Influence of Hydrogen plasma on electrical and optical properties of transparent conductive oxides
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A21.10.1
Influence of Hydrogen plasma on electrical and optical properties of transparent conductive oxides.
L. Raniero, A. Gonçalves, A. Pimentel, I. Ferreira, S. Zhang, L. Pereira, H. Águas, E. Fortunato and R. Martins. Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa and CEMOP-UNINOVA, Campus da Caparica, 2829-516, Portugal ABSTRACT: In this work we study the optical and electrical behavior of ZnO:Ga, ITO and IZO films deposited on glass after sustaining different hydrogen plasma conditions and exposure times. This work was complemented by analyzing the surface morphology of the set of films, which allow us to determine the role of hydrogen plasma on the film’s properties such as Hall mobility, free carrier concentration, sheet resistance, optical transmittance, figure of merit and state of the surface. Apart from that, the performances of solar cells using an intrinsic layer constituted by nanocrystalline silicon will be also presented. The data show that the electrical properties of solar cells were improved by using ZnO:Ga as front contact, allowing a high current density collection and single pin solar cells with efficiencies exceeding 11%. INTRODUCTION Transparent conductive oxide (TCO) has been widely used for a large range of products such as, flat panel displays, opto-electronic components, photovoltaics, etc. The films should be simultaneously highly transparent and conductive [1]. These coatings can be deposited by a variety of techniques, such as pulsed laser deposition, thermal evaporation, chemical vapor deposition, electron beam evaporation, pulsed laser deposition, chemical spray, sol-gel, and magnetron sputtering [2,3]. However, the magnetron sputtering leads to the best features concerning surface cleanness, the use of low substrate temperatures and high deposition rates, besides permitting scalability to large areas, keeping the film’s excellent electro-optical performances [4]. These performances are highly dependent on the film composition, structure and surface morphology, which are influenced by the deposition conditions used, where the ion bombardment of the surface plays an important role. The aim of this work is to know how the electro-optical properties of different TCO’s like ZnO:Ga, ITO and IZO behave when exposed to a plasma of hydrogen under different powers and exposure times, aiming to select the one that should lead to p-i-n amorphous silicon solar cells deposited by plasma enhanced chemical vapor deposition (PECVD) with the highest efficiency. Here we should take into account that the TCOs are exposed to the hydrogen plasma while the first amorphous silicon monolayer begins growth. Apart from that, we should talk into account that ZnO is known to be chemically stable in hydrogen plasma environment, under low to moderate powers densities. EXPERIMENTAL DETAILS ZnO:Ga, ITO and IZO were deposited on commercial glass by magnetron sputtering at 13,56 MHz and some system details are shown in the table 1. The deposition conditions s
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