Aluminum-doped Zinc Oxide Research Articles

High figure-of-merit in Al-doped ZnO thin films grown by ALD through the Al content adjustment

The development of transparent conductive materials is of great interest for a wide variety of semiconducting devices in the fields of optoelectronics and photovoltaics. Here, we optimize the growth and properties of aluminum-doped ZnO (AZO) thin films as an eco-friendly transparent electrode by using atomic layer deposition (ALD) with diethylzinc (DEZn), water vapor and trimethylaluminium (TMA) as zinc, oxygen, and aluminum chemical precursors, respectively. The cycle ratio of DEZn to TMA using ALD is adjusted to control the Al atomic concentration over a broad range of 0.3 - 6.7% while optimizing the structural, optical, and electrical properties of AZO thin films. By incorporating a sufficient amount of Al dopants around 1.1%, we obtain a high quality AZO thin film exhibiting a low electrical resistivity of 6.3 × 10−4 Ω·cm. This AZO thin film grown on quartz substrate also demonstrates an average optical transmittance in the visible range above 85% as well as a high figure-of-merit of 6.4 × 10−3 Ω−1, while maintaining its highly c-axis oriented structure. The present optical and electrical properties result in the fabrication of AZO thin films by ALD with a high figure-of-merit that is highly suitable for many semiconducting devices.

All-optical passive photonic diodes based on perovskite and transparent conducting oxide material

Low dimensional perovskite emerging as a highly promising class of functional materials for semiconductor optoelectronic applications have drawn great attention. Here, we report the nonlinear absorption of low-dimensional perovskite PEA2PbI4 and transparent conducting oxide material Aluminum-doped zinc oxide (AZO) with operating spectral window in telecommunications. Then we fabricate all-optical diodes with nonreciprocity factor of 10.1 dB based on the reverse saturable absorber (PEA2PbI4) and the saturable absorber (AZO). The results show the potential applications of perovskite-based materials in all-optical diode, and may pave way for the development of high-performance photonic devices.

Ultralow Thermal Conductivity and Improved Thermoelectric Properties of Al‐Doped ZnO by In Situ O2 Plasma Treatment

The thriving of Internet‐of‐Things and integrated wireless sensor networks has brought an unprecedented demand for sustainable micro‐Watt‐scale power supplies. Development of high‐performing micro‐thermoelectric generator (μ‐TEG) that can convert waste thermal energy into electricity and provide sustainable micro‐Watt‐scale power is therefore extremely timely and important. Herein, a significant advance in the development of earth‐abundant, nontoxic thermoelectric materials of aluminum‐doped zinc oxide (AZO) is presented. Through nanostructure engineering using a novel in situ O2 plasma treatment, AZO films are demonstrated with ultralow thermal conductivity of 0.16 W m−1 K−1 which is the lowest reported in the literature. This nanostructured film yields a power factor of 294 μW m−1 K−2 at 563 K and has resulted in a state‐of‐the‐art ZT of 0.11 at room temperature and 0.72 at 563 K for AZO thin films. Furthermore, the fabrication and testing of a prototype lateral μ‐TEG are reported based on the AZO thin film which achieves a power output of 1.08 nW with an applied temperature difference of 16.9 °C.

Aluminum and Molybdenum Co-Doped Zinc Oxide Films as Dual-Functional Carrier-Selective Contact for Silicon Solar Cells.

