Tert-butyl Pyridine Research Articles

Effect of D-limonene additive in copper redox-based quasi-solid-state electrolytes on the performance of dye-sensitized solar cells

In dye-sensitized solar cells (DSSCs), the copper redox mediator has been proven to enhance power conversion efficiency (PCE) due to the fairly low driving force for dye regeneration. In this work, we prepared six blended biopolymer-based electrolytes (E1 to E6) to regenerate N3 Dye absorbed in TiO2 for dye-sensitized solar cell application. The regeneration behavior of three different electron-withdrawing substituents on 2-(pyridin-2-yl)− 1 H-benzo[d]imidazole ligands coordinated with copper metal, its forms [Cu(mpimb)2]1+/2+ (methyl 4-((2-(pyridin-2-yl)− 1 H-benzo[d]imidazol-1-yl)methyl) benzoate), [Cu(pbimb)2]1+/2+ (4-((2-(pyridin-2-yl)− 1 H- benzo[d]imidazol-1-yl)methyl) benzonitrile) and [Cu(ptpbi)2]1+/2+ (2-(pyridin-2-yl)− 1(4-(trifluoromethyl)benzyl)− 1 H-benzo[d]imidazole). Commencing their electrochemical and photophysical properties determines the molecular orbital energy level of the complex. A quasi-solid-state electrolyte (QSSE) medium is blended in a biopolymer host (pectin and 2-hydroxyethylcellulose). Additionally, a comparison study has been performed between commercially available pyridine-based-additive [tert-butyl pyridine (TBP)], and a bio-organic compound extracted from orange peel waste (1-methyl-4-(prop-1-en-2-yl) cyclohex-1-ene (limonene)) used as an additive material. Using these newly designed copper redox mediators and additives, the six sets of DSSCs devices has constructed. The cell structure is assembled as TiO2/N3 dye/electrolyte (E1 to E6)/Pt. Among the fabricated devices, C1 and C2 redox couples [Cu(ptpbi)2]1+/2+ having CF3 substituent exhibit maximum Voc and Jsc. Interestingly, the device with limonene additive exhibited PCE up to 4.4 %, whereas with TBP, it showed 4.0 % efficiency. The PCE results of the C2 device sustained some electrochemical factors such as Bulk Resistance (Rb =142.0 Ω), Recombination Resistance (Rrec = 191.4 Ω), Charge Transfer Resistance (Rct = 98.84 Ω), Chemical capacitance (Cμ = 7.882 μF), Ionic Conductivity (σ = 2.816 ×10−04 S cm−1), electron lifetime (τn = 16.24 μs), Diffusion length (Ln =1.39 × 10−01 mm).

Complementary Adsorption of Binary Levelers for Highly Uniform Cu Micropillars.

Highly uniform Cu micropillars were electrodeposited on a Cu seed layer in a micropatterned photoresist in the presence of binary levelers containing pyrrolidine and pyridine functional groups. The adsorption behaviors of binary levelers, i.e., 3-hydroxy-6-(tert-butyl)pyridine and pyridinium tribromide in an electroplating bath were investigated by chronopotentiometry with sequential injection of levelers and linear sweep voltammetry with a rotating disk electrode. From electrochemical analysis, pyridinium tribromide composed of a positively charged pyridine ring was strongly adsorbed on the Cu seed surface, relative to 3-hydroxy-6-(tert-butyl)pyridine. Additional microscopy, surface roughness, and nitrogen concentration analyses revealed that the binary levelers were preferentially adsorbed on the center and the edge region of the Cu seed, resulting in a uniform Cu pillar profile. The possible mechanism of highly uniform Cu pillar deposition was discussed in terms of the adsorption behaviors of the levelers dependent on their molecular structures.

Pyridine Controlled Tin Perovskite Crystallization.

