Synergistic Interaction of Phthalocyanines and Semiconductor Quantum Dots for Advanced Co-Sensitized Solar Cells

Quantum dots (QDs) are among potential key players in the next generation of photovoltaic devices [1] due to their low-cost solution-phase processability, large absorption cross sections, a spectrally tunable absorption onset (achieved via the quantum size effect), and enhanced multiple exciton generation or carrier multiplication.[2] After the first report on a certified QD solar cell, a remarkable progress has been reached just in a couple of years obtaining certified power conversion efficiencies (PCEs) approaching 9%.[3]

On the other hand, phthalocyanines (Pcs) are outstanding dye candidates in dye sensitized solar cells (DSSCs) due to their high extinction coefficient in the infrared spectral region and to their high thermal and chemical stabilities.[4] Pcs incorporated in DSSCs have achieved PCEs as high as 6.4 %,[5] still far away of the 12.75% PCE obtained by porphyrins, their closest relatives. An elegant strategy to improve the light-harvesting ability of the Pcs is the binding, either covalent or supramolecular, to a complementary chromophore, such as QDs, able to undergo efficient electron transfer to the charge injecting system. However, the chemical combination of Pc rings to QDs has hardly been explored probably due to the difficulties to synthesize Pcs with the adequate anchoring groups.

Herein, we will report our more recent results related with the synthesis of different unsymmetrically substituted phthalocyanines containing sulphur atom (see Figure 1 as example) and the improvement in efficiency of QD solar cells through their co-sensitization with phthalocyanines.[6]

Acknowledgements. This work has been supported by the Spanish Ministerio de Economía y Competitividad, Generalitat Valenciana and the European FEDER funds (grants CTQ2011-26455, PROMETEO 2012/010 and ISIC/2012/008)

Figure 1. Chemical structure of a disulfide substituted bisphthalocyanine