Aluminum-doped zinc oxide (AZO) is considered as a promising candidate as transparent conductive oxide (TCO) for silicon heterojunction solar cells due to its high carrier density, nontoxic nature, and low cost. Herein, it is presented that the transparency of the AZO film can be optimized through co-sputtering of AZO and molybdenum oxide (MoOx). Furthermore, aluminum and molybdenum co-doped zinc oxide (MAZO) can be used as both the TCO layer and electron-selective contact (ESC) for silicon heterojunction solar cells. The surface morphology, cation oxidation state, and optical and electrical properties of all MAZO films are characterized. It is found that the transmittance of all MAZO films is significantly increased at a wavelength of 450-800 nm due to MAZO with a stronger Zn-O bond and a wider band gap. The conductivity of MAZO films is approximate to AZO films at a low MoOx target deposit power (50 W), and the sheet resistance of MAZO films increases significantly by increasing the deposition power up to 100 W. Finally, the optimized MAZO films are used as TCO and ESC for silicon heterojunction solar cells, showing a power conversion efficiency of 19.58%. The results show an effective stage to improve the optical properties of AZO through co-doping and the possibility of applying MAZO as a dual-functional layer for silicon solar cells.

Interfacial Engineering of a PCBM/AZO Electron Transport Bilayer for Efficient and Stable Inverted Perovskite Solar Cells

AbstractThe reduced hysteresis index and low‐temperature processed fabrication of inverted p‐i‐n perovskite solar cells (PSC) have attracted substantial attraction for achieving higher photovoltaic performance through interfacial engineering. Despite having certain limitations, fullerene‐based electron transport layers have been used frequently utilized in mixed halide inverted perovskite solar cells. The energy level mismatch between PCBM and metal electrode creates a hindrance in efficient electron extraction and thus a limiting factor in attaining higher device performances. In this work, we report an efficient interlayer of aluminum‐doped zinc oxide (AZO) nanoparticles in‐between PCBM and the metal electrode to suppress interfacial recombination. The PCBM/AZO electron transport bilayer can effectively mitigate the imperfections of the PCBM layer alone. The PCBM/AZO electron transport bilayer with an optimal concentration of 2% Al dopant exhibited greatly improved power conversion efficiency (PCE) of 18.63%, VOC of 1.13 V, and FF of 73% with negligible hysteresis index of 0.04. Further, the optimal device exhibited remarkable stability by retaining 91% of the initial PCE after 200 hours confirming the suitable insertion of the AZO bilayer. The improved photovoltaic performance using PCBM/AZO bilayer can be attributed to higher electron transfer efficiency, suppressed interfacial recombination, and smooth surface morphology of AZO nanoparticles atop the PCBM layer.

Rapid and accurate quality assessment method of recycled food plastics VOCs by electronic nose based on Al-doped zinc oxide

Plastic recycling technologies are being actively developed and implemented to cope with increasing volume of plastic. Such technologies require new analytical tools able to control the quality of the recycled polymers to be further integrated in production processes. Here, we propose a rapid and selective quality assessment method for polymer materials made of high-density polyethylene using electronic nose with aluminum doped zinc oxide sensing material in combination with the RandomForestClassifier machine learning tool. We test total content of volatile organic compounds both odor-active responsible for the smell and odorless of primary and secondary plastics, and evaluate corresponding organic vapors emitted by the plastics by headspace gas chromatography and mass-spectrometry at optimized conditions like sample temperature, sensor signal recovery time. The electronic nose demonstrated the good correlation of vector signal with the emitted volatile compounds with an accuracy more than 98.5% when discriminating between primary and secondary plastics. Addition of zeolites to the recycled plastic is shown to decrease the appearance of off-odors.

The role of a highly optimized approach with superior transparent conductive oxide anode towards efficient organic solar cell

The effort emphasizes the numerical analysis of different transparent conducting oxides (TCOs) perspectives, which include ITO, FTO, AZO, and IZO anode-based organic solar cells (OSCs) with the drift-diffusion approach. The prior selection of aluminum-doped zinc oxide (AZO) as TCO is feasible for more extended transparency and antireflection due to a tailored absorption wavelength of <380 nm and the factors of higher mechanical flexibility, low-cost processing, and realistic performance at lower temperatures. To confirm the stability and reproducibility of the design OSC, the contribution of each interfacial layer thickness, i.e., AZO as TCOs, P3HT: PC61BM as an organic absorbing layer (OAL), Spiro-OMeTAD (SOT) as a hole-transport layer (HTL), and ZnO as an electron-transport layer (ETL), is also investigated. Furthermore, functions of optimum trap-state densities () and charge carrier mobility () in OAL have been performed to aid in increasing the diffusion length of excitons carriers (). These properties led to better photogeneration and transport of charge carriers, decreasing the series resistance (RS), leading to lower bimolecular recombination, a long carrier lifetime (), and consequently higher power conversion efficiency (PCE). The findings revealed that the proposed OSC structure achieves an excellent PCE of 10.28% for AZO as TCO with an 850 nm ultra-thick OAL under AM 1.5 G light irradiation. Hence, a better fabrication process for efficient OSC could also be improved by the optimization of all these critical factors for future research.

