Polar solvent vapor annealing enhanced optoelectronic properties of solution-processed exciplex organic light-emitting diodes

Abstract

Exciplex organic light-emitting diodes (OLEDs) are widely utilized for their high internal quantum efficiency. Although solution-processed devices offer the advantages of simple operation and low cost, few studies have reported on the preparation of exciplex OLED devices using solution methods. This paper presents exciplex OLEDs produced between m-MTDATA and Bphen, fabricated using a solution method and optimized by a polar solvent vapor annealing (PSVA) treatment. Unlike other approaches applied to the transport layer, PSVA treatment was conducted on the exciplex-based light-emitting layer, resulting in successful enhancement of the photoelectric properties of both the light-emitting layer film and OLEDs, thereby achieving the anticipated objective. Optimized performance of exciplex OLEDs was achieved after the emission layer was PSVA treated for 20 min. The maximum luminescence intensity increased by a factor of ∼4 compared to a control device without PSVA treatment. An analysis of charge carrier mobility and impedance spectroscopy also indicated the inevitable presence of interface resistance when PSVA was applied to the exciplex emission layer. However, the total resistance (including interface and bulk resistances) was reduced to a minimum after a 20-minute PSVA treatment. Therefore, higher electron mobility and lower lighting voltage are obtained. The enhanced optoelectronic properties of exciplex OLEDs could be attributed to the PSVA treatment, which induced an alignment of polar molecules and enhanced electron mobility.