A single atom change “switches-on” the solar-to-energy conversion efficiency of Zn-porphyrin based dye sensitized solar cells to 10.5 %

In this work we report how crucial is the correct design of the porphyrin sensitizers in Dye Sensitized Solar Cells (DSSCs). Only a single atom change switches-on the efficiency from 2–3% to over 10% under standard measurement conditions. We used the 2,1,3-benzothiadazole (BDT) group, as a π-conjugated linker, for the porphyrin LCVC01, a thiophene moiety for the porphyrin LCVC02 and also the furan group for the LCVC03 porphyrin, as molecular spacers between the BDT fragment and the molecule anchoring group, respectively. These three porphyrins were investigated for their application in DSSC devices. All the devices were characterized and found to achieve a record cell efficiency of 10.5% for LCVC02 but only 3.84% and 2.55% for LCVC01 and LCVC03 respectively. On one hand, the introduction of a thiophene, instead of a furan group, illustrates the importance of introducing a chemical group as a spacer, such as thiophene, between the BDT and the anchoring group. On the other hand, the selection of this group has to be correct because the change of a single atom increases the charge recombination rate and decreases the device performance. These changes can be rationalized by analyzing the dye dipoles and their interactions.