Improved efficiency of organic solar cells with modified hole‐extraction layers

The aim of this work has been to study the influence of modified hole‐extraction layers on the performance of organic solar cells (OSCs) based on blends of poly (3‐hexylthiophene) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester. The hole‐extraction layers consist of poly (3,4‐ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) doped with different concentrations of bromine. Compared with pristine OSC without adding bromine to the hole‐extraction layer, the bromine‐doped OSCs show a 49% increase in the power conversion efficiency (from 2.12 to 3.16%), which could be attributed to the increase of electrical and optical properties of PEDOT:PSS films after the addition of bromine. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 125–128, 2012     

Ratio-conjugation tool and its application in linear optimization models†

The ratio-conjugation-tool (RC) is constructed systematically, and its applicability for analysis of economic models is demonstrated. One of the main results establishes a general formula for RC of aggregative function. This tool is applied to the analysis of linear economic dynamics models of Neumann–Gale type which can be solved by a dynamic programming method: for each direct problem we construct the corresponding dual RC-problem. Moreover, we consider three examples of the most important economic dynamics models and look at these now from a unified general position.     

A new synthesis of 4′-trifluoromethyl-2,2′:6′,2″-terpyridine

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Galvanomagnetic Properties Of Asf5 -Intercalated Highly-Oriented Pyrolytic Graphite (HOPG)

Due to the anisotropy of the conductivity in AsF₅-intercalated HOPG, eddy current methods have to be used for the measurement of transport effects. The measurements yield carrier concentration, mobility and charge transfer for C8nAsF₅ with n=l-4 at temperatures between 4.2K and 300K.     

An Alternative Way to Generalize the Pentagon

We introduce the concept of a pentagonal geometry as a generalization of the pentagon and the Desargues configuration, in the same vein that the generalized polygons share the fundamental properties of ordinary polygons. In short, a pentagonal geometry is a regular partial linear space in which for all points x, the points not collinear with the point x, form a line. We compute bounds on their parameters, give some constructions, obtain some nonexistence results for seemingly feasible parameters and suggest a cryptographic application related to identifying codes of partial linear spaces.     

Characterization of PI:PCBM organic nonvolatile resistive memory devices under thermal stress

In this study, we fabricated nonvolatile organic memory devices using a mixture of polyimide (PI) and 6-phenyl-C61 butyric acid methyl ester (PCBM) (denoted as PI:PCBM) as an active memory material with Al/PI:PCBM/Al structure. Upon increasing the temperature from room temperature to 470 K, we demonstrated the good nonvolatile memory properties of our devices in terms of the distribution of ON and OFF state currents, the threshold voltage from OFF state to ON state transition, the retention, and the endurance. Our organic memory devices exhibited an excellent ON/OFF ratio (I_ON/I_OFF > 10³) through more than 200 ON/OFF switching cycles and maintained ON/OFF states for longer than 10⁴ s without showing any serious degradation under measurement temperatures up to 470 K. We also confirmed the structural robustness under thermal stress through transmission electron microscopy cross-sectional images of the active layer after a retention test at 470 K for 10⁴ s. This study demonstrates that the operation of PI:PCBM organic memory devices could be controlled at high temperatures and that the structure of our memory devices was maintained during thermal stress. These results may enable the use of nonvolatile organic memory devices in high temperature environments.     

Low temperature molten salt synthesis of YAG: Ce spherical powder and its thermally stable luminescent properties after post-annealing treatment

Spherical YAG: Ce particles were successfully synthesized at 350 °C by the molten-salt method. The effect of temperature and amount of salt on the crystallization and particle size of YAG: Ce were investigated thoroughly. The results demonstrated that the powders prepared at 350 °C in salt to reactant ratio 2:1 were pure YAG: Ce phase with 200–300 nm in particle size. The as-synthesized phosphors were later post annealed at 1200 °C in O₂, air and N₂, respectively. The results showed that the emission intensity of YAG: Ce sensitively depended on the post-treated atmosphere and the phosphor annealed in N₂ showed the highest emission intensities and a good thermal stability.     

A variational approach to second-order approximability of sliding mode control systems

We consider robustness properties of second-order methods for the sliding mode control of nonlinear ordinary differential equations. A new approach is presented based on the theory of well-posed optimization problems. It is shown that the convergence of the real states of the control system to the ideal one is intimately related to Tykhonov well-posedness of suitably defined dynamic optimization problems.     

A low-cost and low-temperature processable zinc oxide-polyethylenimine (ZnO:PEI) nano-composite as cathode buffer layer for organic and perovskite solar cells

Nanocomposite buffer layer based on metal oxide and polymer is merging as a novel buffer layer for organic solar cells, which combines the high charge carrier mobility of metal oxide and good film formation properties of polymer. In this work, a nanocomposite of zinc oxide and a commercialized available polyethylenimine (PEI) was developed and used as the cathode buffer layer (CBL) for the inverted organic solar cells and p-i-n heterojunction perovskite solar cells. The cooperation of PEI in nano ZnO offers a good film forming ability of the composite material, which is an advantage in device fabrication. In addition, power conversion efficiency (PCE) of the ZnO:PEI CBL based device was also improved when compared to that of ZnO-only and PEI-only devices. The highest PCE of P3HT:PC₆₁BM and PTB7-Th:PC₆₁BM devices reached to 3.57% and 8.16%, respectively. More importantly, there is no obvious device performance loss with the increase of the layer thickness of ZnO:PEI CBL to 60 nm in organic solar cells, which is in contrast to the PEI based devices, whose device performance decreases dramatically when the PEI layer thickness is higher than 6 nm. Such a nano composite material is also applicable in inverted heterojunction perovskite solar cells. A PCE of 11.76% was achieved for the perovskite solar cell with a thick ZnO:PEI CBL (150 nm) CBL, which is around 1.71% higher than that of the reference cell without CBL, or with ZnO CBL. In addition, stability of the organic and perovskite solar cells having ZnO:PEI CBL was also found to be improved in comparison with that of PEI based device.