Co-adsorption Of Chenodeoxycholic Acid Research Articles

Starburst-Shaped D-π-A Chromophores Possessing a Hexaethynylbenzene Core for Dye-Sensitized Solar Cells.

Two starburst-shaped organic chromophores, incorporating a hexaethynylbenzene core modified by five donor branches (D-branches) of (p-dioctylaminostyryl)benzene and one acceptor/anchoring branch (A-branch) of either carboxylic acid-terminated phenylethynylbenzene (SB-07) or cyanoacrylic acid-terminated diketopyrrolopyrrole (DPP)-thiophene (SB-08), were synthesized and applied to dye-sensitized solar cells (DSSCs). In these chromophores, the common donor moiety, five (p-dioctylaminostyryl)phenyl groups, exhibits excellent optical absorption in the visible region (molar absorption coefficient ε > 105 M-1 cm-1 below 500 nm). The A-branch of SB-07 does not possess strong electron-accepting properties; however, the A-branch of SB-08, the DPP-thiophene moiety, serves as a strong electron acceptor site. Furthermore, the intramolecular charge-transfer (ICT) transition between the thiophene and DPP moieties extends the optical absorption range to the near-infrared region (∼800 nm). Optimized DSSC devices using SB-08 with coadsorption of chenodeoxycholic acid, in conjunction with iodide/triiodide-based electrolytes, exhibited incident photon-to-current conversion efficiency (IPCE) exceeding 70% in the 370-700 nm range and over 20% even at 800 nm, with a short-circuit photocurrent density (Jsc) of 19.3 mA cm-2 and a power conversion efficiency (PCE) of 6.4% under AM 1.5G illumination (100 mW cm-2). These results are considerably better than those of SB-07 (Jsc = 7.0 mA cm-2, PCE = 3.3%). The starburst-shaped architecture presented here can be used as a novel structural motif for metal-free organic sensitizers because it enables flexible modification of the multiple D-branches that enhance light-harvesting ability and the A-branch that serves as an excited electron transport pathway.

Novel rod-shaped organic sensitizers for liquid and quasi-solid-state dye-sensitized solar cells

Two novel D−π−A dyes (FD and SD) have been synthesized for dye-sensitized solar cells (DSSCs). The two rod-shaped molecules with an identical π-spacer di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole and with a different donor group 5,11-dihydroindolo[3,2-b]carbazole for FD or 11,12-dihydroindolo[2,3-a]carbazole for SD have been investigated. Compared to FD, the sensitizer SD not only showed a broader absorption spectrum extended to infrared region which was conducive to enhancing the light-trapping capability and thus to increase the photocurrent of the device fabricated with SD, but also exhibited better inhibition of dye aggregation resulting in a higher photovoltage. With the co-adsorption of chenodeoxycholic acid (CDCA), the photovoltaic performance of DSSCs based on the two dyes has dropped significantly. The results indicate that the aggregation of the two dyes FD and SD can be controlled by linking multiple branched alkyl chains in the structure. Finally, FD and SD-based cells without CDCA achieved power conversion efficiencies (PCE) of 7.20% and 7.47%, respectively, in liquid DSSCs. Correspondingly, FD and SD displayed PCE values of 5.77% and 6.67% in quasi-solid-state DSSCs, respectively, under standard global 1.5 solar conditions.

Enhancement of quantum efficiency by co-adsorbing small julolidine dye and bulky triphenylamine dye in dye-sensitized solar cells

Julolidine and benzothiadiazole have been employed separately as building blocks for sensitizers to widen absorption spectrum for dye-sensitized solar cells (DSSCs). We synthesize a new dye combining the two blocks. The DSSCs using the dye show incident photon-to-electron conversion efficiency (IPCE) spectrum up to 850 nm and the maximum IPCE value of about 80%. Then we examine various co-adsorbents and find that co-adsorbing with a bulky dye enhances the IPCE of the new dye even at the wavelengths that the bulky dye does not absorb. On the other hand, such effect is not observed with co-adsorption of chenodeoxycholic acid and a flat structured dye. The results suggest that even if small dyes do not have alkyl chains, the dyes can benefit from the blocking function of the alkyl chains attached to the co-adsorbed bulky dyes.

Structural Effect of the Pendant Unit in Thiocyanate‐Free RuII Sensitizers on the Dye‐Sensitized Solar Cell Performance

A combination of Ru complex sensitizers and Co complex redox couples for dye‐sensitized solar cells (DSSCs) generally results in low power conversion efficiency. This has been suggested to be from undesired electron transfer due to strong intermolecular interactions between the dye and the redox couple. To retard the interactions, two thiocyanate‐free ruthenium (Ru) sensitizers were synthesized with a terpyridine attached that has a triphenylamine (TPA) unit with branched alkoxy chains. The main difference between the two dyes is the angle of the three phenyl rings in the TPA unit. The DSSCs using both the new dyes show higher short‐circuit currents and open‐circuit voltages in comparison with those using a Ru complex dye with nonbranched alkyl chains. The Ru sensitizer with a more twisted TPA unit displays relatively high power conversion efficiency without coadsorption of chenodeoxycholic acid, suggesting less intermolecular interaction among dyes and thus also with Co complex redox couples.

