Towards bifacial silicon heterojunction solar cells with reduced TCO use

Reducing indium consumption, which is related to the transparent conductive oxide (TCO) use, is a key challenge for scaling up silicon heterojunction (SHJ) solar cell technology to terawatt level. In this work, we developed bifacial SHJ solar cells with reduced TCO thickness. We present three types of In2O3-based TCOs, tin-, fluorine-, and tungsten-doped In2O3 (ITO, IFO, and IWO), whose thickness has been optimally minimized. These are promising TCOs, respectively, from post-transition metal doping, anionic doping, and transition metal doping and exhibit different opto-electrical properties. We performed optical simulations and electrical investigations with varied TCO thicknesses. The results indicate that (i) reducing TCO thickness could yield larger current in both monofacial and bifacial SHJ devices; (ii) our IWO and IFO are favorable for n-contact and p-contact, respectively; and (iii) our ITO could serve well for both n-contact and p-contact. Interestingly, for the p-contact, with the ITO thickness reducing from 75 nm to 25 nm, the average contact resistivity values show a decreasing trend from 390 m omega cm(2) to 114 m omega cm(2). With applying 25-nm-thick front IWO in n-contact, and 25-nm-thick rear ITO use in p-contact, we obtained front side efficiencies above 22% in bifacial SHJ solar cells. This represents a 67% TCO reduction with respect to a reference bifacial solar cell with 75-nm-thick TCO on both sides.

Automated summary

Reducing the thickness of transparent conductive oxide (TCO) in bifacial silicon heterojunction (SHJ) solar cells can lead to larger current and improved performance. In this study, we developed three types of In2O3-based TCOs (ITO, IFO, and IWO) with optimized thicknesses, each showing different opto-electrical properties. Our findings suggest that reducing TCO thickness benefits both monofacial and bifacial SHJ devices, and IWO and IFO are favorable for n-contact and p-contact, respectively. Using these optimized TCOs, we achieved front side efficiencies above 22% in bifacial SHJ solar cells, representing a significant TCO reduction compared to a reference solar cell.