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.