Organic stacked light-emitting devices based on PEDOT꞉PSS layer

Abstract

Organic light-emitting devices (OLEDs) have been the intensive investigation subject in recent years due to their applications in lighting and displays. The typical OLED structure usually consists of a transparent indium-tin-oxide bottom anode, a top metal cathode, and some organic layers sandwiched between electrodes. After 30 years of unremitting efforts, the performance of OLEDs has been close to the level of inorganic semiconductor light-emitting devices. However, in order to achieve the final application goal of dynamic panchromatic HD display, the luminous efficiency and stability of the device need to be further improved. Especially because organic materials are not resistant to high temperature, improving the luminous efficiency of the device and reducing the heat loss become the key to improving the stability and service life of the device. One of the important factors that affect the life of OLEDs is the thermal aging caused by the high current flowing through it. Therefore, it is of great significance to study a kind of high efficiency device operating at low current. Stacked device structure technology is an effective way to realize low current and high efficiency OLEDs. The major challenge in stacked OLEDs in general is to prepare the effective connecting layer between emitting units so that the current can smoothly flow through without manufacturing difficulties. In this paper, we use PEDOT꞉PSS as the connecting layer of the device, and successfully prepare the stack organic light-emitting device with ITO/PEDOT꞉PSS (15 nm) /PFO (80 nm) /PEDOT꞉PSS (40 nm) /PFO (80 nm) /Al (70 nm) structure. By studying the current-voltage characteristics, voltage-brightness characteristics and current-efficiency characteristics, it is found that the illumination voltage and the illumination current are 12.3 V and 1.39 μA, respectively. The current efficiency (3.97 cd /A) is 8 times higher than that of single-layer comparator. The connection layer of this new type of PEDOT꞉PSS stack device needs neither high temperature evaporation coating nor doping. This method not only simplifies the preparation process of the connection unit of the stacked device, avoids the damage of the device film caused by high temperature evaporation, but also overcomes the problem of the damage of the device performance caused by the atomic scattering of the existing doping process. At the same time, the physical mechanism of PEDOT꞉PSS as the connecting layer of stacked OLED is discussed.