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Direct ablation of ZnO with UV and IR laser for thin film solar modules

S. KU1,2,* , S. HAAS1, G. SCHOEPE1, B. E. PIETERS1, Q. YE2, U. RAU1

Affiliation

  1. IEF-5-Photovoltaik, Forschungszentrum Jülich, D-52425 Jülich, Germany
  2. Department of Physics, Shanghai Jiao Tong University, 200240 Shanghai, China

Abstract

A common procedure to pattern transparent conductive oxides (TCO) for monolithic series connection of thin-film solar modules is to use an infrared (IR) laser incident from the glass side. However, for cheaper opaque substrates this standard procedure cannot be applied and the films need to be ablated directly from the film side. In this article we used two Nddoped solid state pulsed lasers to pattern as-deposited in-house aluminum doped zinc oxide (ZnO:Al) thin-films from the film side. One IR laser with a wavelength of 1064nm (photon energy less than the band-gap of ZnO) and one UV laser with a wavelength of 355nm (photon energy larger than the band-gap of ZnO) were used. For single pulses a smoother ablation of ZnO was obtained with the UV laser compared to the IR laser. Furthermore, using the UV laser we obtained craters with a lower rim and less material melt. The ablation thresholds were determined with three different methods. The ablation threshold of ZnO for the IR is larger than for the UV. The differences in ablation thresholds are explained by the differences in absorption coefficients of the ZnO for the IR and UV. Both wavelengths can achieve good electrical separation even after deposition of a highly conductive µc-Si:H p-layer. In order to compare the various laser processes we prepared 10cm×10cm µc-Si:H modules on ZnO. We obtained comparable results for modules patterned from the film-side and modules patterned with the standard process..

Keywords

Laser patterning, Ablation threshold, Electrical separation, Solar modules.

Submitted at: June 22, 2009
Accepted at: Feb. 27, 2010

Citation

S. KU, S. HAAS, G. SCHOEPE, B. E. PIETERS, Q. YE, U. RAU, Direct ablation of ZnO with UV and IR laser for thin film solar modules, Journal of Optoelectronics and Advanced Materials Vol. 12, Iss. 3, pp. 616-620 (2010)