We have used internal photoemission measurements to determine the electrical band gap of microcrystalline p-type layers used in a-Si:H alloy solar cells, and the band edge discontinuities of the conduction and the valence bands between μc-Si:H and a-Si:H alloys. The band gap ofμc-Si:H is found to be around 1.6 eV, and the discontinuities at the conduction and the valence band edges are −0.02 and 0.26 eV, respectively. Use of these parameters in the numerical simulation of single-junction a-Si:H alloy solar cells is found to accurately predict the experimental results of solar cell performance.