Study of laser-induced damage to GaAs/Ge solar cells

The laser-induced damage of GaAs/Ge single heterojunction solar cells is investigated. The solar cells were irradiated by a continuous wave laser at the wavelength of 532 nm. Results indicate that the GaAs/Ge solar cells would mostly be damaged when laser is focused on its grid lines. Theoretically, the continuous wave laser at the wavelength of 532 nm is absorbed at the surface of solar cells. The continual temperature rise decomposed the material GaAs and melted the material Ge. The melted metal Ge connected the solar cells grid lines and the rear electrode, the solar cell became completely invalid. The major damage of continuous wave mainly comes from both the thermal melting and the thermal stress effects. The huge temperature gradient on the surface of the solar cells generated the crack, and even rupture. Concentric iridescent ring appeared on the damaged surfaces when observed with an optical microscope(OM) of broad spectrum. The damaged surface film was characterized by X-ray photoelectron spectroscopy(XPS) and the Contour Meter. The component of the concentric iridescent is GeO 2 film, when the light irradiated on the film and interfered, the concentric iridescent generated. The different ring indicated the thickness of oxide was different. When the film was corroded by HCl, the iridescent disappeared. The formation mechanism of the film and the cause of the concentric iridescent ring were analyzed. These experimental conclusions are tested and verified by scanning electron microscope with energy dispersive spectroscopy and X-ray photoelectron spectroscopy.