Heteroleptic ruthenium(II) complexes were used for sensitizing ZnO surfaces in organic solar cells (OSCs) as mediators with photoactive layers. The complexes [Ru(4,4-X2-bpy)(Mebpy-CN)2]2+ (with X = -CH3, -OCH3 and -N(CH3)2; bpy = 2,2-bipyridine; Mebpy-CN = 4-methyl-2,2-bipyridine-4-carbonitrile) were synthesized and studied by analytical and spectroscopical techniques. Spectroscopic, photophysical, and electrochemical properties were tuned by changing the electron-donating ability of the -X substituents at the 4,4-positions of the bpy ring and rationalized by quantum mechanical calculations. These complexes were attached through nitrile groups to ZnO as interfacial layer in an OSC device with a PBDB-T:ITIC photoactive layer. This modified inorganic electron transport layer generates enhancement in photoconversion of the solar cells, reaching up to a 23% increase with respect to the unsensitized OSCs. The introduction of these dyes suppresses some degradative reactions of the nonfullerene acceptor due to the photocatalytic activity of zinc oxide, which was maintained stable for about 11 months. Improving OSC efficiencies and stabilities can thus be achieved by a judicious combination of new inorganic and organic materials.
Organic solar cells (OSCs) are currently one of the most promising candidates for developing new green solar light harvesting devices because of their simple and low-cost manufacturing process via different growth techniques and compatibility with lightweight flexible substrates. OSC’s bulk heterostructure photoactive layers (PALs) can be composed of blends of polymer donor/fullerene acceptor (FA) or polymer donor/nonfullerene acceptors (NFAs). In the first case, power conversion efficiency (PCE) values are 17.1 and 15% in single-junction and tandem OSCs, respectively, while for the second case, PCE goes from 16.5% in ternary blend single-junction cells to 17.3% in double-junction tandem cells. Other important parts of the OSC devices are the electrodes and their interfaces with the PAL: they must have excellent charge extraction/transport capability and help with increasing device stability. Transition-metal oxides such as ZnO have been used as the bottom electron transport layers (ETLs) in the inverted device design of these OSCs because of their many useful properties such as n-type electronic transport, simple film formation via solution-processing, transmittance within the visible spectral range, and UV light absorption (which limits UV-light-induced photodegradation of the organic materials in the PALs).
During the last decade, ZnO has also become a very promising material as a semiconductor in dye-sensitized solar cells (DSSCs) due to its unique optical, chemical, electrical, and piezoelectrical properties, as well as to the possibility of using different growth techniques to obtain it in a wide variety of morphologies: film, nanoparticles, nanowires, etc. In spite of all of these advantages, it is necessary to consider the presence of different factors at the ZnO/PAL interface that could hinder the performance of OSC devices and/or reduce its long-time stability. It has been reported that ZnO exhibits an important photocatalytic activity under UV illumination, promoting hydroxyl and superoxide radicals generation on its surface, which induces chemical reactions between the ETL and the PAL, resulting in degradation or decomposition pathways for the NFAs. In addition, the closeness between energy levels of ZnO and the PAL may lead to recombination at the PAL/ZnO interface, reducing the photocurrent.PDCD7 Antibody manufacturer
Many of these issues can be solved by the introduction of an interfacial layer between the electrode and the PAL, and/or by ZnO surface modification, which also has been shown to have various beneficial effects, such as passivation of charge-trap states, controlling energy-level alignment, and facilitating charge extraction.ZBP1 ProteinSource It has been disclosed that surface defects on the ZnO layer can be eliminated by doping or interface passivation, for example, employing multiblock copolymers or small organic molecules with functional groups like carboxyl, amino, and hydroxyl.PMID:34955573 Doping organic dye molecules into the matrix of ZnO effectively reduces the trap states and improves the electron mobility through light-induced electron transfer. Here, we propose the use of ruthenium(II) bipyridine complexes as dyes attached to ZnO surfaces with the aims of reducing deactivation through trap states and enhancing energy-level alignment.
Ruthenium(II) bipyridine complexes have been extensively studied as sensitizing materials for conversion of solar into electrical or chemical energy. Most of those applications rely on the wide range of chemical modifications achievable on the bipyridine ligands that modulate their photochemical and electrochemical properties at will. Moreover, these complexes are important benchmarks for understanding electron transfer processes relevant in solar conversion devices. In the ground state of ruthenium(II) bipyridines, the highest occupied molecular orbitals (HOMOs) consist of three energy-close orbitals mostly centered in the metal but with some contributions from the π orbitals of the ligands. On the other hand, the lowest unoccupied molecular orbitals (LUMOs) are almost entirely centered on the π* orbitals of the ligands. By controlling the electron donor or acceptor capabilities of the bipyridines, it is possible to stabilize or destabilize one or both frontier orbitals and finely tune the rich manifold of physicochemical properties of these complexes.
In a recent publication, we proved that complexes containing two bpy’s (bpy = 2,2-bipyridine) with electron-donating groups -X (where X = -CH3, -OCH3, -N(CH3)2) and one bpy with an electron-acceptor nitrile group show light absorption maxima that shift to longer wavelengths and oxidation potentials that shift cathodically when increasing the donor power of -X; these results are useful for improving energy conversion efficiency in solar cells. The ligand 4-methyl-2,2-bipyridine-4-carbonitrile (MebpyCN) proved to be a good anchoring group to ZnO surfaces. Carbonitrile is an acceptor group, which polarizes the molecule in the direction of the electron injection. Using substituted bipyridines with electron-donating groups as ancillary ligands, we expect to increase the magnitude of injection polarization. With these concepts in mind, we synthesized three new ruthenium(II) bipyridine complexes of formulas [Ru(MebpyCN)2(4,4-X2-bpy)](PF6)2 (where X = -CH3, -OCH3, -N(CH3)2) for using them as interlayers between the ZnO layer and the PAL in an OSC. Spectroscopic, electrochemical, and photophysical studies have been carried out to characterize these complexes. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were also performed to rationalize their electronic structure properties. To the best of our knowledge, this is the first report with ZnO/Ru(II) complexes as the ETL in OSCs. Due to the simplicity and efficacy of the used materials and methods, we show that modifying the ETL layer with ruthenium(II) dyes provides an alternative approach to improve the efficiency and stability in OSCs.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com