Research On Red Non-doped Phosphorescent Organic Light-emitting Diode

In recent years,with the development of organic electronics,organic light-emitting diode(OLED)has become a hot topic in the field of microelectronics.However,the conventional OLED has two disadvantages.First,the doping process usually used in device fabrication has high requirements for experimental equipment.Second,it is difficult for conventional OLED to combine the advantages of high brightness and long lifetime.The current efficiency of tandem OLED multiplied increases with the number of luminescent units in series.With the same initial brightness,the lifetime of tandem OLED is much longer than that of conventional devices.The main work in this paper was the fabrication and research of conventional phosphorescent OLED and tandem phosphorescent OLED based on non-doped light-emitting layer(EML).In the research of red conventional non-doped OLED,the number of repeated periods of host/guest layers,the thicknesses of single-host layer and single-guest layer in EML were optimized respectively.The results showed that:(i)the best number of repeated periods was 4;(ii)the optimal thickness of single-host layer was3 nm;(iii)the optimal thickness of single-guest layer was 0.3 nm.The OLED achieved stable red emission and showed excellent color purity and luminescence stability.In the research of tandem non-doped OLED,the conclusions obtained from the study of conventional non-doped devices were applied to the fabrication of tandem OLED,and the non-doped EML was used in both the bottom and top luminescent units of tandem devices.Charge generation layer(CGL)plays an important role in tandem devices.By investigating the effects of hole transport layer(HTL)material,electron acceptor material and the thickness of CGL on tandem OLED,it was concluded that:(i)the hole injection barrier induced by HTL will affect the luminous efficiency of top luminescent unit;(ii)the choice of electron acceptor material not only relates to the charge generation ability of CGL,but also directly affects theconductivity of CGL,and then affects the driving voltage,power efficiency and current efficiency of tandem OLED;(iii)the performance of tandem devices can be further optimized by adjusting the thickness of CGL.The non-doping method used in the fabrication of conventional OLED and tandem OLED is simple and easy to control,and it has lower requirements for experimental equipment.In addition,this paper discussed the influence of each layer in CGL on tandem OLED and optimized the performance of tandem OLED,which can be used as a reference for further improving the performance parameters of tandem devices.