A novel carbazole-based dye outperformed the benchmark dye N719 for high efficiency dye-sensitized solar cells (DSSCs)

Abstract

Two novel high molar extinction coefficient heteroleptic Ru(II) isomers, NCSU-10 and NCSU-10 0 , based on carbazole antenna were synthesized with the aid of Knoevenagel reaction, to study the influence of the carbazole antenna and anchoring group (COOH) isomerization on the light harvesting efficiency (LHE), ground and excited state oxidation potentials, incident-photon-to-current conversion efficiency (IPCE), short-circuit photocurrent density (J SC ), and total solar-to-electric conversion efficiency (h) for DSSCs, and their device performances were compared to the benchmark dye N719. The photophysical and photoelectrochemical properties discussed herein addressed the significant impact of the carbazole antenna and the position of the anchoring group on J SC and h in DSSCs. Tetrabutylammonium (TBA) substituted NCSU-10 achieved efficient sensitization of nanocrystalline TiO 2 over the whole visible range, extending into the near IR region (ca. 870 nm) with an excellent power conversion efficiency (h) of 9.37% under an irradiation of full sunlight (100 mW cm À2 ) with mask compared to 8.17% of N719 under optimized conditions. NCSU-10 outperformed N719 by 45% in molar absorptivity, 18.8% in J SC , and 14.6% in the total conversion efficiency. Molecular modeling studies (DFT/TD-DFT) of NCSU-10 and NCSU-10 0 showed that the HOMO is delocalized not only on Ru and NCS but also on the carbazole with a large coefficient, indicating that the second charge generation transfer in the visible region at $400 nm is a mixture of metal-to-ligand charge transfer (MLCT) and strong ligand-ligand charge transfer (LLCT) with a significant HOMO coefficient originating from the carbazole antenna (p) to the bipyridyl electron acceptor (p*). Moreover, DFT calculations showed that the 4,4 0 -isomer (NCSU-10) is a significantly stronger electron acceptor than the 5,5 0 -isomer (NCSU-10 0 ), which explained the inferior electron injection and significantly lower J SC of the 5,5 0 -isomer.

More stable and more efficient alternatives of Z-907: carbazole-based amphiphilic Ru(ii) sensitizers for dye-sensitized solar cells

“…This effect can be attributed to the extended π-conjugation and stronger electron donating carbazole ligand, which resulted in destabilization of the metal-based HOMO (t 2g ), and that translated into red shifted absorption spectra due to the decreased HOMO-LUMO gap for HD-14-15 compared to that of N719, as shown schematically in the energy level diagram of Figure 4. Additionally, incorporation of stronger ancillary ligands for HD-14 and HD-15 resulted in stronger emission than N719 as being previously reported for NCSU-10 and MH11 19,25 . Hence, it is expected that under similar conditions and concentration, HD-14 and HD-15 are less prone to radiation-less energy losses through internal conversion and/or intersystem crossing compared to N719.…”

“…Recently, our group reported a much simple yet highly efficient sensitizer NCSU-10 19 based on carbazole bipyridyl ancillary ligand. The corresponding bipyridyl ancillary ligand was synthesized by one step Knoevenagel type condensation reaction [19][20][21][22] . Sensitizer employing that ancillary ligand was coded as NCSU-10 and is shown in Figure 2.…”

Novel heteroleptic ruthenium sensitizers containing carbazole linked 4,5-diazafluorene ligand for dye sensitized solar cells

“…As a consequence of charge localization in dcbpy, there exists an appreciable electron injection from the excited dye to the conduction band of TiO 2 . It is well known that N719 shows weak photoluminescence in the 650 and 800 nm [11], whereas sensitizers S1 and S2 do not…”

“…In this context, highly extended conjugation units such as thiophene [2], ethylenedioxythiophene (EDOT) [3], triphenylamine [4,5] and alkoxybenzene [6][7][8] attached to the bipyridyl ligand were designed to prepare novel sensitizers that exhibit an enhanced molar absorptivity in combination with a red-shifted absorption band. Few research groups revealed that ruthenium sensitizers containing carbazole hole transporting units in the bipyridyl ligand enhance the spectral response and energy conversion efficiency of DSSC's [9][10][11][12][13]. Particularly, Shafei et al [11] reported a novel carbazole containing ruthenium sensitizer exhibiting low energy MLCT peak at 545 nm with high molar absorptivity (2.06 x 10 4 M -1 cm -1 ) and extended absorption into the near IR region (ca.…”

“…Few research groups revealed that ruthenium sensitizers containing carbazole hole transporting units in the bipyridyl ligand enhance the spectral response and energy conversion efficiency of DSSC's [9][10][11][12][13]. Particularly, Shafei et al [11] reported a novel carbazole containing ruthenium sensitizer exhibiting low energy MLCT peak at 545 nm with high molar absorptivity (2.06 x 10 4 M -1 cm -1 ) and extended absorption into the near IR region (ca.…”