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 (V 2 O 5 ) 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 × 10 22 /(cm 3 s)] in the emissive layer, consistent with the measured photophysical properties for the active film, suggesting effective passivation of non-radiative surface states.