Laser Ablation of CuInSe 2 and CuIn/GaSe 2 Alloys For Solar Cell Applications
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LASER ABLATION OF CuInSe. AND CuIn/GaSe 2 ALLOYS FOR SOLAR CELL APPLICATIONS ARTHUR E. HILL*, SEPPO LEPPAVUORI**, ROBERT D. TOMLINSON%, RICHARD D. PILKINGTON, JUHANI LEVOSKA-, E-JAZ AHMED* and JOHANNES FRANTT1**. * University of Salford, Dept. of Electronic and Electrical Engineering, Salford M5 4WT, UK. ** University of Oulu, Microelectronics and Matl. Phys. Laboratories, 90570 Oulu, Finland.
ABSTRACT Copper indium diselenide (CIS) is one of the most promising materials proposed for use in the next generation of solar cells. A successful technique to deposit thin films of this material, which would maximise the advantage offered by its exceptionally high absorption coefficient and radiation resistance, has proved to be elusive. Dissociation of the source material during the physical deposition of these thin films has forced commercial production to adopt a binary (Cu/hI) deposition route with a subsequent selenisation stage. This has proved to be a major difficulty; selenisation has introduced its own problems of non-uniformity and toxicity. Laser ablation is especially suited to the deposition of multi-component films in that the initial composition is conserved. Single crystal and polycrystalline targets of CIS were laser ablated using an XeCl excimer laser. The films were analysed using EDAX, XRD, RBS and Raman spectroscopy. Results from EDAX and RBS measurements indicated that the composition of the source material had largely been maintained in the films. This suggests that laser ablation could prove to be a significant technique in the preparation of complex ternary semiconductor thin films for solar cell applications which would allow the full potential of these materials to be realised in device production.
INTRODUCTION CulnSe2 (CIS), which, in this paper, may be described more generally as CulnI1Ga(1 .,)Se9 (CIGS), has emerged as the most promising semiconducting material for use as an absorber layer in thin-film solar cells and also as an infra red radiation detector. Decreasing the value of x from 1 to 0 results in a progressive increase in the band gap from 1.02eV to 1.68eV. an energy range which is of optimum interest for solar cell absorber layers. CIGS has a very large coefficient of absorption within the visible and near infra-red which allows efficient, light weight thin film solar cells to be fabricated [1]. It has also been shown to exhibit a significant resistance to radiation damage [2]. These are both essential parameters when designing solar cells, particularly for space applications. Thin films of CIS and CIGS have been fabricated by a variety of teclhniques including sputtering, co-evaporation and flash evaporation. Industrially, CIGS films are routinely prepared by deposition of the copper and indium/gallium components followed by a separate selenisation stage. The major disadvantages of this method lies in the toxicity of the selenisation process and the lack of reproducibility of the electrical characteristics. An attractive alternative route is to deposit thin films from CIGS startin
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