PMA-interlayered hole transport layers enabling sub-bandgap emission and improved stability in perovskite LEDs

Abstract

Perovskite light-emitting diodes (PeLEDs) have drawn significant attention for their excellent optoelectronic properties. Although efficiency has improved rapidly, reducing driving voltage and enhancing stability remain key challenges. Here, we propose an interfacial engineering strategy using phosphomolybdic acid (PMA) as a p-type dopant-like interlayer, forming a PMA-sandwiched structure within the hole transport layer (HTL). A PeLED with a [ITO/PEDOT:PSS/TFB/PMA/TFB/Perovskite/TPBi/LiF/Al] configuration exhibited a reduced turn-on voltage (V_on) of 2.7 V, compared to 3.4 V in the control device. The p-doping-like effect of PMA improved hole injection and transport, as supported by UV-vis absorption, hole-only device characteristics, time-resolved photoluminescence, and capacitance–voltage measurements. Furthermore, to match the enhanced hole mobility, a bilayer electron transport layer (ETL) incorporating PO-T2T was introduced. The resulting device achieved excellent charge balance, with a V_on of 2.1 V—below the 2.38 eV bandgap corresponding to 522 nm emission—and a peak power efficiency of 50.03 lm W⁻¹. The operational lifetime was extended by approximately four-fold compared to that of the control. This study presents a simple and effective strategy for achieving low-voltage and stable PeLEDs via HTL interfacial engineering using solution-processable PMA.