Groups For Dye-sensitized Solar Cells Research Articles

Investigation of heterocyclic azo dyes for dye-sensitized solar cells and non-linear optical properties: Synthesis and in-silico studies

Four thiophene-based donor-π-azo-acceptor dyes were designed and synthesized with benzoic and salicylic acids anchoring groups for dye-sensitized solar cells (DSSC). The results show that the orientation of the secondary donor significantly affects molecular planarity, which in turn affects the characteristics of charge transfer (CT) inside the backbones of thiophene-azo-benzoic or salicylic acids. These results have been confirmed by the time-dependent density functional theory (TD-DFT) study, which shows that the dyes' vertical absorption maximum increases as the secondary donors' providing strength increases. Photovoltaic parameters indicate an increase in DSSC performance from PG9 to PG12. Moreover, dye@TiO2 cluster investigations suggest that these dyes could combine with TiO2 to cause dye@TiO2 cluster absorbance to shift red.The synthesis of PG9 to PG12 confirms theoretical predictions, with initial absorption in dimethylformamide (DMF) and energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) following a pattern like that seen in density functional theory (DFT) investigations. According to TGA data, PG9 to PG12 have exceptional thermal stability, making them suitable for DSSCs. The built-in DSSCs had varying efficiencies; PG10 had the highest efficiency at 4.73 ± 0.1, and PG12 had the lowest at 1.72 ± 0.1. According to the theoretical and practical DSSC results, secondary donors are essential in defining molecular properties and device performance.

Introduction thioindigo as new high stability unit in Ru-complex for DSSCs: Theoretical and photovoltaic investigation

New Ru-dyes were designed with indoline and thioindigo groups for dye-sensitized solar cells (DSSCs). Thioindigo was used as an effective substitute for improving fastness properties, and the synthesis efficiency of dyes 1 and 2 was 78 and 82 %, respectively. Cyanoacrylic acid is a suitable electron-withdrawing group in the preparation of photosensitizers, which improved the conversion efficiency by about 88 % in this research. The optical response of the complexes was evaluated theoretically and experimentally. The presence of cyano groups effectively bonds with the semiconductor layer, resulting in a better photovoltaic response. Furthermore, the prepared complexes have two types of electron withdrawing groups, carboxylic acid and cyanoacrylic acid, which yield 3.29 % and 6.23 % efficiency, respectively. In addition, co-sensitization using two prepared complexes and N719 was studied and analyzed. The efficiency of DSSCs prepared with N719 and complexes 1 and 2 was 8.10 and 9.49 %, respectively.

Visible-Light-Active Unsymmetrical Squaraine Dyes with Pyridyl Anchoring Groups for Dye-Sensitized Solar Cells.

Visible-light-active alkyl group-wrapped unsymmetrical squaraine dyes SD1-SD3 were synthesized, featuring an indoline donor and pyridine and carboxylic acid anchoring groups. Their photophysical, electrochemical, and photovoltaic characteristics were examined by fabricating a dye-sensitized solar cell (DSSC) device. Both carboxylic acid and pyridine anchoring groups containing squaraine dyes SD3 and SD2 possess similar photophysical and electrochemical characteristics. However, their photovoltaic performances were completely different. The SD3 dye with the carboxylic acid anchoring group displayed a DSSC device efficiency of 7.20% (VOC 0.81 V; JSC 12.29 mA/cm2) using iodolyte (I-/I3-) electrolyte, compared to SD1 (VOC 0.659 V; JSC 4.97 mA/cm2; and η - 2.34%) and SD2 (VOC 0.629 V; JSC 1.68 mA/cm2; and η - 0.84%), which were featured with pyridyl anchoring groups. These results were attributed to dye loading on the Lewis and Brønsted acidic sites of TiO2 and the importance of aggregated structures for photocurrent generation. In the incident photon-to-current efficiency (IPCE) analysis, SD1 dye-sensitized devices exhibited photocurrent generation from both monomeric and aggregated dyes on the TiO2 surface. In contrast, SD2 showed photocurrent generation solely from aggregated states. Despite the introduction of long alkyl chains to reduce dye aggregation and charge recombination, the results indicated preferential charge injection from only the aggregated SD2 dye on TiO2. Fluorescence-quenching experiments indicated an efficient charge transfer from the aggregated SD2 dye to TiO2 compared to that of the monomeric dye. Cosensitization, a method to enhance the light-harvesting efficiency and photocurrent generation in DSSCs, was explored by simultaneously cosensitizing pyridyl-based dyes (SD1 and SD2) with a blue-colored carboxylic acid-based squaraine dye SD4. IPCE analysis demonstrated that both SD1 and SD4 contributed to generating a photocurrent of 9.11 mA/cm2. The sequential cosensitization of SD1 and SD4 with the coadsorbent CDCA showed the highest performance, with a VOC of 0.663 V, a JSC of 11.43 mA/cm2, and an efficiency (η) of 5.20%.

