Biomimetic solar cells
Eco friendly energy resources are becoming important due to the predicted oil depletion and soared CO2 emission. Of available alternatives, solar energy finds special attention due to its vast availability and high power density of 1000 watts per square meter. Various mechanisms have been carefully employed to harvest the solar power including semiconductor silicon based photovoltaic, inorganic/organic dye sensitized or bulk heterojunction solar devices. Some of the latter devices utilize donor-acceptor supramolecular systems designed based on natural photosynthesis. Here, self-assembly of energy donor and acceptor is proved to be an important criterion. In the present study, we demonstrate an elegant method of self-assembly to modify TiO2 surface using coordinating ligands followed by immobilization of a variety of photosensitizers and dyads. This method, in addition of testing the photoelectrochemical behavior of simple zinc tetrapyrroles also allows us to introduce fairly complex structures involving more than one donor and/or acceptor entities. As will be demonstrated, of all macrocycles studied, a biomimetic zinc porphyrin-ferrocene dyad markedly improves the current-voltage performance of the photoelectrochemical cell due to an electron transfer-hole migration mechanism. Incident photon-to-current efficiency value up to 37%, highest value reported for this type of devices is obtained for the electrode modified with the dyad, highlighting the importance of photocells built based on biomimetic principles for efficient harvesting of solar energy.