Device Study on the Performance of Blue and White Perovskite Light-emitting Diodes

Abstract

Perovskites are newly emerging opto-electronic materials and have widely studied in many areas such as photovoltaics (PVs), light-emitting diodes (LEDs) and photo detectors (PDs). Their low-cost, solution-processability, high defect tolerance and tunable bandgap indicate them to be ideal materials in opto-electronic devices. Perovskite LEDs (PeLEDs), one of the most important application of perovskites, have been well developed since the first electroluminescence (EL) discovered in 2014. PeLEDs with external quantum efficiencies (EQEs) over 25% have been achieved with green, red and near-infrared emissions. However, blue PeLEDs and further integration of blue, green and red PeLEDs to achieve white PeLEDs are still great challenges in this field. Therefore, in this thesis, we will give a device study on the fabrication of high-performance blue and white PeLEDs.

In chapter 1, we gave a comprehensive literature review of the development of PeLEDs with blue and white emissions. We summarized the strategies and methods to fabricate efficient blue and white PeLEDs and also introduced several representative works among them. Basing on that, we further gave the discussion on the potential application and challenges of PeLEDs in the future.

In chapter 2, we gave a study on the method to fabricate high efficiency blue PeLEDs. We utilized carbazole phosphonic acid (CPA) based additives to enhance the efficiency of blue PeLEDs. We found that the CPA-based molecules would modulate the n phase distribution of quasi-2D perovskites and enhance the Photoluminescence Quantum Yields (PLQYs) of blue perovskite emitter. Moreover, when the ITO/Mg_0.1Ni_0.9O_x/4-(7H-dibenzo [c, g] carbazol-7-yl) butyl,) phosphonic acid/poly(9-vinylcarbazole) (PVK) hole injection system was utilized, the CPA-based molecules will preferentially go to the bottom PVK/perovskite interface, where they passivate the buried traps via forming P-O-Pb bonds. Basing on this strategy, high performance blue PeLEDs with EQEs over 15% were achieved.

In chapter 3, in order to get over the out-coupled efficiency limit of bottom-emission (BE) device, we introduced a method to fabricate a top-emission (TE) PeLEDs. In order to enhance the hole injection from the metal anode to blue perovskite emitter, a CPA based self-assembled monolayer (SAM) was introduced on the surface of MoO_x, which can enhance the hole injection and improve the EQEs of blue perovskite emitter. Furthermore, we also gave an optical simulation to analyze the effect of the out-coupling layer (OCL) on device efficiency. And the simulation results showed good agreement with the experiment results. Basing on this, we achieved a blue TE-PeLEDs with EQEs over 10%, which is also the first reported blue TE-PeLEDs to date.

In chapter 4, we tried to fabricate the bi-color and tri-color white TE-PeLEDs basing on the strategy of blue EL + red/green PL strategy. We investigated the micro-cavity effect on the performance of both blue and white TE-PeLEDs and achieved a bi-color white PeLEDs with EQEs over 9%. Basing on the similar strategy, we also successfully fabricated a tri-color white PeLEDs with EQEs of 5%, which paves the way for the device development of high performance white PeLEDs.

Date of Award	8 Sept 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hin Lap YIP (Supervisor)