Surface morphology and light scattering properties of plasma etched ZnO:B films grown by LP-MOCVD for silicon thin film solar cells

Abstract

LP-MOCVD deposited ZnO:B thin films, post-etched by argon plasma processes, were investigated in this study in order to optimise the ZnO:B/p-layer interface when the ZnO:B is used as front electrode of p–i–n a-Si:H solar cells. At varying etching time different surface roughness was obtained and the evolution of the surface morphology was correlated with the texture characteristic and its scattering properties. Atomic force microscopy data were analysed and discussed together with the scattering properties, which are haze parameter and angular resolved scattering (ARS) distribution. The presence of several preferential scattering angles was hypothesized and a deconvolution approach was applied to each angular scattering curve. For each fixed preferential scattering angle θ i we associated a Gaussian distribution of the scattered light amount related to a well-defined scattering surface. The different preferential scattering angles were correlated to different scattering phenomena, the modifications of the angular scattering curves well agreed with SEM and AFM images. It is well known that a:Si–H solar cells fabricated on MOCVD deposited ZnO:B substrates show poor FF and V oc values with good J sc value. We demonstrated that only an effective sharp edge rounding off produced by an appropriately long plasma etching treatment is able to make MOCVD deposited ZnO:B perfectly suitable for high quality a-Si:H based devices.