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Abstract:

We demonstrate proof-of-concept refractive-index structures with large refractive-index-gradient profiles, using a micro-contact photothermal annealing (μCPA) process to pattern organic/inorganic hybrid materials comprising titanium oxide hydrate within a poly(vinyl alcohol) binder. A significant refractive index modulation of up to Δn ≈ +0.05 can be achieved with μCPA within less than a second of pulsed lamp exposure, which promises the potential for a high throughput fabrication process of photonic structures with a polymer-based system.

Abstract:

Copper(I) thiocyanate (CuSCN) is an effective interlayer material for hole injection and transport in organic electronic devices but its solution processing has conventionally utilized undesirable di-n-alkyl sulfide solvents such as diethyl- (DES) and dipropyl-sulfide (DPS). Herein, this paper reports on the use of N,N-dimethylformamide (DMF) and 1-methyl-2-pyrrolidinone (NMP) as alternative solvents for CuSCN interlayers and performs a detailed comparison of the resulting properties relative to films processed from DES and DPS and two other recent alternatives, dimethyl sulfoxide (DMSO) and ammonium hydroxide. The surface roughness, polymorphism, and surface chemistry of the resulting CuSCN layers are reported. The interlayer surface energy and ionization potential that are key to the overlying semiconductor microstructure and interfacial energy barrier, and hence to charge transport and injection, are also discussed. Finally, systematic device tests using well-known organic semiconductors in light-emitting diode, solar cell and field-effect transistor structures demonstrate the overall suitability of DMSO and DMF as solvents for CuSCN interlayer deposition to achieve better device performance. This study broadens the applicability of CuSCN as a highly efficient hole injection/transport material for organic semiconductor devices by expanding the documented range of suitable CuSCN solvents.

Abstract:

Solution-processed metal halide perovskite light-emitting diodes (Pe-LEDs) show great promise in a range of optoelectronic applications. However, these devices can be limited by poor interfaces to the perovskite films due to poor crystallization control during film processing caused by de-wetting from the bottom layer. The deep (Highest Occupied Molecular Orbital) HOMO levels of the emitters also lead to large charge injection barriers for standard electrodes. To improve this, we develop and report on a small molecule, BPS2, based on phenothiazine-benzimidazole with Lewis base sites. This promising interfacial material is then applied to blue PeLEDs where the energy band alignment of BPS2 to the blue perovskite emitter helps to reduce the hole-injection barrier while blocking electrons. BPS2 can be solution-processed with non-chlorinated organic solvents and provides improved wettability towards perovskite precursor solutions compared to conventional PEDOT:PSS hole transport films. A thin interlayer of BPS2 introduced between PEDOT:PSS and a perovskite emission layer is shown to improve both the device external quantum efficiency and luminance in comparison to the reference device without the interlayer.