Dependence of Photovoltage on Incident Photon Energies Investigated by Photo-assisted Kelvin Probe Force Microscopy on Cu(In,Ga)Se2 Solar Cells

Dependence of photovoltage on photon energy of incident light was investigated on Cu(In,Ga)Se₂ [CIGS] solar cells by photo-assisted Kelvin probe force microscopy (P-KFM). As a result, we found that the photovoltage gradually increased as an increase of photon energy when the excess energy from the minimum bandgap was small, while the photovoltage began to decrease when the photon energy exceeded the bandgap energy by a certain value. The relationship between such features and V-shaped band grading in CIGS was discussed in comparison with some numerical simulations.