Enhanced efficiency of dye co-sensitized solar cells based on pulsed-laser-synthesized cadmium-selenide quantum dots

In this study, a new configuration of dye sensitized solar cells (DSSCs), in which a TiO₂ photoanode is co-sensitized by N719 organic dye and CdSe quantum dots (CdSe-QDs), was fabricated. The photovoltaic performance of the cell, which was co-sensitized with an optimum concentration of CdSe-QDs, was found to be superior to that of the cell with a photoanode sensitized using N719 dye. The superior performance can be attributed to the energy-compatible band structures of the N719 dye molecule and the CdSe-QDs, selective transfer of a significant number of photogenerated electrons from the energy state of the dye molecule to the conduction band (CB) of CdSe-QDs, and improved absorbance of the CdSe-QDs in the visible-light spectrum. This initial inflow of electrons to the dye was found to enrich the subsequent dye-mediated electron transfer to TiO₂, thus contributing to the enhanced photocurrent in the DSSC. The novel material implemented in this study was based on CdSe-QDs, which were used as a co-sensitizer in the photoanode of the DSSC synthesized by pulsed laser ablation in liquid (PLAL). Morphological, structural, elemental, optical and electrochemical characterizations of the photoanodic materials were conducted; and the photovoltaic characteristics of the fabricated cell were determined. The photovoltaic conversion efficiency of the cell co-sensitized by CdSe-QDs at a certain concentration (1 mg/15 ml of ethanol) and N719 dye was found to be 7.09%, which corresponds to a 37% enhancement of the photovoltaic efficiency when compared with the cell sensitized only by the N719 dye.