Abstract
The front transparent conductive oxide layer is a source of significant optical and electrical losses in silicon heterojunction solar cells because of the trade-off between free-carrier absorption and sheet resistance. We demonstrate that hydrogen-doped indium oxide (IO:H), which has an electron mobility of over 100 cm(2)/V s, reduces these losses compared to traditional, low-mobility transparent conductive oxides, but suffers from high contact resistance at the interface of the IO:H layer and the silver front electrode grid. This problem is avoided by inserting a thin indium tin oxide (ITO) layer at the IO:H/silver interface. Such IO:H/ITO bilayers have low contact resistance, sheet resistance, and free-carrier absorption, and outperform IO:H-only or ITO-only layers in solar cells. We report a certified efficiency of 22.1% for a 4-cm(2) screen-printed silicon heterojunction solar cell employing an 10:H/ITO bilayer as the front transparent conductive oxide. (C) 2013 Elsevier B.V. All rights reserved.