Fluorinated silane self-assembled monolayer modification of V2O5 for enhanced hole injection and device efficiency

Abstract

This study introduces a new approach to enhance hole injection in organic light-emitting diodes (OLEDs) by modifying the energy band alignment. This enhancement is achieved by incorporating gap states near the Fermi level through the application of a 1H,1H,2H,2H-perfluorooctyltriethoxysilane self-assembled monolayer (F8SAM) coating on V2O5. Compared to thermally evaporated V2O5, the F8SAM coating induces greater oxygen deficiency, reducing the V2O5 (V5+) content from 84.2 % to 76.9 % and increasing the VO2 (V4+) content from 15.7 % to 23.0 %. This modification causes both the highest occupied molecular orbital and gap state levels to move closer to the Fermi level, facilitated by increased oxygen vacancies, high carrier concentration, and delocalized free electrons. The alteration in the gap state provides a more accessible pathway for efficient hole injection, as confirmed in optoelectronic green light devices, which demonstrate a wavelength of 530 ± 5 nm. Significantly, devices incorporating a double-layer hole-injection layer exhibit a 5-fold increase in maximum luminance, a 1.6-fold increase in current efficiency, and a 1.7-fold increase in power efficiency compared to devices with an unmodified V2O5 film. The enhanced performance is attributed to the well-aligned F8SAM on V2O5, which increases the density of hole states and thereby improves device performance. This study demonstrates a practical method for modulating the cation valence state of V2O5, offering a pathway toward improved hole injection and, consequently, more efficient and functional OLED devices.