Achieving　efficient　white　quantum　dot　light-emitting　diodes　(WQLEDs)　is　highly　desired　because　of　their　promising　applications　in　general　illumination　and　display　backlight　systems.　Herein,　a　highly　efficient　WQLED　with　an　extremely　low　input　voltage　is　reported,　which　is　fabricated　via　an　all-solution　process　by　using　an　emitting　layer　with　a　mixture　of　red-,　blue-,　and　green-emitting　quantum　dots.　When　a　facile　strategy　of　light　outcoupling　with　an　optical　lens　is　introduced,　the　device　shows　a　maximum　external　quantum　efficiency　of　28.4%,　which　is　the　highest　value　reported　so　far.　Moreover,　the　device　exhibits　a　standard　white　emission　with　International　Commission　on　Illumination　(CIE)　coordinates　of　(0.36,　0.34)　at　an　extremely　low　input　voltage　of　3.2　V.　This　work　provides　a　promising　way　for　achieving　high-performance　white　quantum-dot　light-emitting　diodes　with　low　driving　voltage.