Infrared Drying of The Active Layer forLight-Emitting Electrochemical Cells

Sammanfattning

The light-emitting electrochemical cell (LEC) is an area-emitting device and apromising technology with future uses in large-scale area lighting. One promisingfeature of LECs is that the active layer can be deposited from a solution, howeverthis also means that the active layer needs to be dried. Currently, the lab-scale ap-proach to drying the active layer is by thermal conduction using a hotplate, which isa time-consuming process and not compatible with large-scale fabrication processeslike roll-to-roll. Another drying process suitable for a scalable and high-throughputfabrication is infrared (IR) heating. This thesis aimed at investigating if IR heating could be an appropriate method tospeed up the drying process of the active layer. The approach was developed usingattenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR)to measure the solvent content in the active layer. The active layer was definedas dry when the cyclohexanone-related signal reached the dry-reference level withinmeasurement uncertainty and showed no further systematic decrease with longerdrying time. We found that using IR heating, the solvent signal reached the dry-reference level after 45 s. Meanwhile, the active layer was dry after < 16 min at70 °C, < 15 min at 80 °C, and 5 min at 90 °C using hotplate drying. Furthermore,photoluminescence quantum yield (PLQY) measurements indicate that IR drying can achieve PLQY comparable to the 70 °C hotplate reference within experimentaluncertainty, while substantially reducing drying time.