Optimization of the electron transport layer in quantum dot light-emitting devices

Abstract

Quantum dot light-emitting devices have emerged as an important technology for display applications. Their emission is a result of recombination between positive and negative charge carriers that are transported through the hole and electron conductive layers, respectively. The selection of electron or hole transport materials in these devices not only demands the alignment of energy levels between the layers but also balances the flow of electrons and holes toward the recombination sites. In this work, we examine a method for device optimization through control of the charge carrier kinetics. We employ impedance spectroscopy to examine the mobility of charge carriers through each of the layers. The derived mobility values provide a path to estimate the transition time of each charge carrier toward the emitting layer. We suggest that an optimal device structure can be obtained when the transition times of both charge carriers toward the active layer are similar. Finally, we examine our hypothesis by focusing on thickness optimization of the electron transport layer.

Bifunctional Electron-Transporting Agent for Red Colloidal Quantum Dot Light-Emitting Diodes

“…InP/ZnSe/ZnS core–shell-based LEDs provide a heavy-metal-free route to efficient LEDs. , High-performance red InP LEDs (external quantum efficiency, EQE > 15%) have been achieved by optimizing their ZnMgO or ZnO ETLs; however, performance drops to <15% when using other ETL materials. − ZnO/ZnMgO ETLs suffer from defects and severe quenching: the deposition of these ETLs on InP induces a photoluminescence quantum yield (PLQY) drop and LED degradation due to trap migration from the ETL to the emitting layer. , Inserting an extra passivation layer between ZnMgO ETL and emitter can partially relieve the PLQY drop and device degradation, − but this needs delicate thickness control to the monolayer limit to minimize the conductivity barrier, complicating the fabrication process.…”

“…11−14 ZnO/ZnMgO ETLs suffer from defects and severe quenching: the deposition of these ETLs on InP induces a photoluminescence quantum yield (PLQY) drop and LED degradation due to trap migration from the ETL to the emitting layer. 15,16 Inserting an extra passivation layer between ZnMgO ETL and emitter can partially relieve the PLQY drop and device degradation, 17−19 but this needs delicate thickness control to the monolayer limit to minimize the conductivity barrier, complicating the fabrication process.…”

Luminescence studies in cadmium telluride nanocrystals grown on glass substrates

“…Most nanocrystal-based EL devices using organic charge transport layers show emission from both the nanocrystal and polymer layers, due to electron hole recombination in both the components. 10,28–30 Therefore, to better resolve the spectra into different peaks, EL spectra were deconvoluted using Gaussian line shape functions, as shown in Fig. 8(b).…”

“…Hybrid organic-inorganic light emitting devices combine the colour purity and durability of inorganic nanocrystals with the efficiency, exibility and low processing cost of organic light emitting diodes (OLEDs). [27][28][29] A major enduring challenge is the identication and synthesis of organic lumophores or phosphors compatible with the required device structures, especially in the blue part of the spectrum. Inorganic nanocrystals have certainly emerged as efficient and alternate lumophores as the colour emission can be tuned across the visible spectrum.…”

Revealing the Negative Capacitance Effect in Silicon Quantum Dot Light-Emitting Diodes via Temperature-Dependent Capacitance-Voltage Characterization

“…C − V measurement is a powerful technique where an AC signal is superimposed on a DC bias and the electrical capacitance and conductance response of the device can be recorded as a function of the applied AC frequency. [12]- [14] Charge injection and kinetics can be studied in a non-destructive manner [15]- [17] and processes that occur at various time scales can be monitored with high sensitivity. [18]- [20] We found a negative capacitance response in SiQD-LEDs.…”