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

• Published in: Journal of applied physics 2017-04, Vol.121 (13)
• Main Authors: Kim, Do Yun, Guijt, Erwin, van Swaaij, René A. C. M. M., Zeman, Miro
• Format: Article
• Language: English
• Subjects: Absorption; Amorphous silicon; Applied physics; Hydrogenation; Incident light; Parasitics (electronics); Photovoltaic cells; Silicon oxides; Silicon wafers; Solar cells; Thin films
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4979690

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-SiO x :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 absorption loss at the n-nc-SiO x :H/Ag interfaces and the parasitic absorption in the n-nc-SiOx: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-SiOx: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/cm2, which is the highest efficiency ever reported for this type of solar cell.