Energy level tuning of push-pull porphyrin sensitizer by trifluoromethyl group for dye-sensitized solar cells

We have introduced trifluoromethyl groups into meta-positions of two meso-phenyl rings of a push-pull-type porphyrin dye (ZnP-CF[Formula: see text] to modulate the energy levels of the porphyrin dye for dye-sensitized solar cells (DSSCs). The light-harvesting ability of ZnP-CF[Formula: see text] is almost comparable to those of reference porphyrins where the trifluoromethyl groups are replaced with methyl (ZnP-CH[Formula: see text] or tert-butyl groups (YD2). We revealed that the introduction of the electron-withdrawing trifluoromethyl groups is effective to lower the excited-state oxidation potential of the porphyrin (–0.80 V vs NHE), which is consistent with the theoretical calculation. Meanwhile, DSSCs with ZnP-CF[Formula: see text] exhibited a lower power conversion efficiency ([Formula: see text] of 5.95% than DSSCs with ZnP-CH[Formula: see text] ([Formula: see text] = 7.33%) and YD2 ([Formula: see text] = 8.97%) because of the severe aggregation tendency of ZnP-CF[Formula: see text] arising from the trifluoromethyl groups. In addition, the insufficient steric bulkiness of the trifluoromethyl and methyl groups relative to tert-butyl groups would result in the lower short circuit current and open circuit voltage for ZnP-CF[Formula: see text] and ZnP-CH[Formula: see text] due to fast charge recombination between electrons in the conduction band of TiO2 and I[Formula: see text]in the electrolyte solution. Overall, introducing both trifluoromethyl groups and bulky substituents into a porphyrin core would be necessary to boost cell performance.

Introduction of new configuration of dyes contain indigo group for dye-sensitized solar cells: DFT and photovoltaic study

The chemical structure engineering of photosensitizers has a major role in photovoltaic devices such as dye-sensitized solar cells. Thus, a novel dye system was designed and prepared with contained indigo group for increasing light resistance as well as cyanoacrylic acid for improving the interaction. All intermediates and dyes were purified and analyzed using FTIR, HNMR, CHN and UV–Visible. The results showed that all the expected dye chemical structures have been achieved. Two semiconductors namely titanium dioxide and Na-doped titanium dioxide, were coated with the synthesized dye to prepare photoanode. All prepared samples illustrated blue shift in UV–Visible due to H-aggregation of dyes on the semiconductor. The energy level of dyes was investigated by Cyclic Voltammetry technique and DFT calculation. The results confirmed the possibility of using dyes in the structure of dye-sensitized solar cells. All prepared dyes were utilized as photosensitizers in dye-sensitized solar cells. The efficiency of Dye 6 in dye-sensitized solar cells based on titanium dioxide and its Na-doped derivative was 7.17% and 7.56%, respectively. Optical devices based on Na-doped semiconductor showed superior performance to those based on pristine titanium dioxide.

