White butterflies as solar photovoltaic concentrators.

Man's harvesting of photovoltaic energy requires the deployment of extensive arrays of solar panels. To improve both the gathering of thermal and photovoltaic energy from the sun we have examined the concept of biomimicry in white butterflies of the family Pieridae. We tested the hypothesis that the V-shaped posture of basking white butterflies mimics the V-trough concentrator which is designed to increase solar input to photovoltaic cells. These solar concentrators improve harvesting efficiency but are both heavy and bulky, severely limiting their deployment. Here, we show that the attachment of butterfly wings to a solar cell increases its output power by 42.3%, proving that the wings are indeed highly reflective. Importantly, and relative to current concentrators, the wings improve the power to weight ratio of the overall structure 17-fold, vastly expanding their potential application. Moreover, a single mono-layer of scale cells removed from the butterflies' wings maintained this high reflectivity showing that a single layer of scale cell-like structures can also form a useful coating. As predicted, the wings increased the temperature of the butterflies' thorax dramatically, showing that the V-shaped basking posture of white butterflies has indeed evolved to increase the temperature of their flight muscles prior to take-off.

Spray deposited copper zinc tin sulphide (Cu2ZnSnS4) film as a counter electrode in dye sensitized solar cells.

Stoichiometric thin films of Cu2ZnSnS4 (CZTS) were deposited by the spray technique on a FTO coated glass substrate, with post-annealing in a H2S environment to improve the film properties. CZTS films were used as a counter electrode (CE) in Dye-Sensitized Solar Cells (DSCs) with N719 dye and an iodine electrolyte. The DSC of 0.25 cm(2) area using a CE of CZTS film annealed in a H2S environment under AM 1.5G illumination (100 mW cm(-2)) exhibited a short circuit current density (JSC) = 18.63 mA cm(-2), an open circuit voltage (VOC) = 0.65 V and a fill factor (FF) = 0.53, resulting in an overall power conversion efficiency (PCE) = 6.4%. While the DSC using as deposited CZTS film as a CE showed the PCE = 3.7% with JSC = 13.38 mA cm(-2), VOC = 0.57 V and FF = 0.48. Thus, the spray deposited CZTS films can play an important role as a CE in the large area DSC fabrication.

Nanocrystalline CdSe thin films of different morphologies in thermal evaporation process.

Cadmium selenide nanocrystalline thin films of quasi-spherical morphology are prepared by evaporating CdSe nanopowders on glass substrates. Slightly oval shaped CdSe particles of about 165 nm average size (in 2-D) could be assembled over glass substrates by controlling the film thickness. Morphologies like assembly of particles, interconnected particles with mosaic-like structures and thin films of smooth surfaces could be prepared simply by controlling film thickness. A mechanism for such morphological variations is proposed. Observed variation of band gap energy in the films is explained in terms of quantum confinement effect and substrate-film interface strain.

Nano-scale ZnO buffer layer for inkjet-printed polymer solar cells.

Zinc oxide (ZnO) was used as a buffer layer in the fabrication of polymer solar cells with the configuration of ITO/PEDOT:PSS/P3HT:PCBM/ZnO/Ag, in which the Ag cathode was prepared by inkjet printing using silver ink. Due to the hydrophobic nature of the P3HT:PCBM active layer surface, the hydrophilic silver ink cannot be coated directly on the top of the P3HT:PCBM layer. To overcome this problem, ZnO particles, prepared in a simple solution method by using polyethylene glycol (PEG) surfactant molecules, were used as a buffer layer between the P3HT:PCBM layer and Ag cathode. The present study discusses and compares the performance of the solar cells with and without the ZnO buffer layer.

Effect of temperature on stacking orientations of zinc phthalocyanine thin films.

This paper reports the structural and optical properties of zinc phthalocyanine (ZnPc) thin films, prepared by thermal evaporation method, and their stacking dependence on the substrate temperature. The thickness of the films was measured by a quartz crystal monitor. X-ray diffraction analysis of the vacuum evaporated ZnPc films identified a phase transformation of metastable alpha-ZnPc phase to stable beta-ZnPc phase due to variation in the substrate temperature. The crystallite size (D), dislocation density (delta) and strain (epsilon) were calculated. The transmittance and absorbance spectra were recorded in the wavelength range 300-2500 nm using a UV-vis spectrophotometer. As the temperature was increased from room temperature to 200 degrees C, the band gap energy was decreased from 1.82 eV to 1.67 eV. The phase transformation was also confirmed by optical studies.