Aluminum-doped Zinc Oxide Substrate Research Articles

Experimental and theoretical aspects of the growth of vertically aligned CNTs by CCVD on AZO substrate

An efficient and reproducible growth of vertically aligned carbon nanotubes by CCVD requires accurate and specific setting of the synthesis parameters and the properties of catalyst thin layers. In this work, the growth of vertically aligned carbon nanotubes onto AZO (= aluminum doped zinc oxide) glass substrate covered by Al2O3 and Fe-Co catalyst layer system is presented. Investigation of the effect of catalyst composition and synthesis temperature on CVD growth revealed the optimum condition of the synthesis. The analysis of as-prepared samples by SEM, TEM and Raman spectroscopy was carried out to prove the structure and quality of carbon deposit. Theoretical considerations have supported speculative ideas about the role of the support layer, the transformation of the catalyst layer in the presence of hydrogen gas and the growth mechanism of carbon nanotubes. The mechanism of CNT growth is modelled and the order of magnitude of experimentally observed vertical linear growth rate of CNT (several nm/s) is reproduced.

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.

Low-Temperature Hydrothermal Growth of ZnO Nanowires on AZO Substrates for FACsPb(IBr)3 Perovskite Solar Cells.

Electron and hole transport layers (ETL and HTL) play an essential role in shaping the photovoltaic performance of perovskite solar cells. While compact metal oxide ETL have been largely explored in planar n-i-p device architectures, aligned nanowires or nanorods remain highly relevant for efficient charge extraction and directional transport. In this study, we have systematically grown ZnO nanowires (ZnO NWs) over aluminum-doped zinc oxide (AZO) substrates using a low-temperature method, hydrothermal growth (HTG). The main growth parameters were varied, such as hydrothermal precursors concentrations (zinc nitrate hexahydrate, hexamethylenetetramine, polyethylenimine) and growing time, in order to finely control NW properties (length, diameter, density, and void fraction). The results show that ZnO NWs grown on AZO substrates offer highly dense, well-aligned nanowires of high crystallinity compared to conventional substrates such as FTO, while demonstrating efficient FACsPb(IBr)3 perovskite device performance, without the requirement of conventional compact hole blocking layers. The device performances are discussed based on NW properties, including void fraction and aspect ratio (NW length over diameter). Finally, AZO/ZnO NW-based devices were fabricated with a recent HTL material based on a carbazole moiety (Cz–Pyr) and compared to the spiro-OMeTAD reference. Our study shows that the Cz–Pyr-based device provides similar performance to that of spiro-OMeTAD while demonstrating a promising stability in ambient conditions and under continuous illumination, as revealed by a preliminary aging test.

Titanium Dioxide-Coated Zinc Oxide Nanorods as an Efficient Photoelectrode in Dye-Sensitized Solar Cells.

Well-arrayed zinc oxide nanorods applied as photoelectrodes for dye-sensitized solar cells were synthesized on an aluminum-doped zinc oxide substrate by the multi-annealing method. In order to improve the chemical stability and surface-to-volume ratio of photoanodes in dye-sensitized solar cells, the synthesized zinc oxide nanorods were coated with pure anatase phase titanium dioxide film using a novel mist chemical vapor deposition method. The effects of the titanium dioxide film on the morphological, structural, optical, and photovoltaic properties of zinc oxide–titanium dioxide core–shell nanorods were investigated. It was found that the diameter and surface-to-volume ratio of zinc oxide nanorods were significantly increased by coating them with titanium dioxide thin film. The power conversion efficiency of dye-sensitized solar cells was improved from 1.31% to 2.68% by coating titanium dioxide film onto the surface of zinc oxide nanorods.

Broadband Polarization Degeneracy of Guided Waves in Subwavelength Structured ZnO Pattern

Polarization degeneracy of electromagnetic plane waves in vacuum and in any bulk isotropic media is the keynote operational principle of many optical devices such as polarizers and interferometers. However, surface and guided waves spectra are typically either not degenerated at all or meet degeneracy only at very specific dispersion points. In this paper, we offer a design of a periodic photonic structure based on zinc oxide (ZnO) nanocylinders providing the broadband polarization degeneracy of the guided waves in the near-IR frequency range. We analyze the impact of the spatial dispersion and substrate on the degeneracy breaking. We offer the design based on ZnO nanocylinders with aluminum-doped zinc oxide substrate, achieving the degeneracy in the vicinity of a telecommunication wavelength, for the practical implementation. Finally, we propose and verify numerically a potentially important device–waveguide polarizer, which is the analogue to the $\lambda /4$ plate for the guided waves.

