Effect of interfacial states on open-circuit voltage

A comparative study of the effects of interfacial-state densities on the open-circuit voltages of solar cells is presented. Several different types of photodiode (n-on-p and p-on-n single-crystal silicon, GaAs homojunction, ITO/p-Si, and polycrystalline CuInSe₂) were examined. No dispersion in capacitance vs. frequency was observed in single-crystal homojunction photodiodes indicating near-zero interfacial-state densities for these devices. High efficiency (about 12%) ITO/Si showed interfacial densities at the Fermi level on the order of 10⁹ eV^-1 cm^-2, but this number increased to 2.5*10¹² for cells with only 5% efficiency. CuInSe₂ solar cells showed zero bias interfacial-state densities in the range of 10¹⁰-10¹¹ eV^-1 cm^-2. This number decreased by an order of magnitude in reverse bias, but it increased substantially with light intensity until saturation near 100 mW/cm².