Pyrimidine-Based Push–Pull Systems with a New Anchoring Amide Group for Dye-Sensitized Solar Cells

New donor–π–acceptor pyrimidine-based dyes comprising an amide moiety as an anchoring group have been designed. The dyes were synthesized by sequential procedures based on the microwave-assisted Suzuki cross-coupling and bromination reactions. The influence of the dye structure and length of π-linker on the photophysical and electrochemical properties and on the photovoltaic effectiveness of dye-sensitized solar cells was investigated. An increase in efficiency with a decrease in the length of π-linker was revealed. The D1 dye with only one 2,5-thienylene-linker provided the highest power conversion efficiency among the fabricated dye sensitized solar cells.

Comparative studies of new pyranylidene-based sensitizers bearing single or double anchoring groups for dye-sensitized solar cells

Mono- and di-anchoring γ-pyranylidene-based organic dyes featuring D–π–A and D–(π–A)2 architectures have been engineered as sensitizers for applications in Dye-Sensitized Solar Cells (DSSCs). Their photophysical, electrochemical and photovoltaic properties were further investigated. TD-DFT calculations were performed to rationalize the trends observed in the optical and electrochemical properties of the dyes. The investigation of the photovoltaic performances of this series of new dyes provided structure–property relationships where their Power Conversion Efficiencies (PCE) could be correlated to structural features, such as the length of the π-conjugated spacer, the nature of the substituents on the pyranylidene electron donor moiety and the number of anchoring groups. Dye-Sensitized Solar Cells based on mono-anchoring dyes were more efficient than the corresponding cells based on di-anchoring analogues due to high dye loading. The highest Power Conversion Efficiency of 5.23% was achieved with the mono-anchoring 17a dye containing t-butyl substituent groups on the pyranylidene fragment and with one thienyl π-conjugated spacer.

Push-Pull Zinc Phthalocyanine Bearing Hexa-Tertiary Substituted Carbazolyl Donor Groups for Dye-Sensitized Solar Cells.

An asymmetrical, push–pull phthalocyanine bearing bulky tert-butylcarbazolyl moieties as electron donor and carboxylic acid as anchoring group was synthetized and tested as a photosensitizer in dye-sensitized solar cells (DSSC). The new photosensitizer was characterized by 1H and 13C NMR, UV–Vis and mass spectrometry. The bulky tert-butylcarbazolyl moieties avoid the aggregation of the phthalocyanine dye. DFT studies indicate that the HOMO is delocalized throughout the π-electron system of the substituted phthalocyanine and the LUMO is located on the core of the molecule with a sizable electron density distribution on carboxyl groups. The new dye has been used as a photosensitizer in transparent and opaque dye-sensitized solar cells, which exhibit poor efficiencies related to a low Jsc.

Porphyrin dyes bearing heterocyclic anchoring groups for dye-sensitized solar cells with enhanced efficiency and long-term stability: Further optimization of champion porphyrin dye SM315

In order to further enhance the long-term stability of porphyrin-based dye- sensitized solar cells (DSSCs) without losing their high efficiency, a serious of porphyrin sensitizers based on the champion dye SM315 but differing in the anchoring groups were theoretically investigated. Compared with SM315 with carboxylic acid anchoring groups, our results demonstrate that porphyrin dyes with hydantoin and barbituric acid anchoring groups exhibit stronger adsorption stability because of the larger orbital interactions between the dye and the semiconductor surface, according to the energy decomposition analysis. Furthermore, porphyrin dyes with these two heterocyclic anchoring groups can also display a superior or comparable charge separation and injection, light harvesting ability and conduction band energy shift, which are the key factors that affect the performance of DSSCs. These results highlight the great potential hydantoin and barbituric acid anchoring groups possess as effective alternatives to carboxylic acid anchoring groups for porphyrin dyes, which could yield an enhanced efficiency and long-term stability and worthy of being experimentally synthesized.

