We　fabricated　triboelectric　nanogenerators　(TENGs)　consisting　of　an　Al　electrode,　a　polyimide　dielectric　layer,　a　ZnO　dielectric　layer,　and　an　indium　tin　oxide　(ITO)　electrode,　and　we　observed　an　enhancement　of　the　output　voltage　that　was　due　to　Al　doping　in　the　ZnO　layer.　The　variation　in　the　surface　of　the　Al　doped　zinc　oxide　(AZO)　layer,　which　was　found　to　depend　on　the　Al　doping　concentration,　was　studied　by　using　scanning　electron　microscopy.　The　existence　of　Al　particles　was　identified　from　the　X-ray　photoelectron　spectroscopy　results.　The　open-circuit　voltage　and　the　short-circuit　current　of　the　TENGs　with　2%　and　5%　Al　doping　in　the　ZnO　layer　and　operating　in　the　vertical　contact-separation　mode　were　larger　than　those　of　TENGs　having　a　ZnO　layer　without　Al　doping,　respectively.　The　Al　doping　reduced　the　asymmetry　of　negative　and　positive　output　voltages　and　shortened　the　duration　of　the　positive　peaks.　The　enhancement　in　the　output　properties　of　the　TENGs　due　to　the　dielectric　properties　of　the　Al　particles,　which　was　theoretically　analyzed　in　the　contact-separation　mode　operated　TENGs　with　dimensionless　formulations,　which　is　compared　with　the　experimental　results.　©　2020　Elsevier　B.V.