Distribution of the electrical potential in hydrogenated amorphous silicon solar cells

Abstract

We report on a direct measurement of the spatial distribution of electrical potential on cross sections of hydrogenated amorphous silicon (a-Si:H) n– i– p solar cells using scanning Kelvin probe microscopy. We found that most voltage has dropped near the p/ i interface up to ∼500 nm into the i-layer, but that the voltage flattens out near the n/ i region for a device with i-layer thickness of ∼800 nm. However, the potential distributes approximate-linearly on the entire i-layer for a device with i-layer of ∼250 nm. The potential measurements suggest that the i-layer is slightly n-type (6–13×10 15/cm 3), and the depletion width is ∼350–500 nm at the i/ p interface. This depletion width provides a direct experimental evidence for the device design criteria that a-Si:H solar cells should be thinner than ∼500 nm, in the point view of electrical potential.