RESUMEN
A typical piezoelectric energy harvester is a bimorph cantilever with two layers of piezoelectric material on both sides of a flexible substrate. Piezoelectric layers of lead-based materials, typically lead zirconate titanate, have been mainly used due to their outstanding piezoelectric properties. However, due to lead toxicity and environmental problems, there is a need to replace them with environmentally benign materials. Here, our main efforts were focused on the preparation of hafnium-doped barium titanate (BaHfxTi1-xO3; BHT) sol-gel materials. The original process developed makes it possible to obtain a highly concentrated sol without strong organic complexing agents. Sol aging and concentration can be controlled to obtain a time-stable sol for a few months at room temperature, with desired viscosity and colloidal sizes. Densified bulk materials obtained from this optimized sol are compared with a solid-state synthesis, and both show good electromechanical properties: their thickness coupling factor kt values are around 53% and 47%, respectively, and their converse piezoelectric coefficient d33∗ values are around 420 and 330 pm/V, respectively. According to the electromechanical properties, the theoretical behavior in a bimorph configuration can be simulated to predict the resonance and anti-resonance frequencies and the corresponding output power values to help to design the final device. In the present case, the bimorph configuration based on BHT sol-gel material is designed to harvest ambient vibrations at low frequency (<200 Hz). It gives a maximum normalized volumetric power density of 0.03 µW/mm3/Hz/g2 at 154 Hz under an acceleration of 0.05 m/s2.
RESUMEN
Due to their excellent properties, Zinc oxide nanowires (ZnO NW) have been attractive and considered as a promising electron-transporting layer (ETL) in flexible Perovskite Solar Cells (FPSCs). Since the first report on ZnO NWs-based FPSCs giving 2.6 % power conversion efficiency (in 2013), great improvements have been made, allowing to reach up toâ¼15 % nowadays. However, some issues still need to be addressed, especially on flexible substrates, to achieve uniform and well-aligned ZnO NWs via low-cost chemical solution techniques. Several parameters, such as the growing method (time, temperature, precursors concentration), addition of seed layer (thickness, roughness, annealing temperature) and substrate (rigid or flexible), play a crucial role in ZnO NWs properties (i.e., length, diameter, density and aspect ratio). In this review, these parameters allowing to control the properties of ZnO NWs, like the growth techniques, utilization of seed layers and the growing method (time or precursors concentration) have been summarized. Then, a particular focus on the ZnO NW's role in FPSCs as well as the use of these results on the development of ZnO NWs-based FPSCs have been highlighted.
RESUMEN
ZnO nanowires (NWs) are very attractive for a wide range of nanotechnological applications owing to their tunable electron concentration via structural and surface defect engineering. A 2D electrical profiling of these defects is necessary to understand their restructuring dynamics during engineering processes. Our work proposes the exploration of individual ZnO NWs, dispersed on a SiO2/p++-Si substrate without any embedding matrix, along their axial direction using scanning capacitance microscopy (SCM), which is a useful tool for 2D carrier profiling. ZnO NWs are hydrothermally grown using 0-20 mM ammonium hydroxide (NH4OH), one of the reactants of the hydrothermal synthesis, and then annealed in a tube oven at 350 °C/1.5-15 h and 450 °C/15 h. While the as-grown ZnO NWs are highly conductive, the annealed ones exhibit significant SCM data with a high signal-to-noise ratio and temperature-dependent uniformity. The SCM signal of ZnO NWs is influenced by both their reduced dimensionality and the electron screening degree inside them. The electrical activity of ZnO NWs is only observed below a critical defect concentration that depends on the annealing temperature. Optimal SCM signals of 200 and 147 mV are obtained for samples with 0 and 20 mM NH4OH, respectively, and annealed at 350 °C/15 h. The corresponding electron concentrations of 3.27 × 1018 and 4.58 × 1018 cm-3 were estimated from the calibration curve, respectively. While thermal treatment in air of ZnO NWs is an effective approach to tune the defect density, 2D electrical mapping enables identifying their optimal electrical characteristics, which could help to boost the performance of final devices exploiting their coupled semiconducting-piezoelectric properties.
RESUMEN
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.
RESUMEN
Flexible piezoelectric nanogenerators (PENGs) are very attractive for mechanical energy harvesting due to their high potential for realizing self-powered sensors and low-power electronics. In this paper, a PENG that is based on zinc oxide (ZnO) nanowires (NWs) is fabricated on flexible and transparent Polydimethylsiloxane (PDMS) substrate. The ZnO NWs were deposited on two different seed layer structures, i.e., gold (Au)/ZnO and tin-doped indium-oxide (ITO)/ZnO, using hydrothermal synthesis. Along with the structural and morphological analyses of ZnO NWs, the electrical characterization was also investigated for ZnO NWs-based flexible PENGs. In order to evaluate the suitability of the PENG device structure, the electrical output performance was studied. By applying a periodic mechanical force of 3 N, the ZnO NWs-based flexible PENG generated a maximum root mean square (RMS) voltage and average power of 2.7 V and 64 nW, respectively. Moreover, the comparison between the fabricated device performances shows that a higher electrical output can be obtained when ITO/ZnO seed layer structure is adopted. The proposed ZnO NWs-based PENG structure can provide a flexible and cost-effective device for supplying portable electronics.
