Conjugated Polyelectrolytes as a Defect-Passivating Hole Injection Layer for Efficient and Stable Perovskite Light-Emitting Diodes

Achieving balanced charge injection and transport is essential for optimal performance in perovskite light-emitting diodes (PeLEDs), where hole injection remains challenging due to the energy barrier between the indium tin oxide (ITO) anode and the perovskite layer. Typically, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used to facilitate hole injection, but its acidic and hygroscopic nature can reduce device efficiency and stability. In this work, we enhanced PeLED efficiency and stability by modifying the ITO work function with conjugated polyelectrolytes (CPEs) containing counterion-dissociating side chains and defect-passivating counterions, specifically poly(9,9-bis(4-(methylsulfonylimidosulfonyl)butyl)fluorene-2,7-diyl- alt -benzene-x (PFS-B-MS-x; x = TEA, Li). These CPEs improved hole injection and passivated A-site vacancy defects, with optimized PeLEDs incorporating PFS-B-MS-TEA, achieving an external quantum efficiency (EQE) of 9.58% at 686 nm─nearly double that of devices with PEDOT:PSS. In addition, the device stability is also more than doubled. Kelvin probe measurements confirmed adjustments in the ITO work function, while optical analyses, such as time-correlated single photon counting (TCSPC) and photoluminescence quantum yield (PLQY) provided insights into reduced exciton quenching at the ITO–perovskite interface.