High-Performance Europium Fluoride Electron-Selective Contacts For Efficient Crystalline Silicon Solar Cells

Dopant-free carrier-selective contacts have attracted considerable research interests, extensively due to the avoidance of high-temperature doping and their simple, environmental-friendly fabrication processes for crystalline silicon (c-Si) solar cells. Herein, a novel dopant-free electron-selective material, europium fluoride (EuFx) is developed. A desired Ohmic contact can be formed between lightly doped n-type c-Si and aluminum (Al) by inserting nanoscale EuF(x)films (2-4 nm) through thermal evaporation so as to avoid the high-temperature phosphorus diffusion and offer a simple, robust process. The contact resistivity is lower than 20 m omega cm(2). EuFx film can effectively select electrons and block holes at the contact interface, which is attributed to its low work function and a large valence band offset with respect to n-type c-Si. Combined with an ultrathin silicon oxide (SiO2) as a passivation layer, a champion power conversion efficiency 21.6% of n-type c-Si solar cells with full-area SiO2/EuFx is achieved. An average of absolute efficiency is increased by 12% compared with the reference. The results show that EuFx has particularly excellent electron-selective transport performance. The new possibility of using lanthanide salts as electron-selective contacts for photovoltaic (PV) devices is set up.