Blue organic seven segment display based on poly (9,9-dioctyfluorene)with β-phase emission

Abstract

In this work, organic seven segment displays based on poly(9,9-dioctyfluorene), PFO, have been fabricated. PFO has consolidated as an attractive material for PLEDs due to its efficient blue emission [1] and high hole mobility. Additionally, PFO has a particular conformation, called β-phase associated to extended PFO chain conformation, which is of great interest for potential device applications because, among all others, it has the highest photoluminescence quantum efficiency [2] and the best colour stability [3]. The structure fabricated uses Indium Tin Oxide (ITO) as anode, Poly(3,4 -ethylenedioxythiophene) /poly(4- styrenesulfonate) (PEDOT:PSS) as hole transport layer and Ba:Al as cathode. After thoroughly cleaning the substrates (covered with ITO) a photolithography process is carried out in order to pattern the anode. Next, the organic layers (PEDOTT:PSS and PFO) are spin casted. Finally, metals (Ba~30 nm and Al~100 nm) are thermally evaporated in an atmosphere of 6x10 -6 Torr. PFO is dissolved in toluene at 1 % wt. A detailed description of the fabrication process can be found in [4]. Finally, the device is encapsulated (using an epoxy and a glass tap) and contacts are indium soldered on the pads. In figure 1, we can observe the shadow mask used for the anode photolitography process (left) and the final device lighting in a zero configuration (right).