Exploring Ln(III)-Ion-Based Luminescent Species as Down-Shifters for Photovoltaic Solar Cells.

In this work, we have compiled our research on lanthanide-based luminescent materials for use as down-shifter layers in photovoltaic (PV) mini-modules. The complexes we have prepared (C1-17), with formulas [Eu2(phen)2(bz)6] (C1), [Eu2(bphen)2(bz)6] (C2), [Eu(tta)3bphen] (C3), [Eu(bta)3pyz-phen] (C4), [Eu(tta)3pyz-phen] (C5), [Eu(bta)3me-phen] (C6), [Er(bta)3me-phen] (C7), [Yb(bta)3me-phen] (C8), [Gd(bta)3me-phen] (C9), [Yb(bta)3pyz-phen] (C10), [Er(tta)3pyz-phen] (C11), [Eu2(bz)4(tta)2(phen)2] (C12), [Gd2(bz)4(tta)2(phen)2] (C13), [EuTb(bz)4(tta)2(phen)2] (C14), [EuGd(bz)4(tta)2(phen)2] (C15), [Eu1.2Gd0.8(bz)4(tta)2(phen)2] (C16), and [Eu1.6Gd0.4(bz)4(tta)2(phen)2] (C17), can be grouped into three families based on their composition: Complexes C1-6 were synthesized using Eu3+ ions and phenanthroline derivatives as the neutral ligands and fluorinated ß-diketonates as the anionic ligands. Complexes C7-11 were prepared with ligands similar to those of complexes C1-6 but were synthesized with Er3+, Yb3+, or Gd3+ ions. Complexes C12-17 have the general formula [M1M2(bz)4(tta)2(phen)2], where M1 and M2 can be Eu3+, Gd3+, or Tb3+ ions, and the ligands were benzoate (bz-), 2-thenoyltrifluoroacetone (tta-), and 1,10-phenanthroline (phen). Most of the complexes were characterized using X-ray techniques, and their photoluminescent properties were studied. We then assessed the impact of complexes in the C1-6 and C12-17 series on the EQE of PV mini-modules and examined the durability of one of the complexes (C6) in a climate chamber when embedded in PMMA and EVA films. This study emphasizes the methodology employed and the key findings, including enhanced mini-module efficiency. Additionally, we present promising results on the application of complex C6 in a bifacial solar cell.

Optical monitoring of detergent pollutants in greywater.

Large amount of wastewater is produced by washing machines and dishwashers, which are used in a daily basis. This domestic wastewater generated in households or office buildings (also called greywater) is drained directly to the drainpipes without differentiation from that with fecal contamination from toilets. Detergents are arguably the pollutants most frequently found in greywater from home appliances. Their concentrations vary in the successive stages in a wash cycle, which could be taken into account in a rational design of home appliances wastewater management. Analytical chemistry procedures are commonly used to determine the pollutant content in wastewater. They require collecting samples and their transport to properly equipped laboratories, which hampers real time wastewater management. In this paper, optofluidic devices based on planar Fabry-Perot microresonators operating in transmission mode in the visible and near infrared spectral ranges have been studied to determine the concentration of five brands of soap dissolved in water. It is found that the spectral positions of the optical resonances redshift when the soap concentration increases in the corresponding solutions. Experimental calibration curves of the optofluidic device were used to determine the soap concentration of wastewater from the successive stages of a washing machine wash cycle either loaded with garments or unloaded. Interestingly, the analysis of the optical sensor indicated that the greywater from the last water discharge of the wash cycle could be reused for gardening or agriculture. The integration of this kind of microfluidic devices into the home appliances design could lead to reduce our hydric environmental impact.

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

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), [Eu1,2Gd0,8(bz)4(tta)2(phen)2] (5) and [Eu1,6Gd0,4(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.

Cu(I)-I-2,4-diaminopyrimidine Coordination Polymers with Optoelectronic Properties as a Proof of Concept for Solar Cells.

Two coordination polymers with formulas [CuI(dapym)]n and [Cu2I2(dapym)]n (dapym = 2,4-diaminopyrimidine) have been synthesized in water at room temperature. According to the stoichiometry used, mono (1D) and the two-dimensional (2D) structures can be obtained. Both are made up of Cu2I2 double chains. Their high insolubility in the reaction medium also makes it possible to obtain them on a nanometric scale. Their structural flexibility and short Cu-Cu distances provoke interesting optoelectronic properties and respond to physical stimuli such as pressure and temperature, making them interesting for sensor applications. The experimental and theoretical studies allow us to propose different emission mechanisms with different behaviors despite containing the same organic ligand. These behaviors are attributed to their structural differences. The emission spectra versus pressure and temperature suggest competencies between different transitions, founding critical Cu2I2 environments, i.e., symmetric in the 1D compound and asymmetric for the 2D one. The intensity in the 2D compound's emission increases with decreasing temperature, and this behavior can be rationalized with a structural constriction that decreases the Cu-Cu and Cu-I distances. However, compound 1D exhibits a contrary behavior that may be related to a change of the organic ligand's molecular configuration. These changes imply that a more significant Π-Π interaction counteracts the contraction in distances and angles when the temperature decreased. Also, the experimental conductivity measurements and theoretical calculations show a semiconductor behavior. The absorption of the 1D compound in UV, its intense emission at room temperature, and the reduction to nanometric size have allowed us to combine it homogeneously with ethyl vinyl acetate (EVA), creating a new composite material. The external quantum efficiency of this material in a Si photovoltaic mini-module has shown that this compound is an active species with application in solar cells since it can move the photons of the incident radiation (UV region) to longer wavelengths.

Cu(i)-I coordination polymers as the possible substitutes of lanthanides as downshifters for increasing the conversion efficiency of solar cells.

This study tries to provide new solutions to increase the efficiency of conversion of photons in solar cells, using photoluminescent Cu(i) coordination polymers (CPs) as possible alternative materials of lower cost, than those used today, based on lanthanides. The selected CP of chemical formula [Cu(NH2MeIN)I]n (NH2MeIN = methyl, 2-amino isonicotinate) absorbs in the utraviolet and emits in the visible region, being also easily nanoprocessable, by a simple and one-pot bottom-up approach. Nanofibers of this CP can be embedded in organic matrices such as ethyl vinyl acetate (EVA), forming transparent and homogenous films, with a thermal stability of up to approximately 150 °C. These new materials maintain the optical properties of the CP used as a dopant, ([Cu(NH2MeIN)I]n), with emission in yellow (570 nm) at 300 K, which is intensified when the working temperature is lowered. In addition, these materials can be prepared with varying thicknesses, from a few microns to a few hundred nanometers, depending on the deposition method used (drop casting or spin coating respectively). The study of their external quantum efficiency (EQE) found an increase in the UV range, which translates into an increase in the conversion efficiency. The optimal CP concentration is 5% by weight in order to not diminish the transparency of the composite material. The calculated cost on the possible incorporation of this material into solar cells shows a 50% decrease over the cost reported in similar studies based on the use of lanthanides.