The influence of working pressure and inter-electrode gap distance on the quality of microcrystalline silicon prepared by PECVD at 40 MHz in three different KAI (TM) reactors designs with inter-electrode gaps of 28 mm, 16 mm and 7 mm has been investigated. The microcrystalline devices were implemented and studied as bottom cells in MICROMORPH (TM) tandem modules or processed with an optical filter to simulate the absorption of a top cell on a module size of 1.43.m(2). Increasing the working pressure from 250 Pa to 2000 Pa resulted in an improvement of the efficiency of 1% absolute due to improvement in the open circuit voltage V-oc and the fill factor FF. The influence of the deposition rate on the quality of the intrinsic absorber layers has been investigated and optimized. An unconventional crystallinity profile throughout the intrinsic absorber layer has been developed to further improve either the current density J(sc) or V-oc and FF. By controlling and tuning the Raman crystallinity a very high open circuit voltage V-oc of >1.42 V in a tandem cell design in full size modules (1.43 m(2)) could be realized. (C) 2016 Elsevier B.V. All rights reserved.