Defect-assisted hole transport through transition metal oxide-based injection layers for passivated nanocrystalline CsPbBr3 emissive thin films: A combined experimental and modeling study

Abstract

The acidic (pKa ≈1.5–2.5) and hygroscopic nature of poly(3,4-ethylene dioxythiophene) polystyrene sulfonate, used as a common hole-injection layer in optoelectronic devices, has a detrimental effect on device stability and is associated with well established device failure mechanisms. In this work, a process with a high green index hole-injection layer material (V2O5) and low surface roughness (RMS roughness ≈1.3 nm) was developed for demonstrating a hybrid polymer–inorganic perovskite light-emitting diode. Test devices with the new hole-injection layer demonstrate nearly identical maximum current efficiencies (4.23 vs 4.19 cd/A), and luminous efficacies (2.99 vs 2.32 lm/W) when compared to a control device fabricated with the conventional hole-injection layer. Furthermore, the peak brightness was achieved at a current density one-third of the value for the control device. To examine the transport of holes in the above hole-injection layer, we carried out device simulations based on a physical charge control model, including defect-assisted tunneling for hole injection. Close agreement for current–voltage characteristics is observed. Experimentally measured mobility in the device and measured radiative lifetimes were found to be sufficient to achieve this agreement without resorting to the introduction of a sheet charge at the injection interface. Despite the use of a bulk-heterojunction device architecture, the model predicts high radiative recombination rates [≈5.6×1022/(cm3s)] in the emissive layer, consistent with the measured photophysical properties for the active film, suggesting effective passivation of non-radiative surface states.