Controlling the crystallization of perovskite in a thin film is essential in making solar cells. Processing tin-based perovskite films from solution is challenging because of the uncontrollable faster crystallization of tin than the most used lead perovskite. The best performing devices are prepared by depositing perovskite from dimethyl sulfoxide because it slows down the assembly of the tin–iodine network that forms perovskite. However, while dimethyl sulfoxide seems the best solution to control the crystallization, it oxidizes tin during processing. This work demonstrates that 4-(tert-butyl) pyridine can replace dimethyl sulfoxide to control the crystallization without oxidizing tin. We show that tin perovskite films deposited from pyridine have a 1 order of magnitude lower defect density, which promotes charge mobility and photovoltaic performance.

Novel Dispersion of 1D Nanofiber Fillers for Fast Ion-Conducting Nanocomposite Polymer Blend Quasi-Solid Electrolytes for Dye-Sensitized Solar Cells.

Electrospun nanocomposite polymer blend poly(vinylidene difluoride-co-hexafluoropropylene) (PVDF-HFP)/poly(methyl methacrylate) (PMMA) membranes with a novel dispersion of x wt % of one-dimensional (1D) TiO2 nanofiber fillers (x = 0.0–0.8 in steps of 0.2) were developed using the electrospinning technique. The developed nanocomposite polymer membranes were activated using various redox agents such as LiI, NaI, KI, and tetrabutyl ammonium iodide (TBAI). Introduction of the 1D TiO2 nanofiber fillers improves the amorphous nature of the blended polymer membrane, as confirmed through X-ray diffraction (XRD) and Fourier transform infrared (FTIR), and yielded an electrolyte uptake of over 480% for a 6 wt % TiO2 nanofiber filler-dispersed sample. PVDF-HFP/PMMA–1D 6 wt % TiO2 nanofiber fillers with the LiI-based redox electrolyte provided a high conductivity of 2.80 × 10–2 S cm–1 and a power conversion efficiency (PCE) of 8.08% to their fabricated dye-sensitized solar cells (DSSCs). The observed better ionic conductivity and efficiency of the fabricated DSSCs could be due to the faster movement of the smaller-ionic-radius (Li) ions entrapped inside the amorphous polymer. This enhanced mobility of ions in the quasi-solid electrolyte leads to faster regeneration of the depleting electrons in the photoanode, resulting in improved efficiency. Further, the achieved high conductivity was analyzed in terms of the dynamics and relaxation mechanisms involved by the ionic charge carriers with complex impedance spectroscopy using a random barrier model and Havriliak–Negami formulation. It was observed that the high-conducting PVDF-HFP/PMMA–1D 6 wt % TiO2 nanofiber fillers with LiI-based redox electrolyte show better ac conductivity parameters such as a σ of 5.82 × 10–2 S cm–1, ωe (12685 rad s–1), τe (0.909 × 10–4 s), and n (0.578). Also, dielectric studies revealed that the high-conducting sample has a higher dielectric constant and subsequently high loss. The J–V characteristics were studied using the equivalent circuit of a single-diode model, and the parameters influencing the photovoltaic performance were determined by Symbiotic Organisms Search (SOS) algorithm. The results suggest that the high-efficient sample possesses a minimum series resistance of 1.33 Ω and a maximum shunt resistance of 997 Ω. Hence, the highest-conducting electrospun-blended polymeric nanocomposite (PVDF-HFP–PMMA–6 wt % TiO2 nanofiber fillers) with LiI-based redox agent and tert-butyl pyridine (TBP) additive as the polymer quasi-solid electrolyte nanofibrous membrane can be a better electrolyte for high-performance dye-sensitized solar cell applications.

Reinforcing self-healing and Re-processable ionomers with carbon black: An investigation on the network structure and molecular mobility

While most self-healing elastomers are mechanically weak, using the most commonly used carbon black (CB) to reinforce self-healing elastomers has not been reported. The possible reason is that the introduction of carbon black will cause complex changes in molecular dynamics, which leads to unpredictable self-healing effects. Herein, carbon black is introduced into a self-healing ionomer based on brominated butyl rubber (BIIR) grafted with tert-butyl pyridine (BP). Interestingly, the hierarchical microstructure and multilevel molecular dynamics of ionomers are well regulated by the strong interfacial π-cation interactions between CB and ionic aggregates. The strong interfacial interaction leads to high content of bound rubber, uniform dispersion of CB and compact physical network. Although such structural change has negligible influence on the segmental motion, it enhances the relaxation time and activation energy of ionic clusters, and thus endows the ionomer with high mechanical properties. Meanwhile, the structural change leads to higher relaxation temperature, thereby increasing the self-healing temperature. Despite this fact, the healing efficiency can still be regulated between 50% and 100%, depending on the filler content and temperature. Moreover, the CB reinforced ionomer is re-processable and recyclable. This study demonstrates that CB reinforcement is feasible to improve the mechanical properties of self-healing elastomers.

