Light induced electrical and macroscopic changes in hydrogenated polymorphous silicon solar cells

¹ TOTAL S.A., Gas & Power – R&D Division, Courbevoie, France
² Laboratoire de Physique des Interfaces et des Couches Minces (UMR 7647 CNRS), École Polytechnique, 91128 Palaiseau, France

^a e-mail: ka-hyun.kim@polytechnique.edu

Received: 5 August 2011
Accepted: 16 April 2012
Published online: 18 July 2012

Abstract

We report on light-induced electrical and macroscopic changes in hydrogenated polymorphous silicon (pm-Si:H) PIN solar cells. To explain the particular light-soaking behavior of such cells – namely an increase of the open circuit voltage (V_oc) and a rapid drop of the short circuit current density (J_sc) – we correlate these effects to changes in hydrogen incorporation and structural properties in the layers of the cells. Numerous techniques such as current-voltage characteristics, infrared spectroscopy, hydrogen exodiffusion, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry are used to study the light-induced changes from microscopic to macroscopic scales (up to tens of microns). Such comprehensive use of complementary techniques lead us to suggest that light-soaking produces the diffusion of molecular hydrogen, hydrogen accumulation at p-layer/substrate interface and localized delamination of the interface. Based on these results we propose that light-induced degradation of PIN solar cells has to be addressed from not only as a material issue, but also a device point of view. In particular we bring experimental evidence that localized delamination at the interface between the p-layer and SnO₂ substrate by light-induced hydrogen motion causes the rapid drop of J_sc.