Suppressing the environmental dependence of the open‐circuit voltage in inverted polymer solar cells through a radical polymer anodic modifier

Developing stable, readily‐synthesized, and solution‐processable transparent conducting polymers for interfacial modifying layers in organic photovoltaic (OPV) devices has become of great importance. Here, the radical polymer, poly(2,2,6,6‐tetramethylpiperidinyloxy methacrylate (PTMA), is shown to not affect the absorption of the well‐studied poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) active layer when incorporated into inverted OPV devices, as it is highly transparent in the visible spectrum due to the non‐conjugated nature of the PTMA backbone. The inclusion of this radical polymer as an anode‐modifying layer enhanced the open‐circuit voltage and short‐circuit current density values over devices that did not contain an anodic modifier. Importantly, devices fabricated with the PTMA interlayer had performance metrics that were time‐independent over the entire course of multiples days of testing after exposing the OPV devices to ambient conditions. Furthermore, these high performance values were independent of the metal used as the top electrode contact in the inverted OPV devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 311–316     

Channel length influenced contribution of hole and electron trapping effect to threshold voltage stability in organic field effect transistors

Effect of channel length on hysteresis and threshold voltage shift in copper phthalocyanine (CuPc) based organic field effect transistors was studied. Contrary to expectation, longer channel length devices exhibited minimum threshold voltage shift. Influence of channel length on the contribution of hole and electron trapping to threshold voltage stability was determined. Shortest channel length devices exhibited highest electron trapping effect while longest channel devices exhibited minimum hole as well as electron trapping. Lower hole trap effect for longer channel length devices was suggested to be due to reduced longitudinal field between source and drain electrodes while minimum electron trapping was attributed to suppression of drain current by increased hole trap centres.     

Beyond direct simulation Monte Carlo (DSMC) modelling of collision environments

ABSTRACT

Direct simulation Monte Carlo (DSMC) models have been successfully adopted and adapted to describe gas flows in a wide range of environments since the method was first introduced by Bird in the 1960s. We propose a new approach to modelling collisions between gas-phase particles in this work – operating in a similar way to the DSMC model, but with one key difference. Particles move in a mean field, generated by all previously propagated particles, which removes the requirement that all particles be propagated simultaneously. This yields a significant reduction in computation effort and lends itself to applications for which DSMC becomes intractable, such as when a species of interest is only a minor component of a large gas mixture.     

Structural,optical and electrical properties of Cu2FeSnSe4 and Cu(In,Al)Se2 thin films

Cu-based semiconductors Cu₂FeSnSe₄ (CFTSe) and Cu(In, Al)Se₂ (CIAS) have been fabricated using radio-frequency magnetron sputtering combined with rapid thermal selenization processing. For CFTSe, the heating rate ranging from 60 to 150 °C/min results in a difference in structure, morphology and optical properties. Thin film exhibits a pure phase structure, smooth surface and a band gap of 1.19 eV as the heating rate elevated to 90 °C/min. Furthermore, the CFTSe thin film selenized at 90 °C/min own the smallest value of cell volume compared with the others samples, which represents a more stable structure. In terms of the other Cu-based material CIAS, three different selenization pressures, i.e., 1, 5 and 10 Torr, have been employed for CIAS preparation. Thin film transforms into single phase with dense morphology along with the pressure of 1 Torr. The diverse band gap of CIAS thin films from 1.34 to 2.18 eV attribute to two reasons: (i) the various Al content will affect the hybridization degree of Al–Se, and finally tunes the band structure, (ii) amounts of CuSe has a certain degree of effect on the band gap of the CIAS. In addition, the electrical properties of CFTSe and CIAS are also researched with the open circuit voltage (V_oc) of 94 and 365 mV, respectively, signifying potential applications of CFTSe and CIAS for the thin film solar cells.     

Investigation of molar concentration effect on structural,optical, electrical,and photovoltaic properties of spray‐coated Cu2O thin films

High quality copper oxide thin films were prepared by nebulizer spray pyrolysis technique using different concentrations of copper precursor solution. Concentration‐dependent structural, morphological, optical, and electrical properties of the prepared films are discussed. X‐ray diffraction studies done for the samples confirmed that the deposited films are in Cu₂O phase with polycrystalline cubic structure. Atomic force microscopy analysis revealed that all the films are composed of nano sheet shaped grains covering the substrate surface. Optical studies done on the samples showed band gap values 2.42, 2.31, and 2.02 eV for the solution concentration 0.01, 0.05, and 0.1 M, respectively. Photoluminescence spectral analysis showed the emission band at 620 nm confirming the formation of cuprous oxide. Electrical analysis of the films showed p‐type conductivity with a low resistivity 2.19 × 10² Ω.cm and high carrier concentration 16.76 × 10 ¹⁵ cm⁻³ for the molar concentration 0.1 M. In this work, Cu₂O/ZnO heterojunctions were also prepared, and solar cell properties were studied; they were found to show increased open circuit voltage and short circuit current for higher copper concentration.     

Georges Sagnac: A life for optics

Georges Sagnac is mostly known for the optical effect in rotating frames that he demonstrated in 1913. His scientific interests were quite diverse: they included photography, optical illusions, X-ray physics, radioactivity, the blue of the sky, anomalous wave propagation, interferometry, strioscopy, and acoustics. An optical theme nonetheless pervaded his entire œuvre. Within optics, an original theory of the propagation of light motivated most of his investigations, from an ingenious explanation of the Fresnel drag, through the discovery of the Sagnac effect, to his quixotic defense of an alternative to relativity theory. Optical analogies efficiently guided his work in other domains. Optics indeed was his true passion. He saw himself as carrying the torch of the two great masters of French optics, Augustin Fresnel and Hippolyte Fizeau. In this mission he overcame his poor health and labored against the modernist tide, with much success originally and bitter isolation in the end.     

All thermal-evaporated surface plasmon enhanced organic solar cells by Au nanoparticles

Au nanoparticles (NPs) are fabricated on indium-tin-oxide substrates by a thermal evaporation method and incorporated to an efficient small molecule organic solar cell (OSC). This renders an all thermal evaporated surface plasmon enhanced OSC. The optimized device shows a power conversion efficiency of 3.40%, which is 14% higher than that of the reference device without Au NPs. The improvement is mainly contributed to the increased short-circuit current which resulted from the enhanced light harvesting due to localized surface plasmon resonance of Au NPs and the increased conductivity of the device.