Silicon Heterojunction Solar Cells with Nanocrystalline Silicon Oxide Emitter for Achieving High Fill Factor

Emitter and transparent conductive oxide (TCO) films are the critical functional layers of extremely promising silicon heterojunction (SHJ) solar cells. Here, p-type nanocrystalline silicon oxide (nc-SiO_<i>x</i>:H(p⁺)) are employed as the emitter, replacing the widely used nanocrystalline silicon. The nc-SiO_<i>x</i>:H shows a mixed-phase structural characteristic of nanocrystalline silicon grains and amorphous silicon oxide, in which the former spans the whole emitter, facilitating the carrier collection. A variety of TCO films, including Ce, Sn, or Hf doped and undoped indium oxides, are optimized for the nc-SiO_<i>x</i>:H(p⁺) emitter. Film quality, work function, and bandgap states of the TCO films affect the contact resistivity of TCO/nc-SiO_<i>x</i>:H(p⁺) and the solar cell performance. Using Ce doped indium oxide (ICO) with high mobility and certain bandgap states as the TCO layers, an efficiency of 26.29% and a high fill factor (FF) of 86.21% are achieved on the champion bifacial SHJ solar cells.