تحضير مواد هجينة عضوية-لاعضوية لبوليمرات اكاسيد الفلزات للتطبيقات الكهروضوئية

Synthesis of Hybrid Organic-Inorganic Polyoxometalates-based Materials for Optoelectronic Applications

ABSTRACT

In this work, a series of new organic-inorganic polyoxometalates-based (POMs) hybrid dyes were designed and synthesized as donor-π bridge-acceptor systems where it can be used as a sensitizer/or co-sensitizers in Dyes Sensitized Solar Cells (DSSCs). Initially, we have theoretically, by using a combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, and systematically studied new chromophores in which hexamolybdate Lindqvist-type derivatives electron acceptors are connected via phenylimido groups to organic electron donors such as acrdine-imido-hexamolybdate (1), acrdine-9-phynylactylene-imido-hexamolybdate (2), aminoanthracene-imido-hexamolybdate (3), 2-amino-3-carboxylanthracene-imido-hexamolybdate (4), anthracene-imido-hexamolybdate (5), anthraquinone-imido-Hexamolybdate (6), aminoanthraquinone-imido-hexamolybdate (7), bromophenyl-imido-hexamolybdate (8). The energy levels of frontier molecular orbitals, absorption spectra with electronic transition characters, and photovoltaic parameters of dyes 1-4 were systematically evaluated. It is found that the HOMO energy levels of dyes 1-4 are more negative than the redox of I-/I3- and the LUMO energy levels are higher than the conduction band of TiO2, suggesting that these dyes to match the requirements of n-type DSSCs. The HOMO levels decrease in the order 4 > 3 > 2 > 1, and the LUMO levels also decrease in the order 4 > 3 > 2 > 1. Based on TD-DFT calculations, all systems 1-4 have absorption bands in visible region ranges from 420 to ~494 nm, with relatively high oscillator strengths despite system 4, where 1 (POM-acridine system) has the largest maximum absorption wavelength λmax of 494 nm with fos = 0.8657 and Δr = 3.66 Å. These results confirm the suitability of all the studied dyes for n-type DSSCs. The investigated dyes could be introduced as an active co-absorbent as well as main dye. All dyes showed remarkable reorganization energy for electron transport (λe) and hence increased electron transfer rate. Due to the strong absorption in the visible region, as well as high light harvesting efficiency (LHE), dye regeneration efficiency (DRE), and electron injection efficiency (Φinj), dyes 2 and 3 are the most promising candidates for high performance DSSC materials.
The promising DFT results have motivated us to explore the experimental synthesis of these dyes using DCC coupling protocol. Dyes 1,5,6,7 and 8 were characterized by FTIR, 1H NMR, and UV-Vis. The computed absorption spectrum for 1 is in a good agreement with the preliminary experimental results. Interestingly, introducing π-linker in dye 2 is blue shifted by 54 nm in λmax and an increase in fos by a factor of ≈ 2.1 and Δr by a factor of ~2 compared to dye 1.