Examining the potential of non-toxic stable double perovskite solar cells based on Cs2CuSbX6

The main issues impeding the commercialization of perovskite solar cells are their toxicity and long-term stability. Thus, it is essential to find a robust and reliable alternative light absorber that is environmentally friendly and provides stability. Herein, we present stable and lead-free Cs2CuSbX6 (where X = Cl, Br, and I) double perovskite light harvesters as a substitute, which can render excellent efficiency and long-term stability. The double perovskite solar cells based on the Cs2CuSbX6 light harvester, the aluminium-doped ZnO electron transport layer, and the MoO3 and Cu2O hole transport layers are critically evaluated using the SCAPS-1D software package. The densities of defects and dopants as well as the thickness of the succeeding layers of the double perovskite solar cells are altered to extract high efficiency. With aluminium-doped ZnO serving as the electron transport layer, the optimized Cs2CuSbI6-based double perovskite solar cells attain a power conversion efficiency (PCE) of about ∼29% for both MoO3 and Cu2O hole transport layers. Several potential back electrodes are also investigated, and their impact on performance is assessed. The fluctuation in PCE concerning operating temperature is computed for authentic analysis of the double perovskite solar cells during real-time operation. Overall, in order to achieve high PCEs in Cs2CuSbI6-based double perovskite solar cells, it is crucial to consider both the thickness of the light harvester layer and the bulk defect density.

Grass-like alumina enhances transmittance and electrical conductivity of atomic layer deposited Al-doped ZnO for thermoelectric and TCO applications

Transparent thermoelectric materials enable the integration of sensing and energy harvesting devices on various surfaces such as windows and user interfaces. A key constraint for device performance in such applications is the available surface area from which the thermoelectric power should be harvested without compromising the optical properties. Here, we demonstrate atomic layer deposition (ALD) of aluminum doped zinc oxide (AZO), the most prominent n-type thermoelectric material, on grass-like alumina (GLA), a high-performance, low-cost antireflective coating. The conformal nature of the ALD process enables the AZO growth to closely follow the topography of the underlying GLA film, therefore providing an increased effective surface area compared to a reference AZO film grown directly on plain glass. The films grown on GLA show an improved electrical conductivity attributed to additional doping by the GLA. The effect is pronounced at lower AZO thicknesses, resulting in a 228% increase in the electrical conductivity and an 80% increase in the thermoelectric power factor of 32 nm thick films. Moreover, the GLA-AZO films partly inherit the antireflective behavior of the GLA film, thus showing improved optical transparency compared to the reference AZO film on glass. Our results promote transparent thermoelectric devices with improved transparency and thermoelectric performance.

Effects of pre-heating method on the optical, wetting, photo-catalytic and UV sensing properties of Al:ZnO thin films

