The effect of TiO₂ nanostructures such as nanoparticles, nanowires, nanotubes on photoanode properties, and dye-sensitized solar cells photovoltaic parameters were studied. The series of dye-sensitized solar cells based on two dyes, that is, commercially N719 and synthesized 3,7′-bis(2-cyano-1-acrylic acid)-10-ethyl-phenothiazine were tested. Additionally, the devices containing a mixture of this sensitizer and chenodeoxycholic acid as co-adsorbent were fabricated. The amount of adsorbed dye molecules to TiO₂ was evaluated. The prepared photoanodes with different TiO₂ nanostructures were investigated using UV-Vis spectroscopy, optical, atomic force, and scanning electron microscopes. Photovoltaic response of constructed devices was examined based on current-voltage characteristics and electrochemical impedance spectroscopy measurements. It was found that the highest UV-Vis absorption exhibited the photoanode with nanotubes addition. This indicates the highest number of sensitizer molecules anchored to the titanium dioxide photoanode, which was subsequently confirmed by dye-loading tests. The highest power conversion efficiency was (6.97%) for solar cell containing nanotubes and a mixture of the dyes with a co-adsorbent.

Two novel sensitizers, 2a and 2b, with D/A–π–D–π–A architectures were designed and synthesized based on a phenothiazine framework connected via ethylene with 3,5-bis(trifluoromethyl)phenyl (A) and p-methoxyphenyl (D), and with cyanoacrylic acid as an anchoring group, acting as an acceptor (A). A comparative analysis was performed to investigate the effect of the electronic character of end-capped D and A groups on the photophysical properties and photovoltaic performance of 2a and 2b. The optical, thermal, electrochemical and photovoltaic properties of the dyes were thoroughly investigated and confronted with DFT and TD-DFT calculations. Compound 2b of D–π–D–π–A type showed better photovoltaic parameters, which verify the general trends, although the parameters for compound 2a of A–π–D–π–A type do not differ significantly from those for 2b. The metal-free 2a and 2b-based DSSC devices exhibited higher power conversion efficiencies of 6.11% (2a) and 5.03% (2b) compared to 3.56% for the N719-based device.

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.

Third-generation solar cells, including dye-sensitized solar cells, bulk-heterojunction solar cells, and perovskite solar cells, are being intensively researched to obtain high efficiencies in converting solar energy into electricity. However, it is also important to note their stability over time and the devices’ thermal or operating temperature range. Today’s widely used polymeric materials are also used at various stages of the preparation of the complete device—it is worth mentioning that in dye-sensitized solar cells, suitable polymers can be used as flexible substrates counter-electrodes, gel electrolytes, and even dyes. In the case of bulk-heterojunction solar cells, they are used primarily as donor materials; however, there are reports in the literature of their use as acceptors. In perovskite devices, they are used as additives to improve the morphology of the perovskite, mainly as hole transport materials and also as additives to electron transport layers. Polymers, thanks to their numerous advantages, such as the possibility of practically any modification of their chemical structure and thus their physical and chemical properties, are increasingly used in devices that convert solar radiation into electrical energy, which is presented in this paper.