Modelling of hydrogen transport in silicon solar cell structures under equilibrium conditions

This paper presents a model for the introduction and redistribution of hydrogen in silicon solar cells at temperatures between 300 and 700 °C based on a second order backwards difference formula evaluated using a single Newton-Raphson iteration. It includes the transport of hydrogen and interactions with impurities such as ionised dopants. The simulations lead to three primary conclusions: (1) hydrogen transport across an n-type emitter is heavily temperature dependent; (2) under equilibrium conditions, hydrogen is largely driven by its charged species, with the switch from a dominance of negatively charged hydrogen (H−) to positively charged hydrogen (H+) within the emitter region critical to significant transport across the junction; and (3) hydrogen transport across n-type emitters is critically dependent upon the doping profile within the emitter, and, in particular, the peak doping concentration. It is also observed that during thermal processes after an initial high temperature step, hydrogen preferentially migrates to the surface of a phosphorous doped emitter, drawing hydrogen out of the p-type bulk. This may play a role in several effects observed during post-firing anneals in relation to the passivation of recombination active defects and even the elimination of hydrogen-related defects in the bulk of silicon solar cells

Poly-Si on glass thin-film PV research at UNSW

Thin-film polycrystalline silicon (poly-Si) on glass is a promising material for lowering the cost of PV electricity. This paper gives an update on the poly-Si on glass thin-film PV research in our group at the University of New South Wales (UNSW). Each of the investigated Si formation methods (solid phase crystallisation, solid phase epitaxy, ion-assisted deposition) is shown to be capable of producing device-grade Si material, with voltages in the 440-530 mV range. Fill factors of over 70% are now frequently obtained using an interdigitated cell metallisation scheme. The best cells presently have efficiencies of 7% and are improving rapidly