Aluminum doped zinc oxide thin films/ nanostructures have great importance in many technological applications such as transparent conducting oxides, photo-catalytic, electrochemical and opto-electronic devices. The pre-heating (drying) stage during sol–gel spin coating method is crucial for achieving better transparency level and smooth unstressed surface. In this research, effects of drying at fixed temperature (220 °C) and gradually rising temperature (rising rate 11 °C/min) under two different environments (i.e. temperature drying on i. hot plate ii. Oven) were explored. The SEM results showed that surface produced by fixed temperature drying on hot plate as well as in oven were cracked and rope stressed type, respectively. The texture obtained by gradually rising temperature was stressed granular on hot plate whereas uniformly distributed plane nano-granular in oven (on petri-dish). The XRD pattern revealed the polycrystalline nature and good crystal quality for sample with gradually rising temperature in oven. In case of gradually rising temperature in oven the maximum transmittance and band gap obtained were > 90% and 3.36 eV respectively. The refractive index and extinction coefficient were used to determine level of transparency in visible region by achieving values of 1.7 and 0.1 respectively. The super hydrophilic character achieved by contact angle 10° and better stain self-cleaning with degradation efficiency around 71% by photo-catalytic effect after UV irradiation. UV sensitivity was performed by using ardino microcontroller and max photo-response (voltage variation) was found 1.5 V. Moreover, response and recovery was around 14 s and 15 s respectively.

Al-ions effect on structural, optical, antibacterial, and photocatalytic activities of ZnO nanostructures

In this work, Pure and aluminum doped zinc oxide nanostructures were successfully synthesized through a well-established hydrothermal method. The hexagonal wurtzite structure, and nano porous shape for Al dopant in ZnO were confirmed via XRD and SEM analysis. The reduction in energy band gap (3.40 to 3.19 eV) for Al dopant samples and enhancement in inhibition zones (7 mm- 17 mm) for pure and Al-doped ZnO were recorded. The photocatalytic activity of Al doped ZnO was shown to be several times more efficient than in prior studies. The enhancement in these parameters suggest that these materials are good candidates for biomedical and optoelectronic applications.

Adaptive plasmonic metasurfaces for radiative cooling and passive thermoregulation

In this work, we investigate a class of planar photonic structures operating as passive thermoregulators. The radiative cooling process is adjusted through the incorporation of a phase change material (Vanadium Dioxide, VO2) in conjunction with a layer of transparent conductive oxide (Aluminum-doped Zinc Oxide, AZO). VO2 is known to undergo a phase transition from the “dielectric” phase to the “plasmonic” or “metallic” phase at a critical temperature close to 68°C. In addition, AZO shows plasmonic properties at the long-wave infrared spectrum, which, combined with VO2, provides a rich platform to achieve low reflections across the atmospheric transparency window, as demanded in radiative cooling applications, while also maintaining a compact size. Using numerical analysis, we study two classes of patterned and non-patterned compact multilayer metal-dielectric-metal metasurfaces, aiming to maximize the overall absorption in the first atmospheric transparency window (8–13 µm) while maintaining a high reflection across the solar spectrum (0.3–2.5 µm). Surfaces are initially designed based on a round of coarse optimization and further improved through analyzing the impact of geometric parameters such as size and periodicity of the metasurface elements. Our findings are relevant to applications in thermal regulation systems and passive radiative cooling of high-temperature devices, such as electronic elements.

Optimal of black anti-static AZO/Al2O3-SiO2-VxOy coatings for spacecraft stray light on high silicon aluminum alloys

It is still challenging to prepare an anti-static and anti-stray astigmatism coating on the high silicon aluminum alloy (>50 wt% Si, Al-50Si) for space material under extreme environments. To address these issues, the black anti-stray light coating with enhanced conductivity on the chemical etching surface of high-silicon Al-70Si alloy were successfully fabricated by the combination of plasma electrolytic oxidation (PEO) technology and deposited aluminum doped zinc oxide (AZO) transparent conductive film by magnetron sputtering technology. The microstructures, phase, elemental compositions, light absorption performance and electrical resistivity of coatings were tested and analyzed by SEM, EDS, XRD and XPS spectroscopy. The effects of process parameters including current density and AZO sputtering times on the structure, optical and electrical properties of the film layer were systematically studied. Convection through the fixation effect in the etched Al-70Si alloy porous layer promoted the internal heat and mass transfer during PEO process which is similar to previous reported mechanism of filling of cracks and pores by nanoparticles leading to the layer densification. The PEO coating had the highest absorptivity of 0.946 and it only decreased to 0.939 after AZO sputtering, at the same time the coating has the lowest resistivity of 1.04 × 107 Ω/sq, indicating excellent anti-stray light and antistatic ability. This two-step route pave the way to improve the conductivity without compromising optical properties of PEO coating on the high silicon aluminum alloy (>50 wt% Si, Al-50Si) for space material.

