AVS 49th International Symposium
    Electronic Materials and Devices Tuesday Sessions
       Session EL+SC-TuA

Paper EL+SC-TuA5
Direct Measurement of the Electrical Potentials in GaInP@sub 2@ Solar Cells

Tuesday, November 5, 2002, 3:20 pm, Room C-107

Session: Semiconductor Characterization
Presenter: C.-S. Jiang, National Renewable Energy Laboratory
Authors: C.-S. Jiang, National Renewable Energy Laboratory
H.R. Moutinho, National Renewable Energy Laboratory
J.F. Geisz, National Renewable Energy Laboratory
D.J. Friedman, National Renewable Energy Laboratory
M.M. Al-Jassim, National Renewable Energy Laboratory
Correspondent: Click to Email
We report the application of electrostatic force microscopy (EFM) to photovoltaic devices. The built-in electric field plays a major role in photovoltaic devices, because it collects photo-excited carriers and is a key factor in determining the open-circuit voltages of solar cells. However, the measurement of the built-in potential has been limited to indirect ways such as the characteristics of current-voltage and capacitance-voltage. In these measurements, it is hard to distinguish the contributions from the multi-junctions or interfaces of a modern solar cell device. In this presentation, we report a direct measurement of the electric potential on cross-sectional planes of a GaInP@sub 2@ device both quantitatively and spatial-resolvedly, by using the Kelvin probe force model of the EFM technique. Two features on the potential profile are assigned respectively to the p-n junction of GaInP@sub 2@ and the band offset between the GaInP@sub 2@ base and the GaAs substrate materials. With varying the light intensities irradiated at the sample, we found that, in addition to the flattening of the p-n junction, two changes in the potential profile happened in the locations of the front window or the back surface field (BSF) layers under the condition of a lower or a higher light intensities, respectively. The two potential changes, together with the flattening of the p-n junction, contribute positively to the open-circuit voltage of the device, indicating the importance of the window and the BSF layers in solar cell designs. Furthermore, the potential change at the window layers is understood in terms of the band offset between the AlInP@sub 2@ window and the GaInP@sub 2@ emitter layers, and the potential change at the BSF layer is understood in terms of the total effect of the photo-induced flattening of the band bending and the band offset at the interface between the base and the BSF, respectively.