Through the tight-binding calculation, we demonstrate that magnetic and quantum confinements have a great influence on the low-energy band structures of one-dimensional (1D) armchair graphene ribbons. The magnetic field first changes 1D parabolic bands into the Hall-edge states which originate in the Landau wavefunctions deformed by one or two ribbon edges. The quantum confinement dominates the characteristics of the Hall-edge states only when the Landau wavefunctions touch two ribbon edges. Then, some of the Hall-edge states evolve as the Landau states when the field strength grows. The partial flat bands (Landau levels), related to the Landau states, appear. The magnetic field dramatically modifies the energy dispersions and it changes the size of the bandgap, shifts the band-edge states, destroys the degeneracy of the energy bands, induces the semiconductor-metal transition and generates the partial flat bands. The above-mentioned magneto-electronic properties are completely reflected in the low-frequency absorption spectra--the shift of peak position, the change of peak symmetry, the alteration of peak height, the generation of new peaks and the change of absorption edges. As a result, there are magnetic-field-dependent absorption frequencies. The findings show that the magnetic field could be used to modulate the electronic properties and the absorption spectra.

Perovskite solar cells display great commercialization potential. Ethylammonium iodide (EAI) has been used as an additive for perovskite solar cells. The EAI-derived devices displayed enhanced PCEs and long term thermal stability.

Recently, thermally activated delayed fluorescence (TADF) materials have become the most promising hosts for realizing high-performance phosphorescent and fluorescent organic light-emitting diodes (OLEDs) because of their ability to upconvert triplet excitons to singlet excitons. However, despite a few TADF hosts having been introduced for low energy phosphorescent and fluorescent dopants, developing host materials with TADF properties for blue phosphorescent and TADF OLEDs is still a great challenge to date. In this study, bipolar hosts exhibiting TADF behavior and high triplet energy, consisting of the carbazole group as the donor, diphenylsulphone moiety as the acceptor, and m-bitolyl as the π-conjugated bridge, are synthesized and applied for the first time to blue devices. The ΔE ST value of the TADF host is tuned via the introduction of a cyano group in the carbazole moiety due to the increase of the LE contribution in the CT excited state. Detailed photophysical studies confirm the efficient TADF properties of bipolar hosts. The blue phosphorescent and TADF devices using BT-01 as the host give external quantum efficiencies of 31.8% and 25.5%, respectively. The blue devices based on the BT-01 host exhibit superior electroluminescence performance and more reduced efficiency roll-off compared with those hosted by BT-02, ascribed to the faster reverse intersystem crossing process on the BT-01 host. These excellent results manifest that the use of the bipolar host with TADF behavior is a promising approach for the realization of highly efficient blue phosphorescent and TADF devices in the future.

We derive a three-dimensional Dirac-cone structure composed of tilted anisotropic Dirac cones around spirally located Dirac points. The Dirac points form a nodal spiral in momentum space due to accidental degeneracy, which can be realized in rhombohedral graphite. Under the interlayer electron hoppings, the Dirac cone varies in orientation and shape along this Diracpoint spiral, like a magic gyro precessing and deforming with time. The cone precession is governed by the hopping along the rhombohedral primitive unit vectors. In a perpendicular magnetic field, the electron orbits are related to different Landau level energies under the same quantization condition. The Landau subbands are thus characterized by a dispersion factor in addition to the zero-mode spectrum determined by the Dirac-point spiral.

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