New ruthenium(II) photosensitizers [Ru(dcbpy)(L)(NCS)₂] (dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine; L = 4,4′-bis{di[4-(N,N′-dimethylamino)phenyl]amino}-2,2′-bipyridine (1), 4,4′-bis[di(4-methoxyphenyl)amino]-2,2′-bipyridine (2), and 4,4′-bis[di(4-tolyl)amino]-2,2′-bipyridine (3)) were prepared and characterized and their application in dye-sensitized solar cells is presented. The optical absorption of these photosensitizers gives a peak at around 540 nm, which is very similar to that of the standard N719. The maximum incident photon-to-current conversion efficiency (IPCE) of 80.6 % was obtained for 3, which corresponded to a power conversion efficiency (η) of 5.68 % under standard air mass (AM) 1.5 sunlight (versus N719 at 6.76 %). Molecular cosensitization of 3 with an organic dye, QS-DPP-I, yielded higher η values up to 6 % relative to the cells based on individual photosensitizers, and the corresponding IPCE can reach 93.6 % at 549 nm. A preliminary stability test of the devices was also conducted.

A series of new triarylamine-based platinum-acetylide complexes (WYs) have been designed and synthesized as new sensitizers for applications in dye-sensitized solar cells (DSSCs). With the aim of investigating the effect of a rigidifying donor structure on the photoelectrical parameters of the corresponding DSSCs, two new sensitizers, WY1 and WY2, with rigid and coplanar fluorene units as an electron donor, were prepared. Moreover, two sensitizers that contained triphenylamine units as an electron donor, WY3 and WY4, were also synthesized for comparison. The photo- and electrochemical properties of all of these new complexes have been extensively explored. We found that the dimethyl-fluorene unit exhibited a stronger electron-donating ability and better photovoltaic performance compared to the triphenylamine unit, owing to its rigidifying structure, which restricted the rotation of σ bonds, thus increasing the conjugation efficiency. Furthermore, WY2, which contained a dimethyl-fluorene unit as an electron donor and bithiophene as a π bridge, showed a relatively high open-circuit voltage (V_oc) of 640 mV and a PCE of 4.09 %. This work has not only expanded the choice of platinum-acetylide sensitizers, but also demonstrates the advantages of restricted rotation of donor σ bonds for improved behavior of the corresponding DSSCs.

A series of new push–pull organic dyes (BT-I–VI), incorporating electron-withdrawing bithiazole with a thiophene, furan, benzene, or cyano moiety, as π spacer have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). In comparison with the model compound T1, these dyes containing a thiophene moiety between triphenylamine and bithiazole display enhanced spectral responses in the red portion of the solar spectrum. Electrochemical measurement data indicate that the HOMO and LUMO energy levels can be tuned by introducing different π spacers between the bithiazole moiety and cyanoacrylic acid acceptor. The incorporation of bithiazole substituted with two hexyl groups is highly beneficial to prevent close π–π aggregation, thus favorably suppressing charge recombination and intermolecular interaction. The overall conversion efficiencies of DSSCs based on bithiazole dyes are in the range of 3.58 to 7.51 %, in which BT-I-based DSSCs showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 81.1 %, a short-circuit photocurrent density (J_sc) of 15.69 mA cm⁻², an open-circuit photovoltage (V_oc) of 778 mV, and a fill factor (ff) of 0.61, which correspond to an overall conversion efficiency of 7.51 % under standard global AM 1.5 solar light conditions. Most importantly, long-term stability of the BT-I–III-based DSSCs with ionic-liquid electrolytes under 1000 h of light soaking was demonstrated and BT-II with a furan moiety exhibited better photovoltaic performance of up to 5.75 % power conversion efficiency.