The doping of indium into absorber layer has been proven to be beneficial for hybrid buffer structured Cu2ZnSn(S, Se)(4) (CZTSSe) solar cells, but it is difficult to precisely control the doping content only relying on In diffusion from In2S3 emitter. Herein, we use the solution method to prepare In-substituted CZTSSe layer by directly doping In2Se3 into metal chalcogenides precursor solution. The doping content can be precisely controlled and the influences of indium doping on cell performance are systematically discussed. Mott-Schottky and resistivity measurements indicate that the carrier concentration and charge transport process are monotonically enhanced with increasing In/(In + Sn) content (0 at.%, 3 at.%, 6 at.% and 12 at.%). The improvements of series resistance also lead to a monotonic increase of fill factor (FF) from 52.1% to 64.8%. Due to the larger recombination at high doping content, the 6 at.% In content device finally contributes the highest power conversion efficiency of 8.47%. It is expected that a precisely controlled indium doping could further improve cell performance for efficient hybrid buffer structured devices. (C) 2017 Elsevier Ltd. All rights reserved.