High‐Performance Europium Fluoride Electron‐Selective Contacts for Efficient Crystalline Silicon Solar Cells

Abstract

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 (EuF x ) 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 mΩ cm2. EuF x 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/EuF x is achieved. An average of absolute efficiency is increased by 12% compared with the reference. The results show that EuF x 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.