Abstract
New D-π-D-π-A low-molecular-weight compounds, based on a phenothiazine scaffold linked via an acetylene unit with various donor moiety and cyanoacrylic acid anchoring groups, respectively, were successfully synthesized. The prepared phenothiazine dyes were entirely characterized using nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The compounds were designed to study the relationship between end-capping donor groups’ structure on their optoelectronic and thermal properties as well as the dye-sensitized solar cells’ performance. The effect of π-conjugation enlargement by incorporation of different heterocyclic substituents possessing various electron–donor affinities was systematically experimentally and theoretically examined. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were implemented to determine the electronic properties of the novel molecules.
Highlights
Dye-sensitized solar cells (DSSCs) based on metal-free organic dyes have drawn greater and greater attention owing to their advantages, such as a relatively low cost, compliance with environmental requirements, and easy device preparation
The synthesis of organic dyes such as carbazole, thiophene, pyrene, phenothiazine to act as donors (D), and quinoline and pyridine as acceptor (A) units, produce in combination D-A systems which have been evolved for the utilization of dye-sensitized solar cells (DSSCs), organic light-emitting diodes (OLEDs), sensors and bio-imaging [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]
We have shown that a DSSC device based on a sensitizer with an electron-acceptor group confirmed a significantly lower power conversion efficiency (PCE), of 5.03%, than one with an electron-donor unit (PCE = 6.21%), with respect to the reference
Summary
Dye-sensitized solar cells (DSSCs) based on metal-free organic dyes have drawn greater and greater attention owing to their advantages, such as a relatively low cost, compliance with environmental requirements, and easy device preparation. Opposite to the complexes with heavy atoms utilized in DSSCs, which show high or even comparable power conversion efficiency (PCE) of 13% [1,2,3,4,5], the use of metal-free sensitizers in DSSCs makes it possible to obtain ever-growing PCE up to 14% [6,7,8,9,10]. Phenothiazine (PTZ), as a heterocyclic compound, encloses electron-abundant sulfur and nitrogen atoms, and plays the role of an strong electron-donating (D) moiety in D-A systems. The large π-conjugated structure, high molar absorption coefficients (ε), high thermal and chemical stability, and the non-planar conformation preventing aggregation of phenothiazine are important requirements making PTZ and its derivatives desirable candidates for photovoltaic applications. The many ways to modify phenothiazine structure by addition of different types of Materials 2020, 13, 2292; doi:10.3390/ma13102292 www.mdpi.com/journal/materials
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