Hydrogenated amorphous silicon oxide (a-SiO_x:H) single junction solar cell with 8.8% initial efficiency by reducing parasitic absorptions

摘要

Hydrogenated amorphous silicon oxide (a-SiO_x:H) solar cells have been successfully implemented to multi-junction thin film silicon solar cells. The efficiency of these solar cells, however, has still been below that of state-of-the-art solar cells mainly due to the low J_(sc) of the a-SiOΛ:H solar cells and the unbalanced current matching between sub-cells. In this study, we carry out optical simulations to find the main optical losses for the a-SiO_x:H solar cell, which so far was mainly optimized for V_(oc) and fill-factor (FF). It is observed that a large portion of the incident light is absorbed parasitically by the p-a-SiO_x:H and n-a-SiO_x:H layers, although the use of these layers leads to the highest V_(oc) × FF product. When a more transparent and conductive p-nc-SiO_x:H layer is substituted for the p-a-SiO_x:H layer, the parasitic absorption loss at short wavelengths is notably reduced, leading to higher J_(sc). However, this gain in J_(sc) by the use of the p-nc-SiO_x:H compromises the V_(oc). When replacing the n-a-SiO_x:H layer for an n-nc-SiO_x:H layer that has low n and k values, the plasmonic absoφtion loss at the n-nc-SiO_xT:H/Ag interfaces and the parasitic absorption in the n-nc-SiO_x:H are substantially reduced. Implementation of this n-nc-SiO_x:H leads to an increase of the J_(sc) without a drop of the V_(oc) and FF. When implementing a thinner p-a-SiO_x:H layer, a thicker i-a-SiO_x:H layer, and an n-nc-SiO_x:H layer, a-SiO_x:H solar cells with not only high J_(sc) but also high V_(oc) and FF can be fabricated. As a result, an 8.8% a-SiO_x:H single junction solar cell is successfully fabricated with a V_(oc) of 1.02 V, a FF of 0.70, and a J_(sc) of 12.3 mA/cm~2, which is the highest efficiency ever reported for this type of solar cell.