Fabrication of Large‐Area Uniform Nanometer‐Thick Functional Layers and Their Stacks for Flexible Quantum Dot Light‐Emitting Diodes

Abstract

Large‐area fabrication and stacking of various nanometer‐thick functional layers from solutions is essentially important for the construction of flexible thin‐film optoelectronic devices, but very challenging. The existing fabrication methods suffer from either non‐uniformity caused by the coffee‐ring effect or serious solution waste (excess of 90% for spin coating), and are hard to scale up and create stacks. Here, it is shown that centrifugal casting is a universal, scalable, and efficient method to fabricate uniform nanometer‐thick films and their stacks of various materials. The coffee‐ring effect is effectively suppressed, the solution utilization ratio is higher than ≈61%, and the films/stacks show a smooth surface/high‐quality interface. Using this method, flexible quantum dot light‐emitting diode displays with uniform luminance in a large lighting area of ≈115 cm2 that have not been achieved even on rigid substrates by the existing methods, are realized. This efficient and low‐cost solution processing method paves a way for large‐area fabrication of various flexible thin‐film optoelectronic devices.

An investigation on the cyclic temperature-dependent performance behaviors of ultrabright air-stable QLEDs

“…Our devices show a high maximum EQE of over 14% and a maximum brightness of 624,000 cd/m 2 at 12 V, unprecedented for QLEDs fabricated under ambient-air conditions (see, e.g., Ref. 37 ) 38 . We have experimentally investigated the temperature-dependent efficiency parameters and brightness by stressing the devices under multiple cooling/heating cycles within a wide temperature range from − 10 to 85 °C.…”

Tailored ZnO Functional Nanomaterials for Solution‐Processed Quantum‐Dot Light‐Emitting Diodes

“…On the other hand, numerous research papers have reported QLED devices fabricated by the traditional “inkjet printing”, [ 5 ] “blade coating”, [ 6 ] “direct writing”, [ 7 ] “pen writing”, [ 8 ] “solution transferring”, [ 9 ] “selective electrophoretic deposition”, [ 10 ] and “centrifugal casting”. [ 11 ]…”

“…On the other hand, numerous research papers have reported QLED devices fabricated by the traditional "inkjet printing", [5] "blade coating", [6] "direct writing", [7] "pen writing", [8] "solution transferring", [9] "selective electrophoretic deposition", [10] and "centrifugal casting". [11] Due to its high electron mobility and excellent energy-level alignment with the conduction band minimum (CBM) of CdSe-based QDs in the emissive layer (EML), [12] zinc oxide (ZnO) has been established as the most widely used electron transport layer (ETL) in QLED architectures. The small energy barrier for electron injection (from the ETL to EML), together with a large energy offset between the hole transport layer (HTL) and EML could cause a charge imbalance in a QLED device.…”