AbstractWe report on recent developments of a‐Si:H/a‐Si:H based thin film solar cells on Gen8.5 module area. The initial efficiency of 5.7 m² modules and 1.4 m² sub‐modules has been increased from 5% to 8% using standard floatline, low‐cost glass substrates coated with SnO2:F front TCO. The improvements based on optimizations of the n1/p2 tunnel recombination junction and of the p/i interfaces. The device simulation software AFORS‐HET has been extended with an improved model for the n/p junction to describe measured module properties. Model input parameters are taken from measured properties of single thin films. The presented progress indicates the high potential of thin‐film silicon based solar cells produced on large area. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)