INFLPR Seminar, Wednesday, 26 April 2017, 10:30, Laser Department, Dr. Cornelia Sima: "Study of dye sensitized solar cells based on TiO2 and ZnO photoelectrodes"

INFLPR Seminar

Wednesday, 26 April 2017, 10:30 am

Laser Department, Seminar Room

Title: "Study of dye sensitized solar cells based on TiO₂ and ZnO photoelectrodes"

Lecturer: Dr. Cornelia Sima

Abstract: Dye sensitized solar cells (DSSCs) based on TiO₂ and ZnO photoelectrodes deposited by picosecond laser ablation and doctor blade methods are reported.

Mesoporous TiO₂ photoelectrodes using picosecond laser (8 ps) with high repetition rate (50 kHz) and low energy/pulse (20 µJ) were successfully used in the fabrication of DSSCs. The variation of the morpho-structural characteristics of TiO₂ films deposited on indium tin oxide (ITO) substrates in the presence of different oxygen pressures (0.04^-1 Torr) was investigated. The oxygen pressure had a significant influence on the film crystallinity, porosity and adherence, and as a result, on the cell global efficiency. In the specific experimental conditions (532 nm laser wavelength, 0.17 J/cm² fluence, 0.3 Torr oxygen pressure, 450⁰C annealed film), a TiO₂ phase mixture of rutile/anatase, with grain size of 17.8 nm, was sintered. Using these films as photoelectrodes, solar cells illuminated with AM 1.5 (100 mW/cm²) provided a maximum power of 1.56 mW/cm² and an integral power conversion efficiency of 1.81%.

We investigated DSSC performances with regard to transparent conducting oxide substrates also: indium-doped tin oxide (ITO) and fluorine-doped tin oxide (FTO). The DSSCs were in a standard configuration: a photoelectrode of TiO₂ nanoparticles (9 nm size, anatase phase) deposited on transparent and electrically conductive substrates, counter electrodes of Pt-coated glass, ruthenium 535 dye, and AN50 iodolyte electrolyte (Solaronix). The cells manufactured from ITO (FTO) had an open circuit voltage of 705 (763) mV and short-circuit current of 7.87 (34.3) mA / cm². A direct correlation was found between transparent conductive film resistivity and cell efficiency. Resistivities of 52 Ω / sq for ITO substrates and 8.5 Ω / sq for FTO led to major differences in internal global efficiency: from 2.24 % for ITO to 9.6 % for FTO.

For deposition of ZnO photoelectrodes by laser ablation, a picosecond Nd:YVO4 laser (8 ps, 50 kHz, 532 nm, 0.17 J/cm2) was used. Depositions were made starting from a Zn pure target on fluorine doped tin oxide (FTO) substrate, in oxygen atmosphere at 10 sccm gas flow rate at room temperature (RT). After deposition, the films were subjected to an annealing treatment at 400⁰C in oxygen for 2 hours.The influence of the ZnO photoelectrodes, prepared by the two different methods, on the performances of the dye sensitized solar cells was investigated. The optimum parameters of the films deposited by laser ablation which to correspond to the best efficiency of the cells were: 450 mTorr oxygen pressure, with 5.83 µm film thickness, delivering 580 mV open circuit voltage (Voc), 1.16 mA/cm² short circuit current density (Jsc), 33% fill factor (FF), 0.22% conversion efficiency (ƞ).

For deposition of ZnO photoelectrodes by doctor blade method, ZnO paste using ZnO nanoparticles (MK Impex Corp. 99.9%, 20 nm) was prepared. Concerning the ZnO photoelectrodes deposited by doctor blade method, almost a double value for ƞ was obtained of 0.43%, 25 µm film thickness, 483 mV Voc, 2.52 mA/cm² and 36% (FF).

Conclusions:

Solar cells with TiO₂/ITO photoelectrode obtained directly by laser ablation
- 1.81% global efficiency / 0.3 Torr / 450⁰C / ps laser

Solar cells using TiO₂ nanometric powder
- on ITO 2.24% global efficiency
- on FTO 9.6% global efficiency

Solar cells using ZnO phototelectrode on FTO substrate
- 0.22% global efficiency by laser ablation
- 0.43% global efficiency by doctor blade

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