Understanding of the Nearly Linear Tunable Open-Circuit Voltages in Ternary Organic Solar Cells Based on Two Non-fullerene Acceptors.

Although the power conversion efficiencies (PCEs) of the state-of-the-art organic solar cells (OSCs) have exceeded 17%, the organic photovoltaic devices still suffer from considerable voltage losses compared with the inorganic or perovskite solar cells. Therefore, the optimization of open-circuit voltage (VOC) is of great significance for the improvement of the photovoltaic performance of OSCs. The origins of VOC have been well-established in the binary system; however, the understanding of VOC in non-fullerene acceptor (NFA)-based ternary OSCs is still lacking. Herein, we have developed a series of ternary organic photovoltaic devices, exhibiting nearly linear increased VOC as the increase of ITIC third content. We found that both the effective charge-transfer (CT) states and the nonradiative recombination losses of the bulk-heterojunction (BHJ) are altered in the ternary blends, and they collectively contribute to the tunable VOC. Our results provide a perspective for understanding the origin of VOC in NFA-based ternary OSCs.

Low-dose real-time X-ray imaging with nontoxic double perovskite scintillators.

X-rays are widely used in probing inside information nondestructively, enabling broad applications in the medical radiography and electronic industries. X-ray imaging based on emerging lead halide perovskite scintillators has received extensive attention recently. However, the strong self-absorption, relatively low light yield and lead toxicity of these perovskites restrict their practical applications. Here, we report a series of nontoxic double-perovskite scintillators of Cs2Ag0.6Na0.4In1-yBiyCl6. By controlling the content of the heavy atom Bi3+, the X-ray absorption coefficient, radiative emission efficiency, light yield and light decay were manipulated to maximise the scintillator performance. A light yield of up to 39,000 ± 7000 photons/MeV for Cs2Ag0.6Na0.4In0.85Bi0.15Cl6 was obtained, which is much higher than that for the previously reported lead halide perovskite colloidal CsPbBr3 (21,000 photons/MeV). The large Stokes shift between the radioluminescence (RL) and absorption spectra benefiting from self-trapped excitons (STEs) led to a negligible self-absorption effect. Given the high light output and fast light decay of this scintillator, static X-ray imaging was attained under an extremely low dose of ∼1 µGyair, and dynamic X-ray imaging of finger bending without a ghosting effect was demonstrated under a low-dose rate of 47.2 µGyair s-1. After thermal treatment at 85 °C for 50 h followed by X-ray irradiation for 50 h in ambient air, the scintillator performance in terms of the RL intensity and X-ray image quality remained almost unchanged. Our results shed light on exploring highly competitive scintillators beyond the scope of lead halide perovskites, not only for avoiding toxicity but also for better performance.

Enhanced thermal stability of inverted perovskite solar cells by interface modification and additive strategy.

Inverted perovskite solar cells (PSCs) have recently gained increasing attention because of the long operation lifetime achieved. However, bathocuproine (BCP): a commonly used buffer layer in inverted PSCs, is experimentally confirmed by us to show fast aggregation at the temperature of 85 °C, which is the protocol temperature required by the International Electrotechnical Commission (IEC) standard. This thermal instability of the BCP interfacial layer makes long-term thermal stability of inverted PSCs questionable. Simply removing or replacing it can directly lead to an inferior PCE of a device. We solve this problem by removing the BCP layer and simultaneously increasing the thickness of C60, which obtains a high efficiency of 18% comparable with the device with BCP. This is possibly attributed to the extended migration path of carriers from C60 to metal electrode Ag, consequently reducing the carrier accumulation at the interface. In addition to the interfacial modification, the addition of ionic liquid: BMIMBF4 into perovskite can further improve a device's thermal stability by its effective suppression of perovskite decomposition. The devices with 0.4 mol% of BMIMBF4 exhibit promising thermal stability by retaining 80% of their initial PCE after thermal aging of 400 h at 85 °C.

