A series of ten cationic complexes of the general formula [(C^C)Au(P^P)]X, where C^C = 4,4′-di-tert-butyl-1,1′-biphenyl, P^P is a diphosphine ligand, and X is a noncoordinating counteranion, have been synthesized and fully characterized by means of chemical and X-ray structural methods. All the complexes display a remarkable switch-on of the emission properties when going from a fluid solution to a solid state. In the latter, long-lived emission with lifetime τ = 1.8–83.0 μs and maximum in the green-yellow region is achieved with moderate to high photoluminescence quantum yield (PLQY). This emission is ascribed to an excited state with a mainly triplet ligand-centered (3LC) nature. This effect strongly indicates that rigidification of the environment helps to suppress nonradiative decay, which is mainly attributed to the large molecular distortion in the excited state, as supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) computation. In addition, quenching intermolecular interactions of the emitter are avoided thanks to the steric hindrance of the substituents. Emissive properties are therefore restored efficiently. The influence of both diphosphine and anion has been investigated and rationalized as well. Using two complexes as examples and owing to their enhanced optical properties in the solid state, the first proof-of-concept of the use of gold(III) complexes as electroactive materials for the fabrication of light-emitting electrochemical cell (LEC) devices is herein demonstrated. The LECs achieve peak external quantum efficiency, current efficiency, and power efficiency up to ca. 1%, 2.6 cd A–1, and 1.1 lm W–1 for complex 1PF6 and 0.9%, 2.5 cd A–1, and 0.7 lm W–1 for complex 3, showing the potential use of these novel emitters as electroactive compounds in LEC devices.

Organic light‐emitting diodes (OLEDs) attract much research attention owing to their superior device characteristics in display and lighting applications. However, multi‐layered organic thin films deposited by thermal evaporation in a high‐vacuum chamber complicate the fabrication processes and increase the production costs. Alternatively, solution‐processable single‐layered light‐emitting electrochemical cells (LECs) possess easy fabrication and good device performance due to in situ electrochemical doping. To take advantages of both types of devices, the study proposes an efficient tandem white OLED/LEC hybrid device by stacking a red OLED on top of a blue LEC with a sophisticatedly designed charge‐generating layer (CGL). The proposed tandem device exhibits a high external quantum efficiency (EQE) of 21.53%, which is almost the sum of the EQEs of the two stacked devices. When fabricated on the diffusive substrate to recycle the trapped light in the substrate, the EQE can be further enhanced to reach 37.88%. Besides connecting the two stacked devices, the CGL improves the carrier balance of the blue LEC due to enhanced electron injection. This study demonstrates that the white tandem OLED/LEC hybrid device has a simpler device structure than all‐vacuum‐processed tandem OLEDs but it still delivers high device efficiency, revealing its potential in lighting applications.