Thin Film Encapsulation On Organic And Perovskite Electroluminescent Devices

Organic light-emitting diode(OLED)has been gradually applied in wearable electronics,mobile phones,micro displays,photodynamic therapy and automotive taillights due to its advantages of light weight,fast response time,low power consumption and low heat generation.Perovskite light-emitting diode(PeLED)has also exceeded 20%in external quantum efficiency(EQE).With the advantages of high fluorescence quantum yield,tunable band gap,excellent color purity and solution processibility,PeLED has a promising future for next-generation display and lighting technology.Apart from achieving high efficiency,the operation lifetime and storage lifespan of the optoelectronic devices are two crucial issues in product commercialization.To deal with these issues,it is critical to utilize a simple but effective encapsulation method to improve the OLED/PeLED durability and lower the manufacturing cost simultaneously.In this thesis,the author mainly focuses on fours kinds of thin film encapsulation materials:silicon nitride,lithium fluoride,aluminum and alumina.Silicon nitride and silicon nitride/aluminum films will be applied to red OLED devices,while the lithium fluoride and alumina will be adopted for PeLED devices.The film properties and device performances particularly the lifetime are studied thoughtfully.In the first work,silicon nitride and alumina films with excellent waterproof properties were fabricated.By optimizing the substrate deposition temperature and the film thickness,the residual stress of silicon nitride film reduced to-23.2 MPa,and the water vapor transmittance rate reached 5×10-5 g/m2/day.The optical transmittance and refractive index of the silicon nitride film were 90.0%and 1.97,respectively.To further improve the reliability of the encapsulated film,I compensate the film stress by combining the compressive stress of silicon nitride with the tensile stress of aluminum film,resulting in a residual stress of-1.0 MPa if using a composite silicon nitride/aluminum configuration.Also,alumina film was prepared by atomic layer deposition and applied to the packaging of perovskite devices.The optimized stress and optical transmittance of the alumina film were 27.6 MPa and 91.7%,respectively.In the second work,the author designed red OELDs with high EQEs and brightness,low efficiency roll-down and stable operating performance,and then applied hybrid encapsulation methods of using silicon nitride/glass and silicon nitride/aluminum/glass to examine the encapsulation effect of these red light-emitting devices.The T95 operation lifetime of the device was 566 hours when driven at a current density 50 mA/cm2,and the storage lifespan was 760 hours at the 85℃/85%RH accelerated condition,which is equivalent to 17 years of lifespan if storage at room temperature and 50%relative humidity.The outstanding lifetime facilitates OLED applications which require exceptional longevity and device stability.In the third work,the author fabricated pure inorganic PeLEDs and encapsulated them with different packaging materials.The results indicate that the encapsulation using lithium fluoride film prepared by vacuum thermal evaporation was simple and effective enough to enhance the device operation lifetime by 170%.This study provides some ideas to protect PeLEDs against degradation.