Oxyfunctionalization of Alkanes Based on a Tricobalt(II)-Substituted Dawson-Type Rhenium Carbonyl Derivative as Catalyst.

POM-supported metal carbonyl derivatives (PMCDs) represent a family of tremendous potential catalysts owing to their peculiar physical and chemical properties. Yet low-valence transition metal-substituted Dawson-type PMCD catalysts are uncommon. Hence, we synthesized a tricobalt-substituted PMCDs by conventional aqueous solution method, [Na(H2O)5](NH4)7[P2W15O56Co3(H2O)3(OH)3Re(CO)3]·13H2O (1), and characterized by single crystal X-ray diffraction crystallography, IR, and thermogravimetric analyses (TGA), etc. The obtained compound 1 was employed as a catalyst for the oxidation of diphenylmethane (DPM) to benzophenone, giving 96.8% yield in the presence of tert-butyl hydroperoxide (TBHP) and pyridine. The control experiments indicate that Co metal ion plays an important role in the catalytic reactions. As a side note, the electrospray ionization mass spectrometry (ESI-MS) and UV spectroscopy showed that 1 can retain its integrity in solution, and magnetic measurements indicated that 1 exhibited a weaker ferromagnetic interaction at low temperature.

Above 800 mV Open-Circuit Voltage in Solid-State Photovoltaic Devices Using Phosphonium Cation-Based Solid Ionic Conductors.

Here, we report phosphonium-based two solid ionic conductors (SICs), namely, triphenylphosphonium methyl iodide (TPPMeI) and triphenylphosphonium iodide (TPPHI), prepared via simple protocol at room temperature and were used as an electrolyte for solid-state photovoltaic devices (ss-PVDs) with open-circuit voltage (Voc) exceeding 800 mV. Here, for the first time, detailed electrochemical investigations with theoretical aspects of phosphonium electrolytes were conducted, where PVDs prepared from these SICs, TPPMeI, showed the highest power conversion efficiency (PCE) of 4.08% with a Voc of 810 mV. However, this performance was further improved up to the PCE of 6.71% with 824 mV of Voc in the presence of additives like LiI and tert-butyl pyridine. This work leads to find the best alternative of liquid and quaternary ammonium ion-based electrolytes that suffers from problems like lower Voc (<800 mV) and stability, leakage, etc.

Light-induced electrolyte improvement in cobalt tris(bipyridine)-mediated dye-sensitized solar cells

We observe a light-induced performance improvement in Co(ii/iii)-mediated DSSCs, and attribute this to an irreversible light effect on the electrolyte system containing Co(iii) together with tert-butylpyridine (TBP).

Low cost and efficient hetero-anthracene based small organic hole transporting materials for solid state photoelectrochemical cells

A series of low cost phenothiazine (PTZ) based small organic hole transporting materials (OHTMs) with high conductivity, hole mobility and low crystallinity were synthesized and systematically investigated for solid state photoelectrochemical cells/dye sensitized solar cells (DSSCs). Thermal, optical, photoelectrical and electrochemical properties of all OHTMs were evaluated using thermal techniques, cyclic voltammetry (CV), UV–vis absorption and other techniques. Density functional theory (DFT) was used to calculate optical and electrochemical properties of OHTMs and compared with experimental data. Role of these OHTMs in solid state photoelectrochemical cells with metal-free carbazole dye, SK3 in presence of additives like lithium bis(trifluoromethyl sulfonyl)imide salt (LiTFSI) and tert-butyl pyridine (TBP) are discussed along with the thickness of photoanode. In order to take an insight into photovoltaic performance, electron transfer kinetics and electron recombination in the OHTMs with different thickness of TiO2 thin film based ss-DSSCs were characterized by I–V, electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD). The hole mobility, conductivity and photovoltaic performance of OHTMs are comparable with commercially available Spiro-OMeTAD. The highest power conversion efficiency (PCE), 4.91% is achieved from thiophene substituted (at 3,6 positions) phenothiazine based SJH-11, is comparable with reference device incorporating Spiro-OMeTAD as HTM with SK3 sensitizer. All the ss-DSSCs with OHTMs exhibit good long-term stability under 1 sun illumination and ambient humidity conditions. The results are promising and have scope for improvement upon optimization of substitution at 3 and 6 positions of PTZ central/core moiety.

