Enhanced photovoltaic performance of inverted polymer solar cells through atomic layer deposited Al2O3 passivation of ZnO-nanoparticle buffer layer.

In this work, an atomic layer deposited (ALD) Al2O3 ultrathin layer was introduced to passivate the ZnO-nanoparticle (NP) buffer layer of inverted polymer solar cells (PSCs) based on P3HT:PCBM. The surface morphology of the ZnO-NP/Al2O3 interface was systematically analyzed by using a variety of tools, in particular transmission electron microscopy (TEM), evidencing a conformal ALD-Al2O3 deposition. The thickness of the Al2O3 layers was optimized at the nanoscale to boost electron transport of the ZnO-NP layer, which can be attributed to the suppression of oxygen vacancy defects in ZnO-NPs confirmed by photoluminescence measurement. The optimal inverted PSCs passivated by ALD-Al2O3 exhibited an ∼22% higher power conversion efficiency than the control devices with a pristine ZnO-NP buffer layer. The employment of the ALD-Al2O3 passivation layer with precisely controlled thickness provides a promising approach to develop high efficiency PSCs with novel polymer materials.

Lasing and Transport Properties of Poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)] (POFP) for the Application of Diode-Pumped Organic Solid Lasers.

This paper demonstrates the lasing and transport properties of a green conjugated polymer, namely POFP. High photoluminescence yields and excellent electron transport of POFP film make it promising for gain media. Low threshold value of 4.0 µJ/cm2 for amplified spontaneous emissions under a pulsed Nd:YAG laser at 355 nm was obtained, as well as a high Q-factor of 159. An inverted waveguide microcavity scheme has been developed to fabricate diode-pumped organic solid lasers (OSLs) using POFP. Gain narrowing with significant radiance increase was observed in the devices, giving evidence of the interference enhancement induced by microcavity and the lasing properties of POFP.

Beating Homogeneous Nucleation and Tuning Atomic Ordering in Glass-Forming Metals by Nanocalorimetry.

In this paper, the amorphous Ce68Al10Cu20Co2 (atom %) alloy was in situ prepared by nanocalorimetry. The high cooling and heating rates accessible with this technique facilitate the suppression of crystallization on cooling and the identification of homogeneous nucleation. Different from the generally accepted notion that metallic glasses form just by avoiding crystallization, the role of nucleation and growth in the crystallization behavior of amorphous alloys is specified, allowing an access to the ideal metallic glass free of nuclei. Local atomic configurations are fundamentally significant to unravel the glass forming ability (GFA) and phase transitions in metallic glasses. For this reason, isothermal annealing near Tg from 0.001 s to 25,000 s following quenching becomes the strategy to tune local atomic configurations and facilitate an amorphous alloy, a mixed glassy-nanocrystalline state, and a crystalline sample successively. On the basis of the evolution of crystallization enthalpy and overall latent heat on reheating, we quantify the underlying mechanism for the isothermal nucleation and crystallization of amorphous alloys. With Johnson-Mehl-Avrami method, it is demonstrated that the coexistence of homogeneous and heterogeneous nucleation contributes to the isothermal crystallization of glass. Heterogeneous rather than homogeneous nucleation dominates the isothermal crystallization of the undercooled liquid. For the mixed glassy-nanocrystalline structure, an extraordinary kinetic stability of the residual glass is validated, which is ascribed to the denser packed interface between amorphous phase and ordered nanocrystals. Tailoring the amorphous structure by nanocalorimetry permits new insights into unraveling GFA and the mechanism that correlates local atomic configurations and phase transitions in metallic glasses.

Dealloying-directed synthesis of efficient mesoporous CoFe-based catalysts towards the oxygen evolution reaction and overall water splitting.

It is a great challenge to design highly active, stable and low-cost catalysts for electrochemically splitting water to realize the clean energy generation and renewable energy storage. Herein, a facile one-step dealloying strategy was proposed to synthesize mesoporous CoFe-based oxides and layered double hydroxides (LDHs). Benefitting from the fast mass transfer and more active sites caused by the open mesoporous structure, the CoFe-based materials exhibit excellent electrocatalytic activities and stability towards the oxygen evolution reaction (OER) in an alkaline electrolyte (1 M KOH). The CoFe-LDH catalyst only needs an overpotential of 0.286 V to achieve 10 mA cm-2, and a small Tafel slope of 45 mV dec-1 for the OER. Moreover, an alkaline electrolyzer was constructed with the CoFe-LDH as both the anode and cathode. The electrolyzer delivers a current density of 10 mA cm-2 at a voltage of 1.69 V toward overall water splitting in the 1 M KOH solution.

Low threshold simultaneous multi-wavelength amplified spontaneous emission modulated by the lithium fluoride/Ag layers.

This paper describes a multi-wavelength amplified spontaneous emission (ASE) with multilayer stacked active planar waveguides. A modulating layer of Ag is applied to make a good confinement of ASE in one active layer, while a lithium fluoride layer is inserted between the active layer and the modulating layer to avoid fluorescence quenching and confine the pump energy in one waveguide. Under optical pumping, ASE at 503 and 662 nm corresponding to the respective active layer are simultaneously observed, with extremely low thresholds at ~37.2 and ~39.7 KW/cm2.

Dependence of crystal nucleation on prior liquid overheating by differential fast scanning calorimeter.

The degree of overheating of a melt often plays an important role in the response of the melt to subsequent undercooling, it determines the nucleation and growth behavior and the properties of the final crystalline products. However, the dependence of accessible undercooling of different bulk melt samples on prior liquid overheating has been reported to exhibit a variety of specific features which could not be given a satisfactory explanation so far. In order to determine uniquely the dependence of accessible undercooling on prior overheating and the possible factors affecting it, the solidification of a pure Sn single micro-sized droplet was studied by differential fast scanning calorimeter with cooling rates in the range from 500 to 10,000 K/s. It is observed experimentally that (i) the degree of undercooling increases first gradually with increase of prior overheating; (ii) if the degree of prior superheating exceeds a certain limiting value, then the accessible undercooling increases always with increasing cooling rate; in the alternative case of moderate initial overheating, the degree of undercooling reaches an undercooling plateau; and (iii) in latter case, the accessible undercooling increases initially with increasing cooling rate. However, at a certain limiting value of the cooling rate this kind of response is qualitatively changed and the accessible undercooling decreases strongly with a further increase of cooling rate. The observed rate dependent behavior is consistent with a kinetic model involving cavity induced heterogeneous nucleation and cavity size dependent growth. This mechanism is believed to be relevant also for other similar rapid solidification nucleation processes.

Size and rate dependence of crystal nucleation in single tin drops by fast scanning calorimetry.

The experimentally accessible degree of undercooling of single micron-sized liquid pure tin drops has been studied via differential fast scanning calorimetry. The cooling rates employed ranged from 100 to 14,000 K/s. The diameter of the investigated tin drops varied in the range from 7 to 40 µm. The influence of the drop shape on the solidification process could be eliminated due to the nearly spherical shape of the single drop upon heating and cooling and the resultant geometric stability. As a result it became possible to study the effect of both drop size and cooling rate in rapid solidification experimentally. A theoretical description of the experimental results is given by assuming the existence of two different heterogeneous nucleation mechanisms leading to crystal nucleation of the single tin drop. In agreement with the experiment these mechanisms yield a shelf-like dependence of crystal nucleation on undercooling. A dependence of crystal nucleation on the size of the tin drop was observed and is discussed in terms of the mentioned theoretical model, which can possibly also describe the nucleation for other related rapid solidification processes.