A crystal capping layer for formation of black-phase FAPbI perovskite in humid air.

Black-phase formamidinium lead iodide (α-FAPbI) perovskites are the desired phase for photovoltaic applications, but water can trigger formation of photoinactive impurity phases such as δ-FAPbI. We show that the classic solvent system for perovskite fabrication exacerbates this reproducibility challenge. The conventional coordinative solvent dimethyl sulfoxide (DMSO) promoted δ-FAPbI formation under high relative humidity (RH) conditions because of its hygroscopic nature.

Sub-Second Long Lifetime Triplet Exciton Reservoir for Highly Efficient and Stable Organic Light-Emitting Diode.

In organic light-emitting diode (OLED), achieving high efficiency requires effective triplet exciton confinement by carrier-transporting materials, which typically have higher triplet energy (E) than the emitter, leading to poor stability. Here, an electron-transporting material (ETM), whose E is 0.32 eV lower than that of the emitter is reported.

Passivating A-Site and X-Site Vacancies Simultaneously via N-Heterocyclic Amines for Efficient CsAgBiBr Solar Cells.

To address the toxicity and stability issues of traditional lead halide perovskite solar cells (PSCs), the development of lead-free PSCs, such as CsAgBiBr solar cells, is of great significance. However, due to the low defect formation energy of CsAgBiBr, a large number of vacancies, including A-site vacancies and X-site vacancies, form during the fabrication process of the CsAgBiBr film, which seriously damage the performance of the devices. The traditional phenylethylammonium (PEA) cation, mainly focusing on passivating A-site vacancies, is incapable of reducing X-site vacancies and so results in a limited performance improvement in CsAgBiBr solar cells.

Superstable CsSnBr@CsBr Nanocrystals with Over 1200 h of Half-Value PLQY in Air.

Tin-based perovskites comprise one of the preferred nontoxic alternatives to Pb-based perovskites due to their desirable optoelectronic properties. However, there remains a crucial stability problem due to the property of Sn oxidation. In this study, we reported stable tin-based perovskite nanocrystals (NCs) using stannous acetate as the Sn source because of its stronger Sn-O bonding.

Separating Crystal Growth from Nucleation Enables the In Situ Controllable Synthesis of Nanocrystals for Efficient Perovskite Light-Emitting Diodes.

Colloidal perovskite nanocrystals (PNCs) display bright luminescence for light-emitting diode (LED) applications; however, they require post-synthesis ligand exchange that may cause surface degradation and defect formation. In situ-formed PNCs achieve improved surface passivation using a straightforward synthetic approach, but their LED performance at the green wavelength is not yet comparable with that of colloidal PNC devices. Here, it is found that the limitations of in situ-formed PNCs stem from uncontrolled formation kinetics: conventional surface ligands confine perovskite nuclei but fail to delay crystal growth.

Multifunctional π-Conjugated Additives for Halide Perovskite.

Additive is a conventional way to enhance halide perovskite active layer performance in multiaspects. Among them, π-conjugated molecules have significantly special influence on halide perovskite due to the superior electrical conductivity, rigidity property, and good planarity of π-electrons. In particular, π-conjugated additives usually have stronger interaction with halide perovskites.

High stability and luminescence efficiency in donor-acceptor neutral radicals not following the Aufbau principle.

With their unusual electronic structures, organic radical molecules display luminescence properties potentially relevant to lighting applications; yet, their luminescence quantum yield and stability lag behind those of other organic emitters. Here, we designed donor-acceptor neutral radicals based on an electron-poor perchlorotriphenylmethyl or tris(2,4,6-trichlorophenyl)methyl radical moiety combined with different electron-rich groups. Experimental and quantum-chemical studies demonstrate that the molecules do not follow the Aufbau principle: the singly occupied molecular orbital is found to lie below the highest (doubly) occupied molecular orbital.

Circularly polarized luminescence of achiral open-shell π-radicals.

Stable luminescent π-radicals with doublet emission have attracted growing attention for functional molecular materials. However, their chiroptical properties, particularly their doublet emission-based circularly polarized luminescence, have never been investigated. Here, we investigate the circularly polarized luminescence (CPL) properties of a series of achiral luminescent open-shell π-radicals through various chirality regulation approaches, including induction by a magnetic field, supramolecular coassembly and chiral liquid crystal encapsulation.

Efficient radical-based light-emitting diodes with doublet emission.

Organic light-emitting diodes (OLEDs), quantum-dot-based LEDs, perovskite-based LEDs and micro-LEDs have been championed to fabricate lightweight and flexible units for next-generation displays and active lighting. Although there are already some high-end commercial products based on OLEDs, costs must decrease whilst maintaining high operational efficiencies for the technology to realise wider impact.  Here we demonstrate efficient action of radical-based OLEDs, whose emission originates from a spin doublet, rather than a singlet or triplet exciton.

Radical-Based Organic Light-Emitting Diodes with Maximum External Quantum Efficiency of 10.6.

A new luminescent radical, tris-2,4,6-trichlorophenylmethyl-1,5-diazarcarbazole (TTM-DACz), was synthesized and characterized. The photoluminescence quantum yield of TTM-DACz in solid 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene matrix film (5 wt %) is as high as 57.0%.

Effects of substituents on luminescent efficiency of stable triaryl methyl radicals.

A series of perchlorotriphenyl methyl (PTM) and tris(2,4,6-trichlorophenyl)methyl (TTM) radical derivatives were synthesized. The factors affecting the photoluminescence quantum yields (PLQYs) of π-radicals were studied systematically for the first time through comparing the photophysical properties of the synthesized PTM and TTM radicals. The room-temperature PLQY of a PTM radical derivative achieves to be 56.

Stable Organic Radicals as Hole Injection Dopants for Efficient Optoelectronics.

Precursors of reactive organic radicals have been widely used as n-dopants in electron-transporting materials to improve electron conductivity and enhance electron injection. However, the utilization of organic radicals in hole counterparts has been ignored. In this work, stable organic radicals have been proved for the first time to be efficient dopants to enhance hole injection.