New D-π-A-conjugated organic sensitizers based on α-pyranylidene donors for dye-sensitized solar cells

Design and Photonics of Merocyanine Dyes

Merocyanines, thanks to their easily adjustable electronic structure, appear to be the most versatile and promising functional dyes. Their D-π-A framework offers ample opportunities for custom design through variations in both donor/acceptor end-groups and the π-conjugated polymethine chain, and leads to a broad range of practical properties, including noticeable solvatochromism, high polarizability/hyperpolarizabilities, and the ability to sensitize various physicochemical processes. Accordingly, merocyanines are applied and extensively studied in various fields, such as light-converting materials for optoelectronics, nonlinear optics, optical storage, solar cells, fluorescent probes, and antitumor agents in photodynamic therapy. This review encompasses both classical and novel more important publications on the structure-property relationships in merocyanines, with particular emphasis on the results by A.  I. Kiprianov and his followers in Institute of Organic Chemistry in Kyiv, Ukraine.

Theoretical investigation of the effect of changing the auxiliary acceptor on the performance of organic D-A'-A dyes used as sensitizers in DSSCs

CONTEXT

Dye-sensitized solar cells (DSSCs) have displayed huge potential in inexpensive, efficient, and clean solar energy technology. In this work, seven new dyes with the structure D-A'-A were designed in which the thiophene in the reference dye was replaced by auxiliary acceptors (A'). These dyes consist mainly of a pyranylidene-based electron donor D and the cyanoacrylic acid moiety as acceptor A. A computational investigation was carried out on the effect of various auxiliary acceptors A' on the efficiency of D-A'-A dyes in isolation and after binding to the semiconductor TiO2. Optimized structures, geometrical, optoelectronic, and photovoltaic parameters were calculated to predict promising dyes for potential use as solar cell sensitizers, including band gap (Egap), natural bond orbital (NBO) analysis, nonlinear optical properties (NLO), UV-Vis absorption spectra, maximum absorption wavelength (λmax), reorganization energy (λtotal), light-harvesting efficiency (LHE), electron injection driving force (ΔGinject) and open-circuit photovoltage (VOC). The results of this study revealed that all designed dyes, compared to the reference dye, are characterized by small Egap and λtotal values as well as large λmax, in addition to significant NLO properties and large adsorption energy (Eads). Therefore, all studied dyes can be used as sensitizers in DSSC.

METHODS

Using Density Functional Theory (DFT) approaches with the B3LYP functional and the 6-31G(d,p) basis set, all ground state geometries of the isolated dyes were fully optimized. Time-Dependent Density Functional Theory (TD-DFT) method using the CAM-B3LYP/6-31G(d,p)/IEF-PCM level was applied to simulate the UV-visible absorption properties. All isolated dye calculations were performed using the Gaussian 09 software package. DFT calculations have been carried out with the DMol3 package included in Materials Studio for simulating the adsorption of the investigated dyestuff on the TiO2 surface of anatase (101), using the generalized gradient corrected approximation (GGA) approach of the Perdew-Burke-Ernzerhof (PBE) functional with the basic set of digital double polarisation (DNP). To study the optical performance of dye@TiO2 the PBE/DNP method present in DMol3 was applied.

Push-Pull Phenoxazine-Based Sensitizers for p-Type DSSCs: Effect of Acceptor Units on Photovoltaic Performance

Finding new efficient p-type sensitizers for NiO photocathodes is a great challenge for the development of promising low-cost tandem dye-sensitized solar cells (DSSCs). Now, the focus of researchers investigating these cells has been to create high-performance p-type systems. With this intention, herein, the design and synthesis of six new phenoxazine-based donor-acceptor (D-A)-configured organic dyes PO_1-6 was reported, comprising different acceptor moieties specially designed for the sensitization of mesoporous p-type semiconductor NiO for the construction of p-type DSSCs (p-DSSCs). This work includes structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies of these dyes, including evaluation of their structure-property relationships. The optical studies revealed that PO_1-6 displayed adequate absorption and emission features in the range of 480-550 and 560-650 nm, respectively, with a bandgap in the order of 2.05-2.40 eV, and their thermodynamic parameters favored an efficient interfacial charge transfer involving NiO. Among the six new dyes, the device based on sensitizer PO₂ carrying electron-withdrawing 1,3-diethyl-2-thiobarbituric acid achieved the highest power conversion efficiency of 0.031 % (short-circuit current density=0.89 mA cm^-2 , open-circuit voltage=101 mV, and fill factor=35 %). Conclusively, the study furnishes an understanding of the intricacies involved in the structural modification of phenoxazine-based sensitizers to further ameliorate the performance of the p-type DSSCs.

Theoretical Investigation on Photophysical Properties of Triphenylamine and Coumarin Dyes

Organic molecules with donor and acceptor configures are widely used in optoelectronic materials. Triphenylamine dyes (TPCTh and TPCRh) are investigated via density functional theory (DFT) and time-dependent DFT. Some microscopic parameters related to light absorption and photoelectric formation are calculated to interpret the experimental performance in dye-sensitized solar cells (DSSCS). Considering that coumarin derivatives (Dye 10 and Dye 11) have good donor and acceptor structures, they also have a COOH group used as an anchoring group to connect with semiconductors. Thus, the two dyes' photophysical and photoelectric properties are analyzed to estimate the performance and application in DSSCs.

Push-pull D-π-Ru-π-A chromophores: synthesis and electrochemical, photophysical and second-order nonlinear optical properties

The present work describes the one-pot synthesis and electrochemical, photophysical and second-order nonlinear optical (NLO) properties of a series of dipolar π-delocalized Ru(ii) dialkynyl complexes. The eight new asymmetrical D-π-Ru-π-A push-pull chromophores incorporate pyranylidene ligands as pro-aromatic donor groups (D) and formaldehyde, indane-1,3-dione, pyrimidine or pyrimidinium as electron-attracting groups (A) separated by ruthenium bis-acetylide fragments and π-conjugated linkers. The second-order nonlinear optical (NLO) properties of all eight complexes were determined by the Electric-Field-Induced Second Harmonic generation (EFISH) technique (operating at 1907 nm), and were compared to those of their purely organic analogs. All investigated compounds (organic and organometallic) exhibited positive μβ values, which dramatically increased for the complexes due to the presence of ruthenium in the π-conjugated core. The second-order NLO response could also be easily modulated by changing the nature of alkynyl substituents. The most promising ruthenium complexes 7 and 8 of the series with the pyrimidinium fragment displayed μβ values of 14 000 × 10^-48 esu. The effect of structural modifications on the redox and spectroscopic properties of the complexes was also studied. The intramolecular charge transfer (ICT) occurring through the ruthenium center of the push-pull σ-dialkynyl complexes was investigated by combining experimental and theoretical data.

Synthesis and characterization of zinc carboxy–porphyrin complexes for dye sensitized solar cells

DOTA-like porphyrin Zn complexes 8 afford new perspectives in DSSCs compared to mono-porphyrin counterpart 2, by displaying a PCE (%) of 7.13.

A detailed experimental and theoretical investigation of the role of cyano groups in the π-bridged acceptor of sensitizers for use in dye-sensitized solar cells (DSCs)

Porphyrin sensitizers LX1, LX2 and LX3 were synthesized for use in DSCs and their electronic properties with TiO₂ were investigated in detail using theoretical calculations.