Widely transparent electrodes based on ultrathin metals

Ghosh, Dhriti Sundar; Martínez, Luis; Giurgola, S.; Vergani, P.; Pruneri, Valerio

doi:10.1364/ol.34.000325

Cited by 142 publications

(100 citation statements)

References 11 publications

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Section: Introductionmentioning

confidence: 99%

“…Recently, it has been demonstrated that the ultrathin transparent metal contacts provide a number of advantages over the more commonly used conductive transparent metal oxides, such as indium tin oxide (ITO) [4]. According to [5], chromium and nickel thin films possess optical transparency comparable to that of the ITO in the visible and near-infrared range (0.4 − 2.5 μm), while it can be significantly higher in the ultraviolet (175 − 400 nm) and mid-infrared (2.5 − 25 μm) regions.The conditions of deposition, as deposition rate, temperature of substrate, etc., influence very strongly the properties of the metal coating [6]. It has been shown that the deposition rate and argon partial pressure in the case of cathode sputtering strongly affect the microstructure and electrical properties of thin chromium films [7,8].…”

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confidence: 99%

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Optical and electrical properties of very thin chromium films for optoelectronic devices

Lozanova¹,

Atanasova²,

Soserov³

et al. 2014

J. Phys.: Conf. Ser.

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Abstract. Establishing the optimal experimental conditions for the development of transparent metal contacts to be used in optoelectronic devices, such as organic light-emitting diodes and solar cells, is an important task. In this paper we present an overview of the development of very thin e-beam-deposited chromium films with high optical transparency. The surface morphology is investigated by scanning electron microscopy. The variation is examined of the films' electrical and optical properties (transmittance and complex refractive index) with the variation of the thickness and deposition rate. We observed that, for a given thickness of the chromium films, the absorption coefficient increases when the deposition rate is decreased. We also found that the thin films with a thickness of less than 10 nm show an average transmittance exceeding 60 % in the spectral range 400 -1500 nm. The films' resistivity, ρ, is determined by the four-point probe method. The value of ρ varies in the range of 10 -3 − 10 −4 Ω cm for chromium coatings in the thickness interval 5 − 100 nm. The results obtained show that very thin metal films could be an alternative to the transparent conductive oxides. IntroductionThin chromium films have found many applications, for example as layers for improvement of the adhesion to transparent substrates [1], in mask production [2] and as transparent electrodes [3]. Recently, it has been demonstrated that the ultrathin transparent metal contacts provide a number of advantages over the more commonly used conductive transparent metal oxides, such as indium tin oxide (ITO) [4]. According to [5], chromium and nickel thin films possess optical transparency comparable to that of the ITO in the visible and near-infrared range (0.4 − 2.5 μm), while it can be significantly higher in the ultraviolet (175 − 400 nm) and mid-infrared (2.5 − 25 μm) regions.The conditions of deposition, as deposition rate, temperature of substrate, etc., influence very strongly the properties of the metal coating [6]. It has been shown that the deposition rate and argon partial pressure in the case of cathode sputtering strongly affect the microstructure and electrical properties of thin chromium films [7,8]. Metal films deposited by ion-beam sputtering display exceptionally low surface roughness, the films being as thin as about 20 Å [3].The goal of the present work is the investigation of the optical and electrical properties of very thin chromium films deposited by an electron-beam technique.

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Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Optical and electrical properties of very thin chromium films for optoelectronic devices

Lozanova¹,

Atanasova²,

Soserov³

et al. 2014

J. Phys.: Conf. Ser.

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show abstract

“…The state-of-the-art solution for commercialized TEs is indium tin oxide (ITO), which has a good tradeoff between electrical conductivity and visible-light transparency. [1][2][3][4] ITO films are normally prepared onto glass and plastic substrates via physical vapor deposition, and the typical sheet resistance value of ITO films is about 20-100 Ω/ □ , depending on the actual thickness of ITO films. However, due to the scarcity of indium element, the price of ITO is fluctuated at a high level and the material resource is quite limited.…”

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confidence: 99%

Ultra-flexible and robust transparent electrodes by embedding silver nanowires into polyimide matrix