Density functional theory study on two D-π-A-type organic dyes containing different anchoring groups for dye-sensitized solar cells

The electronic structure and absorption spectra of two D-π-A-type organic dyes with different anchoring groups have been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The effect of anchoring groups on the electronic absorption of the free dyes on (TiO2)9 has been studied for the two carbazole dyes (MK1 and MK2). Results from DFT calculations indicate that hydroxamic acid anchoring group in MK2 lead to much stronger intermolecular charge transfer and adsorption energies on (TiO2)9 cluster. The effect of four different XC functionals (B3LYP, ωB97xD, M06-2X, and CAM-B3LYP) on the transition energies has been tested in order to explore the valid functional for the studied system. The wavelength values from the ωB97xD/6-31+G** level of theory are in excellent agreement with experimental data so this functional was considered to calculate the electronic absorption of the two studied dyes. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and the gap energy (H–L) of the studied dyes are slightly influenced by change of anchoring group. Results reveal that the LUMO energy levels of all studied dyes are higher than the conduction band (CB) of TiO2 (− 4.00 eV). Deprotonation process enhances the efficiency of dye-sensitized solar cells during decreasing adsorption energy of dyes with (TiO2)9 cluster.

Integrated probing the influence of dye acceptor with several electron withdrawing groups for dye-sensitized solar cells

In order to explore the influence of diverse acceptors with varying amounts of electron withdrawing groups on the organic dye in dye-sensitized solar cell (DSCs), a series of JF419 organic analogues with several cyano groups (CN) on acceptor were engineered. By performing theoretical studies on these investigated dyes and the corresponding dye/(TiO2)38 complexes, two benzoic acid units (benzothiadiazole benzoic acid and vinyl benzoic acid) with more -CNs were identified as alternative acceptors for DSCs. Particularly, S3 and S5 dyes exhibited impressive red-shift in spectra (ca. 77 nm for S3 and 48 nm for S5 compared with JF419), more accessible charge separation state and large driving force for dye regeneration (ΔGreg = 0.51 eV for S3 and ΔGreg = 0.61 eV for S5). According to quantifying the charge transfer (CT) on semiconductor surface, it found that the growing electron withdrawing groups on acceptor can strengthen the interaction between dyes and TiO2 and provide favorable conditions for electron injection. A brilliant balance between the electron injection time (τ = 6.8 fs for S3 and τ = 7.3 fs for S5) and the electron-hole recombination distance (r = 20.5 Å for S3 and r = 19.2 Å for S5) could be acquired for S3 and S5 dyes. Synthetically, introducing electron withdrawing groups on acceptor for organic dyes is a valid approach for gaining great performance of DSCs.

Molecular design and application of novel small molecule organic dyes featuring bis(arylvinyl)phenyl amino group for dye-sensitized solar cells

Small molecule organic dyes (SMODs) FWD7 and FWD8 featuring novel donor bis(arylvinyl)phenyl amino (BAPA) were designed for dye-sensitized solar cells (DSSCs). Absorption spectra of FWD7 featuring furanyl groups and FWD8 featuring thiophenyl groups showed about 20 nm bathochromic shifts and obviously bigger molar extinction coefficients (ε) compared with FWD5 featuring phenyl groups. The DSSCs sensitized by FWD7 and FWD8 exhibited good photovoltaic parameters: short-circuit current density (Jsc) 9.88 and 11.59 mA cm−2, open-circuit voltage (Voc) 0.69 and 0.75 V, and power conversion efficiency (η) 4.89% and 6.01%, respectively. The bigger Rrec and τe values of FWD8 (Rrec = 88.53 Ω cm−2 and τe = 10.76 ms) compared with FWD7 (Rrec = 59.06 Ω cm−2 and τe = 6.80 ms) gave a good explanation of the former’s bigger Voc. The results showed that both bis(furanylvinyl)phenyl amino and bis(thiophenylvinyl)phenyl amino groups are good donor groups, while the latter is more efficient.