4-tert-Butylpyridine Free Hole Transport Materials for Efficient Perovskite Solar Cells: A New Strategy to Enhance the Environmental and Thermal Stability

Organic semiconductors as hole transport materials (HTMs) often require additives, such as LiTFSI and tert-butylpyridine (TBP), in order to enhance their hole conductivities. However, the combination of lithium salts and TBP leads to significant HTM morphological deformation and poor device stability. Here we have successfully applied tetrabutylammonium (TBA) salts to replace both LiTFSI and TBP. A high power conversion efficiency of 18.4% has been achieved for the devices with TBATFSI, which is higher than the control devices with LiTFSI and TBP (18.1%). We also found that the anions in the TBA salts play important roles in the hole conductivity and uniformity of the HTM layer, as well as the hysteresis of the devices. More importantly, the devices with TBATFSI and TBAPF6 demonstrated significantly enhanced environmental and thermal stability. This new strategy of using TBA salts is promising for developing stable organic HTM thin films for solar cell applications.

Molecular Control of the Band Edge Movement and the Recombination Process in Donor–Acceptor Hemicyanine-Sensitized Solar Cells

The presence of downward shift in the band edge and the recombination reactions in the hemicyanine-sensitized solar cell reduces the open-circuit potential (VOC) and the short-circuit current density (JSC), which in turn decreases the dye cell performance. Choosing either an electrolyte possessing minimum overpotentials or a systematic dye design which can efficiently suppress the diffusion of charged species toward the TiO2 can improve the overall power conversion efficiency (PCE). Here, a series of donor–acceptor (D-A) hemicyanine dyes were synthesized utilizing a planar heterotriangulene (HT) or triphenylamine (TPA) donor and alkyl-functionalized indolium carboxylic acid acceptor unit. By introducing strong HT donor instead of TPA, the photophysical, and electrochemical properties of D-A dyes are significantly modulated. The strong donor nature of HT and effective passivation of surface by hydrophobic alkyl chains close to the anchoring group for NC3 dye exhibits an average PCE of 4.34% with a VOC of 0.416 V, JSC of 20.04 mA cm–2, and fill factor (ff) of 52.03% under simulated AM 1.5G illumination (100 mW cm–2) without 3α,7α-dihydroxy-5β-cholic acid coadsorbent (CDCA). The intrinsic dipole of the hemicyanine dye and the presence of Li+ ions in iodide/triiodide redox couple without tert-butylpyridine (TBP) additive induces a downward shift in conduction band edge (ECB) of TiO2. By rational molecular design, the extend of shift in ECB is controlled and enhanced the VOC. Electrochemical impedance spectroscopy (EIS) studies revealed the high charge transfer resistance (Rct) and long lifetime (τ) of injected electrons in HT-based dyes than that of TPA derivatives, which provide insight into the passivation of Li+ and I– ions by current D-A dye design possessing alkyl functionalities to increase both the JSC and VOC.

Efficiency Enhancement of Hybrid Perovskite Solar Cells with MEH-PPV Hole-Transporting Layers.

