Solar Energy, Vol.218, 346-353, 2021
Enhanced light harvesting in panchromatic double dye-sensitized solar cells incorporated with bilayered TiO2 thin film-based photoelectrodes
In this study, panchromatic dye-sensitized solar cells (DSSCs) incorporated with N719 and N749 dyes are fabricated and evaluated. First, bilayered TiO2 thin films of the photoelectrodes of DSSCs are formed by pressing a freestanding TiO2 thin film (top layer) atop another preformed TiO2 thin film (bottom layer). An optimized compaction pressure improves the contact between the top and bottom TiO2 thin films, leading to effective transport of the photogenerated electrons. Further, for bilayered TiO2 thin films assembled by pressing at the optimized compaction pressure, the effect of the dye sequence on the photovoltaic performance of the DSSC is investigated. The best power conversion efficiency (PCE) of - 7.45% is obtained for panchromatic DSSCs composed of an N719 dye-coated TiO2 bottom layer and N749 dye-coated TiO2 top layer. When either the reversed dye sequence or cosensitization of N719 and N749 dyes is applied, the resulting PCE of the DSSC decreases significantly owing to ineffective light absorption characteristics and negative interactions between the two dyes. This result suggests that the N719 dye with the capability to highly absorb light over near UV and green ranges should be positioned in the bottom layer, while the N749 dye with orange, red and near IR light absorption range should be in the top layer.