Influence of wavelength on laser doping and laser-fired contact processes for c-Si solar cells

Abstract

This work investigates the influence of the laser wavelength on laser doping (LD) and laser - fired contact (LFC) formation in solar cell structures . We compare the results obtained using the three first harmonics (corresponding to wavelengths of 1064 nm, 532 nm and 355 nm) of fully commercial solid state laser sources with pulse width in the ns range. The discussion is based on the impact on the morphology and electrical characteristics of test structures. In the case of LFC the study includes th e influence of different passivation layers and the assessment of the process quality through electrical resistance measurements of an alumin i um single LFC point for the different wavelengths. Values for the normalized LFC resistance far below 1 .0 m Ω cm 2 have been obtained, with better results at s horter wavelen g ths. To assess the influence of the laser wavelength on LD we have created n+ regions into p - type c - Si wafers , using a dry LD approach to define punctual emitters. J - V characteristics show exponen tial trends at mid - injection for a broad parametric window in all wavelengths, with local ideality factors well below 1.5. In bot h processes the best results have been obtained using green (532 nm) and , specially, UV (355 nm) . This indicates that to minim ize the thermal damage in the material is a clear requisite to obtain th e best electrical performance, thus indicating that UV laser shows better potential to be used in high efficiency solar cells.