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 emerging class of 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 hole transport layer (HTL) with reduced device complexity are proposed and 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 and a sufficiently large electron barrier with respect to the CdSe/ZnS quantum dot (QD) emission layer, and thus it is beneficial for hole injection into and electron leakage blocking from the QD layer. Interestingly, the QLEDs exhibit an excellent conversion efficiency (97%) in turning the injected electron-hole pairs into light emission. The performance of the resulting QLEDs possesses a low turn-on voltage of +1.2 V and a maximum external quantum efficiency of 25.19%, enabling low power consumption with high efficiency. Additionally, those QLEDs also exhibit excellent long-term stability without encapsulation with over 90% luminous intensity after 200 days and superior durability with over 70% luminous intensity after 2 h operation under the luminance of 1000 cd m^-2. The outstanding device features of our proposed QLEDs, including low turn-on voltage, high efficiency, and long-term stability, can advance the development of QLEDs toward facile large-area mass production and cost-effectiveness.