Nitrogen-Doped Hierarchically Porous Carbons Derived from Polybenzoxazine for Enhanced Supercapacitor Performance.

Nitrogen-doped hierarchically porous carbons (HPCs), which are synthesized from benzoxazine resins, were successfully prepared following the processes of polymerization, carbonization, and potassium hydroxide (KOH) activation. As the key factor, the KOH activation temperature influences the pore structure and surface functionality, which are crucial for the excellent performance. The HPC-800 material, with the highest activation temperature (800 °C), displays a hierarchical pore structure, a high specific surface area (1812.4 m²·g-1), large total pore volume (0.98 cm³·g-1), high nitrogen content (1.27%), and remarkable electrical conductivity. It has also presented an excellent electrochemical performance of high specific capacitance of 402.4 F·g-1 at 0.1 A·g-1, excellent rate capability of 248.6 F·g-1 at 10 A·g-1, and long-term cycling stability with >99.0% capacitance retention after 500 cycles at 1 A·g-1 in 6 M KOH aqueous solution.

Synthesis and Electrochemical Performance of Molybdenum Disulfide-Reduced Graphene Oxide-Polyaniline Ternary Composites for Supercapacitors.

Molybdenum disulfide/reduced graphene oxide/polyaniline ternary composites (MoS2/rGO/PANI) were designed and synthesized by a facile two-step approach including hydrothermal and in situ polymerization process. The MoS2/rGO/PANI composites presented an interconnected 3D network architecture, in which PANI uniformly coated the outer surface of the MoS2/rGO binary composite. The MoS2/rGO/PANI composites with a weight percent of 80% (MGP-80) exhibits the best specific capacitance (570 F g-1 at 1 A g-1) and cycling stabilities (78.6% retained capacitance after 500 cycles at 1 A g-1). The excellent electrochemical capacitive performance is attributed to its 3D network structure and the synergistic effects among the three components that make the composites obtain both pseudocapacitance and double-layer capacitance.

Enhanced Specific Capacitance of Few-Layer MoS2 Nanosheets via SDBS-Assisted Hydrothermal Method.

Few-layer MoS2 nanosheets have been successfully synthesized by a facile anionic surfactantassisted hydrothermal approach. The as-prepared samples are characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) plays a crucial role in the formation of MoS2 nanosheets with few layers and rich exposed edges. The electrochemical performances of the as-prepared samples are evaluated by cyclic voltammogram, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Compared with the pristine MoS2 without SDBS, the MoS2 nanosheets show a high specific capacitance of 223 F g-1 and its capacitance can still maintained a stable specific capacitance of 147 F g-1 after 500 cycles at 1 A g-1. The enhancement in supercapacitors is attributed to few-layer structure and exposed active edges, which enables fast electron transportation between the electrode and electrolytes. Therefore, the MoS2 nanosheets will be a suitable candidate for electrochemical supercapacitor applications.

Facile synthesis and electrochemical performances of hollow graphene spheres as anode material for lithium-ion batteries.

The hollow graphene oxide spheres have been successfully fabricated from graphene oxide nanosheets utilizing a water-in-oil emulsion technique, which were prepared from natural flake graphite by oxidation and ultrasonic treatment. The hollow graphene oxide spheres were reduced to hollow graphene spheres at 500°C for 3 h under an atmosphere of Ar(95%)/H2(5%). The first reversible specific capacity of the hollow graphene spheres was as high as 903 mAh g(-1) at a current density of 50 mAh g(-1). Even at a high current density of 500 mAh g(-1), the reversible specific capacity remained at 502 mAh g(-1). After 60 cycles, the reversible capacity was still kept at 652 mAh g(-1) at the current density of 50 mAh g(-1). These results indicate that the prepared hollow graphene spheres possess excellent electrochemical performances for lithium storage. The high rate performance of hollow graphene spheres thanks to the hollow structure, thin and porous shells consisting of graphene sheets. PACS: 81.05.ue; 61.48.Gh; 72.80.Vp.