SEM CHARACTERIZATION OF EFG POLYCRYSTALLINE SILICON SOLAR CELLS REALIZED BY ION IMPLANTATION AND LASER ANNEALING WITH OVERLAPPING PULSES

Résumé
On a étudié par microscopie électronique (SEM) et par EBIC des cellules solaires préparées sur du silicium polycristallin en ruban de type EFG dont la jonction était réalisée par incrustation (AMI) d'ions atomiques et moléculaires issus d'une source contenant PF₅. La recristallisation du domnage était effectuée par recuit laser pulsé Nd-YAG. Alors qu'au voisinage de la surface la recombinaison des porteurs est due essentiellement aux recouvrements des impulsions laser (diamètre 100 µm, taux de répétition 10 kHz), on constate qu'aux profondeurs plus grandes la recombinaison aux joints de grains est dominante. La recristallisation par épitaxie en phase liquide conserve exactement la structure polycristalline sous-jacente.

Abstract
Atomic and molecular ion implantation (AMI) of non mass separated PF₅ ions has been used to form the N⁺ layer on EFG ribbon. A pulsed Nd-YAG laser operating at a high repetition rate (10 kHz) was then employed to anneal the amorphized layer via liquid phase epitaxy. The properties of the recrystallized layers have been analyzed by SEM with secondary electron micrography and EBIC. The following results have been observed. At low electron beam energies (below 12 keV), strong EBIC recombination currents resulting from the overlapping laser pulses is clearly visible. At higher energies (above 20 keV), the recombination due to the grain boundaries in the ribbon becomes dominant. The regrowth after annealing replicates exactly the underlying structure. Finally, some electrical characteristics of the doped layers (doping profile) as well as the photovoltaïc performance are presented. Efficiencies up to 11 % have been obtained under AMI conditions.