Photosensitizers are dye compounds that absorb the photons from incoming light and eject electrons, producing an electric current that can be used to power a device or a storage unit. According to a new study performed by Michael Grätzel and fellow scientist Anders Hagfeldt, advances in photosensitizers have resulted in a substantial improvement in performance of DSSC’s under solar and ambient light conditions. Another key factor to achieve power-conversion records is cosensitization, due to its ability combine dyes that can absorb light across a wider range of the light spectrum. Cosensitization is a chemical manufacturing method that produces DSSC electrodes containing two or more different dyes with complementary optical absorption capabilities, enabling the use of all available sunlight.
The researchers from Switzerland’s École polytechnique fédérale de Lausanne (EPFL) found that the efficiency to cosensitized solar cells can be raised by the pre-adsorption of a monolayer of hydroxamic acid derivative on a surface of nanocrystalline mesoporous titanium dioxide, which functions as the electron transport mechanism of the electrode. The two photosensitizer molecules used in the study were the organic dye SL9, which served as the primary long wavelength-light harvester, and the dye SL10, which provided an additional absorption peak that compensates the SL9’s inefficient blue light harvesting. It was found that adding this hydroxamic acid layer improved the dye layer’s molecular packing and ordering. This slowed down the adsorption of the sensitizers and augmented their fluorescence quantum yield, improving the power conversion efficiency of the cell.
The DSSC developed by the team showed a record-breaking power conversion efficiency of 15.2% under standard global simulated sunlight and long-term operational stability over 500 hours. In addition, devices with a larger active area exhibited efficiencies of around 30% while maintaining high stability, offering new possibilities for the DSSC field.