Transparent Conductive Oxide Glass Research Articles

(Invited) Exploitation of Advanced Materials and Process for Sustainable Perovskite Solar Cells

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to 26.1% and further improvements are expected up to 27%. Now, the research on perovskite solar cells (PSCs) has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, Pb-related hazardous materials, and environmentally-burdened toxic solvent-based process need to be solved.This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass [1, 2]. Also, novel strategies for recycling toxic solvents such as DFM, used in fabricating PSCs are introduced, which is critical to realize close loop recycling process of PSCs. Finally, recent studies for achieving high efficiency PSC using ecofriendly solvent are demonstrated.

Electrical energy efficiency of dye sensitized solar cells by polymer electrolyte

This research aims to prepare by mixtures method with dope carbon black as a working electrode and the apply it to the dye sensitized solar cells (DSSCs). The thin film of titanium dioxide nanocrystalline semi - conductor with dope carbon black, the cells were coated on to transparent conducting oxide glass sheet by means of the doctor blade technique as a working electrode. But the polymer electrolyte were prepare by adding potassium iodide and iodine salts with a ratio of KI:I2 was 10:1, into a polymer electrolyte composed of poly-ethylene glycol, ethylene carbonate and poly(styrene–co–acrylonitrile). The polymer electrolyte mixtures became homogeneous and stirring at a temperature of 80 °C. Found that efficiency for the DSSCs by polymer electrolyte based on yielded an overall light to electrical energy conversion efficiency ( ) of the DSSCs was 5.5095%, An open-circuit voltage of 0.58 V, voltage at the point of maximum power output of 0.42 V, short-circuit current density of 11.11 mA.cm–2, current density at the point of maximum power output of 10.50 mA.cm–2 fill factor of 0.684 under an irradiation of 80 mW.cm–2. And the long-term stability test of the DSSCs with a polymer electrolyte is evidently superior to the DSSCs with liquid electrolyte based on the observation period lasting for 90 days. GRAPHICAL ABSTRACT HIGHLIGHTS prepare by mixtures method with dope carbon black as a working electrode The efficiency for the DSSCs by polymer electrolyte based on yielded an overall light to electrical energy conversion

(Invited) Progress in Materials and Process for Sustainable Perovskite Solar Cells

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells (PSCs) has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, simple fabrication technologies for realizing large scale perovskite module are introduced and recent effort for achieving high efficiency module is going to be presented. Finally, recent interesting results regarding ultra flexible perovskite cells will be discussed.

Conductive Glass with Simple Spray Deposition Method for Dye-Sensitized Solar Cell Application

Dye-sensitized solar cells utilize a transparent conductive oxide (TCO) glass which is mainly Fluorine-doped tin oxide (FTO) for the working electrode and counter electrode. The TCO is one of the important parts of DSSC. TCO glass becomes the part that determines the price of mass production of DSSC. Low-cost TCOs with high conductivity and high light transmittance are required. In this study, We proposed a simple fabrication of TCO glass by spray deposition method of Tin (II) Chloride (SnCl2) on top of the lime glass substrate. Fabrication was started with 3 mm of Lime glass cleaned with distilled water and ethanol in sonication for 15 minutes and 10 minutes heating at 500°C. The variation of layer thickness was performed by multilayer spray using 2 mg SnCl2 and 5 ml ethanol mixture and then baked for 10 minutes at 500°C. The electrical conductivity, light transmittance, and roughness of the glass at one spray layer were 20 Ω/cm2, 87.1 %, and 0.010 µm respectively, and decrease along with the increase of the number of spray layers. A multimeter, UV-VIS Spectrophotometer, and 3D Measuring Laser Microscope are used to measure these parameters in this study. Compared to the properties of commercially available Fluorine doped Tin Oxide (FTO) glass, this method can be used as an alternative for conductive glass production for Dye-Sensitized Solar cells.

Understanding the Interfacial Reactions and Band Alignment for Efficient and Stable Perovskite Solar Cells Built on Metal Substrates with Reduced Upscaling Losses.

