No benefit from microcrystalline silicon N layers in single junction amorphous silicon p-i-n solar cells

The use of phosphorous-doped microcrystalline silicon (muc-Si:H) as the n-type electrode in single junction hydrogenated amorphous silicon solar cells has been studied both experimentally and through computer modeling. The aim is to understand why, in spite of a considerable decrease in the activation energy of the n layer-from 0.2 eV in n-a-Si:H to 0.03 eV in n-muc-Si:H-the open-circuit voltage of solar cells fabricated using these two types of n layer remains almost unchanged. Experimental determination of the work function of n-muc-Si: H and n-a-Si:H by the flatband heterojunction'' technique, has revealed that n-muc-Si:H has a higher electron affinity. Thus, in spite of the fact that the difference in activation energy is 0.17 eV, the difference in built-in potential between the two types of cells reduces to about half. Moreover, modeling of the output characteristics of solar cells, having these two types of N layer, indicates a sharp localization of the field at the N/I interface for the cell with a muc-Si:H N layer. As a consequence, the field in the bulk of the intrinsic layer and, hence, the open-circuit voltage for the two types of cell, remain unchanged. (C) 2003 American Institute of Physics.