Tin oxide (SnO _x ) electron‐extraction layers are fabricated via a reactive electron‐beam evaporation process from a metal source under a partial pressure of oxygen. These are then used in standard (n‐i‐p) architecture perovskite solar cells and achieve power conversion efficiencies up to 19.3%. The SnO _x deposition process is performed onto substrates maintained at low temperature compared to similar techniques, with films not requiring any subsequent high‐temperature post‐deposition annealing. This demonstrates the potential compatibility of reactive electron‐beam evaporation with roll‐to‐roll processing onto flexible polymeric substrates.