Textured Aluminum Doped Zinc Oxide Research Articles

Wet-chemical surface texturing of AZO substrate for improved perovskite solar cells

Aluminum-doped zinc oxide (AZO) is a promising substrate for perovskite solar cells (PSCs) because of its low cost, easy accessibility, and good conductivity. However, its relatively low transmittance with low resistance and inevitable reflectance loss makes it unfavorable for high-performance AZO-based PSCs. Herein, a simple and effective strategy that textures the surface of AZO substrate via a diluted HCl etching, is developed to boost PSC performance. The textured AZO substrate exhibits greater haze, higher transmittance, and lower reflectance for permitting more photons to reach and be absorbed within PSCs. In addition, the textured AZO substrate not only exhibits improved surface wettability that can enhance the buried interfacial contact and enable the growth of high-quality perovskite film, but also possesses reduced oxygen vacancies and lower work function (WF) that can suppress the recombination and reduce the energy barrier for electron extraction. As a result, the PSC on textured AZO substrate shows improved fill factor (FF, 70 %) and enhanced short-circuit current density (Jsc, 23.7 mA/cm2) compared with the reference cells (63 % and 21.1 mA/cm2), yielding a much-increased power conversion efficiency (PCE) from 13.9 % to 17.6 %. The present work opens the door for the employment of AZO substrate in future commercialization of PSCs.

Vapor textured aluminum-doped zinc oxide on cellophane paper for flexible thin film solar cells

Paper-based flexible thin film solar cells are promising power sources for the emerging portable and wearable electronics, for which high conversion efficiency and flexibility are demanded. Herein, flexible thin film silicon solar cells using textured aluminum-doped zinc oxide (AZO) for light scattering, and ultrathin silver electrodes combined with cellophane paper substrates, were demonstrated. A universal route to form textured AZO thin film by chemical etching with hydrochloric acid vapor was proposed. The AZO layers textured in this way exhibited similar light scattering properties as compared with state-of-the-art AZO thin films. Applying textured AZO to solar cells on cellophane paper substrates resulted in current density and conversion efficiency increase from 8.7 to 9.5 mA/cm2 and from 4.1% to 5.7%, respectively. Thin film solar cells on cellophane exhibited excellent mechanical flexibility, which maintained 90% of their initial efficiency after bending at a radius of 1 mm for 50 cycles.

Using the light scattering properties of multi-textured AZO films on inverted hemisphere textured glass surface morphologies to improve the efficiency of silicon thin film solar cells

We report the light scattering characteristics of multi-textured aluminum-doped zinc oxide (AZO) thin films with high optical transmittance, haze ratio and step coverage for amorphous silicon thin film solar cells (a-Si TFSCs). Multi-textured AZO films were deposited on inverted hemisphere textured (IHT) glass surface morphologies. Multi-textured process was used to create modulated surface morphologies with micro and nano-features useful for the light scattering in visible as well as near-infrared wavelength region. Highly transparent IHT glass surface morphologies with high haze ratio were prepared by wet chemical etching of periodic glass substrates. Total transmittance of the IHT glass substrates showed higher average values (91.38–93.40%) as compared to that of bare glass (90.94%) in the visible wavelength region due to lower reflectance. Multi-textured AZO films showed higher rms roughness 100.479 nm, optical transmittance 82.60% and haze ratio 75.09% in the visible wavelength region. X-ray photoelectron spectroscopic analysis of multi-textured AZO thin films was used to study the atomic compositions and chemical binding states. Multi-textured AZO films with high transmittance and haze ratio were used as front transparent conductive oxide layers for the fabrication of a-Si TFSCs using an absorber layer thickness of 400 nm. Multi-textured AZO films deposited on the optimal textured glass surface morphologies yield the maximum performance of a-Si TFSCs as; Voc = 871 mV, Jsc = 16.55 mA/cm2, FF = 66.6% and η = 9.61%. An enhancement of photocurrent was noticed from 15.64 to 16.55 mA/cm2 for the a-Si TFSCs deposited on as deposit AZO to optimal textured AZO films.

Clinical Characteristics and Survival of Patients with Multiple Metachronous Esophageal Tumor

Composite transparent conductive layers (TCLs) were deposited on the GaP window layer of p-side-up thin-film AlGaInP light-emitting diodes (LEDs) in order to enhance their light-extraction efficiency. The composite TCLs were fabricated from aluminum-doped zinc oxide (AZO) layers grown through atomic-layer deposition and pulsed-laser deposition. The results showed that wet-etching of composite AZO thin films improved the light-extraction efficiency of the corresponding LED devices. The droop efficiencies of LEDs with flat AZO thin films, composite AZO thin films, and optimum textured composite AZO thin films were 29%, 30%, and 22%, respectively. LEDs with textured composite AZO layers exhibited favorable optoelectronic performance. When the injection current was increased from 20 to 1000 mA, the emission wavelengths of LEDs with flat AZO thin films, composite AZO thin films, and optimum textured composite AZO thin films shifted by 3, 5, and 3 nm, respectively. The optimum textured composite AZO thin film can not only improve LED performance but also effectively substitute flat TCLs in AlGaInP LED applications.

