Transmittance In Near-infrared Region Research Articles

28.3%-efficiency perovskite/silicon tandem solar cell by optimal transparent electrode for high efficient semitransparent top cell

Perovskites with tuned bandgap provide an attractive opportunity to realize perovskite/silicon tandem solar cells that offer tremendous potential in exceeding the intrinsic power conversion efficiency (PCE) of each subcell. The transparency and conductivity of the top electrode for top cell are the main keys in tandem solar cell. Here, we demonstrate a continuous, ultrathin Au film as the top electrode by introducing a Cr seed layer, which improves the efficiency of semitransparent perovskite devices and tandem solar cells. The Cr seed layer has large surface energy, which induces Au growth according to the Frank-van der Merwe principle to form a continuous, ultrathin film with exciting transmittance and conductivity. As a result, the highest PCE of 19.8% for semitransparent perovskite cells is achieved. The simulated optical field distribution by COMSOL and experimental results reveal that the semitransparent perovskite device has high transmittance in the near-infrared range, demonstrating that it is optimal top cell in a tandem solar cell with a silicon heterojunction device. The tandem solar cell, with the semitransparent perovskite top cell mechanically stacked on the silicon heterojunction bottom cell, demonstrates a PCE of 28.3%. This breakthrough in the design of the tandem cell architecture based on a transparent electrode offers an efficient route towards the transition of perovskite and tandem solar cells. The efficiency of 28.3% for 4T perovskite/silicon tandem solar cell is obtained using semitransparent perovskite top cell with the highest efficiency of 19.8% as a window, whose transparent electrode employs the ultrathin gold film possessed excellent conductivity and outstanding transmittance in near-infrared region. • The ultrathin hybrid metal transparent electrode has been developed to fabricate semitransparent perovskite solar cell. • A COMSOL Multiphysics software is employed to simulate the optical field distribution in semitransparent device. • The highest efficiency of 19.8% for semitransparent perovskite cell and 28.3%-efficiency are achieved.

Effect of thickness on characteristics of ZnSe thin film synthesized by vacuum thermal evaporation

Zinc selenide (ZnSe) thin films with various thicknesses were grown on ultrasonically clean glass substrates using vacuum evaporation of 99.99% pure ZnSe powder. Thickness dependence of the structural, optical and electrical properties was thoroughly investigated. X-ray diffraction (XRD) analyses revealed that (110) ZnSe plane is the dominant crystal plane for all the fabricated films. Both dislocation density and micro-strain go down with the increase in film thickness, indicating lower lattice defects and improvement in crystallinity at higher film thickness. Transmittance spectra show that all the films have almost linear upward tendency of transmittance in near-infrared region and small fluctuations in visible region for higher-thickness films. With the increase in film thickness, the optical bandgap increases and also an increasing tendency of dielectric constant was observed. Studies of electrical properties showed a sharp increase in carrier mobility and concentration with film thickness. As the film thickness increases from 30 to 90 nm, the carrier mobility goes up from 255 to 1250 cm2/VS and the carrier concentration increases from 2.14 × 1018 to 9.37 × 1018 cm−3. The electrical transport properties of the deposited thin films were explained in terms of scattering of the charge carrier.

Effect of residual water vapor on the performance of indium tin oxide film and silicon heterojunction solar cell

In this study, we investigate the effect of residual H2O pressure (PH2O) on the structural, electrical, and optical properties of indium tin oxide (ITO) film and the current-voltage (I-V) performance of silicon heterojunction (SHJ) solar cells. The ITO films and SHJ solar cell were prepared under different PH2O (3.75 × 10−7 Pa, 6 × 10−7 Pa, 10.25 × 10−7 Pa) by varying the pumping time before starting the fabrication process. The experimental results revealed the crystallinity of ITO films was suppressed with the increase in PH2O. Further, the sheet resistance of ITO films was reduced from 103 Ω/sq to 60 Ω/sq due to the enhanced carrier mobility, and the transmittance in near- infrared (NIR) region exhibited a slight increase, but the conversion efficiency of SHJ solar cells dropped dramatically from 23.3% to 22.79% due to the degradation of fill factor (FF). The analysis on n-a-Si:H/ITO and ITO/Ag contact properties indicated that such FF degradation could be attributed to the increased specific contact resistance for the two contacts, when PH2O was high. Finally, SHJ solar cell with conversion efficiency of 23.53% was achieved by restraining the residual H2O vapor during ITO deposition along with the optimization of transmittance in NIR region by adjusting the amount of O2 flow.

VO2-ZnO composite films with enhanced thermochromic properties for smart windows

VO2 film is a promising thermochromic material in smart windows due to its reversible metal to insulator transition (MIT) accompanied with an abrupt change of transmittance in near-infrared region at around 68 °C (T>68 °C, translucent; T < 68 °C, transparent), but which has not been widely applied because its low luminous transmittance (<60%) and solar modulation efficiency (<10%) are difficult to be improved simultaneously. In order to solve this problem, the ZnO-VO2 composite film was prepared by a facile method, in which commercial ZnO nanoparticles (NPs) and VO2 micro-particles were mixed by ball milling method to form the composites. By introducing ZnO NPs into the composite film, the luminous transmittance (Tlum) of the composite film was increased by 16.9% (from 54.9% to 63.9%) and the solar modulation efficiency (ΔTsol) was increased by 14.1% (from 9.9% to 11.3%) compared to the pure VO2 composite film. This was because ZnO NPs not only played the role of antireflection, but also prevented VO2 particles from agglomeration by dispersing around VO2 particles. Furthermore, the two-layered film based on ZnO-VO2 composites exhibited an astonishing ΔTsol of 18.8%, while maintaining excellent Tlum of 54.3%. This work could provide a simple and novel idea for us to improve the thermochromic properties of VO2 films and simultaneously to promote their practical application.

