Polymer　light-emitting　devices　(PLEDs)　with　a　MoO3　hole　injection　layer　(HIL)　were　fabricated　to　enhance　their　luminance　efficiency.　Ultraviolet　photoelectron　spectroscopy　spectra　showed　that　the　valence　band　maximum　level　of　the　MoO3　layer　was　located　between　the　work　function　of　the　the　indium-tin-oxide　anode　and　the　highest　occupied　molecular　orbital　level　of　the　poly[N,N＇-bis(4butylphenyl)-N,　N＇-bis(phenyl)　benzidine]　hole　transport　layer.　The　surface　of　the　MoO3　layer　formed　by　using　an　ethanol　solvent　was　smoother　than　that　of　the　MoO3　layer　formed　by　using　a　deionized　water　solvent　due　to　a　decrease　in　the　aggregation　of　the　MoO3　resolved　in　ethanol.　The　MoO3　HIL　decreased　the　operating　voltage　of　the　PLED　and　increased　the　luminance　and　the　luminance　efficiency　of　the　PLED　due　to　a　decrease　in　the　hole　injection　barrier.　The　operating　voltage,　the　luminance,　and　the　luminance　efficiency　of　the　PLEDs　with　the　MoO3　HIL　formed　by　using　an　ethanol　solvent　were　enhanced　in　comparison　with　those　of　the　PLEDs　with　a　MoO3　HIL　formed　by　using　a　deionized　water　solvent　due　to　a　decrease　in　the　surface　roughness　of　the　HIL.