doping on the microstructure of AZO films. Particle size analysis using X-ray line broadening shows marginally increasing trend with increasing Al impurity. The average particle size for pure ZnO is 22.75 nm. It increases to 24.26 nm for 1% AZO film and 25.13 nm for 2% AZO film. Incorporation of Al was confirmed from elemental analysis using EDX. SEM micrograph shows that pure ZnO particles are spherical shaped. However, AZO films show particles with off-spherical shape with compact interconnected grains. The value of band gap for pure ZnO is 3.229 eV and it increases to 3.29 eV for 1% AZO indicating a blue-shift for 1% AZO film. However, for 2% AZO film, a decrease in band gap compared to pure ZnO is observed indicating a red-shift of fundamental absorption edge. Electrical resistance shows an initial decrease with increasing Al content. With further enhancement of Al incorporation, the resistance increases.     

Nanocrystalline ZnO Film Grown on Porous SnO2/Si(111) Substrate

Porous tin oxide was prepared on silicon(111) substrate by the sol–gel route. Then, the samples were dried in air at 600°C for 30 min in an electric furnace. Scanning electron microscope (SEM) images indicated the high density of the pores. Circular microvoids formed by the rigid shaped microarray network of 200–300 nm sizes are clearly seen in the plan view SEM image. The high homogeneity and uniformity of the porous region could also be visualized by this easy method. Nanocrystalline zinc oxide (ZnO) thin films have been deposited onto porous SnO₂substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The surface morphology of the nanocrystalline ZnO films was characterized by scanning electron microscope (SEM). Photoluminescence (PL) spectroscopy is a powerful, contactless and excellent nondestructive optical tool to study the acceptor binding energy of ZnO nanostructures. The PL measurements were also operated at room temperature. The peak luminescence energy in nanocrystalline ZnO on porous SnO₂ is blue-shifted with regard to that in bulk ZnO (381 nm). PL spectra peaks are distinctly apparent at 375 nm for ZnO film grown on porous SnO₂/Si(111) substrates.     

H2 气对脉冲磁控溅射铝掺杂氧化锌薄膜性能的影响

实验采用脉冲磁控溅射法制备铝掺杂氧化锌(AZO)薄膜.为了进一步提高AZO薄膜的光电性能,在溅射过程中加入一定流量的氢气,以高纯ZnO ∶Al₂O₃陶瓷靶为溅射靶材,制备AZO/H透明导电薄膜.通过测试薄膜的结构特性、表面形貌及其光电性能,详细地研究了氢气流量对AZO薄膜性能的影响.溅射过程中引入氢气,可以促进薄膜的晶化,提高薄膜的迁移率和透过率(400—1100 nm).采用纯氩气溅射制备AZO薄膜的电阻率为5.664×10^-4 Ω·cm 关键词： 氧化锌 氢气流量 磁控溅射 太阳电池     

射频溅射功率对AZO薄膜结构及光电特性和热稳定性的影响

采用射频磁控溅射法,在玻璃基片上制备了ZnO:Al(AZO)透明导电薄膜。用X射线衍射(XRD)仪、紫外-可见分光光度计、方块电阻测试仪和台阶仪对不同溅射功率下Al掺杂ZnO薄膜的结晶、光学、电学性能、沉积速率以及热稳定性进行了研究。研究结果表明:不同溅射功率下沉积的AZO薄膜具有六角纤锌矿结构,均呈c轴择优取向;(002)衍射峰强和薄膜的结晶度随溅射功率的提高逐渐增强;随溅射功率的提高,AZO薄膜的透射率有所下降,但在可见光(380～780nm)范围内平均透射率仍80%;薄膜的方块电阻随溅射功率的增加逐渐减小;功率为160～200W时,薄膜的热稳定性最好,升温前后方块电阻变化率为13%。     

Structural and optical properties of ZnO thin films on (111) CaF2 substrates grown by magnetron sputtering

ZnO thin films were grown on (111) CaF₂ substrates by magnetron sputtering at room temperature. Structural and optical properties of the ZnO thin films were studied. XRD analysis showed that the ZnO thin films had the (002) preferential orientation. The transmittance of ZnO thin films was over 80% in the visible range. The optical band gap of the ZnO thin films was 3.26 eV. The optical constants (n,k)$(n,k)$ of the ZnO thin films in the wavelength range 300–1000 nm were obtained by infrared spectroscopic ellipsometry measurement. PL spectra of ZnO thin films showed strong UV near-band-edge emission peak at 376.5 nm and weak visible red emission at 643.49 nm using He–Cd laser as the light source, using a synchrotron radiation light source PL spectra showed three emission peak at 320 nm, 410 nm and 542 nm respectively.