Interfacial dipole-engineered fiber optoelectronic devices with enhanced efficiency and stability

Organic light-emitting diodes (OLEDs) have been developed to enhance device lifetime, efficiency, and operational stability. However, the widely used hole injection layer (HIL) material poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) exhibits limitations such as high work function and acidity, which degrade device performance. This study introduces a [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) self-assembled monolayer (SAM) as an alternative to PEDOT:PSS. 2PACz-based OLEDs achieved lower turn-on voltages and higher external quantum efficiencies (EQEs) compared with PEDOT:PSS-based devices. The maximum EQE of green and red fiber organic light emitting diodes (FOLEDs) were 10.71% and 8.97%, respectively, representing 16.9% and 12.9% improvements compared with those of reference devices using PEDOT:PSS as the HIL. Furthermore, compared with TiO2 fiber-shaped dye-sensitized solar cells (FS-DSSCs), the incorporation of TiO2/2PACz increased the power conversion efficiency (PCE) from 5.67% to 6.53%, corresponding to an improvement of approximately 17%. Notably, the TiO2/2PACz-based fiber-shaped gas sensors (FS-GSs) also exhibited enhanced gas sensing characteristics, including increased response and sensitivity, highlighting the multifunctionality and broad applicability of this interfacial engineering strategy across diverse optoelectronic platforms. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1186/s40580-026-00549-x.