Surface modification of sputtered NiOx hole transport layer for CH3NH3PbI3 perovskite solar cells

The modification of the sputtered NiOx (x ≧ 1)/CH3NH3PbI3 interface by 2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl] phosphonic acid (MeO-2PACz) considerably enhances the power conversion efficiency of perovskite solar cells whose structure is ITO/NiOx/CH3NH3PbI3/[6,6]-phenyl C61 butyric acid methyl ester (PCBM)/aluminum-doped zinc oxide (AZO)/Ag. In devices without MeO-2PACz, the internal quantum efficiency (IQE) above 450 nm increases with the increase in NiOx thickness from 4 to 53 nm, although even in the thickest case, the IQE never reaches 90%. On the other hand, devices with MeO-2PACz modified NiOx show thickness-insensitive IQE of ca. 90%. We propose that (1) MeO-2PACz effectively fills the pinholes in thinner NiOx and (2) it passivates the carrier trapping/recombination defects at the NiOx/perovskite interface.

Towards All-Non-Vacuum-Processed Photovoltaic Systems: A Water-Based Screen-Printed Cu(In,Ga)Se2 Photoabsorber with a 6.6% Efficiency.

During the last few decades, major advances have been made in photovoltaic systems based on Cu(In,Ga)Se2 chalcopyrite. However, the most efficient photovoltaic cells are processed under high-energy-demanding vacuum conditions. To lower the costs and facilitate high-throughput production, printing/coating processes are proving to be effective solutions. This work combined printing, coating, and chemical bath deposition processes of photoabsorber, buffer, and transparent conductive layers for the development of solution-processed photovoltaic systems. Using a sustainable approach, all inks were formulated using water and ethanol as solvents. Screen printing of the photoabsorber on fluorine-doped tin-oxide-coated glass followed by selenization, chemical bath deposition of the cadmium sulfide buffer, and final sputtering of the intrinsic zinc oxide and aluminum-doped zinc oxide top conductive layers delivered a 6.6% maximum efficiency solar cell, a record for screen-printed Cu(In,Ga)Se2 solar cells. On the other hand, the all-non-vacuum-processed device with spray-coated intrinsic zinc-oxide- and tin-doped indium oxide top conductive layers delivered a 2.2% efficiency. The given approaches represent relevant steps towards the fabrication of sustainable and efficient Cu(In,Ga)Se2 solar cells.

Aluminum-doped zinc oxide (AZO) ultra-thin films deposited by radio frequency sputtering for flexible Cu(In,Ga)Se2 solar cells

Zinc oxide ultra-thin films doping with aluminum (AZO) were produced through radio frequency (rf) sputtering at a fixed pressure of 10 mTorr while varying the rf power between 80 and 140 W. The crystal structure of hexagonal Wurtzite was consistent throughout, with improved crystallinity observed at higher rf powers due to optimal diffusivity of the sputtered particles during nucleation and growth. The size of the crystallite was increased from 10.37 to 16.58 nm with increasing the rf power from 80 to 140 W. The Raman spectra provided evidence of the formation of ultra-thin AZO films, with discernable changes in morphology due to the influence of rf power. The value of optical band gap fluctuated between 3.49 and 3.58 eV as a function of rf power, a basis of the Burstein–Moss effect. The resistivity of the ultra-thin AZO films declined while augmenting rf power. A bilayer structure of intrinsic ZnO (i-ZnO) and AZO was fabricated and exhibited good transmittance, well-crystalline morphology, and excellent electrical conductivity. The optimized window layer (i-ZnO and AZO) was used to produce flexible Cu(In,Ga)Se2(CIGSe) solar cells with a photo conversion efficiency of 9.53%. Therefore, ultra-thin ZnO films exhibit potential as a favorable option for a window layer in the production of high-efficient flexible solar cells in cost effective way.

