Performance Limits of an Alternating Current Electroluminescent Device

Abstract

The use of an alternating current (AC) voltage is a simple, versatile method of producing electroluminescence from generic emissive materials without the need for contact engineering. Recently, it was shown that AC‐driven, capacitive electroluminescent devices with carbon nanotube network contacts can be used to generate and study electroluminescence from a variety of molecular materials emitting in the infrared‐to‐ultraviolet range. Here, performance trade‐offs in these devices are studied through comprehensive device simulations and illustrative experiments, enhancing understanding of the mechanism and capability of electroluminescent devices based on alternating as opposed to direct current (DC) schemes. AC‐driven electroluminescent devices can overcome several limitations of conventional DC‐driven electroluminescent devices, including the requirement for proper alignment of material energy levels and the need to process emitting materials into uniform thin films. By simultaneously optimizing device geometry, driving parameters, and material characteristics, the performance of these devices can be tuned. Importantly, the turn‐on voltage of AC‐driven electroluminescent devices approaches the bandgap of the emitting material as the gate oxide thickness is scaled, and internally efficient electroluminescence can be achieved using low‐mobility single‐layer emitter films with varying thicknesses and energy barrier heights relative to the contact.

A Resonantly Driven, Electroluminescent Metal Oxide Semiconductor Capacitor with High Power Efficiency

“…Voltage-dependent measurements of the device operating at this frequency show that EL is generated at much lower supply voltages when driven resonantly as opposed to nonresonantly (Figure d). As established previously, the turn-on voltage for electroluminescence can be fundamentally reduced by decreasing the equivalent gate oxide thickness to the several nanometers range; however, this imposes constraints on the precision of the fabrication process. Absent the resonant driving scheme, the turn-on voltage is reduced by half by using a device with a thinner, high- k gate dielectric layer.…”

“…Although the net power consumption of AC-driven devices is lower than equivalently driven DC devices due to the largely nondissipative charging and discharging-based operation, the peak current densities into the semiconducting layer can still be high. Furthermore, temporal simulations of the device’s operating mechanism suggest that pulsed carrier injection is less efficient above a certain threshold voltage, since returning carriers are swept out through the source contact more rapidly and are less likely to recombine with incoming injected carriers of the opposite polarity . Finally, heating effects may play a role in degraded device behavior.…”

“…Furthermore, temporal simulations of the device's operating mechanism suggest that pulsed carrier injection is less efficient above a certain threshold voltage, since returning carriers are swept out through the source contact more rapidly and are less likely to recombine with incoming injected carriers of the opposite polarity. 26 Finally, heating effects may play a role in degraded device behavior.…”

Optimising the electroluminescence performance of ZnS: Cu/epoxy composites via exploring the relationship between electroluminescence intensity and filler intrinsic attributes

“…It can be visualised that the electroluminescence characteristics of ZnS: Cu particles are related to the quantum process of electron transition [28]. Therefore, it is necessary to study the electroluminescence properties of ZnS: Cu particles from the microscopic point of view, which is inadequate in this area [29]. Density functional theory (DFT), as a powerful tool, is widely used to calculate the band structure of ZnS: Cu particles [30,31].…”

Efficiency Roll-Off Free Electroluminescence from Monolayer WSe2

“…The external quantum efficiency (QE) is lower than 1% in most cases, ,,,,, and efficiency roll-off has been observed in WS 2 EL devices with the MIS structure . Although a relatively high external QE of around 1–10% has been reported with the use of a complex quantum well structure of graphene/ h -BN/TMDC/ h -BN/graphene, bipolar ohmic contact is still challenging. , A transient-mode EL device, which consists of a simple capacitor structure with a single source contact, can achieve a large band bending enabling a high injection current rate during the gate voltage transient regardless of the Schottky barrier height. − Here, we demonstrate a roll-off free transient-mode EL device based on TMDC monolayers. The PL QY of WSe 2 monolayers reaches near-unity even at high exciton density by applying external tensile strain together with gate modulation due to the inhibition of VHS resonance.…”