Self-assembled mono-hole-injecting layers towards efficient deep-blue perovskite light-emitting diodes

Hole-injection layers (HILs) play crucial roles in enhancing the performance of perovskite light-emitting diodes (PeLEDs) by lowering the energy barrier between the anode and the hole-transport layer (HTL). However, the commonly employed HIL, poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT: PSS) has notable drawbacks, such as extreme acidity and susceptibility to corrosion, which severely hampers device efficiency and stability. Herein, a self-assembled monolayer (SAM)-[2-(9H-Carbazol-9-yl) ethyl] phosphonic acid (2PACz) instead of PEDOT: PSS was employed in PeLEDs, which could reduce the negative impacts on neighboring perovskite sites and indium tin oxide electrodes. To obtain favorable energy level alignment between 2PACz and the perovskite layer, poly(9-vinylcarbazole) (PVK) was introduced as an indispensable HTL. Consequently, the 2PACz/PVK-based deep-blue PeLEDs exhibit a lower turn-on voltage of 3.20 V, and a peak external quantum efficiency of 4.42 % at 467 nm, which is a threefold improvement over the control devices. This impressive performance boost can be attributed to the reduction in interfacial defects and the improved balance of carrier injection, leading to more efficient light emission. Our study not only introduces an innovative and cost-effective HIL solution for PeLEDs but also provides valuable insights and guidance for the development of highly efficient and stable PeLEDs in the future.