Interpretation of thin-film polycrystalline solar cell capacitance

Variation of thin-film polycrystalline solar cell capacitance with frequency and voltage is used to determine (1) carrier density, and hence Fermi-level position, in the more lightly doped semiconductor, (2) width of the intrinsic layer often found adjacent to a polycrystalline heterojunction, and (3) density of extraneous states at the Fermi level in the depletion region. For CuInSe₂ cells from three laboratories, the values extracted show a relatively modest dependence on temperature and light intensity. Reliable interpretation of the capacitance measurements requires continual monitoring of actual junction voltage, the real to imaginary impedance ratio, and the degree of voltage sweep hysteresis