Conventional perovskite solar cells (PSC) built on transparent conductive oxide (TCO) glass face a fundamental challenge to retain fill factor (FF) for large-area upscaling due to series resistance loss. Building a perovskite solar cell on metal has the potential to reduce this FF loss and is promising for flexible applications. However, their efficiency and stability lag far behind their TCO counterparts. Herein, findings on the complex chemical reactions and degradation-promoting processes at different perovskite/metal (Cu, Au, Ag, and Mo) interfaces, which are closely linked with the inherent stability; and the interlayer engineering for perovskite/metal interface's band alignment, which plays an essential role in achieving high efficiency, are reported. Leveraging these findings, 21% power conversion efficiency (PCE) is achieved for 1 cm2 perovskite solar cells using a p-i-n top-illumination structure on a molybdenum substrate, the highest reported for a PSC built on metal. Notably, the FF and PCE losses due to area upscaling are remarkably reduced by one order of magnitude relative to the counterparts on conventional TCO glass, highlighting an alternative pathway for PSC upscaling and module design.

Synthesis and multicolored electrochromism of polycarbazoles containing oxadiazole

A carbazole derivative (COP) containing (trifluoromethyl)pyridine and oxadiazole and a carbazole derivative (COI) containing isoxazole and oxadiazole are synthesized, and their corresponding polymers (P(COP) and P(COI)) are electrosynthesized on a transparent conductive indium tin oxide glass surface using potentiostatic techniques. The P(COP) and P(COI) films exhibit reversible electrochemical and spectrochemical behaviors from the neutral-to-oxidized and oxidized-to-neutral states. The P(COP) is yellow ocher, grayish-green, and khaki green at 0.0, 1.4, and 1.5 V, respectively, whereas P(COI) is light grayish-green, light greenish-yellow, and light green at 0.2, 1.2, and 1.4 V, respectively, in solutions. The P(COP) demonstrates a transmittance change (ΔT = 40.1% at 1100 nm) and an adequate coloration efficiency (η = 162.1 cm2 C−1 at 1100 nm). Dual-layer polymeric electrochromic devices (ECDs) are fabricated using polycarbazoles containing oxadiazole and poly(3,4-propylenedioxythiophene) (PProD) as the anodic and cathodic layers, respectively. The P(COI)/PProDBz2 ECD displayed four color transitions (light bluish-gray, bluish-gray, xenon blue, and indigo) from the bleached to the colored state. Moreover, the P(COP)/PProDBz2 ECD displays a considerable ΔT (48.0% at 624 nm), and the P(COI)/PProDBz2 ECD displays a substantial coloration efficiency (η = 530.6 cm2 C−1 at 623 nm). In addition, polycarbazoles containing oxadiazole/PProD ECDs demonstrate high electrochemical redox stability and a short bleaching and coloring time. These findings indicate that polycarbazoles containing oxadiazole are promising electrochromic materials and can be used in multicolored and energy-saving ECDs.

Cylindrical transparent conductive oxide-free dye-sensitized solar cells with treated flat titanium sheet

Conventional dye-sensitized solar cells (DSSCs) require two transparent conductive oxide (TCO) glasses as working and counter electrodes and are one of the most costly components posing an appreciable cost burden for production and commercialization. To circumvent this issue, we propose a TCO-free device structure utilizing titanium (Ti) sheets as a substitute for TCO. This back contact device structure not only allows the removal of the costly TCO component from the working electrode but also enhances the extent of photons absorbed by the photoanode. A flat titanium sheet with microholes (FTS-MH) was successfully applied to fabricate cylindrical TCO-free-DSSCs) with a titanium sheet as a back contact electrode. When the H2O2 surface-treated FTS-MH substrate generating dense anatase TiO2 nanosheets was used as a photoanode, there was a pronounced improvement in efficiency from 5.76% to 8.59%. This was mainly attributed to the lower interfacial resistance facilitated by improved electrical contact between the conducting FTS-MH substrate and mesoporous TiO2 layer since enhancement in the dye loading was only 8.6%.

(Invited) Functional Materials and Sustainable Process for Commercialization of Perovskite Solar Cells

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells (PSCs) has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, simple fabrication technologies for realizing large scale perovskite module are introduced and recent effort for achieving high efficiency module is going to be presented. Precursor technology is of great importance for yielding high efficiency and reproducibility of PSC, which is one of topics in this talk.