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.

Dye-sensitized solar cells with aluminum-doped zinc oxide nanoparticles-loaded electrolyte: A breakthrough solution for recombination and hysteresis suppression

Dye-sensitized solar cells (DSCs) suffer from reduced power conversion efficiency due to electron recombination with triiodide (I3−) ions at the photoanode/electrolyte interface. Organic additives are conventionally used in electrolyte to reduce recombination and improve the efficiency of the device. These additives react covalently with iodine (I2) in the electrolyte, leading to a reduction in the concentration of I3− ions. Other inorganic oxides, such as silica (SiO2), titania (TiO2), and magnesia (MgO), have been shown to improve the efficiency of the solar cell. These oxides can adsorb heavy ions to some extent. In this study, we investigated aluminum-doped zinc oxide nanoparticles (AZO NPs) as an inorganic additive with ionic adsorption properties towards I− and I3− anions in the electrolyte. We confirmed the ionic adsorption of AZO NPs through zeta potential and electrochemical impedance measurements. We observed a significant decrease in recombination between photogenerated electrons and electrolyte ions after adding AZO NPs, which resulted in an increase in open circuit voltage (VOC) and fill factor (FF) values. Furthermore, the incorporation of AZO NPs reduced the compelled hysteresis caused by the mismatch in current density-voltage curves for the forward and reverse scan direction. Mott-Schottky analysis confirmed the increase in VOC due to the negative shift in the Fermi level of the TiO2 photoanode. Additionally, open circuit voltage decay measurements indicated a longer electron lifetime at the TiO2/electrolyte interface in AZO NPs loaded electrolyte. Our findings suggest that AZO NPs have potential as an effective inorganic additive for improving the performance of DSCs.

RETRACTED: Interfacial passivation by Mono-ethanolamine in planar perovskite solar-cell

Aluminium doped zinc oxide (AZO) is a potential replacement for the conventionally used TiO2 as an electron transport layer (ETL) in low-temperature solution processes for hybrid perovskite solar cells (PvSCs). However, the defects and energy-band mismatch at the ETL/perovskite interface accelerate the interfacial carrier's recombination, leading to a decrease in the fill factor (FF) and current density (JSC). To address this issue, a thin interfacial modification layer of monoethanolamine (MEA) has been used which not only reduces the energy barrier between AZO/perovskite for accelerating the charge transfer but also passivates the trap states on the perovskite interface. Due to the synergistic effect of charge extraction promotion and trap density passivation , the champion PvSCs exhibit a higher value of PCE of 8.25 % with a current density (JSC) of 22.59 mA/cm2 and FF of 46.55% compared to the without MEA passivate PvSCs and the device maintains 70% of its topmost PCE after 1000 h under ambient atmosphere, without any encapsulation. This interface engineering based on MEA provides a feasible and excellent strategy to fabricate the PvSCs with improved efficiency and stability of planar device architecture.

Comparative Performance Evaluation of Transparent Conducting Oxides With Different Mobilities for All-Optical Switching in Silicon

All-optical switching is an appealing approach for signal processing, optical communications or sensing systems. In this work, we compare the performance of doped cadmium oxide, aluminum doped zinc oxide, and indium tin oxide as transparent conducting oxide (TCO) materials with different mobilities in thin-film configuration integrated into a hybrid silicon photonic waveguide. Our results reveal the best operational parameters and trade-offs for enabling high-performance and energy-efficient switching by using TCOs with moderate mobility but more environmental-friendly. Extinction ratios of 10 dB∙μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and insertion losses of 2 dB∙μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> are achieved by an AZO/Si amplitude switch with an energy consumption of only 90 fJ. These results reveal that cadmium-free TCO materials can also be leveraged to build high-performance all-optical switches in silicon.