Determination of the mobility gap of intrinsic μc-Si:H in p-i-n solar cells

Microcrystalline silicon (mu c-Si:H) is a promising material for application in multijunction thin-film solar cells. A detailed analysis of the optoelectronic properties is impeded by its complex microstructural properties. In this work we will focus on determining the mobility gap of mu c-Si:H material. Commonly a value of 1.1 eV is found, similar to the bandgap of crystalline silicon. However, in other studies mobility gap values have been reported to be in the range of 1.48-1.59 eV, depending on crystalline volume fraction. Indeed, for the accurate modeling of mu c-Si:H solar cells, it is paramount that key parameters such as the mobility gap are accurately determined. A method is presented to determine the mobility gap of the intrinsic layer in a p-i-n device from the voltage-dependent dark current activation energy. We thus determined a value of 1.19 eV for the mobility gap of the intrinsic layer of an mu c-Si:H p-i-n device. We analyze the obtained results in detail through numerical simulations of the mu c-Si:H p-i-n device. The applicability of the method for other than the investigated devices is discussed with the aid of numerical simulations.