Self-Assembled Monolayer for Low-Power-Consumption, Long-Term-Stability, and High-Efficiency Quantum Dot Light-Emitting Diodes

Quantum dot light-emitting diodes (QLEDs) are an emergingclassof optoelectronic devices with a wide range of applications. However,there still exist several drawbacks preventing their applications,including long-term stability, electron leakage, and large power consumption.To circumvent the difficulties, QLEDs based on a self-assembled holetransport layer (HTL) with reduced device complexity are proposedand demonstrated. The self-assembled HTL is prepared from poly-[3-(6-carboxyhexyl)-thiophene-2,5-diyl](P3HT-COOH) solution in N,N-dimethylformamide(DMF) forming a well-ordered monolayer on an indium-tin-oxide (ITO)anode. The P3HT-COOH monolayer has a smaller HOMO band offset anda sufficiently large electron barrier with respect to the CdSe/ZnSquantum dot (QD) emission layer, and thus it is beneficial for holeinjection into and electron leakage blocking from the QD layer. Interestingly,the QLEDs exhibit an excellent conversion efficiency (97%) in turningthe injected electron-hole pairs into light emission. The performanceof the resulting QLEDs possesses a low turn-on voltage of +1.2 V anda maximum external quantum efficiency of 25.19%, enabling low powerconsumption with high efficiency. Additionally, those QLEDs also exhibitexcellent long-term stability without encapsulation with over 90%luminous intensity after 200 days and superior durability with over70% luminous intensity after 2 h operation under the luminance of1000 cd m(-2). The outstanding device features ofour proposed QLEDs, including low turn-on voltage, high efficiency,and long-term stability, can advance the development of QLEDs towardfacile large-area mass production and cost-effectiveness.