Impact on Thin Film Silicon Properties and Solar Cell Parameters of Texture Generated by LaserAnnealing and Chemical Etc
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Impact on Thin Film Silicon Properties and Solar Cell Parameters of Texture Generated by LaserAnnealing and Chemical Etching of ZnO:Al Rym Boukhicha1, Erik Johnson1, D. Daineka1,Antoine Michel1, J.F. Lerat2, Thierry Emeraud2, and Pere Roca i Cabarrocas1 1 2
CNRS, LPICM, Ecole Polytechnique, 91128 Palaiseau, France Excico Group NV,KempischeSteenweg 305/2, B-3500 Hasselt, Belgium
ABSTRACT The use of a laser annealing and chemical texturing process (dubbed the LaText process) on room-temperature sputtered ZnO:Al has been shown to generate unusually high haze properties, favorable for thin film silicon solar cells.This is due to the melting of the ZnO:Al layer by the XeCl laser, and the formation of crystalline domains onthe surface, for which the grains and grain boundaries are subsequently etched at different rates. The unusual surface morphology produced through this process can strongly impact the nature of the amorphous or microcrystalline silicon material deposited thereupon. In this paper, we report on results for amorphous silicon devices, for which the surface texture is seen to slightly impact thelight absorption in the material, but more interestingly, also the light-induced degradation of the cells.For co-deposited cells, devices deposited on surfaces with the characteristic "LaText" morphologyundergo a much lesser degradation. Furthermore, the decreased degree of degradation coincides with a notable shift in the Raman scattering peak. This provides a rapid diagnostic for testing multiple textures and deposition parameters. INTRODUCTION Doped ZnO is used in both research and industry as the transparent conducting oxide (TCO) front contact in thin film silicon solar photovoltaic cells, as well as in optoelectronics[1]. In the superstrate configuration, the upper front contact layer should meet a number of requirements: high transparency in the visible to near-infrared solar spectrum, a high electrical conductivity, a suitable surface texture in order to enhance light scattering and absorption inside the cell, a high chemical stability, and good adhesion to silicon. To meet these goals, either sputtered ZnO:Al is used after a chemical etching step [2, 3], or low-pressure chemical vapour deposited (LP-CVD) ZnO:B [4]. In this work, we examine a third structural option, wherein the surface morphology is created by an excimer laser annealing and chemical etching technique, which we dub the LaText technique. LaText treated ZnO:Al layers have a low resistivity, high transmission in the visible range, and a high haze [5]. It has been previously shown that such a substrate treatment dramatically increases the photocurrent in hydrogenated microcrystalline silicon (ȝc-Si:H) solar cells [6]. In this work, we study the influence of the LaText process on the optoelectronic and light-induced degradation (LID) properties of hydrogenated amorphous silicon (a-Si:H) solar cells. EXPERIMENT ZnO:Al thin films were deposited on Corning Eagle glass at room temperature by radio frequency magnetron sputtering from a ceramic ZnO tar
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