Jin-Yun Liao

Oriented hierarchical single crystalline anatase TiO2 nanowire arrays on Ti-foil substrate for efficient flexible dye-sensitized solar cells

Hierarchical anatase TiO2 nanowire (HNW) arrays consisting of long single crystalline nanowire trunks and short single crystalline nanorod branches have been synthesized on Ti-foil substrate via a two-step hydrothermal growth process. The formation of the HNW arrays based on anatase TiO2 nanowire (NW) arrays can be ascribed to the crystallographic relationship between trunk and branch. The power conversion efficiency of dye-sensitized solar cells (DSSCs) based on such a HNW photoelectrode (4.51%) shows a significant enhancement compared to TiO2 nanowire (NW) array photoelectrode (3.12%) with similar thickness (∼15 μm in nanowire length), which can be attributed to more dye loading, superior light scattering ability and comparable electron transport rate for the former. Furthermore, flexible DSSC using TiO2 HNW arrays on Ti substrate as working electrode and transparent PEDOT/ITO-PET prepared via in situelectrodeposition as counter electrode shows a comparable photovoltaic performance to the rigid Pt/FTO-glass cell. A power conversion efficiency as high as 4.32% (Jsc = 7.91 mA cm−2, Voc = 796 mV, FF = 0.69) is obtained for the first time for fully flexible DSSC based on hierarchical TiO2 nanowire arrays and Pt-free counter electrode.

Tri-functional hierarchical TiO2 spheres consisting of anatase nanorods and nanoparticles for high efficiency dye-sensitized solar cells

Hierarchical anatase TiO2 spheres consisting of nanorods and nanoparticles are successfully prepared via a simple acid thermal method using titanium n-butoxide and acetic acid, which will overcome the kinetic and light-scattering limitations of nanoparticles and the surface area limitations of one-dimensional nanostructures, as photoelectrodes for dye-sensitized solar cells. The as-prepared and calcined hierarchical spheres were characterized by transmission electron microscopy, scanning electron microscopy and X-ray powder diffraction. The DSSC based on hierarchical TiO2 spheres as the photoelectrode shows a highly efficient power conversion efficiency (10.34%) accompanied by 18.78 mA cm−2 in short-circuit photocurrent density and 826 mV in open-circuit voltage. The great improvements of photocurrent density and power conversion efficiency for hierarchical TiO2 spheres compared to P25 nanoparticle photoelectrodes are mainly attributed to a considerable surface area, a higher light scattering ability, and faster electron transport rates and slower recombination rates for the former.

Dynamic Study of Highly Efficient CdS/CdSe Quantum Dot-Sensitized Solar Cells Fabricated by Electrodeposition

An in situ electrodeposition method is described to fabricate the CdS or/and CdSe quantum dot (QD) sensitized hierarchical TiO(2) sphere (HTS) electrodes for solar cell application. Intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS) and electrochemical impedance spectroscopy (EIS) measurements are performed to investigate the electron transport and recombination of quantum dot-sensitized solar cells (QDSSCs) based on HTS/CdS, HTS/CdSe, and HTS/CdS/CdSe photoelectrodes. This dynamic study reveals that the CdSe/CdS cosensitized solar cell performs ultrafast electron transport and high electron collection efficiency (98%). As a consequence, a power conversion efficiency as high as 4.81% (J(SC) = 18.23 mA cm(-2), V(OC) = 489 mV, FF = 0.54) for HTS/CdS/CdSe photoelectrode based QDSSC is observed under one sun AM 1.5 G illumination (100 mW cm(-2)).

Metal-free organic dyes derived from triphenylethylene for dye-sensitized solar cells: tuning of the performance by phenothiazine and carbazole

Four novel D–D–π–A configuration metal-free organic dyes (C3, P2, C2 and P3) with triphenylethylene phenothiazine moieties or triphenylethylene carbazole moieties as additional electron donors for dye-sensitized solar cells (DSSCs) have been synthesized. The cells based on C3, P2, C2 and P3 dyes with efficiencies of 2.14%, 2.69%, 5.51% and 6.55%, respectively, are obtained. The P3 based cell exhibits the highest efficiency of 6.55% accompanied by a short-circuit current density (Jsc) of 12.18 mA cm−2, a rather high open-circuit photovoltage (Voc) of 826 mV, and a fill factor (ff) of 0.65, performances which are remarkable in the DSSCs based on metal-free organic dyes. The twisted non-planar configuration in P3 decelerates the charge recombination in the charge-separated state and hence contributes to the improvement of the performance of DSSCs.

Organic Dye Bearing Asymmetric Double Donor-π-Acceptor Chains for Dye-Sensitized Solar Cells

A novel efficient metal free sensitizer containing asymmetric double donor-π-acceptor chains (DC) was synthesized for dye-sensitized solar cells (DSSCs). Comparing to 3.80%, 4.40% and 4.64% for the DSSCs based on the dyes with single chain (SC1, SC2) and cosensitizers (SC1 + SC2), the overall conversion efficiency reaches 6.06% for DC-sensitized solar cells as a result of its longer electron lifetime and higher incident monochromatic photon-to-current conversion efficiency.