Seed Free Growth of Aligned ZnO Nanowire Arrays on AZO Substrate

In the absence of commonly used seed layer, we can still successfully synthesized aligned ZnO nanowire arrays by the hydrothermal method. By using aluminum-doped zinc oxide (AZO) glass as a substrate, high-density and vertically aligned ZnO nanowires were synthesized directly on the substrate in the absence of the ZnO seed layer. The current-voltage curve indicated that the sample grown on AZO glass substrate in the absence of seed layer possesses better conductivity than that synthesized on FTO glass substrate with ZnO seed layer. Thus, a simplified, seed-free and low-cost experimental protocol was reported here for large-scale production of high quality ZnO nanowire arrays with promoted conductivity.

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.

Fabrication of well-aligned ZnO nanorod photoanodes for perovskite solar cells

ZnO nanorods grown on aluminum doped zinc oxide (AZO) substrate and ZnO seed layer coated substrates, including glass slides, fluorine doped tin oxide, and indium tin oxide substrates were studied. ZnO nanorods grown on AZO substrate had the best alignment and highest packing density. The growth rate of ZnO nanorods was regulated by adding polyethyleneimine (PEI) and introducing contact potential. ZnO nanorods co-adjusted by adding PEI and introducing contact-potential-driven growth formed a textured structure that led to a higher transmittance at 600–800 nm. The strong ultraviolet band emission indicated a relatively low concentration of deep level defects in ZnO nanorods. Good crystallization, together with a small amount of aluminum-doping, guaranteed high electron transfer in the ZnO nanorods. The well-aligned ZnO nanorods were incorporated into a perovskite solar cell prepared with carbon counter electrode under completely open-air conditions. A J sc of 15.53 mA cm−2 and an efficiency of 2.71 % were obtained for ZnO nanorods under contact-potential-driven growth. In addition, for ZnO nanorods co-adjusted by adding PEI and introducing contact potential, a J sc of 14.87 mA cm−2 and an efficiency of 3.62 % were obtained. However, fill factors were very low for hybrid solar cells with the structure of AZO/ZnO nanorods-CH3NH3PbIxCl3−x/carbon.

Electrodeposition of silver nanoparticle arrays on transparent conductive oxides

In this paper, we present a facile method for the preparation of silver nanoparticles on aluminum-doped zinc oxide (AZO) via electrodeposition techniques at room temperature. The morphology and structure of silver nanoparticles are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), respectively. Due to localized surface plasmon resonances, as-prepared silver nanoparticles on AZO glass exhibited different reflectivity in contrast with bare AZO glass. The weighted reflection of AZO substrate increased from 10.2% to 12.8%. The high reflection property of silver nanoparticle arrays on AZO substrate might be applicable for thin film solar cells and other optoelectronics applications.

Probing the Molecular Orientation of ZnPc on AZO Using Soft X-ray Spectroscopies for Organic Photovoltaic Applications

The interfacial electronic structure between zinc phthalocyanine (ZnPc) and aluminumdoped zinc oxide (AZO) substrates has been evaluated by ultraviolet photoemission spectroscopy and angle-dependent x-ray absorption spectroscopy to understanding the molecular orientation of a ZnPc layer on the performance of small molecule organic photovoltaics (OPVs). We find that the ZnPc tilt angle improves the π-π interaction on the AZO substrate, thus leading to an improved short-circuit current in OPVs based on phthalocyanine. Furthermore, the molecular orientation-dependent energy level alignment has been analyzed in detail using ultraviolet photoemission spectroscopy. We also obtained complete energy level diagrams of ZnPc/AZO and ZnPc/indium thin oxide.

Annealing effects on the optical and morphological properties of ZnO nanorods on AZO substrate by using aqueous solution method at low temperature

Vertically aligned ZnO nanorods (NRs) on aluminum-doped zinc oxide (AZO) substrates were fabricated by a single-step aqueous solution method at low temperature. In order to optimize optical quality, the effects of annealing on optical and structural properties were investigated by scanning electron microscopy, X-ray diffraction, photoluminescence (PL), and Raman spectroscopy. We found that the annealing temperature strongly affects both the near-band-edge (NBE) and visible (defect-related) emissions. The best characteristics have been obtained by employing annealing at 400°C in air for 2 h, bringing about a sharp and intense NBE emission. The defect-related recombinations were also suppressed effectively. However, the enhancement decreases with higher annealing temperature and prolonged annealing. PL study indicates that the NBE emission is dominated by radiative recombination associated with hydrogen donors. Thus, the enhancement of NBE is due to the activation of radiative recombinations associated with hydrogen donors. On the other hand, the reduction of visible emission is mainly attributed to the annihilation of OH groups. Our results provide insight to comprehend annealing effects and an effective way to improve optical properties of low-temperature-grown ZnO NRs for future facile device applications.