Reassessment of different flat TCO integrated reflectors for the crystalline silicon solar PV module in view of its longer operational life

AbstractIn the present simulation work with experimental validation, the performance of a transparent conductive oxide (TCO) film‐coated spectrally selective reflector in the low‐concentrated photovoltaic application has been analysed. The use of mirrors in solar photovoltaic (PV) applications is a well‐established thing. However, it increases the operating temperature and requires more thermally stable, expensive solar modules. In this regard, for the first time, commercially available TCO‐coated glasses such as fluorine‐doped tin oxide (FTO) and indium tin oxide (ITO) have been integrated with mirrors. The spectrally selective reflector is a promising technology to achieve a high‐power yield from the commercially available crystalline silicon photovoltaic (C‐Si PV) module during its lifetime. They have the property to absorb unwanted photons in the region of the AM1.5 spectrum (1200 to 2000 nm), which partially thermalises the solar module through plasmonic absorption. The present study found that the proposed approach helps to restrict the increase in PV module temperature caused by the reflected rays from a mirror. The electrical performance of a standalone C‐Si PV was compared with that of the same system after the addition of FTO, ITO and a conventional mirror system. Our analysis indicates that, with the mirror integration, the degradation rate can increase to 1.5% per year if the standalone PV module's ageing rate is 0.8% per year. Through FTO incorporation with the same, the ageing rate has been reduced by up to 1.18% per year due to a reduction in temperature. This result is quite interesting, considering that spectrally selective reflectors do not stop high‐energy photons from thermalizing the PV module. The entire work has been done on commercially available materials, which makes it easier and ready to be implemented in large PV plants.Highlights A spectrally selective mirror for PV power boosting. Transparent conductive oxide (TCO) glass integration with mirror reduces the IR concentration approximately 50%. The reduction in thermalisation of PV module from the mirror by 3–5°C. This integration increases the PV module operational life by at least 4 years compared with commercial mirror.

Dye and activated carbon from Canarium ovatum Engl. as photosensitizer and counter electrode for Titania-based dye sensitized solar cell

Natural dye from exocarp and activated carbon from charred shells of Canarium ovatum Engl nut was used in the fabrication of dye sensitized solar cell (DSSC). Anatase titania (titanium dioxide, TiO2) nanoparticles was used as semiconducting layer deposited on a transparent conductive indium tin oxide glass using doctor blade method. TiO2 film thickness and soaking time in dye were varied to show response in terms of fill factor (FF), short circuit current density (Jsc), open circuit photovoltage (Voc), and conversion efficiency (η). In a 2.0 cm2 active surface area tested under solar irradiance, assembled DSSC at optimum conditions garnered 0.768 desirability with FF, Jsc, Voc and n values of 0.601, 6.293 mA/cm2, 0.446 V, and 1.792, respectively.

(Invited) Progress in Materials and Process of Perovskite Solar Cells Toward Commercialization

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, recent interesting results regarding ultra-flexible perovskite cells will be discussed in terms of stress analysis. Finally, simple fabrication technologies for realizing large scale perovskite module is going to be introduced.

Effect of sputtering gas pressure on the performance of WO3 thin films electrochromic device

WO3 films were deposited on transparent conductive indium tin oxide (ITO) glass under different working pressure conditions via radio frequency magnetron sputtering technology, and their electrochromic properties were studied. The morphology, electrochromic cyclic voltammetry characteristics, and light modulation properties of the films were studied using a scanning electron microscope, an electrochemical test station, and an ultraviolet-visible spectrophotometer. The transmittance modulation amplitude increases first and then decreases with the change of sputtering gas pressure, reaching the maximum transmittance modulation amplitude at 1.0 Pa. For the response time, the increase in sputtering gas pressure also shows a change of shortening and then increasing. By comprehensively considering the stability of the transmittance modulation amplitude and the stability of the response time, it can be found that as the sputtering gas pressure increases, the stability of the device’s electrochromic performance increases first and then decreases. Therefore, the sputtering gas pressure needs to be maintained in a relatively reasonable range. When it is too high or too low, it is not conducive to achieving good stability.

Direct Growth of Vertically Aligned Carbon Nanotubes onto Transparent Conductive Oxide Glass for Enhanced Charge Extraction in Perovskite Solar Cells

AbstractVertically aligned carbon nanotubes (VACNTs) present an exciting avenue for nanoelectronics due to their predetermined orientation and exceptional transport capabilities along the tube length, with the potential to be employed in a variety of optoelectronic applications. However, growth of VACNTs using conventional chemical vapor deposition (CVD) methods requires elevated temperatures (>720 °C) and therefore, the suitability of commonly used transparent conductive oxide (TCO) glasses, such as fluorine‐doped tin oxide (FTO) and indium‐tin oxide (ITO), as the substrates for nanotube growth are limited by their temperature‐sensitive nature. Here, the successful growth of multi‐walled VACNTs directly onto commonly used TCO glasses, FTO and ITO, using the photo‐thermal chemical vapor deposition (PTCVD) growth method is reported. The benefit of reflection, within the infrared region, of the TCO substrate and the effect of surface roughness on the growth of VACNTs is investigated. The application of VACNTs on ITO in inverted planar perovskite solar cells is investigated, which shows superior charge transfer, larger grain sizes in the perovskite film, and a champion device efficiency approaching 16%.

