Singlet fission is usually the only reaction channel for excited states in rubrene-based organic light-emitting diodes (OLEDs) at ambient temperature. Intriguingly, we discover that triplet fusion (TF) and intersystem crossing (ISC) within rubrene-based devices begin at moderate and high current densities (j), respectively. Both processes enhance with decreasing temperature. This behavior is discovered by analyzing the magneto-electroluminescence curves of the devices. The j-dependent magneto-conductance, measured at ambient temperature indicates that spin mixing within polaron pairs that are generated by triplet-charge annihilation (TQA) causes the occurrence of ISC, while the high concentrations of triplets are responsible for generating TF. Additionally, the reduction in exciton formation and the elevated TQA with decreasing temperature may contribute to the enhanced ISC at low temperatures. This work provides considerable insight into the different mechanisms that occur when a high density of excited states exist in rubrene and reasonable reasons for the absence of EL efficiency roll-off in rubrene-based OLEDs.

The large amount of iron rust yielded in steel industries is undoubtedly a useless and undesired product since its substantial formation and recycle/smelting would give rise to enormous financial costs and environmental pollution issues. To best reuse such rusty wastes, we herein propose a smart and applicable method to convert them into uniform α-Fe 2 O 3 nanospheres. Only after a simple and conventional hydrothermal treatment in HNO 3 solution, nearly all of the iron rust can evolve into sphere-like α-Fe 2 O 3 products with a typical size of ∼30 nm. When serving as actives for electrochemical energy storage, the in situ generated α-Fe 2 O 3 nanospheres exhibit prominent anodic performance, with a maximum specific capacity of ∼269 mAh/g at ∼0.3 A/g, good rate capabilities (∼67.3 mAh/g still retains even at a high rate up to 12.3 A/g), and negligible capacity degradation among 500 cycles. Furthermore, by paring with activated carbons/Ni cathodes, a unique full hybrid Ni−Fe cell is constructed. The assembled full devices can be operated reversibly at a voltage as high as ∼1.8 V in aqueous electrolytes, capable of delivering both high specific energy and power densities with maximum values of ∼131.25 Wh/kg and ∼14 kW/kg, respectively. Our study offers a scalable and effective route to transform rusty wastes into useful α-Fe 2 O 3 nanospheres, providing an economic way to make sustainable anodes for energy-storage applications and also a platform to develop advanced Fe-based nanomaterials for other wide potential applications.

Non-emissive triplet excited states in devices that undergo thermally activated delayed fluorescence (TADF) can be up-converted to singlet excited states via reverse intersystem crossing (RISC), which leads to an enhanced electroluminescence efficiency. Exciton-based fluorescence devices always exhibit a positive magneto-electroluminescence (MEL) because intersystem crossing (ISC) can be suppressed effectively by an external magnetic field. Conversely, TADF devices should exhibit a negative MEL because RISC is suppressed by the external magnetic field. Intriguingly, we observed a positive MEL in TADF devices. Moreover, the sign of the MEL was either positive or negative, and depended on experimental conditions, including doping concentration, current density and temperature. The MEL observed from our TADF devices demonstrated that ISC in the host material and RISC in the guest material coexisted. These competing processes were affected by the experimental conditions, which led to the sign change of the MEL. This work gives important insight into the energy transfer processes and the evolution of excited states in TADF devices.

We fabricated quantum-well organic light-emitting diodes (QW-OLEDs) based on thermally activated delayed fluorescence (TADF) and measured their magnetic field effects curves over various magnetic field ranges.

An in situ heating method was used to investigate the effect of high temperature on the magneto-electroluminescence (MEL) of rubrene-based organic light-emitting diodes.