Photovoltaic properties of a ZnO nanorod array affected by ethanol and liquid-crystalline porphyrin

Abstract

A vertically aligned array of ZnO nanorods, fabricated on conductive ITO substrate in aqueous solution, was characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-visible transmission spectroscopy. Surface photovoltage (SPV) techniques based on a lock-in amplifier and a Kelvin probe were both employed to study the photogenerated charges in the system. The effects of ethanol solvent and a liquid-crystalline porphyrin, [5-(para-dodecyloxy)phenyl-10,15,20-tri-phenyl] porphyrin (DPTPP), on the photovoltage enhancement in the ZnO nanorod array were studied via SPV comparison between different irradiation directions on the system. We demonstrate that the ethanol adsorption could induce the space charge region to expand towards the ZnO/ITO interface. In the absence of ethanol, the ZnO nanorod array with the DPTPP adsorption showed enhanced SPV with reduced attenuation rate of photogenerated charge carriers. We found that the separation of photogenerated charges could be further improved by coating the surface with DPTPP and ethanol together. Furthermore, the SPV spectra patterns of the composite system with opposite incident-light directions reveal that the DPTPP molecules adsorbed just at the surface of ZnO nanorods adopt a more monomeric alignment in contrast to the aggregative state in the DPTPP bulk.

Facile synthesis and characterizations of copper–zinc-10,15,20-tetra(4-pyridyl) porphyrin (Cu–ZnTPyP) coordination polymer with hexagonal micro-lump and micro-prism morphologies

“…Furthermore, in visible light region, the SPV value of hexagonal micro-prisms is higher than that of micro-lumps, which may be due to the size effect, thus, the larger size is beneficial for the transport of charge carriers and decreasing the charges recombination possibility [33]. The enhanced SPV response may be attributed to the expanded structure of Cu-ZnTPyP micro-prisms, which provides much more available space for the effective separation of photo-induced charges.…”

Hydrothermal growth of ZnO nanostructures in supercritical domain: Effect of the metal salt concentration (Zn(NO3)2) in alkali medium (KOH)

“…However, if the SCW process is an interesting way to produce various nanopowders, the nucleation/growth mechanisms are still unknown [3]. Consequently, in order to improve the knowledge of these mechanisms in supercritical water domain, it was useful to select an uncomplicated reference material such as ZnO which is largely studied in SCW hydrothermal synthesis and also well documented in the literature [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Indeed, ZnO material crystallizes in a single stable wurtzite phase without secondary phases such as hydroxide in SCW domain compared to other metal oxides (TiO 2 , Cu x O, Ce x O y .…”

“….). Moreover, ZnO NPs find various applications in different fields such as optoelectronic transducers, chemical and gas sensors, photocatalyst, etc., because of a very wide range of morphologies as wires, flowers, rods, tubes, sheets, ribbons, plates, dumbbell, disks and springs [4][5][6][7][8][9][10][11][12][13][14]. The crystallite characteristics of ZnO NPs in terms of size and morphology can be tuned with experimental conditions such as the temperature [15][16][17][18], the nature and the concentration of the metallic precursor and the alkali solution [15,16,[19][20][21].…”

“…About the effect of the metal precursor concentration, Ohara et al [21] showed that the ZnO rods are smaller when Zn(II) concentration is increased without an addition of alkali solutions whereas other studies performed in alkali medium showed that spherical ZnO NPs are produced with reduced size when the Zn(II) concentration decreases [15,16,19,20]. However, it is very difficult to compare the size and the morphology of ZnO particles obtained from these studies [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] because of differences in residence time, ranges of pressure and temperature, type of reactor (batch or continuous process) and reactants, especially the counter-ion nature of the alkali solution (Na + , K + , Li + ) and the metallic precursor (nitrate, acetate and sulfate).…”

Surface photovoltage phase spectroscopy study of the photo-induced charge carrier properties of TiO2 nanotube arrays

“…In this type of SPV technique, usually only the SPV amplitude spectrum has been considered in the literature [8][9][10][11][12][13][14][15], and little attention has been paid to the information in the SPV phase spectrum. In some reports [16,17], the SPV phase spectrum has been discussed, but just as a complement of the SPV amplitude spectrum. However, the SPV phase spectrum also carries important information about the processes which take place in the sample during the SPV experiment.…”