Effect of TiO2 morphology on photovoltaic performance of dye-sensitized solar cells: nanoparticles, nanofibers, hierarchical spheres and ellipsoid spheres

Different morphologies of anatase TiO2 from nanoparticles, nanofibers, and hierarchical spheres to ellipsoid spheres are successfully fabricated via solvothermal reactions of titanium n-butoxide and acetic acid. The variations of morphology, size and crystal phase of TiO2 micro-/nanostructures are investigated in detail by XRD, FTIR, SEM and TEM. Effects of different TiO2 morphologies on the photovoltaic performance of dye-sensitized solar cells (DSSCs) are also discussed based on I–V, IPCE, IMPS, IMVS and UV-vis absorption and diffuse spectra. The DSSC based on the hierarchical anatase TiO2 sphere photoelectrode shows an overall light-to-electricity conversion efficiency of 9.35% accompanying a short-circuit current density of 17.94 mA cm−2, an open-circuit voltage of 803 mV and fill factor of 0.65, which is much higher than that of nanoparticles (7.37%), nanofibers (8.15%) and ellipsoid TiO2 spheres (7.93%). The significant enhancement of short-circuit current density and power conversion efficiency for the hierarchical sphere-based DSSC compared to other nanostructures is mainly attributed to the larger dye loading, superior light scattering ability, and/or faster electron transport and longer electron lifetime.

Dye-sensitized solar cells based on a double layered TiO2 photoanode consisting of hierarchical nanowire arrays and nanoparticles with greatly improved photovoltaic performance

A novel double layered photoanode consisting of oriented hierarchical anatase TiO2 nanowire arrays (HNW) and nanoparticles (NP) has been successfully fabricated on a Ti-foil substrate via a two-step hydrothermal and screen-printing process, respectively. Compared to a NP based cell, the photovoltaic performance of the TiO2 HNW cell highlights several outstanding properties, including superior light scattering, rapid electron transport and lower electron recombination rate. Furthermore, the effect of the TiO2 NP film thickness (top layer) on the power conversion of the DSSCs has been investigated in detail. The DSSC based on a Ti/TiO2 HNW + NP photoelectrode with a total thickness of 31 μm (HNW: 13 μm; NP: 18 μm) shows the highest power conversion efficiency of 7.92%, which is remarkably higher than those of 13 μm HNW (4.52%), 18 μm NP (6.50%) and 31 μm NP (5.99%) photoelectrodes. The enhancement of the efficiency for the double layered photoanode based cell compared to the single NP is mainly attributed to better light scattering capability, faster electron transport and lower electron recombination for the former.

High-performance dye-sensitized solar cells based on hierarchical yolk–shell anatase TiO2 beads

Yolk–shell TiO2 beads consisting of nanoparticles are synthesized by using a facile hydrothermal method. The influences of hydrothermal reaction temperature on the size of TiO2 particles and the photovoltaic performance of dye-sensitized solar cells (DSSCs) have been investigated in detail. A DSSC based on the yolk–shell TiO2 bead photoelectrode (∼15 μm) exhibits an energy conversion efficiency of 9.05%, which is much higher than that of P25 (7.56%). This can be mainly attributed to the fast electron transport and long electron lifetime resulting in a larger electron diffusion coefficient and higher charge collection efficiency for the former, which are confirmed by intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS). In addition, the superior light scattering ability of hierarchical yolk–shell TiO2 beads compared to P25 film measured by UV-vis diffuse spectrum also contributes to higher photocurrent and photovoltaic performance.

Hydrothermal Fabrication of Quasi‐One‐Dimensional Single‐Crystalline Anatase TiO2 Nanostructures on FTO Glass and Their Applications in Dye‐Sensitized Solar Cells

One-dimensional and quasi-one-dimensional semiconductor nanostructures are desirable for dye-sensitized solar cells (DSSCs), since they can provide direct pathways for the rapid collection of photogenerated electrons, which could improve the photovoltaic performance of the device. Quasi-1D single-crystalline anatase TiO(2) nanostructures have been successfully prepared on transparent, conductive fluorine-doped tin oxide (FTO) glass with a growth direction of [101] through a facile hydrothermal approach. The influences of the initial titanium n-butoxide (TBT) concentration, hydrothermal reaction temperature, and time on the length of quasi-1D anatase TiO(2) nanostructures and on the photovoltaic performance of DSSCs have been investigated in detail. A power conversion efficiency of 5.81% has been obtained based on the prepared TiO(2) nanostructure photoelectrode 6.7 μm thick and commercial N719 dye, with a short-circuit current density of 13.3 mA cm(-2) , an open-circuit voltage of 810 mV, and a fill factor of 0.54.

Effect of polyphenyl-substituted ethylene end-capped groups in metal-free organic dyes on performance of dye-sensitized solar cells

A novel series of highly similar and comparable metal-free organic dyes have been designed and synthesized for dye-sensitized solar cells (DSSCs). The end-capped groups, namely, diphenylethylene, triphenylethylene, and tetraphenylethylene, have significant effects on the performance of DSSCs. The DSSC based on a triphenylethylene end-capped dye exhibits the highest power conversion efficiency (η) of 6.29%, whereas that based on a tetraphenylethylene end-capped dye has the highest open-circuit photovoltage (Voc) of 804 mV. The Voc of the DSSCs can be greatly improved upon the incorporation of a twisted non-planar aggregation-induced emission (AIE) moiety in the molecular structure of the dyes. The triphenylethylene group with a moderately twisted non-planar structure is found to be suitable for the improvement of the power conversion efficiency. The dyes exhibit an aggregation-caused emission quenching effect, i.e., the dyes do not emit light after being adsorbed on TiO2 films, although they contain aggregation-induced emission triphenylethylene and tetraphenylethylene moieties.