Substrate effect on ultra-thin hydrogenated amorphous silicon solar cells

We report a comprehensive study of ultra-thin a-Si:H solar cells on various transparent conductive oxide (TCO) coated glass substrates. We find that the highly textured boron doped zinc oxide (BZO) with multi-scale features made with metal organic chemical vapor deposition (MOCVD) outperforms the flat aluminum doped zinc oxide (AZO) deposited by sputtering and the highly textured AZO with only large features after the chemical etching with diluted HCl. We believe that the much larger features than the cell thickness provide only an enhancement of the effective area for increasing the light absorption, while the variable sizes of features similar to and smaller than cell thickness provide- a highly effective light trapping for thin film solar cells. In addition, the ultra-thin a-Si:H solar cell on the BZO has a better p/i interface than the cell on the AZO substrates, which leads to a high cell performance. A high efficiency of 8.15% was obtained using an a-Si:H p-i-n structure on the BZO with the intrinsic layer of 70nm.

Performance of p-side-up thin-film AlGaInP light-emitting diodes with textured composite aluminum-doped zinc oxide transparent conductive layers

Composite transparent conductive layers (TCLs) were deposited on the GaP window layer of p-side-up thin-film AlGaInP light-emitting diodes (LEDs) in order to enhance their light-extraction efficiency. The composite TCLs were fabricated from aluminum-doped zinc oxide (AZO) layers grown through atomic-layer deposition and pulsed-laser deposition. The results showed that wet-etching of composite AZO thin films improved the light-extraction efficiency of the corresponding LED devices. The droop efficiencies of LEDs with flat AZO thin films, composite AZO thin films, and optimum textured composite AZO thin films were 29%, 30%, and 22%, respectively. LEDs with textured composite AZO layers exhibited favorable optoelectronic performance. When the injection current was increased from 20 to 1000mA, the emission wavelengths of LEDs with flat AZO thin films, composite AZO thin films, and optimum textured composite AZO thin films shifted by 3, 5, and 3nm, respectively. The optimum textured composite AZO thin film can not only improve LED performance but also effectively substitute flat TCLs in AlGaInP LED applications.

Optical scattering modeling of etched ZnO:Al superstrates and device simulation studies of a-Si:H solar cells with different texture morphologies.

Transparent conductive oxide (TCO) materials have been widely used as the front electrodes of thin-film amorphous silicon (a-Si:H) solar cells. To improve the performance of solar cells, textured front TCO is required as the optical layer which effectively scatters the incoming light and thus enhances the photon absorption within the device. One promising TCO material is aluminum-doped zinc oxide (AZO), which is most commonly prepared by magnetron sputtering. After deposition, sputtered AZO films are typically wet-chemically etched using diluted hydrochloric (HCl) or hydrofluoric (HF) acid to obtain rough surface morphologies. In this paper, we report the effects of a textured AZO front electrode on the performance of a-Si:H solar cells based on optical scattering modeling and electrical device simulations, involving four different AZO surface morphologies. The simulated light scattering behaviors indicate that a better textured surface not only scatters more light, but also allows more light get transmitted into the absorber (∼90% of visible light), due to greatly reduced front reflection by the rough surface. Device simulation results show that the two-step AZO texturing process should give improved a-Si:H solar cell performance, with an enhanced short-circuit current density of 16.5 mA/cm2, which leads to a high photovoltaic (PV) efficiency of 9.9%.

Effects of target angle on the properties of aluminum doped zinc oxide films prepared by DC magnetron sputtering for thin film solar cell applications.

An aluminum doped zinc oxide (AZO) films for front contacts of thin film solar cells, in this work, were prepared by DC magnetron sputtering with different target angles. Effects of target angles on the structural and electro-optical properties of AZO films were investigated. Also, to clarify the light trapping of textured AZO film, amorphous silicon thin film solar cells were fabricated on the textured AZO/glass substrate and the performance of solar cells were studied. The surface became more irregular with increasing the target angle due to larger grains. The self-surface textured morphology, which is a favorable property as front layer of solar cell, exhibited at target angle of 72.5 degrees. We obtained the films with various opto-electronic properties by controlling target angle from 32.5 degrees to 72.5 degrees. The spectral haze increased substantially with the target angle, whereas the electrical resistivity was increased. The conversion efficiency of amorphous silicon solar cells with textured AZO film as a front electrode was improved by the increase of short-circuit current density and fill factor, compared to cell with relatively flat AZO films.

