Jen-Shyang Ni

Anthracene/Phenothiazine π-Conjugated Sensitizers for Dye-Sensitized Solar Cells using Redox Mediator in Organic and Water-based Solvents

Metal-free dyes (MD1 to MD5) containing an anthracene/phenothiazine unit in the spacer have been synthesized. The conversion efficiency (7.13 %) of the dye-sensitized solar cell using MD3 as the sensitizer reached approximately 85 % of the N719-based standard cell (8.47 %). The cell efficiency (8.42 %) of MD3-based dye-sensitized solar cells (DSSCs) with addition of chenodeoxycholic acid is comparable with that of N719-based standard cell. The MD3 water-based DSSCs using a dual-TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl)/iodide electrolyte exhibited very promising cell performance of 4.96 % with an excellent Voc of 0.77 V.

Organic sensitizers with a rigid dithienobenzotriazole-based spacer for high-performance dye-sensitized solar cells

New D–π–A type sensitizers (YC dyes), comprising arylamine as the electron donor, dithieno[3′,2′:3,4;2′′,3′′:5,6]benzo[1,2-d][1,2,3]triazole (DTBZ) as the rigidified π-conjugated spacer, and 2-cyanoacrylic acid as both the acceptor and anchor, have been synthesized. The YC sensitizers displayed broad absorption of light, from 362 nm to 550 nm, with a molar extinction coefficient as high as ∼54 800 M−1 cm−1. The light-to-electricity conversion efficiencies of the dye-sensitized solar cells (DSSCs) ranged from 5.82 to 8.51% under simulated AM 1.5 G illumination. Upon addition of 5 mM of CDCA as a coadsorbent, the best performing cell displayed an efficiency of 9.10%, surpassing that of the N719-based standard cell (8.12%), and even achieved an efficiency of 10.56% under quarter sunlight illumination.

Naphtho[2,3-c][1,2,5]thiadiazole and 2H-Naphtho[2,3-d][1,2,3]triazole-Containing D–A−π–A Conjugated Organic Dyes for Dye-Sensitized Solar Cells

Dipolar dyes comprising an arylamine as the electron donor, a cyanoacrylic acid as electron acceptor, and an electron deficient naphtho[2,3-c][1,2,5]thiadiazole (NTD) or naphtho[2,3-d][1,2,3]triazole (NTz) entity in the conjugated spacer, were developed and used as the sensitizers in dye-sensitized solar cells (DSSCs). The introduction of the NTD unit into the molecular frame distinctly narrows the HOMO/LUMO gap with electronic absorption extending to >650 nm. However, significant charge trapping and dye aggregation were found in these dyes. Under standard global AM 1.5 G illumination, the best cell photovoltaic performance achieved 6.37 and 7.53% (∼94% relative to N719-based standard cell) without and with chenodeoxycholic acid (CDCA) coadsorbent, respectively. Without CDCA, the NTz dyes have higher power conversion efficiency (7.23%) than NTD dyes due to less charge trapping, dye aggregation, and better dark current suppression.

2H-[1,2,3]Triazolo[4,5-c]pyridine Cored Organic Dyes Achieving a High Efficiency: a Systematic Study of the Effect of Different Donors and π Spacers

New D-A-π-A-based isomeric sensitizers, PTNn (n = 1-2) and NPTn (n = 1-5), were synthesized using 2H-[1,2,3]triazolo[4,5-c]pyridine (PT) as an auxiliary acceptor, triphenylamine or N,N-bis[4-(hexyloxy)phenyl]aniline as the donor, furan, thiophene, phenyl, or 3-hexylthiophene as the conjugated spacer, and 2-cyanoacrylic acid as the acceptor and anchor as well. They were used as the sensitizers of dye-sensitized solar cells. The NPTn dyes show better performance than the PTNn dyes. Among them, the best efficiency of 7.92% (∼96%, N719) was obtained with the NPT5 dye, indicating that the PT core could be used as a new building block for the design of high-performance sensitizers in the future. The negative Mulliken charge from the auxiliary acceptor was found to be useful as a semiempirical index for correlation of the molecular structure with the cell efficiency among structurally similar D-A-π-A-type congeners.

Ruthenium complex dye with designed ligand capable of chelating triiodide anion for dye-sensitized solar cells

Ru(4,4′-dicarboxyl-2,2′-bipyridine)[4,4′-bis(styrylaminocarbonyl)-2,2′-bipyridine](NCS)2, denoted as RuAS dye, was synthesized and well characterized by 1H-NMR, 13C-NMR, heteronuclear single quantum coherence, UV-vis and ESI-MS spectra. Its capability of chelating triiodide anions with the 4,4′-bis(styrylaminocarbonyl)-2,2′-bipyridine ligand, which was revealed by ATR-FTIR and 1H-NMR spectroscopies, reduced the charge recombination for dye-sensitized solar cells (DSSCs) by keeping the triiodide ions away from contact with the mesoporous TiO2 layer. Therefore, the open-circuit photovoltage of the DSSC barely changed with the triiodide concentration in the electrolyte. Moreover, the electron-withdrawing ability of the amide groups in the ligand increased the molar extinction coefficient of the dye, leading to the increase of photocurrent for DSSCs. The enhanced photovoltaic performance was further examined by incident photon-to-current conversion efficiency spectra, electrochemical impedance spectroscopy and open-circuit potential decay transient measurements.

Phenothiazinedioxide‐Conjugated Sensitizers and a Dual‐TEMPO/Iodide Redox Mediator for Dye‐Sensitized Solar Cells

Metal-free dyes containing a phenothiazinedioxide entity in the spacer were synthesized. The best conversion efficiency (7.47%) of the dye-sensitized solar cell (DSSC) by using new sensitizers with chenodeoxycholic acid as a co-adsorbent and the I(-) /I3 (-) electrolyte reached over 90% of that of the standard N719-based cell (8.10%). A new type of ionic liquid containing the nitroxide radical (N-O(.) ) and iodide was successfully synthesized and applied to the DSSCs. If the I(-) /I3 (-) electrolyte was replaced with a dual redox electrolyte, that is, a TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) derivative with a dangling imidazolium iodide entity, the cell exhibited a high open-circuit voltage of 0.85 V and a cell efficiency of 8.36%.

Synthesis and characterization of novel symmetrical two-photon chromophores derived from bis(triphenylaminotetrathienoacenyl) and fused-thiophene units

Four new donor–π–donor (D–π1–π2–π1–D) fused-thiophene-based chromophores, end-functionalized with electron-donating triphenylamine (TPA) groups, were developed and characterized for a two-photon absorption study. Within this series, tetrathienoacene (thieno[2′,3′:4,5]thieno[3,2-b]thieno[2,3-d]thiophene; TTA) moieties were employed as side-conjugated (π1) units, and the central conjugated core (π2) units were altered with thiophene (T), bithiophene (bT), thienothiophene (TT), and dithienothiophene (DTT) for chromophores 1–4, respectively. The structural and photophysical relationships of the four compounds were compared, and all four chromophores showed strong fluorescence with good thermal stability. The energy gap compression of these chromophores was verified by electrochemistry and density functional theory (DFT) calculations. The two-photon-related properties of 1–4 were examined using femtosecond laser pulses as the probing tool. The magnitude of the two-photon absorptivity was found to be strongly dependent on the molecular conjugation length and the center fused-thiophene unit. Within the family, the most conjugated DTT-centered chromophore (4) exhibits the strongest and the most widely dispersed two-photon absorption cross-section value up to 3000 GM. To the best of our knowledge, this is the highest 2PA cross section value reported to date among the studied fused thiophene-based chromophores.