Origin of the Voc enhancement with a p-doped nc-SiOx:H window layer in n-i-p solar cells

The introduction of a nc-SiOx:H material as window layer in single junction a-Si:H n-i-p solar cell leads to a V enhancement of 80 mV compared to a p-layer. According to numerical modeling of the V-oc, both the higher work function p-layer and the conduction band offset (CBO) at the i/p interface match well with the experimental V-oc increase with the oxygen content. Using the differential temperature method, the built-in voltage (V-bi) of the cells with the two different p-layers is measured to be similar, agreeing well with the CBO model. Thus we attribute the improvement of the V-oc to the reduction of recombination at the i/p interface, as a consequence of the CBO in this region. (C) 2012 Elsevier B.V. All rights reserved.