From light harvesting to charge transport: phthalocyanines in hybrid-organic photovoltaics

The absorption properties of phthalocyanines have been intensively applied to the light-harvesting process in third-generation photovoltaics, particularly in dye-sensitized solar cells (DSSC). Their highly conjugated macrocycle results in a high molar extinction coefficient and in an excellent photoresponse in the red region of the solar spectrum, which can be tuned by chemical modification of the aromatic ring and of the central metal ion. These properties, along with high chemical and thermal stability, have given interesting results in terms of efficiencies in the last years1-3 and the lack of blue and green dyes within this technology keeps the synthesis of these chromophores as a valuable research target. Furthermore, phthalocyanines possess excellent p-type semiconducting properties that make them appealing materials as hole transporters (HTMs) in perovskite-solar cells. This emerging technology has reached certified efficiency values above 21%4 but has shown several drawbacks, some of which are related to the use of Spiro-OMeTAD as HTM. Phthalocyanines may be candidates for replacing it and have shown very promising results with cell efficiencies up to 17.5%5. With the aim of obtaining an easily processable material minimizing its synthetic pathway and optimizing its HOMO-LUMO values, we have synthesized a symmetrical tetra-n(butoxy)zinc phthalocyanine in one synthetic step. When tested as hole transporting material (HTM) in a methylammonium lead triiodide perovskite solar cell, it has shown a photovoltaic response comparable with that of a reference Spiro-OMeTAD cell prepared and tested in the same conditions. References: 1. Ikeuchi T., Nomoto H., Masaki N., Griffith M.J., Mori S. and Kimura M. Chem. Commun. 2014; 50: 1941-1943. 2. Martin-Gomis, L.; Fernandez-Lazaro, F; Sastre-Santos, A. J. Mater. Chem. A, 2014, 2, 15672-15682. 3. Zanotti, G.; Angelini, N; Paoletti, A.M.; Pennesi, G.; Rossi, G.; Amore Bonapasta, A.; Mattioli, G.; Di Carlo, A.; Brown, T.M.; Lembo, A.; Reale, A. Dalton Transactions, 2011, 40, 38-40. 4 Saliba, M.; Matsui, T.; Seo, J.-Y; Domanski, K.; Correa-Baena, J.-P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, Abate, A.; Hagfeldt, A.; Grätzel, M. Energy Environ. Sci., 2016, 9, 1989-1997. 5 Cho, K. T.; Trukhina, O.; Roldán-Carmona, C.; Ince, M.; Gratia, P.; Grancini, G.; Gao, P.; Marszalek, T.; Pisula, W.; Reddy, P. Y.; Torres, T.; Nazeeruddin, M. K. Adv. Energy Mater. 2017, 1601733.