Anomalous EL–PL Lifetime Inversion in Silicon Quantum-Dot Light-Emitting Diodes

Abstract Diamond-cubic silicon is a promising quantum-dot material for sustainable optoelectronics owing to its abundance, nontoxicity, and size-tunable photoluminescence (PL). However, silicon quantum-dot light-emitting diodes (Si-QLEDs) suffer from severe efficiency roll-off at high current densities, and the underlying electroluminescence (EL) dynamics remain poorly understood. Here, transient EL measurements using time-correlated single-photon counting reveal that the EL lifetime of Si-QLEDs remains nearly constant at ∼13 μs under varied off-bias conditions and is approximately 8.7 times shorter than the corresponding PL lifetime (∼114 μs). In contrast, CdSe/ZnS QLEDs exhibit the conventional relationship in which the EL lifetime exceeds the PL lifetime. This anomalous EL–PL lifetime inversion in Si-QLEDs is accompanied by a pronounced EQE roll-off at high current densities. Time-resolved current analysis reveals a slow relaxation component possibly associated with trap-related carrier dynamics, while the EL peak energy shows a stronger dependence on current density than on applied voltage. Carrier imbalance and Auger recombination remain possible nonradiative mechanisms under electrical excitation, although their individual contributions to the shortened EL lifetime and efficiency roll-off cannot be independently quantified from the present measurements. In addition, increasing reverse off-bias markedly prolongs the EL delay time, indicating that charge accumulation and trap filling primarily govern the carrier-preparation stage preceding radiative recombination. These findings reveal distinct carrier dynamics in Si-QLEDs and highlight charge-balance control and trap-state reduction as important strategies for mitigating efficiency roll-off.