Development of organic co-sensitizers based on piperonal for over 10% efficient ruthenium complex dye-sensitized solar cells

In this study, two new piperonal-based organic dyes, designated D-1-2, were synthesized for use in dyesensitized solar cells (DSSCs). The dyes studied have a D-pi-A configuration and have undergone molecular engineering to fine-tune their spectral properties and energy levels. A comprehensive analysis involving both experimental and theoretical approaches was performed to investigate their optical, electrochemical, photovoltaic, geometrical, and electronic features. These newly developed dyes exhibit notably strong UV-vis absorption, with high molar extinction coefficients, making them an attractive option as co-sensitizers for ruthenium-based dye-sensitized solar cells (DSSCs). Co-sensitization at a concentration of 0.2 mM resulted in a significant increase in the PCEs of DSSCs, ranging from 7.90 % to 10.43 %, compared to the PCE of 7.31 % for DSSCs sensitized solely with N719. The improvement in PCEs can be attributed to the enhanced JCSS and Voc achieved through co-sensitization, highlighting the potential benefits of utilizing co-sensitizers to develop more efficient DSSCs. The highest PCE achieved was 10.43 %, with a Jsc of 19.05 mA.cm(-2) and a VOC of 750 mV for the mixed co-sensitizers (D-1 + D-2 + N719). These findings indicate that cocktail co-sensitization is a promising strategy for constructing efficient D-pi-A-type sensitizers and for evaluating the performance of DSSCs. Additionally, incident photon-to-current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) studies provide insights into the mechanisms responsible for these improvements. Based on the IPCE study, the increase in Jsc during co-sensitization is due to less photocurrent loss from the electrolyte. EIS experiments showed that making a monolayer of sensitizers that was denser and more organized probably led to less electron recombination between the injected electrons and the electrolyte. This could be because the dyes were absorbed more. The findings of this study suggest that D-1-2 co-sensitizers might be game-changers in the development of more effective DSSCs. In addition, this investigation provides crucial information regarding the underlying systems.