Material and device design for organic optoelectronics

Optoelectronic devices--Design and construction;Organic compounds--Optical properties;Optical materials;Photodiodes

Levell, Jack William ; Samuel, Ifor D. W. ; Samuel, Ifor D. W.

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Optoelectronic devices--Design and construction;    Organic compounds--Optical properties;    Optical materials;    Photodiodes;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/2066/JackW.LevellPhDThesis.pdf?sequence=7&isAllowed=y

来源: DR-NTU

【 摘 要 】

This thesis describes investigations into the photophysical properties of luminescentmaterials and their application in optoelectronic devices such as light emitting diodesand photodetectors. The materials used were all solution processable because of theinterest in low cost processing of organics.I have investigated the photophysics of 1,4,5,8,9,12-hexamethyltriphenylene, atriphenylene derivative which has its luminescence enhanced by the addition ofmethyl groups. These groups change the planar shape of the triphenylene moleculeinto a twisted one, changing the symmetry of the molecule and increasing its dipolemoment in absorption and emission by ~4 fold. This increased its rate of radiative deexcitationby ~20 times. In addition, the twisted shape of the molecule preventsintermolecular interactions and concentration effects from affecting the luminescence.This results in an efficient solid-state photoluminescence quantum yield of 31%.This thesis also includes an investigation into phosphorescent polymer dendrimers,designed to have suitable viscosities in solution for inkjet printed OLED applications.A photophysical study of the intra-chain aggregation effects on the luminescence wasundertaken in both homopolymers and copolymers with high energy gap spacer units.Using double dendrons to increase the steric protection of the luminescent cores, thebest homopolymers achieved 12.1% external quantum efficiency (39.3 cd/A) at 100cd/m² brightness and the best co-polymer achieved 14.7% EQE (48.3 cd/A) at 100cd/m². This compares favourably with 11.8% EQE for the best phosphorescentpolymer and 16% for the best solution processed dendrimer OLED previouslyreported.Finally I have applied a solution processed enhancement layer to silicon photodiodesto enhance their ultraviolet response. Using a blend of materials to give favourableabsorption and emission properties, 61% external quantum efficiency was achieved at200 nm, which is better than the 20-30% typical for vacuum deposited lumogenenhancement layers used commercially.