Numerical modelling of AC-characteristics of CdTe and CIS solar cells

A complete electrical characterisation of thin-film solar cells necessitates the analysis of capacitance vs. voltage measurements at different frequencies and illumination intensities. The authors developed a fully numerical device simulation tool for polycrystalline CdTe and CuInSe₂ solar cells, which carries out frequency-domain calculations. Numerical simulations of I-V and C-V characteristics of CdTe cells are compared with measurements. It is shown that capacitance-voltage measurements not only confirm the thesis that a back contact barrier limits the current at high forward bias-they also yield additional information on the CdTe doping in the vicinity of the contact. The numerical model has also been applied to CuInSe₂ . The authors indicate that especially the doping profiles which are deduced from C-V data may be misinterpreted when interface states are present at the heterojunction