Effect of annealing on silicon heterojunction solar cells with textured ZnO:Al as transparent conductive oxide

We report on silicon heterojunction solar cells using textured aluminum doped zinc oxide (ZnO:Al) as a transparent conductive oxide (TCO) instead of flat indium tin oxide. Double side silicon heterojunction solar cell were fabricated by radio frequency plasma enhanced chemical vapor deposition on high life time N-type float zone crystalline silicon wafers. On both sides of these cells we have deposited by radio frequency magnetron sputtering ZnO:Al layers of thickness ranging from 800 nm to 1400 nm. These TCO layers were then textured by dipping the samples in a 0.5% hydrochloric acid. External quantum efficiency as well as I -V under 1 sun illumination measurements showed an increase of the current for the cells using textured ZnO:Al. The cells were then annealed at 150 °C, 175 °C and 200 °C during 30 min in ambient atmosphere and characterized at each annealing step. The results show that annealing has no impact on the open circuit voltage of the devices but that up to a 175 °C it enhances their short circuit current, consistent with an overall enhancement of their spectral response. Our results suggest that ZnO:Al is a promising material to increase the short circuit current (J sc ) while avoiding texturing the c-Si substrate.

In situ micro-Raman spectroscopic study of laser-induced crystallization of amorphous silicon thin films on aluminum-doped zinc oxide substrate

The effects of laser irradiation condition and deposition substrate on the laser crystallized 330 nm Si films structure were investigated using in situ micro-Raman spectroscopy. Results showed that crystallization of amorphous silicon (a-Si) films started at laser irradiation power density of 0.6 × 105 W/cm2 for 20 s. The crystalline volume fraction of Si films depended mostly on the laser power density but not on the laser irradiation time. The Si films on both smooth and textured aluminum-doped zinc oxide (AZO) substrates exhibited lower crystalline volume fraction and smaller average grain size than the Si films on glass did. The Si films on textured AZO revealed higher crystalline volume fraction and larger average grain size than the Si films on smooth AZO did. The stress in crystalline Si films was observed to be compressive on AZO and tensile on glass. The compressive stress in crystalline Si films on textured AZO was slightly less than that on smooth AZO. The present work indicated that the structure of crystalline Si films on textured AZO was improved than that on smooth AZO, which may be helpful to crystalline Si thin-film solar cell.

Influence of Surface Texturing on the Electrical and Optical Properties of Aluminum Doped Zinc Oxide Thin Films

An aluminum doped zinc oxide (AZO) film for front contacts of thin film solar cells, in this work, were deposited by r.f. magnetron sputtering, and then etched in diluted hydrochloric acid solution for different times. Effects of surface texturing on the electro-optical properties of AZO films were investigated. Also, to clarify the light trapping of textured AZO film, amorphous silicon thin film solar cells were fabricated on the textured AZO/glass substrate and the performance of solar cells were studied. After texturing, the spectral haze at the visible range of 400 ~750 nm increased substantially with the etching time, without a change in the resistivity. The conversion efficiency of amorphous Si solar cells with textured AZO film as a front electrode was improved by the increase of short-circuit current density (<TEX>$J_{sc}$</TEX>), compared to cell with flat AZO films.

Influence of surface texture by NH4Cl aqueous solution on the electrical and optical properties of al-doped zinc oxide films

Aluminum-doped zinc oxide (AZO) films were prepared on glass substrate by mid-frequency direct current reactive magnetron sputtering (MF-DC-MS). The influence of surface texture by NH4Cl aqueous solution on the surface morphology, electrical and optical properties of the AZO films was systematically investigated by scanning electron microscope, four-point probe and ultraviolet-visible-near infrared spectrophotometer, respectively. The results indicate that textured AZO film obtains a better texture surface for light trapping. The reflectivity for textured AZO film decreases drastically in visible light region and the electrical resistivity increases, which can be explained by the textured surface morphology of AZO film. The results above prove that NH4Cl aqueous solution is an appropriate candidate for AZO wet etching because of its easy control and relatively low cost.

Damp heat stability and annealing behavior of aluminum doped zinc oxide films prepared by magnetron sputtering

The damp heat stability and subsequent vacuum annealing behavior of aluminum doped zinc oxide (AZO) films was investigated using Hall effect measurements, X-ray diffraction (XRD) and optical spectrometry techniques. The AZO films were deposited on glass or silicon wafers using reactive and non-reactive magnetron sputtering from metallic and ceramic targets, respectively. Additionally, we characterized surface textured AZO films, which are used as light scattering transparent conductive oxide (TCO) in silicon thin film solar cells. For all films a degradation of the electrical film properties was found after the damp heat treatment. For thick compact films, with large grain size, only a small increase in the electrical resistivity was observed, whereas less compact films prepared at high deposition pressures or very thin films (< 300 nm) showed an increase in resistivity by up to a factor of three already after 300 h. The conductivity degradation during damp heat treatment could be largely reversed by annealing in vacuum. However, annealing temperatures of at least 150 °C were required. Possible mechanisms explaining the experimental results are discussed.