High transmittance in IR region of conductive ITO/AZO multilayers deposited by RF magnetron sputtering

The widely commercial used transparent conductive oxides (TCOs), such as ITO, combine ideal transmittance in visible light region and low electrical resistivity. However, its transmittance in near infrared (NIR) region is very limited. In contrast, AZO as a promising candidate of ITO possesses better optical transmittance in NIR region but presents poor electrical properties. In order to extend the applications of TCO materials in NIR region, ITO/AZO multilayers were designed in this work. The influence of the AZO monolayer thickness on the film's optoelectronic properties in NIR region was investigated. The results show that with AZO monolayer thickness increasing, the film's electrical resistivity increases, but always lower than that of single AZO film. In addition, the film's transmittance in NIR region is greatly improved by increasing AZO monolayer thickness. In point of the figure of merit, all ITO/AZO multilayers present enhanced optoelectronic properties in NIR region with respect to single ITO film or single AZO film. When AZO monolayer thickness is about 6nm, the optimal film is realized. Its resistivity is around 8.6 × 10−3Ωcm, while its average transmittance in NIR region reaches 90.0%.

Study on the thermal stability of Ga-doped ZnO thin film: A transparent conductive layer for dye-sensitized TiO2 nanoparticles based solar cells

Generally, optoelectronic devices are fabricated at a high temperature. So the stability of properties for transparent conductive oxide (TCO) films at such a high temperature must be excellent. In the paper, we investigated the thermal stability of Ga-doped ZnO (GZO) transparent conductive films which were heated in air at a high temperature up to 500°C for 30min. After heating in air at 500°C for 30min, the lowest sheet resistance value for the GZO film grown at 300°C increased from 5.5Ω/sq to 8.3Ω/sq, which is lower than 10Ω/sq. The average transmittance in the visible light of all the GZO films is over 90%, and the highest transmittance is as high as 96%, which is not influenced by heating. However, the transmittance in the near-infrared (NIR) region for the GZO film grown at 350°C increases significantly after heating. And the grain size of the GZO film grown at 350°C after annealing at 500°C for 30min is the biggest. Then dye-sensitized TiO2 NPs based solar cells were fabricated on the GZO film grown at 350°C (which exhibits the highest transmittance in NIR region after heating at 500°C for 30min) and 300°C (which exhibits the lowest sheet resistance after heating at 500°C for 30min). The dye-sensitized solar cell (DSSC) fabricated on the GZO film grown at 350°C exhibits superior conversion efficiency. Therefore, transparent conductive glass applying in DSSCs must have a low sheet resistance, a high transmittance in the ultraviolet–visible–infrared region and an excellent surface microstructure.

Tungsten-doped In 2O 3 transparent conductive films with high transmittance in near-infrared region

Polycrystalline tungsten-doped In 2O 3 (IWO) thin films prepared by dc reactive magnetron sputtering exhibit the high transparency in near-infrared region. The optoelectrical properties of the films were investigated in terms of different oxygen contents. The average transmittance of the films at oxygen content from 3.3% to 8.3% is approximately 90% in near-infrared region from 700 to 2500 nm, and about 94% in visible region from 400 to 700 nm. The high transparency is ascribed to the low carrier concentration of less than 3.8×10 20 cm −3 of IWO films. The as-deposited IWO films with minimum resistivity of 3.1×10 −4 Ω cm were obtained at 6.7% oxygen content. Carrier mobility reaches its highest value of 67 cm 2 V −1 s −1. Indium tin oxide (ITO) thin film prepared under the same sputtering condition shows a similar resistivity of 3.2×10 −4 Ω cm but a much lower mobility of 21 cm 2 V −1 s −1 and high carrier concentration of 9.4×10 20 cm −3, with the average transmittance of about 48% in near-infrared region and about 92% in visible region.

P-type strontium–copper mixed oxide deposited by e-beam evaporation

P-type thin films of strontium–copper mixed oxide have been deposited by e-beam evaporation technique on glass and quartz substrates starting from SrCu 2O 2 powders. A study of optical, electrical and structural properties was performed on the thin films, varying deposition parameters such as the substrate temperature and the oxygen partial pressure. For the first time, polycrystalline films of SrCu 2O 2 were obtained using e-beam evaporation in O 2 atmosphere at relatively low temperature (350 °C) with transparency of over 60% in the visible light range and a high optical transmittance in near-infrared region. The optical band gap of thin film was estimated to be ∼3.12 eV. Seebeck and Hall effects measurements confirmed the p-type nature of semiconductors and conductivity as high as 5.3×10 −2 S/cm for non-intentionally doped materials was measured. Hole concentration and mobility at room temperature were 1.5×10 17 cm −3 and 2.2 cm 2/Vs, respectively. X-Ray diffraction measurements revealed a polycrystalline structure of the films.