RESUMEN
In this study, different seed layers like gold (Au), zinc oxide (ZnO) and aluminum-doped ZnO (AZO) have been associated to ZnO nanowires (NWs) for the development of mechanical energy harvesters. ZnO NWs were grown by using a low temperature hydrothermal method. The morphological properties were investigated using Scanning Electron Microscopy (SEM) and the analysis of crystalline quality and growth orientation was studied using X-ray Diffraction (XRD). The obtained ZnO NWs are found to be highly dense, uniformly distributed and vertically well aligned on the ZnO and AZO seed layers, while ZnO NWs grown on Au possess a low density and follow a non-uniform distribution. Moreover, the NWs exhibited good crystal quality over the seed layers. The piezoelectric nanogenerator (PENG) consists of ZnO NWs grown on the three different seed layers, parylene-C matrix, Ti/Al top electrode and poly(dimethylsiloxane) (PDMS) encapsulated polymer composite. The measurements of the open circuit voltage (VOC) were around 272 mV, 36 mV for ZnO, AZO seed layers while the PENG including Au seed layer presented a short-circuited state. This study is an important step in order to investigate the effect of different seed layers influencing the magnitude of the generated electrical performances under identical growth and measurement conditions. It will also help identify the most suitable seed layers for energy harvesting devices and their future integration in industrial applications.
RESUMEN
The production of high-quality semiconducting nanostructures with optimized electrical, optical, and electromechanical properties is important for the advancement of next-generation technologies. In this context, we herein report on highly obliquely aligned single-crystalline zinc oxide nanosheets (ZnO NSs) grown via the vapor-liquid-solid approach using r-plane (01-12) sapphire as the template surface. The high structural and optical quality of as-grown ZnO NSs has been confirmed using high-resolution transmission electron microscopy and temperature-dependent photoluminescence, respectively. To assess the potential of our NSs as effective building materials in high-performance flexible electronics, we fabricate organic (parylene C)/inorganic (ZnO NS) hybrid field-effect transistor (FET) devices on flexible substrates using room-temperature assembly processes. Extraction of key FET performance parameters suggests that as-grown ZnO NSs can successfully function as excellent n-type semiconducting modules. Such devices are found to consistently show very high on-state currents (Ion) > 40 µA, high field-effect mobility (µeff) > 200 cm2/(V s), exceptionally high on/off current modulation ratio (Ion/off) of around 109, steep subthreshold swing (s-s) < 200 mV/decade, very low hysteresis, and negligible threshold voltage shifts with prolonged electrical stressing (up to 340 min). The present study delivers a concept of integrating high-quality ZnO NS as active semiconducting elements in flexible electronic circuits.
RESUMEN
The production of large quantities of single crystalline semiconducting ZnO nanowires (NWs) at low cost can offer practical solutions to realizing several novel electronic/optoelectronic and sensor applications on an industrial scale. The present work demonstrates high-density single crystalline NWs synthesized by a multiple cycle hydrothermal process at â¼100 °C. The high carrier concentration in such ZnO NWs is greatly suppressed by a simple low cost thermal annealing step in ambient air at â¼450 °C. Single ZnO NW FETs incorporating these modified NWs are characterized, revealing strong metal work function-dependent charge transport, unobtainable with as-grown hydrothermal ZnO NWs. Single ZnO NW FETs with Al as source and drain (s/d) contacts show excellent performance metrics, including low off-state currents (fA range), high on/off ratio (10(5)-10(7)), steep subthreshold slope (<600 mV/dec) and excellent field-effect carrier mobility (5-11 cm(2)/V-s). Modified ZnO NWs with platinum s/d contacts demonstrate excellent Schottky transport characteristics, markedly different from a reference ZnO NW device with Al contacts. This included abrupt reverse bias current-voltage saturation characteristics and positive temperature coefficient (â¼0.18 eV to 0.13 eV). This work is envisaged to benefit many areas of hydrothermal ZnO NW research, such as NW FETs, piezoelectric energy recovery, piezotronics and Schottky diodes.
RESUMEN
A perfect control of nanostructure growth is a prerequisite for the development of electronic and optoelectronic device/systems. In this article, we demonstrate the growth of various ZnO-derived nanostructures, including well-ordered arrays of high aspect ratio single crystalline nanowires with preferred growth direction along the [0001] axis, nanowalls, and hybrid nanowire-nanowall structures. The growths of the various ZnO nanostructures have been carried out on SiC substrates in a horizontal furnace, using Au thin film as catalyst. From experimental observations, we have ascribed the growth mechanisms of the different ZnO nanostructures to be a combination of catalytic-assisted and non-catalytic-assisted vapor-liquid-solid (VLS) processes. We have also found that the different ZnO nanoarchitectures' material evolution is governed by a Zn cluster drift effects on the SiC surface mainly driven by growth temperature. Au thin film thickness, growth time, and temperature are the parameters to optimize in order to obtain the different ZnO nanoarchitectures.