(Invited) Exploitation of Innovative Materials and Process of Perovskite Solar Cells Toward Commercialization

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, recent interesting results regarding ultra-flexible perovskite cells will be discussed in terms of stress analysis. Finally, simple fabrication technologies for realizing large scale perovskite module is going to be introduced.

Broadband enhancement of devices and microsystems for light harvesting and photocatalysis

Plasmonic materials, stochastically roughened, can provide localized field enhancement under optical irradiation (light trapping). The use of plasmonic materials in semiconductor photocatalists also leads to drastic enhancement of their photoreactivity. Plasmonic enhancement can be seen in an extension of the useful range of solar spectrum, and in a high increase of the amount of collected light energy. The structures we propose here not only can be utilized for a vast majority of photocatalytic systems (including those microreactor-based,) but also for the enhancement of light harvesting devices of any kind, including all types of solar cells, as well as for ultrasensitive chemical sensing. Here we consider a structure with a roughened metallic film on the bottom and a roughened transparent conductive oxide (TCO) or silica glass layer on the top, separated by a thin dielectric layer. We fabricated experimental structures and simulated their electromagnetic properties by the finite element method. Thus we verified that the combined influence of two rough films significantly improves light trapping within the dielectric layer between them, while plasmonic effects lead to concentration of electromagnetic field into subwavelength volumes. Consequently, the radiation intensities are vastly increased within the dielectric layer, even for several orders of magnitude, compared to the incident beam. Another interesting property observed is that while both TCO and silica glass structures act as diffractive light traps well into the UV range, the TCO structure simultaneously acts as a plasmonic superabsorber for IR light, turning the increase of TCO opaqueness with wavelength into a benefit since it significantly expands the useful spectral range. Tuning of dopant levels in TCO or using alternative plasmonic materials, together with varying coarseness of the films can further be used to tailor the electromagnetic response.

A novel cheap, one-step and facile synthesis of hierarchical TiO2 nanotubes as fast electron transport channels for highly efficient dye-sensitized solar cells

The well-aligned hierarchical TiO2 nanotubes (HTNTs) have been synthesized by a one-step hydrothermal method employing potassium titanium oxalate, ethanol and H2O, which are strongly adhered onto transparent conducting oxide glass. The preparation is straightforward, cheap and applicative for mass manufacture. The thickness of membranes is changed from 12 to 22 μm by adjusting the reaction time. The HTNTs consist of one-dimensional (1D) long TiO2 nanotube trunks and numerous short TiO2 nanorod branches, which can balance surface area and charge transport. By employing optimized HTNTs for dye-sensitized solar cells, a remarkable power conversion efficiency of 9.89% is obtained. The result is superior to P25 (8.34%), because 1D trunk-1D branch structure of HTNTs offers the advantages of strong light-harvesting, directed electron transport, and efficient charge collection. The HTNTs may find an underlying application in the manufacture of photovoltaic devices.

Transparent 3 nm-thick MoS2 counter electrodes for bifacial dye-sensitized solar cells

Molybdenum disulfide (MoS2) counter electrode (CE) is considered one of the most viable alternatives to Pt CE in dye-sensitized solar cells (DSSCs) owing to its abundance, low cost, and superior electrocatalytic activity. However, mostly, MoS2 CEs for DSSCs are prepared by conventional chemical reactions and annealing at a high temperature. By these conventional processes, deposition of sufficiently thin and transparent MoS2 layers is challenging; therefore, bifacial DSSCs employing transparent MoS2 CEs have not been studied. Here, we report transparent few-nanometer-thick MoS2 CEs prepared by atomic layer deposition at a relatively low temperature (98°C) for bifacial DSSC applications. MoS2 nanofilms with precisely controlled thicknesses of 3–16nm are conformally coated on transparent conducting oxide glass substrates. With increase in the MoS2 nanofilm thickness, the MoS2 CE electrocatalytic activity for the iodide/triiodide redox couple enhances, but its transparency decreases. Notably, the application of a thinner MoS2 nanofilm in a bifacial DSSC leads to lower conversion efficiency under front-illumination, but higher conversion efficiency under back-illumination. In particular, only the 3nm-thick MoS2 nanofilm shows reasonable photovoltaic performances under both front- and back-illumination conditions.

