The　quality　of　P-N　heterojunction　is　crucial　for　the　performance　of　antimony　selenide　(Sb2Se3)　solar　cells　and　thus　attracting　urgent　attention.　In　this　work,　the　monovalent　cation　Ag+　is　doped　in　CdS,　which　enhances　the　N-type　conductivity　of　CdS　film　anomalously　and　reduces　its　parasitic　absorption　simultaneously.　Furthermore,　Ag　doping　of　CdS　promotes　the　diffusion　of　Cd　into　the　Sb2Se3　layer,　forming　CdSb　defects,　which　enhances　the　P-type　conductivity　of　Sb2Se3　and　reduces　the　density　of　deep-level　centers.　With　further　chemical　etching　treatment　on　the　CdS　surface,　the　quality　of　the　CdS/Sb2Se3　P-N　heterojunction　is　distinctly　improved,　making　the　energy　band　alignment　of　CdS/Sb2Se3　more　favorable　for　carrier　transportation.　Finally,　a　remarkable　efficiency　of　8.14%,　which　is　the　highest　efficiency　among　those　with　Jsc　of　30.96　mA　cm−2,　is　achieved　for　vapor　transport　deposition　processed　Sb2Se3　solar　cells.　This　work　provides　a　strategy　to　simultaneously　optimize　the　CdS　and　Sb2Se3　functional　layers　and　enhance　the　quality　of　P-N　heterojunction　for　efficient　Sb2Se3　solar　cells.　©　2024　Wiley-VCH　GmbH.