In this study, hybrid perovskite solar cells are fabricated using poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(3-hexylthiophene-2,5-diyl) (P3HT) as dopant-free hole-transporting materials (HTMs), and two solution processes (one- and two-step methods, respectively) for preparing methylammonium lead iodide perovskite. By optimizing the concentrations and solvents of MEH-PPV solutions, a power conversion efficiency of 9.65% with hysteresis-less performance is achieved, while the device with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′spirobifluorene (Spiro-OMeTAD) doped with lithium salts and tert-butylpyridine (TBP) exhibits an efficiency of 13.38%. This result shows that non-doped MEH-PPV is a suitable, low-cost HTM for efficient polymer-based perovskite solar cells. The effect of different morphologies of methylammonium lead iodide perovskite on conversion efficiency is also investigated by incident photon-to-electron conversion efficiency (IPCE) curves and electrochemical impedance spectroscopy (EIS).

Role of the Dopants on the Morphological and Transport Properties of Spiro-MeOTAD Hole Transport Layer

The use of a solid hole transport layer (HTL) was transformational for the recent perovskite solar cell (PSC) revolution in solar energy technology. Often high efficiency PSC devices employ heavily doped hole transport materials such as spiro-MeOTAD. Independent of HTL chemistry, lithium-bis-trifluoromethanesulfonyl-imide (LiTFSI) and tert-butylpyridine (TBP) are commonly used as additives in HTL formulations for PSCs. LiTFSI and TBP were originally optimized for dye-sensitized solar cells, where their roles have been extensively studied. However, in the case of PSCs, the function of TBP is not clearly understood. In this study, properties of the HTL composite deposited on flat silicon substrates were systematically measured at several length scales, e.g., macroscopically (profilometry, 4-point probe conductivity, and thermogravimetry-differential thermal analysis), microscopically, and at the nanoscale to investigate film morphology, conductivity, and dopant distribution. Microscopic distributions of spi...

Investigation of the Effects of Li+-doping on the Photovoltaic Performance of SnO2-based Quasi-Solid-State Dye-Sensitized Solar Cells

SnO2 has high electron mobility and low photocatalytic action compared to TiO2. However, SnO2-based DSCs have shown limited performance due to their high electron recombination. Recombination can be suppressed to a certain extent using Li+ as an electron screening layer on the SnO2 surface. Li+ ions are adsorbed on to the SnO2 surface as the surface is negatively charged by O2- sites and –OH groups. This will shift the conduction band edge of SnO2 towards more positive direction thus increasing the electron harvesting efficiency of the device. Also, recombination occurring at the FTO/electrolyte interface can be reduced using tert-butylpyridine (TBP) as a gel electrolyte-additive as it covers the uncovered FTO surface. The gel electrolyte showed 4.7 x 10-3 S cm-1 of ionic conductivity and 4.91 x 10-6 cm2 s-1 of diffusivity for triiodide ions. These values agreed with the reported values in literature. In this study, the DSCs were fabricated with the device structure of FTO/Li+-doped SnO2/D358 dye/gel electrolyte/lightly platinized FTO counter electrode. The device containing 1:0.06 molar ratio of SnO2 to Li+ gave an efficiency of 4.3% while undoped device gave 1.6%. Li+-doped system showed 30% increase in current density and 61% increase in VOC.

Charge recombination losses in thiophene-substituted porphyrin dye-sensitized solar cells

Two new porphyrins that incorporate thiophene substituents as spacers between the conjugated porphyrin core and the anchoring cyanoacrylate group have been synthesised. The two dyes differ in the number of thiophene bridges; porphyrin 1a has only one thiophene group and porphyrin 1b has two thiophene rings connected by a double bond. The measured light-to-energy conversion efficiencies in 1a and 1b were assessed using two different electrolytes, LP1 and LP2, which differ in the presence of tert-butyl pyridine in LP1. An efficiency of 6% under standard measurement conditions has been achieved for 1a + LP1. However, for porphyrin 1b the use of electrolyte LP1 led to lower efficiencies and a value of approximately 4% was obtained. The differences between the two types of solar cells and the electrolytes have been studied in-depth using photo-induced time-resolved techniques such as CE (Charge Extraction) and TPV (Transient PhotoVoltage).

