Description of the ideality factor of a-Si:H photovoltaic cells under different illumination intensity levels

This paper presents a closed form for the behavior of the ideality factor n of amorphous silicon (a-Si:H) photovoltaic cells under different illumination intensity Φ levels and applied voltage V. The advantage of this model, over other existing models, is its effectiveness of describing the dependency of n on both V and Φ even without evaluating n itself. Therefore, the errors of calculating n using various existing methods are minimized in this paper. The variations of the current voltage J/V data under different levels of Φ are monitored where the illumination intensity dependence of parallel resistance Rp(Φ) is taken into account. The resulting model is a first order differential equation with non-constant coefficients whose solution expresses the variations of n in V- and Φ-domain. From the solution of the differential equation, it is found that n increases as V or Φ increases.