Synthesis of photosensitizing molecules and fabrication of inorganic nanostructures for dye-sensitized solar cell

Abstract

Dye-sensitized solar cells (DSSC) have drawn much attention due to their

higher versatility and lower production cost compared to inorganic photovoltaics.

The top performers of DSSC have achieved power conversion efficiency over

10%, which is comparable to amorphous silicon solar cells. In this work, new

photosensitizers and nanostructure for improving the photovoltaic performance of

DSSC were developed and evaluated.

Two series of cyclometalated ruthenium(II) complex photosensitizer were

presented and their photosensitizing properties in DSSC were studied. Eight

cyclometalated ruthenium(II) terpyridine complexes with three carboxylic acid

groups on the terpyridine ligand were synthesized. Series A (M1 to M4) consist of

C,N,N’ ligands substituted with phenyl group whereas series B (M5 to M8)

consist of C,N,N’ ligands substituted with m-fluorophenyl group. All of the

complexes exhibited broad aborption spectra covering the whole visible spectrum.

The complexes in series B generally showed better photovoltaic performance than

those in series A in the DSSCs. DSSC fabricated from M7 achieved the highest

Voc, Jsc and power conversion efficiency among other DSSC, which were 0.56 V,

7.30 mAcm-2 and 2.63 % respectively.

Truxene-core donor--acceptor dyes were presented and their

photosensitizing properties in DSSC were studied. Eight dyes with either one

donor two acceptors system (T2, B2, T2R and B2R) or two donor one acceptor

system (T1, B1, T1R and B1R) were synthesized. Dyes with two acceptors have

high molar extinction coefficients originated from the charge-transfer transition

band, which are almost two times higher than those with only one accceptors.

Both the enhanced absorption and better anchoring geometry on TiO2 contribute

to the better photovoltaic performance of the two acceptors dyes in the DSSCs.

Devices fabricated from B2 and volatile solvent electrolyte exhibited the best

photovoltaic performance among the truxene-core dyes. The Voc, Jsc, FF and

power conversion efficiency of the device were 0.59 V, 9.69 mAcm-2, 0.63 and

3.62 % respectively. Dyes based on cyanoacrylic acid anchoring groups (T1, T2,

B1 and B2) were found to perform better than those based on rhodanine-3-acetic

acid dyes (T1R, T2R, B1R and B2R) in both donor--acceptor configurations.

ITO nanorod/TiO2 nanoparticle composite films with the three different

types of ITO nanorod with different length (150 nm, 600 nm and 1.5 μm) were

fabricated on FTO glass substrate. The transmittance and sheet resistance of the

ITO nanorod array on the FTO glass substrate were found decreased with

increasing the length of the ITO nanorod. When the ITO nanorod/TiO2

nanoparticle composite films were applied as the anode in DSSCs, the device

fabricated from 600 nm ITO nanorod with TiO2 ‘double layer‘ film showed

enhanced photocurrent generation. The improved photocurrent generation is

suggested to be due to an improved charge collection efficiency at the ITO

nanorod back electrode.