Conjugated Polyelectrolytes as a Defect-Passivating\nHole Injection Layer for Efficient and Stable Perovskite Light-Emitting\nDiodes

Achieving\nbalanced charge injection and transport is essential\nfor optimal performance in perovskite light-emitting diodes (PeLEDs),\nwhere hole injection remains challenging due to the energy barrier\nbetween the indium tin oxide (ITO) anode and the perovskite layer.\nTypically, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)\n(PEDOT:PSS) is used to facilitate hole injection, but its acidic and\nhygroscopic nature can reduce device efficiency and stability. In\nthis work, we enhanced PeLED efficiency and stability by modifying\nthe ITO work function with conjugated polyelectrolytes (CPEs) containing\ncounterion-dissociating side chains and defect-passivating counterions,\nspecifically poly(9,9-bis(4-(methylsulfonylimidosulfonyl)butyl)fluorene-2,7-diyl-<i>alt</i>-benzene-x (PFS-B-MS-x; x = TEA, Li). These CPEs improved\nhole injection and passivated A-site vacancy defects, with optimized\nPeLEDs incorporating PFS-B-MS-TEA, achieving an external quantum efficiency\n(EQE) of 9.58% at 686 nmnearly double that of devices with\nPEDOT:PSS. In addition, the device stability is also more than doubled.\nKelvin probe measurements confirmed adjustments in the ITO work function,\nwhile optical analyses, such as time-correlated single photon counting\n(TCSPC) and photoluminescence quantum yield (PLQY) provided insights\ninto reduced exciton quenching at the ITO–perovskite interface.