Deciphering the Electroluminescence Behavior of Silver(I)-Complexes in Light-Emitting Electrochemical Cells: Limitations and Solutions toward Highly Stable Devices

Ionic transition-metal complexes based on silver(I) metal core (Ag-iTMCs) represent an appealing alternative to other iTMCs in solid-state lighting owing to (i) their low cost and well-known synthesis, (ii) the tunable bandgap, and (iii) the highly efficient photoluminescence. However, their electroluminescence behavior is barely studied. Herein, the archetypal green-emitting Ag-iTMCs, namely [Ag(4,4′-dimethoxy-2,2′-bipyridine)(Xantphos)]X (X = BF₄, PF₆, and ClO₄), are thoughtfully investigated, revealing their electroluminescent features in light-emitting electrochemical cells (LECs). Despite optimizing device fabrication and operation, luminance of 40 cd m⁻², efficacy of 0.2 cd A⁻¹, and a very poor stability of 30 s are achieved. This outcome encourages the comprehensive study of the degradation mechanism combining electrochemical impedance spectroscopy, X-ray diffraction, and cyclic voltammetry techniques. These results point out the irreversible formation of silver nanoclusters under operation strongly limiting the device performance. As such, LECs are further optimized by (i) changing the counterions (PF₆⁻ and ClO₄⁻) and (ii) decoupling electron injection and exciton formation using a double-layered architecture. The synergy of both approaches leads to a broad exciplex-like whitish electroluminescence emission (x/y CIE of 0.40/0.44 and color rendering index of 85) with an outstanding improved stability of ≈4 orders of magnitude (>80 h) without losing brightness (35 cd m⁻²).