We have applied a micro-tip Scanning Kelvin Probe to produce high-resolution surface potential maps of silicon nitride (Si3N4) coated multi-crystalline Silicon (mc-Si) solar cells in a non-contact, non-invasive fashion. We show this technique highlights two types of defects: localised surface charge and shunts. In the latter case we contrast the non-contact surface potential maps with contact measurements made by the Shuntscan technique. Using a guarded micro-tip with active shield we show for the first time surface potential changes at the mc-Si grain boundaries which are due to different mc-Si polytypes. The high-resolution scanning Kelvin probe (HR-SKP) has a surface potential resolution of < 10 mV at a tip diameter < 200 mum. (C) 2003 Elsevier Science B.V. All rights reserved.