Tetraoctylammonium\nBromide Interlayer between NiLiO<sub><i>x</i></sub> and\nPerovskite for Light-Emitting Diodes

Physical vapor deposition is a favorable\ntechnique for\nfabricating\nlight-emitting diodes (LEDs) due to its scalability and reproducibility.\nHowever, the performances of LEDs fabricated via this method are worse\nthan those prepared via solution processing owing to the generation\nof high defect densities. In this study, we introduce a layer of tetraoctylammonium\nbromide (TOABr), an interfacial-modification compound containing four\nlong octyl chains that are symmetrically arranged around an N atom,\nto reduce nonradiative recombination and trap densities in CsPbBr<sub>3</sub>. We examined the impacts of adding TOABr on perovskite thin\nfilms deposited on hole injection layers made of Li-doped NiO<sub><i>x</i></sub> and poly(3,4-ethylenedioxythiophene)/polystyrenesulfonate.\nOur investigations reveal that TOABr addition slightly increases crystallinity,\ndramatically increases photoluminescence, and achieves the preferred\norientation in the perovskite films. Additionally, the interfacial\nlayer passivates defects and improves charge balance in the device,\nthereby enhancing performance. Consequently, perovskite LEDs with\na TOABr layer exhibit a lower turn-on voltage of 3 V than their pristine\ncounterparts, achieving a maximum luminance of 11,133 cd m<sup>–2</sup> and an external quantum efficiency of 1.24%, whereas the pristine\nperovskite LEDs achieve an EQE of 0.015%. The approach proposed in\nthis study can be used to fabricate efficient vacuum-thermal-evaporated\nperovskite LEDs.