Carbocation Lewis Acid Catalyzed Redox-Neutral α-C(sp3)H Arylation of Amines

The α-substituted nitrogen-containing heterocycles (N-heterocycles) like tetrahydroisoquinolines (THIQs) and piperidines are common in nature and are present as the key functional group in bioactive and pharmacologically active compounds. The two traditional approaches for the synthesis of α-substituted N-heterocycles are Pictet-Spengler condensa- tion and hydrogenation of the α-substituted cyclic imines. Recently, direct C(sp 3 )-H functionalization of N-heterocycles with various nucleophiles catalyzed by transition metal complex under the oxidants presents an atom-economic protocol without prior installation of activating group. However, new catalytic strategy or catalysts are still desirable in order to further address the use of excess oxidants and expensive transition metal complex. Stable carbocations, such as tritylium ions, have been widely used as organic Lewis acid catalysts and reagents in organic synthesis. In our studies, it was found that tritylium salts (Ph3C)(BArF) (10 mol%) in situ generated by Ph3CBr (0.02 mmol) and NaBArF (0.02 mmol) could promote the three com- ponent redox-neutral α-arylation of amines reaction with tetrahydroisoquinoline 2 (0.3 mmol), aldehyde 3 (0.2 mmol) and indole 4 (0.3 mmol) in toluene (1.0 mL) to afford the desired α-substituted N-heterocyclic compounds 5 in good yields (up to 99% yield) at ambient temperature to 50 ℃. To our satisfaction, a variety of differently substituted indoles 4a~4i could work well with tetrahydroisoquinoline 2 and 2,6-dichlorobenzaldehyde 3a to provide the corresponding α-substituted N-heterocyclic compounds 5a~5i in good to excellent yields at room temperature. When other substituted benzaldehydes 3b~3f were used, the reactions could also proceed smoothly to give the compounds 5j~5o with moderate yield (up to 66% yield) at 50 ℃. Moreover, we have also developed redox-neutral α-arylation of tetrahydroisoquinoline 2 with other aromatic nucleophile such as substituted phenol, β-naphthol and pyrrole under the optimal reaction conditions. Importantly, the model reaction, conducted in the presence of Na2CO3(1.0 equiv.) or 2,6-bis(tert-butyl) pyridine (0.5 equiv.) at room temperature in toluene also proceeded smoothly to give the desired adduct 5a with comparable yields (82% and 92% yield, respectively), which could exclude the possibility of free acid catalysis in this reaction.

Theoretical Evaluation of Electron Transport in Aniline Tetramer-based Dye-sensitized Solar Cells

The essential electron transporting function of EPAT in phenyl-capped aniline tetramer (EPAT)/tert-butylpyridine (TBP)-based dye-sensitized solar cells (DSC) is evaluated by density functional theory (DFT). DFT-based molecular modeling coupled with molecular mechanics optimization reveal that EPAT molecules in-situ self-organizes to dimeric molecular complexes through van der Waals and Coulombic interactions. TBP molecules assist to form TBP-hydrogen-bonded EPAT complexes, (EPAT-H-TBP)2 and (EPAT-H-2TBP)2. The molecular complexes have stacked structures as well, and the electron-accepted states of radical anions, (EPAT-H-TBP)2.− and (EPAT-H-2TBP)2.− give narrow band gaps (0.26∼0.28eV), and the singly occupied molecular orbitals (SOMO) are comparable in configurations with the lowest unoccupied molecular orbital (LUMO). We understand that electron in photo-irradiated EPAT/TBP phase should transport effectively by hopping on SOMO of (EPAT-H-TBP)2.− and (EPAT-H-2TBP)2.−.

A novel metal–organic gel based electrolyte for efficient quasi-solid-state dye-sensitized solar cells