Zhao

Wang

et al. 2018

AIP Advances

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Silver nanowires (AgNWs) percolated films have been extensively considered as promising candidates for alternative transparent electrodes. However, due to their high surface roughness, poor adhesion and thermal stability, their practical use in transparent conducting film application is still heavily limited. In this paper, we report ultra-flexible transparent electrodes by imbedding AgNWs into polyimide (PI) thin films to achieve smooth surface, pronounced thermal stability, and high adhesion. Besides the excellent electrical conductivity of about 7-13Ω/□ in sheet resistance, the obtained AgNWs/PI films have excellent transparency and mechanical resilience due to the intrinsic physical and chemical properties of PI organic polymer. By embedding AgNWs into PI, the surface roughness of AgNWs percolated films can be reduced from 39.5 nm to 6 nm (RMS values), and the adhesion of AgNWs to PI is greatly enhanced if compared to the case of only AgNWs onto glass or plastic substrates. Additionally, the AgNWs/PI films show extraordinary stability in terms of electrical conductivity after the arbitrary twisting and thermal heating test, respectively, which are demonstrated by the electrical-thermal measurements via thermal IR imaging.

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“…These two parallel electrodes also produce a nonclosed optical cavity for the exciton radiation. One of the electrodes is a perfect conductor with unit reflectivity while the other is a thin metal electrode 11 with a partial light transmission in order to let the sun photons through but at the same time contribute in forming a cavity for the fluorescence photons. The device configuration that we consider is shown schematically in Fig.…”

mentioning

confidence: 99%

“…We also consider the finite absorption of the semitransparent electrode of thickness d = 5 nm. 11 The inclusion of sunlight interference effects 14,15 are neglected because they do not change the illustrated trends.…”

mentioning

confidence: 99%

Cavity-controlled radiative recombination of excitons in thin-film solar cells

Vuong

Kozyreff

Betancur

et al. 2009

Applied Physics Letters

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We study the performance of photovoltaic devices when controlling the exciton radiative recombination time. We demonstrate that when high-quantum-yield fluorescent photovoltaic materials are placed within an optical cavity, the spontaneous emission of the radiative exciton is partially inhibited. The corresponding increase of the exciton lifetime results in an increase of the effective diffusion length and diffusion current. This performance maximizes when the thickness of the cell is comparable to the absorption length. We show that when typical parameter values of thin solar-cell devices are used, the efficiency may improve by as much as three times. © 2009 American Institute of Physics. ͓doi:10.1063/1.3262954͔In many photovoltaic devices, a major limitation to high efficiency stems from a short exciton diffusion length given that excitons recombine quickly before reaching the chargeseparation layer. 1,2 It is assumed possible to reduce some of the recombination rates, except for the radiative one which, in photovoltaics, is generally treated as a material parameter that cannot be changed. However, the radiative rate of recombination is not an immutable property of the radiationmatter interaction, and instead it may be modified by the presence of a cavity or a reflecting surface that alters the electromagnetic environment for the exciton radiation. Indeed, linked to the Purcell effect, 3 it has been shown that the spontaneous emission rate can be inhibited when a radiative system in the excited state is placed near a reflecting surface, 4,5 in a dielectric slab, 6 within a Fabry-Pérot type cavity, 7,8 or photonic crystal. 9,10 Yet, this very compelling phenomenon has found not many interesting real applications. In photovoltaic materials that exhibit a high-quantumyield fluorescence, where radiative recombination is one of the dominant recombination paths, a reduction of the fluorescence rate may result in a larger exciton diffusion length and ultimately a larger short-circuit current or efficiency.In the present letter we analyze in detail this effect on the exciton diffusion current when a thin layer of photovoltaic material is placed between two metallic electrodes to form a Schottky diode-type photovoltaic cell. These two parallel electrodes also produce a nonclosed optical cavity for the exciton radiation. One of the electrodes is a perfect conductor with unit reflectivity while the other is a thin metal electrode 11 with a partial light transmission in order to let the sun photons through but at the same time contribute in forming a cavity for the fluorescence photons. The device configuration that we consider is shown schematically in Fig. 1. The z-axis is perpendicular to the plane of the device, the semitransparent metal electrode has thickness d and the active layer has thickness h. Inside the active region, excitons are generated and transported via diffusion. Charge separation occurs at z = 0 or at the metal electrode with the lower work function.To determine the diffusion current, we use the FengG...

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Widely transparent electrodes based on ultrathin metals

Cited by 142 publications

References 11 publications

Optical and electrical properties of very thin chromium films for optoelectronic devices

Optical and electrical properties of very thin chromium films for optoelectronic devices

Ultra-flexible and robust transparent electrodes by embedding silver nanowires into polyimide matrix

Cavity-controlled radiative recombination of excitons in thin-film solar cells

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