Highly　efficient　light-emitting　electrochemical　cells　(LECs)　have　attracted　tremendous　interest　because　of　their　simple　structures　and　low-cost　fabrication　processing,　showing　great　potential　for　full-color　displays　and　solid-state　lighting.　In　this　work,　we　rationally　designed　and　synthesized　two　red-emitting　cationic　Ir(III)　complexes,　[Ir(tBuPBI)2(biq)]PF6　(R1)　and　[Ir(tBuPBI)2(qibi)]PF6　(R2),　in　which　a　tert-butyl-functionalized　1,2-diphenyl-1H-benzo[d]imidazole　(PBI)　unit　and　conjugated　2,2′-biquinoline　(biq)　and　2-(1-phenyl-1H-benzo[d]imidazol-2-yl)quinolone　(qibi)　were　employed　as　cyclometalated　and　ancillary　ligands,　respectively.　The　introduced　tert-butyl　group　led　to　homogeneous　and　highly　emissive　thin　films　by　increasing　the　solubility　and　suppressing　the　strong　intermolecular　interactions　due　to　steric　hindrance.　Based　on　the　abovementioned　high-quality　emissive　layer,　high-efficiency　LECs　were　achieved.　An　efficient　red-emitting　LEC　fabricated　on　a　glass　substrate　achieved　a　current　efficiency　(ηC)　of　7.18　cd/A　and　an　external　quantum　efficiency　(ηext)　of　9.32%.　By　doping　both　complexes　into　a　blue-green-emitting　cationic　Ir(III)　complex,　high-performance　white　LECs　were　also　successfully　fabricated　with　Commission　International　de　L＇Eclairage　(CIE)　coordinates　of　(0.39,0.39),　a　ηC　of　17.43　cd/A,　and　a　ηext　of　8.92%.　In　addition,　we　also　fabricated　flexible　red　and　white　LECs　with　outstanding　efficiencies　and　mechanical　flexibilities.　The　ηC　and　ηext　values　of　a　flexible　white　LEC　could　be　as　high　as　13.50　cd/A　and　6.86%,　respectively.　The　efficiency　of　the　flexible　device　remained　at　approximately　95%　of　the　initial　value　after　500　bends　with　a　radius　of　curvature　of　5　mm,　demonstrating　the　great　potential　of　these　complexes　for　full-color　displays　and　flexible　optoelectronics.　Copyright　©　2020　American　Chemical　Society.