Metal–organic skeleton based gel electrolytes are prepared for the first time for high efficiency quasi-solid-state DSSCs. The gel electrolytes feature in their sponge-like porous matrix of a metal–organic gel (MOG) assembled by coordination of Al3+ and 1,3,5-benzenetricarboxylate (H3BTC), which can provide an excellent ability to accommodate electrolyte ingredients, thus largely preserving the properties of the liquid electrolyte. Meanwhile, the MOG electrolyte can well penetrate into the photoanode film to ensure a good interfacial contact. The effects of the concentration of active species in the MOG electrolyte on the photoelectrical performances are investigated. On increasing the concentration, Jsc of gel-state cells improves gradually due to the enhanced I−/I3− redox couple content, while Voc undergoes an increase first but decreases subsequently. The synergistic function of cations (such as Al3+, Li+, etc.) and tert-butylpyridine (TBP), which can induce a conductive band (CB) shift of the TiO2 photoanode and affect the electron recombination, may contribute to the variation of Voc. By optimizing the composition of the gel electrolyte, a high conversion efficiency of over 8.60% can be obtained, which is a little lower than that of a liquid-state cell (9.13%). This research study will open up a new way to fabricate quasi-solid-state DSSCs with high efficiency.

Cross-Linkable Molecular Hole-Transporting Semiconductor for Solid-State Dye-Sensitized Solar Cells

In this study, we investigate the use of a cross-linkable organosilane semiconductor, 4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi2), as a hole-transporting material (HTM) for solid-state dye-sensitized solar cells (ssDSSCs) using the standard amphiphilic Z907 dye which is compatible with organic HTM deposition. The properties and performance of the resulting cells are then compared and contrasted with the ones based on poly(3-hexylthiophene) (P3HT), a conventional polymeric HTM, but with rather limited pore-filling capacity. When processed under N2, TPDSi2 exhibits excellent infiltration into the mesoporous TiO2 layer and thus enables the fabrication of relatively thick devices (∼5 μm) for efficient photon harvesting. When exposed to ambient atmosphere (RHamb ∼ 20%), TPDSi2 readily undergoes cross-linking to afford a rigid, thermally stable hole-transporting layer. In addition, the effect of tert-butylpyridine (TBP) and lithium bis(trifluoromethylsulfonyl)imide salt (Li-TFSI) additi...

Panchromatic Light Harvesting and Hot Electron Injection by Ru(II) Dipyrrinates on a TiO2 Surface

Three Ru(II) dipyrrinate complexes, [Ru(bpy)2(3-TDP)](PF6) (1), [Ru(H2dcbpy)(Hdcbpy)(3-TDP)] (2), and [Ru(H2dcbpy)(Hdcbpy)(TPADP)] (3) (bpy = 2,2′-bipyridine; dcbpy = 4,4′-dicarboxylato-2,2′-bipyridine; 3-TDP = 3-thienyl-dipyrrinate; TPADP = triphenylamino-dipyrrinate), have been synthesized and characterized by electrochemical and photophysical methods as well as by theoretical electronic structure calculations on the DFT level. The complexes exhibit panchromatic light harvesting due to complementary ligand-based absorption around 450 nm and metal-to-ligand charge transfer (MLCT) absorption around 530 nm. Complexes 2 and 3 have been investigated as potential sensitizers for the dye-sensitized solar cell (DSSC). Time-dependent DFT calculations reveal the preferential localization of an excited-state electron on the H2dcbpy ligands, leading to a favorable scenario for electron injection from these anchoring ligands into TiO2. Solution-phase transient absorption spectroscopy was used to follow the excited state dynamics of methyl-ester derivatives of 2 and 3. Excitation with a 400-nm laser pulse resulted in two bleaches centered at 460 and 540 nm and corresponding to the ligand-based and MLCT transitions, respectively. A rapid 2 ps loss of the ligand based bleach corresponded with a growth of the MLCT bleach that were interpreted as the result of vibrational relaxation between metal-centered and ligand-centered frontier orbitals. The electron-injection kinetics were studied on dyes 2 and 3 anchored on the TiO2 surface. The excited state electron-injection yield and incident photon-to-current efficiency were dramatically suppressed by addition of tert-butylpyridine (TBP), indicating that the lowest excited state was positioned close in energy to the TiO2 acceptor states. Nevertheless, the injection yield measured with 416-nm excitation was less sensitive to the TBP concentration than that measured with 532-nm excitation, thus suggesting the possibility of hot-electron injection from the upper excited states generated by the ligand-based excitations. Based on the findings of this study, a pathway is proposed for improving the electron-injection yield of Ru-dipyrrinate dyes and increasing the power-conversion efficiency of the DSSC incorporating these dyes.