Microcrystalline silicon thin film solar cells exhibit optimal PV efficiency when the absorber layer contains similar proportions of crystalline and amorphous phases. When the crystalline fraction is reduced below 30%, efficiency falls very steeply, from around 8% to as low as 2%, and does not recover until fully amorphous growth conditions are established. We demonstrate that an electrical model, comprising two parallel-connected diodes scaled to reflect material composition, qualitatively predicts the features observed in the PV parameters. However the scale of the reduction in fill-factor is not reproduced. As an alternative approach, a homogeneous transport model is proposed in which carrier mobilities are scaled in accordance with values determined by the time-of-flight experiment. This model predicts a large reduction in fill-factor for low-crystallinity absorbers more in keeping with measurement. A novel carrier transport landscape is proposed to account for mobility variations. © 2014 The Authors.
Reynolds, S., Gordijn, A., & Smirnov, V. (2014). Equivalent-circuit and transport-based mobility models of microcrystalline silicon solar cells. In Energy Procedia (Vol. 44, pp. 192–202). https://doi.org/10.1016/j.egypro.2013.12.027