High-Efficiency Dye-Sensitized Solar Cells with Molecular Copper Phenanthroline As Solid Hole Conductor

Abstract

Until recently, there have been no viable alternatives for Spiro-OMeTAD as a hole-transport material (HTM) for dye-sensitized solar cells (DSSC).1 In this study we show that copper phenanthroline complexes in the solid phase can act as efficient molecular hole conductors in DSSCs. Normally, DSSCs utilize a liquid redox electrolyte, but there are significant advantages in replacing it by a solid state hole transport material (HTM): The use of an HTM prevents dye desorption, electrolyte leakage and evaporation problems, as well as making series connection between cells much easier.2 The photovoltaic performance of solid state-DSSCs is, however, usually much lower than its liquid counterparts.3 Here we present a new HTM alternative: bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) (Cu(dmp)2). This copper complex has a straightforward synthetic route from low cost starting materials. We prepared solid-state DSSCs with the organic dye LEG44 and Cu(dmp)2 as HTM with a power conversion efficiency of 8.2% under 1000 W m-2AM1.5G illumination, having an open-circuit potential higher than 1.0 V. The successful application of a copper complex-based HTM paves the way for low-cost and efficient hybrid solar cells, as well as other optoelectronic devices. This type of material is anticipated to have large impact on current DSC and MSC research. (1) Bach, U.; Lupo, D.; Comte, P.; Moser, J. E.; Weissortel, F.; Salbeck, J.; Spreitzer, H.; Gratzel, M. Nature 1998, 395, 583. (2) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Chem. Rev. 2010, 110, 6595. (3) Bai, Y.; Yu, Q.; Cai, N.; Wang, Y.; Zhang, M.; Wang, P. Chem. Commun. 2011, 47, 4376. (4) Yang, L.; Xu, B.; Bi, D.; Tian, H.; Boschloo, G.; Sun, L.; Hagfeldt, A.; Johansson, E. M. J. J. Am. Chem. Soc. 2013, 135, 7378. Figure 1