High-efficiency p-i-n microcrystalline silicon single-junction solar cells are fabricated and their longterm stability is investigated. We focus in particular on the stability of the absorber layer after atmospheric storage in absence of light and compare non-encapsulated devices with different cell design and crystalline volume fractions. Furthermore, an innovative stack of transparent conductive oxide is used as front electrode in order to investigate the effect of small surface roughness on the electrical properties and the stability of solar cells. Finally, an outstanding single-junction microcrystalline cell showing 10.4% conversion efficiency without anti-reflection coating is presented.