Determination of the electronic properties of Cu2ZnSnSe4-based solar cells by impedance spectroscopy and current–voltage characteristics analysis

Cu2ZnSnSe4 (CZTSe) thin films were synthesized by a cosputtering–annealing process and characterized as absorber layer of solar cells. Electrical characteristics of the solar cells were analyzed by coupling current–voltage measurements with impedance spectroscopy. The slightly p-type nature of the CZTSe absorber is evidenced with a doping level as low as 1.4 × 1015 cm−3. The solar cells exhibit a dominant recombination pathway in the space charge region in which it was revealed an apparent increase of the doping due to the ionization of deep level in the bandgap. Moreover, open circuit voltage of solar cells is found to be mainly limited by the low built-in voltage at the CdS/CZTSe interface. We conclude that the device architecture can play a major role in the electrical properties of solar cells.