The open-circuit voltage of amorphous silicon p–i–n solar cells is 0.1–0.3 V less than the total Fermi level shift in the p- and n-type layers. It was hypothesized that a dipole layer at the p–i interface reduces the potential drop across the i-layer. We determine the electrostatic potential profile using an in situ Kelvin probe during incremental depositions of p-type a-Si,C:H and undoped a-Si:H layers by direct current reactive magnetron sputtering. We confirm the existence of a dipole layer, but which produces a potential loss of only ∼20 mV. Thus, most of the “missing” voltage in solar cells must have other origins. © 1997 American Institute of Physics.