Triindole-modified push–pull type porphyrin dyes for dye-sensitized solar cells

Two novel push–pull type Zn(II) porphyrin dyes (QX09 and QX10) have been synthesized for dye-sensitized solar cells (DSSCs). The two porphyrin dyes consist of the same porphyrin core with a triindole unit directly attached in its meso-position and different acceptor/anchoring groups carboxylic acid (for QX09) and cyanoacylic acid (for QX10) have been investigated. The photophysical, electrochemical and theoretical studies indicated that the two porphyrin dyes were both suitable as the photosensitizers. The dye QX10 exhibited a broader absorption region and significantly improved IPCE values compared with QX09, which ensured a better light-harvesting ability and a higher photocurrent. With the coadsorption of chenodeoxycholic acid (CDCA), the DSSCs based on the two dyes both obtained improved photovoltaic performances. Finally, QX10-based cell with CDCA achieved a high power conversion efficiency of 6.65% under AM 1.5G irradiation.

Donor–π–acceptor organic hybrid TiO2 interfaces for solar energy conversion

It is reported herein that the co-adsorption of chenodeoxycholic acid (CDCA) with the D–π–A organic dyes (E)-3-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid (Dye-O) or (E)-3-(5-(4-(bis(4-(hexylthio)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid (Dye-S) has a significant influence on the ground state absorption spectra of sensitized TiO2 thin films. In the absence of CDCA, evidence for aggregation was observed at even the lowest measured surface coverages. The presence of CDCA also had a significant and very beneficial influence on the unwanted charge recombination reaction between TiO2(e−) and oxidized cobalt mediators.

Organic sensitizers incorporating 3,4-ethylenedioxythiophene as the conjugated bridge: Joint photophysical and electrochemical analysis of photovoltaic performance

Two novel D–π–A organic dyes containing either an indoline donor or a triphenylamine donor with each containing the 3,4-ethylenedioxythiophene unit as the conjugated bridge, were developed for dye-sensitized solar cells. Incorporating 3,4-ethylenedioxythiophene as the conjugated bridge brings several characteristics, such as broadening absorption range and increasing molar extinction coefficients, and improving electron injection with enhancement of the short-circuit photocurrent. The indoline containing dye shows a more negative oxidation potential and a bathochromic shift in absorption spectra than the triphenylamine substituted dye, indicative of the more powerful electron-donating capability of the indoline unit. With coadsorption of chenodeoxycholic acid, the indoline dye based dye-sensitized solar cell exhibited promising conversion efficiency of 6.05%, with a short-circuit photocurrent of 13.23 mA cm−2, open circuit voltage of 642 mV, and a fill factor of 0.711. In the indoline dye system, the dye-sensitized solar cell is workable with the driving force of 150 mV for the dye regeneration process, paving a road toward minimizing energy losses in the dye regeneration process.

Femto- to Millisecond Photophysical Characterization of Indole-Based Squaraines Adsorbed on TiO2 Nanoparticle Thin Films

In this paper, we address femto- to millisecond transient absorption studies of TiO2 nanoparticle (NP) thin films sensitized with four squaraine (SQ) molecules, with and without a deaggregating agent, chenodeoxycholic acid (CDCA). On the femto- to picosecond time scale, we determined the presence of three transient species by using singular value decomposition (SVD) analysis, i.e., S1 of the SQ monomers, S1 of the SQ H-aggregates, and the SQ radical cation formed after the electron injection. Both monomers and H-aggregates are proven to inject electrons to the TiO2 conduction band, being 5 times faster in the monomers (e.g., keimon = 5.1 × 1011 s–1 and keiH-agg = 1.1 × 1011 s–1 for SQ 41). Besides, the undesired singlet–singlet annihilation is an active process in these samples, constituting the drain of a high percentage of the absorbed photons. The coadsorption of CDCA on the TiO2 NP avoids the formation of H-aggregates, and therefore, only two transient species are present in these samples: S1 of the m...

