Recombination rates in heterojunction silicon solar cells analyzed by impedance spectroscopy at forward bias and under illumination

Impedance spectroscopy (at forward bias and under illumination) of solar cells comprised thin hydrogenated amorphous silicon (a-Si:H) films deposited on crystalline silicon (c-Si) wafers was analyzed in terms of ac equivalent circuits. Shockley–Read–Hall recombination at states on the device interfaces governs the cell dynamic response. Recombination process was modeled by means of simple RC circuits which allow to determine the capture rate of electrons and holes. Carrier lifetime is found to be stated by the electron capture time τSRH≈τn, and it results in the range of 300 μs. The Al-annealed back contact was regarded as the dominating recombination interface.