One-Step Formation of Low Work-Function, Transparent and Conductive MgF x O y Electron Extraction for Silicon Solar Cells.

The development of high-performance dopant-free silicon solar cells is severely bottlenecked by opaque electron selective contact. In this paper, high transmittance (80.5% on glass) and low work function (2.92 eV) lithium fluoride (LiF x )/MgF x O y electron contact stack by tailoring the composition of MgF x O y hybrid film is reported. This hybrid structure exhibits a high conductivity (2978.4 S cm -1 ) and a low contact resistivity (2.0 mΩ cm 2 ). The element profile of LiF x /MgF x O y contact is measured and the reaction kinetics is analyzed. As a proof-of-concept, this electron selective contact is applied for dopant-free silicon solar cells. An impressive efficiency of 21.3% is achieved on dopant-free monofacial solar cell with molybdenum oxide (MoO x )/zinc-doped indium oxide (IZO) hole contact. An efficiency bifaciality of 71% is obtained for dopant-free bifacial solar cell with full-area LiF x /MgF x O y /ITO (tin-doped indium oxide) transparent electron contact. It is the highest efficiency bifaciality so far for dopant-free bifacial solar cells to the best knowledge. Both cell configurations with LiF x /MgF x O y contacts show excellent environment stability. The cell efficiency maintains more than 95% of its initial value after keeping in air for 1500 h. This work provides a new idea to achieve transparent electron contact, showing a great potential for high-efficiency and low-cost optoelectronic devices.