Modifications of $TiO_2$ photoelectrode for performance enhancement of quantum dot solar cell (QDSC)

Abstract

At present Dye sensitized solar cells (DSSC) acts as a promising alternative to the conventional silicon solar cells due to their superior benefits of low cost, easy fabrication and processing and suitable efficiency. One of the research issues related to the DSSC performance enhancement is the innovation and development of nanomaterials as photosensiztiers and modification of the nasnosturcured $TiO_2$ electrode for the enhancement of the cell performance. Recently inorganic semiconductor nanocrystals known as as quantum dots have been received a wider attention as photosensitizers due to their superior and interesting properties like tunable bandgaps and impact ionization induced by quantum size effects. Additionally quantum dots have high extinction coefficients as compared to dyes. Contrary to all such advantages the efficiency and the fill factors of Quantum dot sensitized solar cells (QDSC) are still very low (Fill Factor even less than 0.50) as compared to DSSC. Focusing the issue of well assembly of QDs into mesoporous $TiO_2$, an attempt was made by mimicking the dye adsorption upon the $TiO_2$ surface in DSSC. In case of DSSC, the carboxylic acid groups in N3 dyes plays an important role in adsorption of the dyes upon $TiO_2$ surface via electronic coupling. Such an approach was followed to enhance the adsorption of the CdS QDs into mesoporous $TiO_2$ electrode via surface modification of the CdS QDs with organic compound 2-mercaptoethanol (ME). 2-mercaptoethanol as revealed form formula $HOCH_2CH_2SH$ consists of thiol group (SH) at one end and hydroxyl group (OH) at the other end. The thiol groups of ME get linked to the CdS nanocrystal surface while the hydroxyl group at the other end binds to the $TiO_2$ surface. But the cell performance but unfortunately found to be very low. The main reason was low photocurrent may be due to the spatial distance between CdS QDs and $TiO_2$ electrode and partial coverage of CdS QDs by ME. Additional surface ...