title: Microelectrical characterizations of junctions in solar cell devices by scanning Kelvin probe force microscopy.
abstract: Scanning Kelvin probe force microscopy was applied to the microelectrical characterizations of junctions in solar cell devices. Surface Fermi-level pinning effects on the surface potential measurement were avoided by applying a bias voltage (V(b)) to the device and taking the V(b)-induced potential and electric field changes. Two characterizations are presented: the first is a direct measurement of Bi-induced junction shift in GaInNAs(Bi) cells; the second is a junction-uniformity measurement in a-Si:H devices. In the first characterization, using Bi as a surfactant during the molecular beam epitaxy growth of GaInNAs(Bi) makes the epitaxial layer smoother. However, the electrical potential measurement exhibits a clear Bi-induced junction shift to the back side of the absorber layer, which results in significant device degradation. In the second characterization, the potential measurement reveals highly non-uniform electric field distributions across the n-i-p junction of a-Si:H devices; the electric field concentrates much more at both n/i and i/p interfaces than in the middle of the i-layer. This non-uniform electric field is due possibly to high defect concentrations at the interfaces. The potential measurements further showed a significant improvement in the electric field uniformity by depositing buffer layers at the interfaces, and this indeed improved the device performance.
authors.affiliation: National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, USA. chun.sheng.jiang@nrel.gov
authors.forename: C-S
authors.initials: CS
authors.lastname: Jiang
authors.forename: A
authors.initials: A
authors.lastname: Ptak
authors.forename: B
authors.initials: B
authors.lastname: Yan
authors.forename: H R
authors.initials: HR
authors.lastname: Moutinho
authors.forename: J V
authors.initials: JV
authors.lastname: Li
authors.forename: M M
authors.initials: MM
authors.lastname: Al-Jassim