RESUMEN
Two novel symmetrical blue squaraine sensitizers were synthesized, which exhibit panchromatic light harvesting and a record efficiency over 6% with Jsc exceeding 14 mA cm(-2), and Voc over 620 mV under 1 sun. Their color, low cost, easiness of synthesis, and relatively high photo- and thermal stability open up the way for commercial applications.
RESUMEN
Novel organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at molecular level and synthesized. The functionalized unsymmetrical organic sensitizers 3-{5-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-thiophene-2-yl}-2-cyano-acrylic acid (JK-1) and 3-{5'-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-2,2'-bisthiophene-5-yl}-2-cyano-acrylic acid (JK-2), upon anchoring onto TiO2 film, exhibit unprecedented incident photon to current conversion efficiency of 91%. The photovoltaic data using an electrolyte having composition of 0.6 M M-methyl-N-butyl imidiazolium iodide, 0.04 M iodine, 0.025 M LiI, 0.05 M guanidinium thiocyanate, and 0.28 M tert-butylpyridine in a 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 14.0 +/- 0.2 mA/cm2, an open circuit voltage of 753 +/- 10 mV, and a fill factor of 0.76 +/- 0.02, corresponding to an overall conversion efficiency of 8.01% under standard AM 1.5 sunlight. DFT/TDDFT calculations have been performed on the two organic sensitizers to gain insight into their structural, electronic, and optical properties. Our results show that the cyanoacrylic acid groups are essentially coplanar with respect to the thiophene units, reflecting the strong conjugation across the thiophene-cyanoacrylic groups. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, while TDDFT calculations allowed assignment of the visible absorption bands.
RESUMEN
A ruthenium complex trans-[Ru(L)(NCS)2], L = 4,4' ''-di-tert-butyl-4',4' '-bis(carboxylic acid)-2,2':6',2' ':6' ',2' ''-quaterpyridine (N886), was synthesized and characterized by spectroscopic and electrochemical methods. The absorption spectrum of the N886 complex shows metal-to-ligand charge-transfer transitions in the entire visible region and quasi-reversible oxidation and reduction potentials at E(1/2) = +0.38 and -1.92 V vs ferrocene, respectively. The electronic spectra of the N886 complex were calculated by density functional theory (DFT)-time-dependent DFT, which qualitatively reproduces the experimental absorption spectra for both the protonated and deprotonated species. From the analysis of the computed optical transitions of N886, we assign its absorption bands as mixed Ru/SCN-to-quaterpyridine charge-transfer transitions, which extend from the near-IR to the UV regions. The panchromatic response of the N886 complex renders it as a suitable sensitizer for solar energy conversion applications based on titanium dioxide mesoporous electrodes. The preliminary results using the N886 complex as a sensitizer in a dye-sensitized solar cell, with an electrolyte containing 0.60 M butylmethylimidazolium iodide, 0.03 M I2, and 0.50 M tert-butylpyridine in a mixture of acetonitrile and valeronitrile (volume ratio 1:1), show 40% incident photon-to-current efficiencies, yielding under standard AM 1.5 sunlight a short-circuit photocurrent density of 11.8 +/- 0.2 mA/cm(2), an open-circuit voltage of 680 +/- 30 mV, and a fill factor of 0.73 +/- 0.03, corresponding to an overall conversion efficiency of 5.85%.
RESUMEN
Amphiphilic ligands 4,4'-bis(1-adamantyl-aminocarbonyl)-2,2'-bipyridine (L(1)), 4,4'-bis[5-[N-[2-(3beta-cholest-5-en-3-ylcarbamate-N-yl)ethyl]aminocarbonyl]]-2,2'-bipyridine (L(2)), 4,4'-bis[5-[N-[2-(3beta-cholest-5-en-3-ylcarbamate-N-yl)propyl]aminocarbonyl]]-2,2'-bipyridine (L(3)), and 4,4'-bis(dodecan-12-ol)-2,2'-bipyridine (L(4)) and their heteroleptic ruthenium(II) complexes of the type [Ru(II)LL(1)(NCS)(2)] (5), [Ru(II)LL(2)(NCS)(2)] (6), [Ru(II)LL(3)(NCS)(2)] (7), and [Ru(II)LL(4)(NCS)(2)] (8) (where L = 4,4'-bis(carboxylic acid)-2,2'-bipyridine) have been synthesized starting from dichloro(p-cymene)ruthenium(II) dimer. All the ligands and the complexes were characterized by analytical, spectroscopic, and electrochemical techniques. The performance of these complexes as charge-transfer photosensitizers in nanocrystalline TiO(2)-based solar cells was studied. When complexes 5-8 anchored onto a 12 + 4 microm thick nanocrystalline TiO(2) films, very efficient sensitization was achieved (85 +/- 5% incident photon-to-current efficiencies in the visible region, using an electrolyte consisting of 0.6 M butylmethylimidazolium iodide, 0.05 M I(2), 0.1 M LiI, and 0.5 M tert-butyl pyridine in 1:1 acetonitrile + valeronitrile). Under standard AM 1.5 sunlight, the complex 8 yielded a short-circuit photocurrent density of 17 +/- 0.5 mA/cm(2), the open-circuit voltage was 720 +/- 50 mV, and the fill factor was 0.72 +/- 0.05, corresponding to an overall conversion efficiency of 8.8 +/- 0.5%.