This paper reports the development of a VHF PECVD process at 40.68 MHz for deposition of device-grade nc-Si:H. It further reports the evaluation of textured ZnO:Al films produced by hollow cathode sputtering as regards their suitability to serve as a TCO substrate for a-Si:H/nc-Si:H tandem device fabrication. The tandem devices were produced using an established VHF PECVD process at 100 MHz. Both VHF processes are capable of producing similar nc-Si:H material based on their analysis using micro-Raman spectroscopy. For the tandem junction devices, a peak in device efficiency was obtained at a Raman crystalline fraction of 50-52 % and a microstructure parameter of 0.60-0.68. A best tandem cell efficiency of 9.9% was achieved on HC ZnO compared to 11.3% on a reference Type-U SnO2 substrate.