Studies on Quantum Dot Light Emitting Diode with Conjugated Polymer Having Gradient HOMO Levels as Hole Transport Layer

• Main Authors: Wu, Shuo En, 吳碩恩
• Other Authors: Chen, Show En
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/67217299954795236485

碩士 === 國立清華大學 === 化學工程學系 === 104 === Abstract Colloidal Quantum dots have unique characteristics, such as high photoluminescence quantum efficiency, pure color emission, solution process, large area production and are potential candidate to replace OLED and PLED. Recently, CdSe/ZnS-based quantum dots device demonstrates high current efficiency, high brightness and long operating life time. In this work, gradient core-shell CdSe/ZnS is coated with additional ZnS shell for longer exciton life time (CdSe@ZnS/ZnS). It is found that insulating oleophilic ligands oleic acid (OA) and trioctylphosphine (TOP) are both on QDs film/surface as examined by X-ray photoelectron spectroscopy (XPS). With high temperature annealing process, the loss of partial ligands lead to enhanced electron injection, improved PL intensity and resistivity to organic solvent. In general, the alignment between QDs layer and hole transport layer have large hole injection barrier (>1 eV), resulting in unbalanced charge injection. To solve this high injection barrier problem, we design molecular-scale graded HOMO levels polymer for improved hole injection, which allows hole carriers to inject to QDs layer via four consecutive steps by grafting triphenylamine (TPA), carbazole (Cz) and 1,3-Bis(N-carbazolyl)benzene (mCP) hole transport moieties on the side chains of spiro-polyfluorene. The inverted-type structure ITO/ZnO/(CdSe@ZnS/ZnS)/gradient spiro-polyfluorene/MoO3/Al have the brightest luminance over 200,000 cd/m2 and the highest current efficiency 36.1 cd/A, among the reported results of inverted-type QD-LED. Furthermore, the first all solution-processable invert type structure is fabricated also by replacing vacuum-deposited MoO3 with solution-processed MoO3. It gives the performance with the maximum brightness 239,500 cd/m2 and efficiency 22.4 cd/A.