EBIC investigation of the influence of hydrogen passivation on thin-filmpolycrystalline silicon solar cells obtained by aluminium inducedcrystallization and epitaxy

摘要

The relatively new "thin-film polycrystalline-silicon (pc-Si) (grain size of 0.1-100 μm)solar cell on foreign substrate" technology aims at low-cost devices with energy conversionefficiencies above 12 %. A very promising technique to obtain thin pc-Si layers is aluminum-induced crystallization (AIC). Solar cell absorber layers can be made by epitaxial thickening ofthese AIC seed layers. So far, we have reached energy conversion efficiencies of up to 8% with thisapproach. In contrast to what is expected a performance independent of the grain size is foundwhich is explained by the presence of intragrain defects. In this paper the electrical activity of boththe intragrain defects as well as the grain boundaries is investigated with electron beam inducedcurrent (EBIC) measurements before and after hydrogen plasma passivation. Metal-insulator-semiconductor contacts were used as collecting junction to eliminate the interference of the junctionshape with the EBIC measurement as found when diffused emitters where used. It is shown thatboth grain boundaries and intragrain defects are electrically active before and after hydrogenplasma passivation. Finally we argue that Leff mono, the diffusion length inside the grains, is probablymuch closer to 1μM in our layers than equal to 100μm as often expected in the literature