Organic photovoltaic (OPV) devices have attracted much interest in recent decades because they have a great potential
for low cost solar cells. Among different kinds of organic solar cells, conjugated polymer/fullerene bulk heterojunction
(BHJ) solar cells have exhibited improvements in the power conversion efficiency (PCE) in recent years. The
performance of BHJ solar cells is highly dependent on different fabrication processes. To address this issue, we focus on
the dependence of different photovoltaic parameters on the fabrication methods. BHJ solar cells fabricated using
platinum metallopolyyne (P1) with a low band gap of 1.85 eV as an electron donor and phenyl-C61-butyric acid methyl
ester (PCBM) as an electron acceptor have been studied. The fabrication parameters, such as ratios of P1 to PCBM,
solvents used, thickness of the active layers and top contact materials, have been systematically investigated. Blend ratio
and solvent used had most significant influence on photovoltaic performance with several times higher efficiency of the
best condition compared to the worst condition. They affected all photovoltaic parameters [open circuit voltage (Voc),
short circuit current density (Jsc) and the fill factor (FF)]. Top contact materials affected the Voc and the FF, while
thickness of the active layer mainly affected the Jsc and FF. The influence of different fabrication conditions on
photovoltaic performance has been discussed.
KEYWORDS: Annealing, Dye sensitized solar cells, Titanium, Crystals, Solar cells, Electron transport, Temperature metrology, Transmission electron microscopy, Nitrogen, Scanning electron microscopy
It has been shown that dye sensitized solar cells (DSSCs) based on porous titanium dioxide (titania) layers have
efficiencies exceeding 10%. Although porous structure has the advantage of large surface area for light harvesting,
electron transport through the random nanoparticle network forming a porous film results in electron mobilities which
are two orders of magnitude lower compared to the single crystal materials. Therefore, considerable efforts have been
made to fabricate DSSC based on one dimensional nanostructures, such as nanowires or nanotubes. Titania nanotube
arrays are typically made by anodization of titanium, followed by annealing to improve crystallinity. In this work, we
investigated the influence of annealing temperature and annealing atmosphere on the crystal structure, the electron
transport, and the solar cell performance of titania nanotube arrays. The titania nanotube arrays were prepared from
electrochemically anodized titanium foils and their morphology and crystal structure were characterized by scanning
electron microscopy and transmission electron microscopy. The crystal phases and the compositions of nanotube arrays
were further investigated by X-ray diffraction for different annealing temperatures and X-ray photoelectron spectroscopy
for different annealing atmospheres. For optimal annealing conditions, the short circuit current density of 4.27 mA/cm2
and power conversion efficiency of 1.30% could be achieved under AM 1.5 simulated solar irradiation for 2 μm long
nanotubes.
Zinc Oxide (ZnO) photonic crystals (PCs) are of great interest in recent years due to its potential applications in
optoelectronic devices. However, most of the growth temperatures in fabricating ZnO nanostructures in periodic
structures reported up to date are very high (>500°C), which is not favorable for low cost manufacture. In this work, a
method involving low growth temperature (90°C), hydrothermal synthesis, was used to fabricate ZnO nanostructures.
Self-assembly of polystyrene (PS) spheres was used to fabricate periodic arrays. PS spheres were self-assembled on the
silicon (Si) or fluorine-doped tin oxide (FTO) substrate with ZnO seed layer derived from zinc acetate. After crosslinking
the PS sphere layer, hydrothermal growth was performed. The influence of growth conditions (concentration, addition of
PEI, etc.) on fabricated ZnO nanorod array has been studied. Then, PS spheres were removed by annealing in air, and
fabricated ZnO nanorod arrays were studied by scanning electron microscopy (SEM) and photoluminescence (PL)
spectroscopy. Periodicity of the array was strongly substrate dependent (better on Si than on FTO). Light emitting diodes
were also fabricated in order to demonstrate the potential use of this ZnO periodic array.
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