Solid-phase crystallization of amorphous silicon on ZnO:Al for thin-film solar cells

Becker, Christiane; Conrad, E.; Dogan, P.; Fenske, F.; Gorka, B.; Hänel, T.; Lee, K.Y.; Rau, B.; Ruske, F.; Weber, Tim; Berginski, M.; Hüpkes, J.; Gall, S.; Rech, Bernd

doi:10.1016/j.solmat.2008.09.059

Cited by 26 publications

(14 citation statements)

References 13 publications

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“…Single-junction efficiencies above 10% have already been reported 7 and an adaptation of the formation process to a substrate configuration including a TCO front contact is being worked on. 8 In this approach the poly-Si layers are formed by crystallization of amorphous silicon by solid phase crystallization ͑SPC͒ at 600°C.…”

Section: Introductionmentioning

confidence: 99%

Improved electrical transport in Al-doped zinc oxide by thermal treatment

Ruske

Roczen

Lee

et al. 2010

Journal of Applied Physics

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A postdeposition thermal treatment has been applied to sputtered Al-doped zinc oxide films and shown to strongly decrease the resistivity of the films. While high temperature annealing usually leads to deterioration of electrical transport properties, a silicon capping layer successfully prevented the degradation of carrier concentration during the annealing step. The effect of annealing time and temperature has been studied in detail. A mobility increase from values of around 40 cm2/Vs up to 67 cm2/Vs, resulting in a resistivity of 1.4×10−4 Ω cm has been obtained for annealing at temperatures of 650 °C. The high mobility increase is most likely obtained by reduced grain boundary scattering. Changes in carrier concentration in the films caused by the thermal treatment are the result of two competing processes. For short annealing procedures we observed an increase in carrier concentration that we attribute to hydrogen diffusing into the zinc oxide film from a silicon nitride barrier layer between the zinc oxide and the glass substrate and the silicon capping layer on top of the zinc oxide. Both are hydrogen-rich if deposited by plasma-enhanced chemical vapor deposition. For longer annealing times a decrease in carrier concentration can occur if a thin capping layer is used. This can be explained by the deteriorating effect of oxygen during thermal treatments which is well known from annealing of uncapped zinc oxide films. The reduction in carrier concentration can be prevented by the use of capping layers with thicknesses of 40 nm or more.

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Section: Introductionmentioning

confidence: 99%

Improved electrical transport in Al-doped zinc oxide by thermal treatment

Ruske

Roczen

Lee

et al. 2010

Journal of Applied Physics

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175

100

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“…2 In recent years, sputtered aluminum-doped ZnO (ZnO:Al) films could be considerably improved by thermal treatments at temperatures around 650 C yielding carrier mobilities up to 67 cm 2 /V s, enabling a low resistivity down to 1.5 Á 10 À4 X cm 2 accompanied by a very high optical transparency-provided that the ZnO:Al films were covered by a protective silicon capping. 3,4 Therefore, such ZnO:Al layers were attracting a strong interest in the field of thin-film solar cells based on amorphous/ microcrystalline 5 and polycrystalline silicon: 6,7 A highmobility ZnO:Al front contact layer in the silicon thin-film solar cell stack not only enables the application of industrially established monolithic large-area contacting schemes by laser scribing but also the implementation of enhanced light trapping structures. 8,9 As in photovoltaic devices, the performance of the ZnO:Al front contact layer is only one aspect, there is also a strong interest in understanding modifications of the ZnO:Al/Si interface and the silicon absorber material itself upon thermal treatments.…”

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confidence: 99%

Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cells on ZnO:Al

Becker

Pagels

Zachäus

et al. 2013

Journal of Applied Physics

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The combination of polycrystalline silicon (poly-Si) thin films with aluminum doped zinc oxide layers (ZnO:Al) as transparent conductive oxide enables the design of appealing optoelectronic devices at low costs, namely in the field of photovoltaics. The fabrication of both thin-film materials requires high-temperature treatments, which are highly desired for obtaining a high electrical material quality. Annealing procedures are typically applied during crystallization and defect-healing processes for silicon and can boost the carrier mobility and conductivity of ZnO:Al layers. In a combined poly-Si/ZnO:Al layer system, an in-depth knowledge of the interaction of both layers and the control of interface reactions upon thermal treatments is crucial. Therefore, we analyze the influence of rapid thermal treatments up to 1050 °C on solid phase crystallized poly-Si thin-film solar cells on ZnO:Al-coated glass, focusing on chemical interface reactions and modifications of the poly-Si absorber material quality. The presence of a ZnO:Al layer in the solar cell stack was found to limit the poly-Si solar cell performance with open circuit voltages only below 390 mV (compared to 435 mV without ZnO film), even if a silicon nitride (SiN) diffusion barrier was included. A considerable amount of diffused zinc inside the silicon was observed. By grazing-incidence X-ray fluorescence spectrometry, a depth-resolving analysis of the elemental composition close to the poly-Si/(SiN)/ZnO:Al interface was carried out. Temperatures above 1000 °C were found to promote the formation of new chemical compounds within about 10 nm of interface, such as zinc silicates (Zn2SiO4) and aluminium oxide (AlxOy). These results give valuable insights about the temperature-limitations of Si/ZnO thin-film solar cell fabrication and the formation of high-mobility ZnO-layers by thermal anneal.

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“…Underlying substrate is believed to have a significant influence on the a-Si films property and the crystallization process of a-Si films. Recently, aluminum-doped zinc oxide (AZO) films substrate has attracted a considerable attention, it exhibits high optical transmittance and conductivity thus can be used for front contact [3,5,6]; and textured AZO films achieved by post-deposition etching in hydrochloric acid (HCl) can be used for light trapping [7].…”

Section: Introductionmentioning

confidence: 99%

In situ micro-Raman spectroscopic study of laser-induced crystallization of amorphous silicon thin films on aluminum-doped zinc oxide substrate

Wang

Huang

et al. 2011

J Mater Sci: Mater Electron

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The effects of laser irradiation condition and deposition substrate on the laser crystallized 330 nm Si films structure were investigated using in situ microRaman spectroscopy. Results showed that crystallization of amorphous silicon (a-Si) films started at laser irradiation power density of 0.6 9 10 5 W/cm 2 for 20 s. The crystalline volume fraction of Si films depended mostly on the laser power density but not on the laser irradiation time. The Si films on both smooth and textured aluminum-doped zinc oxide (AZO) substrates exhibited lower crystalline volume fraction and smaller average grain size than the Si films on glass did. The Si films on textured AZO revealed higher crystalline volume fraction and larger average grain size than the Si films on smooth AZO did. The stress in crystalline Si films was observed to be compressive on AZO and tensile on glass. The compressive stress in crystalline Si films on textured AZO was slightly less than that on smooth AZO. The present work indicated that the structure of crystalline Si films on textured AZO was improved than that on smooth AZO, which may be helpful to crystalline Si thin-film solar cell.

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Solid-phase crystallization of amorphous silicon on ZnO:Al for thin-film solar cells

Cited by 26 publications

References 13 publications

Improved electrical transport in Al-doped zinc oxide by thermal treatment

Improved electrical transport in Al-doped zinc oxide by thermal treatment

Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cells on ZnO:Al

In situ micro-Raman spectroscopic study of laser-induced crystallization of amorphous silicon thin films on aluminum-doped zinc oxide substrate

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