Improved Passivation of n-Type Poly-Si Based Passivating Contacts by the Application of Hydrogen-Rich Transparent Conductive Oxides
Leonard Tutsch, Frank Feldmann, Bart Macco, Martin Bivour, Erwin Kessels, Martin Hermle
Abstract
In recent years, the incorporation of hydrogen into indium and zinc oxide based TCOs has been recognized as an effective technique to improve the charge carrier mobility and hereby to relax the transparency-conductivity tradeoff within the thin films. On the other hand, the process sequence of poly-Si/SiOx based contacts typically requires an extra rehydrogenation step in order to improve the chemical interface passivation. This article addresses the combination of the two matters by studying the ability of both atomic layer deposited and sputter-deposited TCOs to serve as hydrogenation sources. Here, we demonstrate improved passivation of poly-Si(n)/SiOx contacts subsequent to TCO coatings and postdeposition thermal treatments resulting in iVoc values of up to 743 and 730 mV for planar and random pyramid textured surfaces, respectively. Thus, a high passivation quality could be obtained without the need of additional hydrogenation treatments. For the textured interface morphology, a substantial hydrogen flux toward the SiOx region turned out to be essential. This could either be ensured by adjusting the hydrogen partial pressure during the TCO growth process or by the addition of a thin AlOx layer, serving as a effusion barrier.