A Transparent Electrode Based on Solution-Processed ZnO for Organic Optoelectronic Devices (original) (raw)
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We have investigated ZnO thin films prepared via photochemical reaction as the electron transport layer (ETL) of inverted organic solar cells (OSCs). Morphological and electrical properties of the ZnO thin films prepared by the photosensitive ZnO sol were studied according to the annealing temperature and their effects on the performance of the inverted poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) OSCs was characterized. It was found that the optimal annealing temperature of the ZnO thin films was 330 • C, and that devices with the ZnO ETL annealed at this temperature exhibited the largest short-circuit current density (J sc ) of 9.39 mA/cm 2 , as well as the highest power conversion efficiency (PCE) of 2.31%, which can be attributed to enhanced electron transport and interfacial properties. Devices containing ZnO films formed at optimal annealing condition exhibited an open circuit voltage (V oc ) of 0.60 V and a fill factor (FF) of 41.0%. However, further increase of the annealing temperature led to degradation of the device performance, despite further improvements in electrical properties. We have found that marked increase in the surface roughness of the ZnO films occurred at temperatures above 350 • C which could be detrimental to the OSCs characteristics due to a high contact resistance and a large leakage current.
Preparation, Fabrication and Characterization of Sol-Gel ZnO Thin Films for Organic Solar Cells
Journal of Ravishankar University PART-B Science, 2020
In this work, ZnO has been prepared by the sol-gel method and thin films have been deposited onto the ITO (Indium-Tin-Oxide) coated glass substrates by spin coating method at different ZnO concentration and spin parameters. For this, Sol-gel ZnO was synthesized by Zinc acetate dehydrate, 2-methoxethanol and ethanolamine as a starting material, solvent and stabilizer respectively. The study of deposition parameters on the structural, optical and electrical properties of the ZnO thin films was carried out. The Roughness and thickness were calculated by Profilometer. X-ray diffraction (XRD) analysis of the films showed the polycrystalline nature of the prepared films. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) was used to describe the surface morphology and optical properties were studied using UV-VIS-IR Spectroscopy. The fabricated results showed that ZnO thin films is crystalline and low-cost techniques with good features that will be useful for Organic Solar Cells (OSCs) device as an electron transport layer.
Organic Photovoltaic Cells Based on ZnO Thin Film Electrodes
Journal of Nanoscience and Nanotechnology, 2010
Due to its wide band-gap (ca. 3.4 eV), ZnO is a possible candidate material to be used as transparent electrode for a new class of photovoltaic (PV) cells. Also, an increased interest for the photovoltaic properties of several organic monomers and polymers (merocyanines, phthalocyanines and porphyrins) was noticed, because of their high optical absorption in the visible region of the spectrum allowing them to be used as potential inexpensive materials for solar cells. Preparation and properties of CuPc (copper phthalocyanine) based photovoltaic cells using ZnO thin films as transparent conductor electrodes are presented in this paper. ZnO layers are grown by pulsed laser deposition, while the organic layers are obtained by thermal evaporation. Structural characterization is performed by electron microscopy. Optical and transport properties of the mutilayered structures are obtained by electrical and spectro-photometric measurements. The influence of the ZnO-polymer interface on the external quantum efficiency (EQE) of the photovoltaic cell is clearly evidenced by our measurements.
