Influence of TCO and a-Si:H Doping on SHJ Contact Resistivity

Resistive losses in silicon heterojunction (SHJ) solar cells are partly linked to transport barriers at the amorphous silicon/crystalline silicon (a-Si:H/c-Si) and transparent conductive oxide (TCO)/a-Si:H interfaces. A key parameter is the position of the Fermi-level on either side of the junction which we modify by a systematic doping variation of the amorphous silicon and the transparent conductive oxide. We identify the charge carrier concentration to be the main driver for low contact resistance. For a-Si:H, this is achieved by using a sufficient but not too high doping gas concentration during deposition. For indium tin oxide (ITO) and aluminum zinc oxide (AZO), no or only a very low oxygen (O-2) gas concentration during deposition is needed. We show that a stack of low-oxygen ITO interlayer and an oxygen-rich ITO bulk layer is not only an effective means to combine efficient transport and low TCO absorption but also to improve the thermal stability of the a-Si:H/TCO/metal contact resistivity (rho(c)). Such a layer stack helps to relax the constraints regarding the optoelectrical performance and improves the efficiency of SHJ solar cells.

Automated summary

Doping variation of amorphous silicon and transparent conductive oxide can modify the position of Fermi-level to improve efficiency in SHJ solar cells. Control of doping gas concentration during deposition is crucial for low contact resistance in a-Si:H, while little to no oxygen gas concentration is needed for ITO and AZO.