Donal Bradley

Abstract:

ABSTRACT Spontaneous orientational polarization (SOP) in organic electron transport layers (ETLs) introduces internal electrostatic fields that influence charge injection and interfacial charge accumulation in organic light‐emitting diodes (OLEDs), adversely affecting device performance. Here we combine displacement current measurements (DCM) and charge modulation spectroscopy (CMS) to resolve the formation and magnitude of SOP‐driven charge populations. Using SOP‐active ETLs with positive giant surface potentials (GSPs) in OLEDs employing archetypal host–guest emissive layers (EMLs), we show via DCM that, prior to turn‐on, charge accumulates to counter the SOP‐derived GSP. In most cases, DCM further reveals charge extraction exceeding that required for local SOP compensation. CMS then provides the spatial resolution required to interpret these electrical measurements, resolving two distinct hole populations located at the electron blocking layer/emission layer (EBL|EML) and EML|ETL interfaces that spatially coincide with the primary and secondary recombination zones, respectively. ETL dilution with lithium quinolate (Liq) systematically suppresses SOP and shifts the hole‐injection onset voltage. Conversely, accumulation at the EBL|EML interface does not scale with SOP magnitude, indicating a distinct origin. Together, these results define a unified picture in which the intrinsic electrostatic vulnerability of host–guest EML OLED architectures must be considered alongside ETL SOP.

Abstract:

Perovskite nanocrystals (NCs) demonstrate exceptional potential as emitters to address Rec. 2020 standards for wide color gamut displays. However, the pure-red-targeted CsPbI₃ NCs generally suffer from imprecise synthetic control over emission wavelength and from structural instabilities that significantly diminish performance. We report a novel halogen engineering framework that addresses the otherwise unfavorable wavelength-efficiency-stability nexus. Our approach leverages surface I^-···I₂ interactions to simultaneously unlock exceptional optical characteristics and the elusive structural robustness needed for application. It achieves: (i) controlled quantum-confinement-tuned emission wavelength, (ii) near-unity photoluminescence (PL) quantum yield through iodide vacancy defect management, and (iii) excellent environmental stability, even under harsh (85°C/85%) temperature and humidity conditions, through lattice-distortion suppression. Rec. 2020 compliant, 638 nm peak light-emitting diodes (LEDs) are then demonstrated with Commission Internationale de l'Éclairage coordinates (X, Y) = (0.703, 0.297), 22% external quantum efficiency, luminance ≥ 11,000 cd m^-2, and long lifetime, establishing a materials-by-design paradigm for advancing next-generation perovskite display technologies.

Abstract:

In this paper, we present a one-step low-temperature solution combustion synthesis (SCS) of CuS nanoparticulated functional films processed via a simple blade-coating technique. This SCS route uses thiourea as a fuel and sulfur source, combined with copper(II) nitrate as an oxidant and a cupric ion source in an aprotic solvent such as non-toxic DMSO. It is hereby shown that the proposed SCS process formed a stable and completely dissolved molecular ink of thiourea and copper ion complexes, crucial for obtaining the pure crystalline phase of CuS nanoparticles (NPs). The CuS was formed by calcination at a low temperature of 200 °C during a brief annealing time of 20 min, to promote the synthesis of ~10 nm CuS NPs. The obtained CuS NPs were thoroughly analyzed in terms of structure and optoelectronic properties using various analytic and spectroscopic techniques, including TGA, XRD, FE-SEM, EDS, AFM, and four-point probe electrical resistivity measurements. The functionality of the prepared CuS nanoparticulated interlayers was evaluated by incorporating them as a hole injection layer (HIL) in Super Yellow (SY) organic light-emitting diodes (OLEDs).