ACS Applied Materials & Interfaces, 2015
The role of cathode buffer layer (CBL) is crucial in determining the power conversion efficiency (PCE) of inverted organic solar cells (IOSCs). The hallmarks of a promising CBL include high transparency, ideal energy levels and tendency to offer good interfacial contact with the organic bulk-heterojunction (BHJ) layers. Zinc oxide (ZnO), with its ability to form numerous morphologies in juxtapose to its excellent electron affinity, solution processability, and good transparency is an ideal CBL material for IOSCs. Technically, when CBL is sandwiched between the BHJ active layer and the indium-tin-oxide (ITO) cathode, it performs two functions viz, electron collection from the photoactive layer that is effectively carried out by morphologies like nanoparticles or nanoridges obtained by ZnO sol-gel (ZnO SG) method through an accumulation of individual nanoparticles and secondly, transport of collected electrons towards the cathode, which is more effectively manifested by 1D nanostructures like ZnO nanorods (ZnO NRs). This work presents the use of bilayered ZnO CBL in IOSCs of poly (3-hexylthiophene) (P3HT): [6, 6]-phenyl-C 60 -butyric acid methyl ester (PCBM) to overcome the limitations offered by a conventionally used single layer CBL. We found that the PCE of IOSCs with an appropriate bilayer CBL comprising of ZnO NRs-ZnO SG is ~18.21% higher than those containing ZnO SG-ZnO NRs. We believe that, in bilayer ZnO NRs-ZnO SG, ZnO SG collects electrons effectively from photoactive layer while ZnO NRs transport them further to ITO resulting significant increase in the photocurrent to achieve highest PCE of 3.70%. The enhancement in performance was obtained through improved interfacial engineering, enhanced electrical properties and reduced surface/bulk defects in bilayer ZnO NRs-ZnO SG. This study demonstrates that the novel bilayer ZnO CBL approach of electron collection/transport would overcome crucial interfacial recombination issues and contribute in enhancing PCE of IOSCs.
Fabrication of organic photovoltaic cells with double-layer ZnO structure
Solar Energy Materials and Solar Cells, 2009
The fabrication process of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/double ZnO/C 60 / poly(3-hexylthiophene) (PAT6)/Ag has been investigated. The C 60 /PAT6 heterojunction of this cell was fabricated by spin-coating a chloroform solution of PAT6 onto the C 60 thin film formed on double-layer ZnO-coated ITO. The fabrication of this double-layer ZnO was a new method, which was a composite of a sputtered ZnO layer and oriented zinc oxide nanograins layer fabricated at low temperature (343 K). Insertion of the double-layer ZnO in the photovoltaic cells produced enhanced performance with the power conversion efficiency of 1.31% under AM1.5 illumination.
Organic Photovoltaic Cells Using Indium Zinc Tin Oxide Electrode
Journal of Nanoscience and Nanotechnology, 2017
In recent years, indium zinc tin oxide (IZTO) thin films have been assessed as alternative materials for the commonly used indium tin oxide (ITO) with comparable electrical and optical properties for transparent electrode applications. In addition, IZTO films with a lower indium content of up to 40 at.% was found to have a high work function, which is beneficial for OPV applications. This finding raised expectations for OPV cells with IZTO films to bring higher efficiency. In this study, OPV cells were fabricated with two different structures, i.e., conventional and inverted structures, where IZTO films were used as the anode and cathode, respectively. The IZTO films were deposited at 400 C or at room temperature with an average thickness of approximately 150 nm by RF magnetron sputtering. The improvement of the photoelectric conversion efficiency of the fabricated OPV cells is discussed in detail.
Zinc Oxide Nanostructures for Efficient Energy Conversion in Organic Solar Cell
Journal of Technology Innovations in Renewable Energy, 2014
We present a new approach of solution-processed using zinc oxide (ZnO) nanostructures as extraction layer material for organic solar cells. It is low chemical reaction compatibility with all types of organic blends and its good adhesion to both surfaces of ITO/glass substrate and the active layer (blends). Parameters such as the thickness and the morphology of the films were investigated to prove that these factors greatly affect the efficiency of organic solar cells. In this work, ZnO layer with thickness of approximately 53 nm was used as an interlayer to prevent pin-holes between the electrode and the polymer layer. The polymer layer was coated on the ZnO layer with the thickness of about 150 nm. The thick polymer layer will form a non-uniform surface because of the solvent, 1-2dichlorobenzene will etch away some region of the polymer layer and forming pin-holes. ZnO nanostructures layer was used to prevent pin-holes between the polymer layer and electrode. From the surface morphology of ZnO layer, it shows a uniform surface with particle grain size obtained between 50-100 nm. The presence of the interlayer has a positive effect on the electrical characteristics of the solar cells. It was found that an organic solar cell with thickness less than 150 nm shows the optimum performance with efficiency of 0.0067% and Fill Factor (FF) of about 19.73.