N-type PbS colloidal-quantum-dot (CQD) films are fabricated using a controlled halide chemical treatment, applied in an inert processing ambient environment. The new materials exhibit a mobility of 0.1 cm2 V -1 s-1. The halogen ions serve both as a passivating agent and n-dope the films via substitution at surface chalcogen sites. The majority electron concentration across the range 1016 to 1018 cm-3 is varied systematically. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.