Photoanode Engineering for developing lower cost higher efficiency Dye Sensitized Solar Cells

Abstract

Renewable energy resource exploration and utilization is inevitable in today’s world, especially, solar energy harvesting due to the alarming decay in other sources of energy with the passage of time. Solar energy had a tremendous potential to solve the energy catastrophes by means of photovoltaic technology. Achieving high threshold efficiency while keeping the expenditure cost of solar cells at minimum, are main objectives that needs to be confronted in order to overcome the world’s energy shortage. The third-generation solar cell technology, that includes; dye-sensitized solar cells, quantum dots, perovskite and organic solar cells have gained great consideration due to their ease of manufacturing, economical prices, availability of numerous alternative materials at potentially lower cost, high threshold efficiency limit and exclusive applications. The present research is focused on the photoanode engineering for developing the lower cost higher efficiency dye-sensitized solar cell technology. For improving the efficiency of DSSC, the cell was fabricated employing silver nanoparticles doped commercially available high performance photoanode. The nanoparticles of silver were produced using the pulsed laser ablation technique. The I-V characteristics and impedance spectroscopic measurements were performed on the doped and undoped photoanode based devices. The nanoparticles doped photoanode based plasmonic DSSC exhibited about 46.3 % higher efficiency than the reference cell. This improved behavior of the plasmonic DSSC can be attributed to enhanced interfacial charge transfer, decrease of charge recombination, decrease of series resistance and plasmonic enhanced absorption of radiation by the dye. The impedance spectra also revealed higher photovoltaic performance of the plasmonic cell. High performance TiO2 photoanodes undoped and doped with silver nanoparticels of size about 15 nm were fabricated by chemical route and were employed in dye-sensitized solarcells (DSSCs). Current-voltage measurements were performed, and the electrical parameters of the fabricated cells were extracted from the current-voltage data that include open-circuit voltage, short-circuit current, shunt resistance, series resistance, fill-factor, ideality factor and solar energy-to-electricity conversion efficiency. The comparison of parameters revealed improvement in both the photovoltaic and electrical parameters of the plasmonic cell. The conversion efficiency measured for the reference cell without Ag NPs in TiO2 was 7.43 %, whereas the efficiency of plasmonic device with TiO2:Ag NPs was 9.26 %, resulting an overall efficiency improvement of 23 % with Ag NPs. The increased performance of the plasmonic DSSC can be assigned to the improvement of its photovoltaic and electrical parameters. The improved short-circuit photocurrent density appears to be boosted due the enhanced light harvesting capability of the photoanode caused by the localized surface plasmon resonance effect induced in Ag nanoparticles. While, the rise in Voc can be credited to the upward shift of Fermi level of TiO2 due to the doping of Ag nanoparticles in TiO2 network. In another research undertaken, TiO2 photoanodes with and without a compact layer were fabricated. The photoanode with compact layer was further treated with TiCl4 and were utilized in dye-sensitized solar cells (DSSCs). Current-voltage studies were carried out under the illumination in standard conditions. From the current-voltage curves, the important electrical parameters of cell like open-circuit voltage, short-circuit current, fill factor, solar energy-to-electricity conversion efficiency, series resistance, shunt resistance, and ideality factor were extracted and compared. The efficiency of the reference DSSC without the TiO2 compact layer and TiCl4 blocking layer was 4.13 %, while the efficiency of DSSC with the TiO2 compact layer and TiCl4 treated photoanode was 7.43 %, representing an efficiency enhancement of more than 80 %. The increased efficiency in the later DSSC can be assigned to the enhancement in overall parameters due to the addition of compact layer in the photoanode and treatment of photoanode with TiCl4. To enhance the dye-sensitized solar cell (DSSC) performance employing a low cost and simple approach, devices were fabricated using N719 dye sensitized titania photoandes without and with diluted silver paste treatment. The current-voltage measurements and all other electrical parameters of cells were extracted. The comparison of the cell’s parameters shows an advancement in the modified device. The overall power conversion efficiency and the fill factor of the device made using treated photoanode were observed higher than the reference cell by 5 % and 3.7 % respectively while the value of shunt resistance was improved from 5.2 k to 13 k. The electrical properties, optical properties, structure and aggregation state of the dye have an influential effect on the solar cell. To utilize a well-designed sensitizing dye effectively and reduce the dye aggregation, the right amount and right solvent needs to be employed. Acetonitrile, t-butanol as solvents and dichloroacetone as an additive, mixed in proper amounts were utilized to make the solution of sensitizing black dye (N749). Fabrication and characterization of the DSSCs, based on TiO2 with N479 dye prepared in the above-mentioned solvents were carried out. The device using acetonitrile-butanol in a fixed ratio as a solvent along with DCA additive gives the highest power conversion efficiency, which was 81.74 % and 21.33 % higher as compared to the efficiencies of DSSC using only acetonitrile or acetonitrile/t-butanol respectively. This is accredited to the positive shift in conduction band edge, improving the electron’s drift velocity from the dye’s exited state to the TiO2 conduction band. Also, to the reduction in dye aggregation by the DCA additive.