Highly luminescent mixed-ligand bimetallic lanthanoid(III) complexes for photovoltaic applications.

Six new mixed-ligand bimetallic complexes [Eu 2 (bz) 4 (tta) 2 (phen) 2 ] (1), [Gd 2 (bz) 4 (tta) 2 (phen) 2 ] (2), [EuTb(bz) 4 (tta) 2 (phen) 2 ] (3), [EuGd(bz) 4 (tta) 2 (phen) 2 ] (4), [Eu 1,2 Gd 0,8 (bz) 4 (tta) 2 (phen) 2 ] (5) and [Eu 1,6 Gd 0,4 (bz) 4 (tta) 2 (phen) 2 ] (6) have been prepared with the Eu 3+ , Gd 3+ and Tb 3+ ions and the benzoate (bz - ), 2-thenoyltrifluoroacetonate (tta - ) and the 1,10-phenanthroline (phen) ligands. The compounds combine highly efficient antennas to obtain highly luminescent complexes to enhance solar cell efficiency. The benzoate ligand has been chosen to take its advantage as a bridging ligand to end up with bimetallic complexes to study the effect of combining two metal ions in the luminescent molecule. The structure of 1 was obtained by single-crystal X-ray diffraction, and 1-6 were found to be isostructural by powder X-ray diffraction analysis. The photophysical properties were studied by the absorbance and emission spectra and emission lifetimes. The magnetic properties of 2 were studied, and we found intramolecular antiferromagnetic interactions between the Gd 3+ ions. We prepared luminescent down-shifting layers (LDSL) with the 1, 3-6 complexes embedded in ethylene-vinyl-acetate and studied their effect in the external quantum efficiency (EQE) and intensity-voltage ( I - V ) plots of a solar mini-module. We found that LDSL containing the bimetallic complexes 3 and 6 enhance the efficiency of the solar mini-module from 11.26(3)% to 11.76(4)% (+0.52%) and to 11.44(2)% (+0.21%), respectively.