Improvement of spectral response using tandem structured dye-sensitized solar cells

Abstract

Dye-sensitized solar cells (DSSCs) have attracted great attention and one of the strong alternatives to conventional Si-based solar cells because of their advantages such as transparency, comparable efficiency, various colors, and simple processes with low costs, etc. In order to get high solar-toelectrical conversion efficiency, improved the spectral response of the sensitizer is necessary. At the principals of DSSCs, the dye molecules act as a primary active component for the absorption of the solar spectrum and generating electrons. If the dye molecules should absorb the sun’s spectrum as wide as possible, the number of generated electrons should be increased and higher conversion efficiency can be achieved with increased spectral response. However, the individual sensitizer can only absorb its own particular range of wavelength. To maximize energy harvesting of DSSCs, many researchers approaching to make a panchromatic system, which could absorb the photons over the entire range of wavelength. Here, I present the prominent way to fabricating panchromatic structured dye-sensitized solar cells. In order to fabricate working electrodes, newly method of pre-dye coating (PDC) of TiO2 nanoparticles (NPs) and an approach of a dip coating have been adopted for the panchromatic DSSCs. A bi-layer photoanode with two distinct TiO2 layer, which were individually sensitized with N719 and N749 dyes were coated on a transparent conducting oxide (TCO) in a sequenced manner. The improvement of spectral response and efficiency of panchromatic DSSCs has been checked with the absorption characteristics of each dye. Furthermore, by using intensity modulated photovoltaic spectroscopy (IMVS), I could check the dynamic electron kinetic and calculate lifetime in ambient conditions with τn = 1/(2πƒmin(IMVS)). In addition, here I report a novel structure of DSSCs with reversely form by constructing all the components together as one substrate. With this new structure, comparable cell properties was achieved to the conventional structure. The electrochemical properties and photochemical properties were checked by electrochemical impedance spectroscopy. Moreover, the present approach could be an encouraging new direction in research while facilitating the fabrication of hybrid-tandem solar cells. Furthermore, I also present a systematic approach of carbon black in order to optimize the catalytic ability of iodide/tri-iodide electrolyte. Replacement of the Pt counter electrode with an inexpensive but electro-chemically stable alternative is one key technological challenge that must be overcome to make DSSCs more economical. Based on the electrochemical analysis, the chargetransfer resistance and photo-electrochemical properties were characterized.