Effects of the vacuum chamber cleaned with ozone on the lifetime of organic light-emitting diodes

This study is dedicated to prolonging the lifetime of OLEDs, and discussing the factors that affect the lifetime of OLEDs, including: the ITO surface roughness, the cleanliness of the ITO substrate, and the cleanliness inside the vacuum chamber. According to the AFM measurement, it is found that there are some spikes on the ITO surface on glass substrate, which will cause the burnt phenomenon of the encapsulated OLED, resulting in the failure of good reproducibility and lifetime. Therefore, a PEDOT:PSS layer is employed and first spin-coated on ITO, where the surface roughness Ra value is reduced from 3.31 to 1.58 nm. Then the OLED is fabricated on PEDOT:PSS layer to solve the problem of burning when lighting up. Thus its lifetime was prolonged. The ozone gas can effectively decompose the lipids harmful to organic materials released by the heat-resistant tape and vacuum glue inside the vacuum chamber for thermal evaporation. Therefore, this study uses ozone to clean the vacuum chamber, and then proceed to fabricate OLED devices to improve the efficiency and lifetime of OLEDs. Compared with the processes without using ozone to clean the chamber, it is found that the OLEDs fabricated in ozone-cleaned chamber, whether encapsulated with glass or not, had a relatively longer lifetime. The lifetime of OLED without glass encapsulation is extended from 9.9 to 34.3 min, and that of OLED with encapsulation is extended from 34.4 to 404.7 min. With ozone cleaned chamber, the OLED lifetime obtains much improvement.