A Simple Structured Exciplex Device with a Multi-Color Sensing Capability

Over the past decades, color sensors have been of great interest among researchers for conveying information. The color sensors are required to detect any deformation or structural change occurring in our surrounding infrastructures as well as the internal activities in the operating devices. To fabricate an efficient sensor, researchers are in search of a material that can exhibit large structural change in response to a small applied voltage. Many investigations have been carried out to explore the applications of organic light-emitting diodes (OLEDs) for testing the devices subjected to stress. Among them, exciplex based OLED has demonstrated various advantages over simple structured OLED. Enormous efforts have been devoted to discover its applications in the field of science and engineering. However, a very few investigations have been carried out to explore the applications of exciplex.<br/>Here, we suggest another way to applicate the exciplex device for the voltage sensor. The color of exciplex device changes as the recombination zone changes according to the driving voltage. Using color variability of exciplex device, a visible voltage sensor was fabricated. 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl1-H-benzimidazole) (TPBi), and tris(4-carbazoyl-9-ylphenyl)amine (TCTA) were used as hole transport layer (HTL), electron transport layer (ETL) and excitons blocking layer (EBL). In the construction of emissive layer (EML) composed of TAPC and TPBi, the color coordinates changes for each driving voltage according to the composition ratio of two materials. With 2:1 (TAPC:TPBi) composition ratio, the color changes from reddish yellow to white by increasing the voltage, and it changes from blue to white with 1:1 composition ratio. Furthermore, in the case of 1:2, the variation of color is similar to 1:1, however, the degree of change with applied voltage is larger than 1:1. Hence, we implemented a sensor device that changes from two colors (reddish yellow, blue) to white according to the applied voltage. This application can be used as a safety device in a limited space due to noise and can also be employed as a sensor for electronic device equipment.