Enhanced hole injection and electroluminescence in PLEDs via vertical stacking of 2PACz and PEDOT:PSS

We investigate three hole injection layer architectures-PEDOT:PSS, PEDOT:PSS/2PACz, and 2PACz/PEDOT:PSS-in polymer light-emitting diodes (PLEDs), where PEDOT:PSS stands for poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2PACz denotes [2-(9H-carbazol-9-yl)ethyl]phosphonic acid. Hole-only device measurements show that placing 2PACz atop PEDOT:PSS significantly enhances hole transport, as evidenced by the highest slope in the Poole-Frenkel plot. This configuration enables the lowest turn-on voltage (5.8 V), peak luminance (2,230 cd/m²), current efficiency (13 cd/A), and a 1.74-fold increase in electroluminescence intensity. These results underscore the importance of vertical layer ordering in optimizing interfacial charge injection and recombination for high-performance PLEDs.