Efficient and stable organic DSSC sensitizers bearing quinacridone and furan moieties as a planar π-spacer

In this work, three new quinacridone-based dyes containing a furan moiety (QA1–3) have been synthesized through simple synthetic routes for the application of dye-sensitized solar cells (DSSCs). Their absorption spectra, electrochemical, photovoltaic properties and the cell long-term stability have been extensively investigated. Electrochemical measurement data indicates that the tuning of the HOMO and LUMO energy levels can be conveniently realized by alternating the donor moiety. The theoretical calculations show that the dihedral angle between the quinacridone moiety and the furan ring is less than 1 degree, indicating excellent planarity between the two groups, which is beneficial for intramolecular charge transfer. All of these dyes performed as sensitizers for DSSCs tested under similar AM 1.5 experimental conditions, and a maximum solar energy to electricity conversion efficiency of 7.70% (Jsc = 13.25 mA cm−2, Voc = 804 mV, FF = 0.73) for the 20 mM chenodeoxycholic acid (CDCA) co-adsorbed DSSCs based on QA1 is obtained. Electrochemical impedance experiments indicate that the electron lifetime is improved by co-adsorption of CDCA, accounting for the significant improvement of Voc. Most importantly, the long-term stability of the QA1–3-based DSSCs with ionic-liquid electrolytes under 1000 h light-soaking has been demonstrated.

A nickel-complex sensitiser for dye-sensitised solar cells

Abstract We report the first example of a Ni(II) complex that demonstrates sensitiser function in a Dye-Sensitised Solar Cell (DSSC). Complexes [Ni(dcbpy)(qdt)] (1), [Ni(decbpy)(qdt)] (2) and [Ni(decbpy)Cl2] (3) (where dcbpy = 4,4′-dicarboxy-2,2′-bipyridine; decbpy = 4,4′-di(CO2Et)-2,2′-bipyridine; and qdt = quinoxaline-2,3-dithiolate) have been prepared. Characterisation was carried out using electrochemical, spectroscopic and computational techniques. Intensive visible transitions of 1 and 2 have been assigned predominantly to Ligand-to-Ligand Charge Transfer (LLCT) from the qdt to the diimine ligand, suggesting appropriate charge separation for application in a photoelectrochemical device. TiO2 sensitised with 2, following charge injection, processes a recombination time significantly long for photovoltaic function. In a DSSC, using I - / I 3 - redox electrolyte, photocurrents and photovoltages of 0.293 mA and 521 mV were observed, with optimum values requiring TiCl4 post-treatment of TiO2 and co-adsorption of Chenodeoxycholic acid (Cheno). Although photovoltaic function was observed, the low photocurrent is attributed to a short-lived excited state lifetime resulting in poor charge injection from the Ni(II) sensitiser.

Effect of chenodeoxycholic acid (CDCA) additive on phenothiazine dyes sensitized photovoltaic performance

The effects of chenodeoxycholic acid (CDCA) in a dye solution as a co-adsorbent on the photovoltaic performance of dye-sensitized solar cells (DSSCs) based on two organic dyes containing phenothiazine and triarylamine segments (P1 and P2) were investigated. It was found that the coadsorption of CDCA can hinder the formation of dye aggregates and improve electron injection yield and thus Jsc. This has also led to a rise in photovoltage, which is attributed to the decrease of charge recombination. The DSSC based on dye P2 showed better photovoltaic performance than P1: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 89.5%, a short-circuit photocurrent density (Jsc) of 9.57 mA/cm2, an open-circuit photovoltage (Voc) of 697 mV, and a fill factor (FF) of 0.66, corresponding to an overall conversion efficiency of 4.42% under the standard global AM 1.5 solar light condition. The overall conversion efficiency was further improved to 5.31% (Jsc = 10.36 mA/cm2, Voc = 0.730 V, FF = 0.70) upon addition of 10 mM CDCA to the dye solution for TiO2 sensitization. Electrochemical impedance data indicate that the electron lifetime was improved by coadsorption of CDCA, accounting for the significant improvement of Voc. These results suggest that interfacial engineering of the organic dye-sensitized TiO2 electrodes is important for highly efficient photovoltaic performance of the solar cell.

New Diketopyrrolopyrrole (DPP) Dyes for Efficient Dye-Sensitized Solar Cells

Two novel metal-free dyes (DPP-I and DPP-II) with a diketopyrrolopyrrole (DPP) core were synthesized for dye-sensitized solar cells (DSSCs). The absorption spectra and electrochemical and photovoltaic properties of DPP-I and DPP-II were extensively investigated. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the π-conjugated systems. Besides, coadsorption of chenodeoxycholic acid (CDCA) can hinder the formation of dye aggregates and might improve electron injection yield and, thus, Jsc. This has also led to a rise in the photovoltage, which is attributed to the decrease of charge recombination. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80%, a short-circuit photocurrent density (Jsc) of 9.78 mA cm−2, an open-circuit photovoltage (Voc) of 605 mV, and a fill factor (FF) of 0.69, corresponding to an overall conversion efficiency of 4.14% under standard global AM 1.5 solar light condition. This work suggests that the metal-free dyes based on a DPP core are promising candidates for improvement of the performance of DSSCs.