“All That Glisters Is Not Gold”: An Analysis of the Synthetic Complexity of Efficient Polymer Donors for Polymer Solar Cells

Although organic photovoltaic technology offers many advantages, no consolidated commercial applications have been achieved after more than a decade of intensive research. Several challenges have yet to be overcome, including the scalability of the active material production, which is usually complex even at the laboratory scale. In this Perspective, this fundamental challenge is addressed by surveying and analyzing the synthetic complexity (SC) of active-layer donor polymers used in single-junction polymer solar cells published through 2013 with power conversion efficiencies (PCEs) over 6%. Five parameters are taken into account to evaluate the SC: (i) the number of synthetic steps, (ii) the yields of the monomers, (iii) the number of unit operations (in particular, (iv) of the column chromatographies) required for the purification of the monomers, and (v) the safety characteristics of the chemicals used for their preparation. Finally, the polymers are ranked according to a figure of merit based on SC and PCE, and some guidelines for the design of the materials and for the synthesis are given.