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

Abstract

Six new mixed-ligand bimetallic complexes [Eu₂(bz)₄(tta)₂(phen)₂] (1), [Gd₂(bz)₄(tta)₂(phen)₂] (2), [EuTb(bz)₄(tta)₂(phen)₂] (3), [EuGd(bz)₄(tta)₂(phen)₂] (4), [Eu_1,2Gd_0,8(bz)₄(tta)₂(phen)₂] (5) and [Eu_1,6Gd_0,4(bz)₄(tta)₂(phen)₂] (6) have been prepared with the Eu³⁺, Gd³⁺ and Tb³⁺ 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 Gd³⁺ 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.