Versatile copper complexes as a convenient springboard for both dyes and redox mediators in dye sensitized solar cells

In the early 1990s, dye-sensitized solar cells (DSSCs), fabricated by O'Regan and Graetzel, emerged as a realistic solution for harnessing the energy of the sun and converting it into electricity. Since then, an impressive amount of work has been carried out in order to improve the global photovoltaic efficiency of DSSCs, trying to optimize every components of the device in terms of material, structure and activity. Up to now, the best efficiencies have been reached with zinc-porphyrin and Ru(II) photosensitizers, but recently an exponential growth of articles showed the great potential of copper(I) coordination compounds as a convenient and cheap alternative. Similarly, it appeared that the use of copper complexes as electron transfer mediators for DSSCs can be an excellent way to solve the problems related to the more common I3-/I- redox couple.The goal of this review is to report on the promising use of versatile copper complexes as photosensitizers and electron shuttles in DSSCs which had a real boom in the last few years. The coverage, mainly from 2010 up to now, is not exhaustive, but allows the non-specialist reader to get into this specific field and to understand its potentiality.An important message that the review will convey is the mandatory role of comparing results on novel photosensitizers and/or on alternative redox mediators with well-established literature reference systems such as N719 dye and I3-/I--based electrolyte, respectively. In fact, reporting the performance of new compounds with respect to proper standard materials is the unique secure method to correctly and, firstly, constructively compare data from different studies.