A series of new fluorinated 9,9′-spirobifluorene derivatives (SFs) have been designed and synthesized for organic light-emitting devices (OLEDs). The spatial structure of 2,2′,7,7′-tetrakis(2,4-bifluorophenyl)spiro-9,9′-bifluorene was determined by X-ray diffraction analysis. With the different substitution patterns of electron-withdrawing groups, such as F and CF₃, the photophysical properties, energy levels and thermal stabilities of these SFs can be tuned, which is supported by density functional studies of their geometries and electronic structures. A non-doped deep blue OLED using 2,2′,7,7′-tetrakis(3-fluorophenyl)spiro-9,9′-bifluorene (Spiro-(3)-F) as the emitter shows excellent Commission Internationale de l'Éclairage (CIE) coordinates of (0.169, 0.122) with emission peaking at ca. 408 nm. Furthermore, these SFs serve as an excellent host material for the 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl dopant to form high-performance OLEDs with low turn-on voltages and high efficiencies, especially for Spiro-(3)-F as the fluorescent host with pure blue CIE coordinates of (0.149, 0.187), a low turn-on voltage of 3.4 V, high luminance of over 10 000 cd m⁻², a high current efficiency of 6.66 cd A⁻¹, and a high external quantum efficiency of 4.92%. The high efficiency is attributed to the high carrier mobility together with the low injection barriers for both the electron and the hole in the Spiro-(3)-F-based device.

A series of new fluorinated 9,9′-bianthracene derivatives (BAnFs) have been designed and synthesized to serve as deep-blue dopants in organic electroluminescent (EL) devices. With the different substitution patterns of the electron-withdrawing groups, such as F and CF₃, the photophysical properties, the energy levels and thermal stability of these BAnFs are tuned, which are supported by a density functional study of their geometry and electronic structure. In the thin film state, the fluorescent emissions of the BAnFs are fine-tuned from 448 to 439 nm, with varied fluorinated phenyl rings attached to the 9,9′-bianthracene core. All the BAnFs show a considerable thermal stability, which have high T_g values, above 150 °C. A pure blue emission at the Commission Internationale de l'Éclairage (CIE) coordinates (0.156, 0.083), has been achieved using the host 4,4′-bis(N-carbazolyl)biphenyl (CBP) doped with 10,10′-bis(3,5-bis(trifluoromethyl)phenyl)-9,9′-bianthracene (BAn-(3,5)-CF₃). The maximum current efficiency and power efficiency of the BAn-(3,5)-CF₃-doped device are 3.05 cd A⁻¹ and 2.62 lm W⁻¹, corresponding to 5.02% of the maximum external quantum efficiency. The synthesized new fluorinated 9,9′-bianthracene derivatives show potential applications as highly efficient pure blue emitters for organic light emitting devices.

The electric field-modulation of the spontaneous emission (SE) and amplified spontaneous emission (ASE) in organo-lead halide perovskite CH₃NH₃PbI₃ (aliased as MAPbI₃) layer has been investigated. With the increase of the external applied electric field, the electric field-induced quenching of the SE and ASE intensity was observed, accompanying with a blue-shift of the ASE emission peaks, which can be attributed to field-induced ionization of photogenerated excitons in the MAPbI₃ layer. Based on the analysis of quenching factor and the dielectric constant, we estimated an exciton binding energy ∼36 meV at room temperature, which will provide useful insights into the optical-electrical characteristics of MAPbI₃ and pave the way for the future optoelectronic applications.

Ligand-assisted interface engineering has been considered as a promising strategy to improve the performance and stability of perovskite solar cells (PSCs) simultaneously. Due to the insulating properties of conventional non-conjugated ligands, trap passivation is always at the expense of the interface/bulk carrier transport of the perovskite film. To overcome this paradox, a functional organic amine salt, 3-phenyl-2-propen-1-amine iodide, (PPEAI), is introduced to modify the interfacial characteristics of perovskite films via an “interfacial stitching effect”. This typical ligand could effectively contribute to the suppression of surface defects and ion migration. Furthermore, improved charge transport behavior of perovskite films can be achieved due to the conjugation and delocalization characteristics of PPEAI. By employing the optimized PPEAI modified perovskite film, a 21.01% efficiency was obtained from the champion device, with good stability under both ambient conditions and operation conditions without encapsulation.

We report the electroluminescent (EL) performance of a series of fluorinated 9,9′-bianthracene derivatives (BAnFs) to serve as host materials for selected dopants in organic light-emitting diodes (OLEDs). Different F substitution patterns strongly affect the EL performances. In particular, 10,10′-bis(4-fluorophenyl)-9,9′-bianthracene (BAn-(4)-F) works as an excellent fluorescent host for N,N-diphenylamino phenyl vinyl biphenyl (DPAVBi) and 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano(6,7,8-ij)quinolizin-11-one (C545T) dopants to obtain high-performance OLEDs with excellent external quantum efficiencies (EQEs) of 5.43% and 5.20%, respectively. We demonstrate that the improved EQEs are due to the enhanced occurrence of singlet excitons in BAn-(4)-F-based EL devices. The BAn-(4)-F host molecule with a particular twisted intramolecular charge-transfer (TICT) excited state, which participates in a charge-transfer (CT) intersystem crossing mechanism, realizes transitions from the triplet to singlet CT-states. At the dopant site, the available singlet excitons formed via Förster energy transfer from host BAn-(4)-F to dopant are greatly increased. We conclude that the BAn-(4)-F host based on 9,9′-bianthracene can significantly enhance the singlet generation fraction in EL devices.