Synthesis of multibranched NIR sensitizers for p-type DSCs

The idea of using p-DSCs as components in dye-sensitized tandem devices (pn-DSCs) has recently generated renewed interest in p-DSCs[1]. The most used dyes in n-DSCs are commonly red or violet. Organic synthesis can help in developing easy and fast synthetic pathways to obtain new dyes with green appearance and complementary optical absorption. Therefore, NIR sensitizers have been developed in order to cover the absorption spectrum which is usually not covered by conventional Ru-based dyes with high performance. Among NIR sensitizers (such as phtalocyanine, porphyrin and cyanine) squaraine dyes represent the most interesting group with fast and easy synthesis, and present also a good photochemical stability. Taking into account the standard synthetic procedures reported in the literature,[2] squaraine preparation procedures were improved by microwave assisted synthesis[3] and by using the Buchwald-Hartwig reaction[4]. Then new dyes have been conceived and developed in order to study their performance in p-DSCs. We increased the number of anchoring groups and we reduced the HOMO-LUMO separation by adding strong electron-withdrawing groups in the squaraine structure. We present the results of these molecular modifications on NiO electrodes.