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

Abstract

Microcrystalline silicon (μc-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 μc-Si:H material. Commonly a value of 1.1eV 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 1.48–1.59eV, depending on crystalline volume fraction. Indeed, for the accurate modeling of μc-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 1.19eV for the mobility gap of the intrinsic layer of an μc-Si:H p-i-n device. We analyze the obtained results in detail through numerical simulations of the μc-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.