Nonlinear optical features of δ-BiB3O6/PVA polymer nanocomposites deposited on aluminum-doped zinc oxide substrates containing Ag nanoparticles

For the first time the Z-scan measurements and second harmonic generation of δ-BiB3O6:Pr3+ large-size nanocrystallites embedded into the polyvinyl alcohol (PVA) polymer matrices and deposited on AlZnO substrates decorated with Ag NP were studied. The comparison of the second and third order NLO is presented. The Z-scan measurements were done by 5ns Nd:YAG laser and the second harmonic generation was measured using the 25ns Nd:YAG laser with frequency repetition about 10Hz. The measurements have shown that both second as well as third-order susceptibilities are sensitive to the sizes of the Ag NP deposited on the AlZnO substrate. The obtained results confirm a principal role of the Ag NP on the output nonlinear optical properties which may be a consequence of the contribution of the low-dimensional nano-trapping levels.

Efficient indium-tin-oxide free inverted organic solar cells based on aluminum-doped zinc oxide cathode and low-temperature aqueous solution processed zinc oxide electron extraction layer

Indium-tin-oxide (ITO) free inverted organic solar cells (IOSCs) based on aluminum-doped zinc oxide (AZO) cathode, low-temperature aqueous solution processed zinc oxide (ZnO) electron extraction layer, and poly(3-hexylthiophene-2, 5-diyl):[6, 6]-phenyl C61 butyric acid methyl ester blend were realized in this work. The resulted IOSC with ZnO annealed at 150 °C shows the superior power conversion efficiency (PCE) of 3.01%, if decreasing the ZnO annealing temperature to 100 °C, the obtained IOSC also shows a PCE of 2.76%, and no light soaking issue is observed. It is found that this ZnO film not only acts as an effective buffer layer but also slightly improves the optical transmittance of AZO substrates. Further, despite the relatively inferior air-stability, these un-encapsulated AZO/ZnO IOSCs show comparable PCEs to the referenced ITO/ZnO IOSCs, which demonstrates that the AZO cathode is a potential alternative to ITO in IOSCs. Meanwhile, this simple ZnO process is compatible with large area deposition and plastic substrates, and is promising to be widely used in IOSCs and other relative fields.

Plasma enhanced chemical vapor deposition process optimization for thin film silicon tandem junction solar cells

Industry has previously established a 10% stable total module efficiency 1.1×1.3m2 thin film silicon tandem junction (TJ) module manufacturing baseline. A similar silicon TJ cell manufacturing process has been established, using a plasma enhanced chemical vapor deposition (PECVD) tool with an excitation frequency of 13.56MHz, which was modified to handle 30×30cm2 substrates. Extensive PECVD process window characterization was undertaken for the silicon layers that have the biggest impact on device performance. Single layer silicon on glass data and 1×1cm2 single junction and TJ solar cell data for amorphous intrinsic silicon and microcrystalline intrinsic silicon layers have been collected. Single layer characterization data for p-doped microcrystalline silicon oxide layer (μc-SiOx:H-p) for aluminum doped zinc oxide substrates is being presented, as well as solar cell data. The manufacturability of the μc-SiOx:H-p process is being considered. Finally, we present the best solar cell results obtained with the optimized PECVD process, as well as baseline performance data.

Laser stimulated light reflection reduction for silver nanoparticle-attached aluminum-doped zinc oxide substrate

A principal possibility to operate the light reflection within the 350nm–680nm spectra wavelength range and related extinction efficiency of silver nanoparticle-attached aluminum-doped zinc oxide substrate using an external laser light was shown. The treatment was performed by a nanosecond Nd:YAG (1064nm) and Er:glass (1540nm) lasers and by the corresponding bicolor regime. The principal role of the interfaces separating the ZnO:Al substrate and topology of Ag NP is established using AFM analysis of the Ag NP possessing 20nm, 40nm and 60nm average sizes. Different possible physical mechanisms are discussed including quadrupolar interaction of the electromagnetic wave and nanocomposites following the overlap between the surface plasmon resonance and the nano-trapping levels. The high selectivity to the photoexcited wavelength is explored. The sensitivity to the observed photoinducing laser wavelengths is discussed.

Pump-probe third harmonic generation kinetics of gold nanoparticle-attached aluminum-doped zinc oxide substrate

Size-aligned gold nanoparticles (AuNPs) of 5, 10, and 20nm were attached on aluminum-doped zinc oxide (Al–ZnO) substrates chemically using for the first time 3-aminopropyl-trimethoxysilane as a linker molecule. By using these substrates, we present the pump-probe studies of the AuNPs deposited on the Al–ZnO with the different particle sizes and inter-particle distances. The obtained results may be a consequence of interaction of surface Plasmon resonances with the intra-band contributions to the nonlinear optical susceptibilities and to the interactions with the phonons.

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.