Photodetector Characterization Based on DSSC (Dye-Sensitized Solar Cell)

A photodetector performance as a light sensor based on the design and material of DSSC (Dye-Sensitized Solar Cell) has been characterized. Oxide Semiconductor nanoparticle of TiO2 and extracted natural dye are used to absorb and convert incident photon to electric energy using a sandwich structure of 1.5 x 1.5 cm2 active area. The sensor materials were used include TCO (Transparent Conductive Oxide) glass as substrate, electrolyte solution and carbon. Method of TiO2 deposition to the TCO glass substrate is spin coating and firing at 1,500 rpm and 450 °C, respectively. Natural dye was extracted from green algae by a different variation of solution concentration according to the ratio of mass and volume. The chlorophyll absorbance was investigated by spectrophotometer at a wavelength of 300-800 nm. SEM (Scanning Electron Microscope) is used to observe TiO2-coated TCO glass morphology. Fabricated sensors are characterized according to the electrical parameters of voltage and current towards light illuminance from the light source. This natural dye-based optical photodetector performance has been analysed to obtain linearity, sensitivity, uncertainty error, and other electrical transient response characteristics. The result of extracted chlorophyte absorbance shows a wavelength peak at 580 to 680 nm with different intensity; it indicates the visible light absorbance spectra occurred. Sensor measurement using light illumination up to 30,000 lux produces the highest rated voltage of 626.4 mV and current 78,7 (µA) at the ratio of 6:5 (m:v) solution. This sensor has a voltage sensitivity of 1,0875 mV/10lux and the current sensitivity of 0.0024 µA/lux. The voltage and current uncertainty error are 0.36% and 0.481%, respectively.

Pulsed Laser Fabrication of TiO2 Buffer Layers for Dye Sensitized Solar Cells.

We report on the fabrication of dye-sensitized solar cells with a TiO2 buffer layer between the transparent conductive oxide substrate and the mesoporous TiO2 film, in order to improve the photovoltaic conversion efficiency of the device. The buffer layer was fabricated by pulsed laser deposition whereas the mesoporous film by the doctor blade method, using TiO2 paste obtained by the sol–gel technique. The buffer layer was deposited in either oxygen (10 Pa and 50 Pa) or argon (10 Pa and 50 Pa) onto transparent conducting oxide glass kept at room temperature. The cross-section scanning electron microscopy image showed differences in layer morphology and thickness, depending on the deposition conditions. Transmission electron microscopy studies of the TiO2 buffer layers indicated that films consisted of grains with typical diameters of 10 nm to 30 nm. We found that the photovoltaic conversion efficiencies, determined under standard air mass 1.5 global (AM 1.5G) conditions, of the solar cells with a buffer layer are more than two times larger than those of the standard cells. The best performance was reached for buffer layers deposited at 10 Pa O2. We discuss the processes that take place in the device and emphasize the role of the brush-like buffer layer in the performance increase.

Hydrothermal growth of well-aligned TiO2 nanorods on fluorine-doped tin oxide glass

Abstract One-dimensional titanium dioxide nanostructures have been studied intensively and extensively due to their outstanding properties and their diverse technological applications in photovoltaic cells. Interestingly, single crystalline TiO2 nanorods (TiO2 NRs) offer more advantageous compared with TiO2 particles and polycrystalline. TiO2 NRs produce direct electrical pathways of photogenerated carriers as well as large surface areas between NRs. This work presents a synthesis of vertically-aligned and uniform TiO2 NRs that were hydrothermally grown on a transparent conductive fluorine-doped tin oxide (FTO) glass substrate. The substrates were seeded with TiO2 compact layer (CL) using titanium (IV) butoxide as a precursor in HCl solution. Various techniques, including field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were employed to investigate the morphology and crystalline structure of the prepared TiO2 NRs. FE-SEM results revealed that the TiO2 NRs showed a rod-like nanostructure which could increase the accessible surface area. In addition, the effect on Ti initial reactant concentration was optimized to have desirable properties on the TiO2 NRs’ density, diameter and length. As a result, the as-prepared TiO2 NRs could have very good prospects in high-performance perovskite solar cell as electron transporting layers.