Direct measurement of electrical potentials in GaInP2 solar cells

We report on the application of electrostatic force microscopy to photovoltaic devices. Profiles of electrical potentials on cross sections of a GaInP2 solar cell device were measured quantitatively and spatially resolved. Two potentials are assigned, respectively, to the p–n junction of GaInP2 and the band offset between the GaInP2 base layer and the GaAs substrate. In addition to the flattening of the p–n junction by the light irradiations, two changes of the potential that positively contribute to the open-circuit voltage of the device are found at locations close to the window and the back surface field layers.