Study On Device Stability Of OLED Anthracene Based Blue Light Host Materials

Organic light-emitting diodes(OLED)are the latest generation of display technology and have been rapidly promoted and widely applied.The current deficiency in the lifespan of blue light is a key factor limiting its further development,and is a hot topic and technical difficulty in this field.As an important functional layer material in OLED devices,the blue light host material not only serves as a carrier for exciton recombination and energy transfer,but also plays a key role in the stability of the material itself in the device,which affects the lifespan of the device.The development and synthesis of blue light host materials with low operating voltage and good film-forming properties is one of the key technologies for preparing low-cost and long-lived OLED devices,and is also the research purpose of this article.This article adopts a combination of experimental and simulation calculations to select anthracene derivatives,a classic non-donor acceptor type bipolar blue light host material,and explores the two key factors affecting the stability of the host material device,namely isotope effect and the reduction of device working voltage by the host material.The internal mechanism by which these two factors affect device stability is predicted and verified.The specific research content is as follows:(1)Research on the influence of isotopic effects.Design and synthesize an anthracene based non deuterated molecule REF01 and test it with a deuterated REF01 device as the blue light host material(hereinafter referred to as REF01 device).The results show that deuterated REF01 can effectively improve the stability of the blue light host material in the device without changing the device’s luminescent performance.The reason for the poor stability of REF01 device is that the reaction of intramolecular cyclization followed by degradation reaction occurred.The transition state calculation shows that for the above degradation mechanism,REF01 has four degradation paths.The transition state calculation of hydrogen transfer reaction shows that the internal cyclization reaction occurred in the first step is the key factor of the degradation reaction.The transition state calculation of REF01 molecules with different deuterium substitution sites shows that benzene deuterization reduces the degradation rate to 90.7% of non deuterium,and anthracene deuterization reduces the degradation rate to 76.4% of non deuterium.The simultaneous deuterization of benzene and anthracene has a synergistic effect,and the degradation rate is 4.5%of non deuterium.The total deuterization of REF01 is the same as the former.(2)Verification of the influence law of isotope effects.Design and use another set of anthracene based molecules BH016 and test it with deuterium based BH016 as the blue light host material.The results show that the two host materials have the same device stability.In order to investigate the accuracy of the degradation reaction mechanism of BH016 through intramolecular cyclization followed by hydrogen transfer,simulation calculations were used to verify the degradation reaction mechanism of BH016.There are three degradation pathways for BH016,and the degradation rate calculations for BH016 and deuterated BH016 indicate that they have the same degradation rate,thus proving the correctness of the degradation reaction mechanism of intramolecular cyclization followed by hydrogen transfer.(3)Research on reducing device operating voltage with host material.Design and synthesize a molecule BH017 that can reduce the operating voltage of the device,and test it with deuterium substituted REF01 as the host material of the device.The results show that BH017 reduces the operating voltage of the device but does not have higher device stability as expected.The reason for the poor stability of the BH017 device is that the chemical bond broke.The BDE and bond dissociation barrier were used to evaluate the strength of the chemical bond in BH017.Through calculation,the bond with the lowest BDE and bond dissociation barrier value in BH017 is C-N bond,which is lower than the BDE and bond dissociation barrier of all chemical bond in REF01.From this analysis,it can be concluded that the dissociation of the CN bond in BH017 is the main factor leading to poor stability of the material device.In order to investigate the relative stability of the three C-N bonds contained in the carbazole group in BH017,AIM analysis and bond local vibrational constant methods were used to evaluate.The results showed that the three C-N bonds had the same stability.