Thiazolocatechol: Electron-Withdrawing Catechol Anchoring Group for Dye-Sensitized Solar Cells.

Anchoring groups adopting a five-membered bidentate chelating are attractive to realize high power conversion efficiency (η) and long-term durability in dye-sensitized solar cells (DSSCs). In this regard, we chose catechol as an anchoring group that can adopt the chelating. However, the DSSCs with catechol-based sensitizers have never exceeded an η-value of 2 %. These poor photovoltaic performances may be associated with the electron-donating ability of the hydroxy groups in catechol. Considering these, we envisioned that fusing an electron-withdrawing thiazole moiety with a catechol anchoring group would improve its photovoltaic performance. Herein, we report a push-pull porphyrin sensitizer ZnPTC with a thiazolocatechol anchoring group. The DSSC with ZnPTC exhibited η=4.87 %. This value is the highest ever reported for catechol-anchor based DSSCs. Meanwhile, the long-term cell durability was not improved, although the robust anchoring properties were attained under harsh conditions.

Synthesis and characterization of new squaraine dyes with bis-pendent carboxylic groups for dye-sensitized solar cells

In the present study, we introduce a new plan to boost the charge transfer between squaraine sensitizers and the conduction band of TiO2 by increasing the anchoring number. Two new symmetric squaraine sensitizers (SQIND-1 and SQIND-2) derived from indoline and having pendant bis-COOH as anchor groups to inject the electron into the TiO2 nanoparticles were tested as DSSC. The theoretical calculations and absorbance results showed that the electron density of LUMO of SQIND-1 is delocalized in the whole carboxylic group resulting in strong electronic interaction between SQIND-1 sensitizer and the conducting band of TiO2. Also, the relatively longer alkyl chain present in SQIND-1 would lower the aggregation of the dye on the TiO2 surface compared to SQIND-2. Hence, the SQIND-1 sensitized exhibit better photovoltaic performance. Dye-sensitized solar cell base fabricated in SQIND-1 was on TiO2 with the long wavelength and NIR region up to 750 nm of the spectrum and showed higher noteworthy performance properties, such as energy conversion efficiency (η) of 6.2% (AM 1.5 G), a short-circuit photocurrent density of 6.64 mA/cm2, an open-circuit photovoltage of 0.53, a fill factor of 0.72 and an incident photon-to-current conversion efficiency of 45% at 668 nm.

Role of hexyloxy groups in zinc phthalocyanines bearing sulfonic acid anchoring groups for dye-sensitized solar cells

Zinc phthalocyanine dyes bearing four sulfonic acid anchoring groups with (A-ZnPc) and without (H-ZnPc) four chloro and eight hexyloxy groups were used as sensitizers for dye-sensitized solar cells (DSSCs). The dyes were investigated in terms of their optical, electrochemical and photovoltaic properties. The presence of these groups in dye A-ZnPc resulted in both red-shifted absorption and decreased dye aggregation, which are beneficial for the improvement of device performance. In the presence of chenodeoxycholic acid (CDCA) as a coadsorbent, the DSSC based on H-ZnPc shows a power conversion efficiency (PCE) of 0.96%, which is improved by [Formula: see text]40% as compared to the device without CDCA. However, the PCE of an A-ZnPc-based device with CDCA slightly enhances from 1.15% (without CDCA) to 1.22%, indicating that the bulky hexyloxy groups with large steric hindrance can effectively suppress aggregation of the adsorbed dye. The results showed that the zinc phthalocyanine dye bearing bulky hexyloxy groups is a promising candidate to construct efficient coadsorbent-free DSSCs.

How to screen a promising anchoring group from heterocyclic components in dye sensitized solar cell:A theoretical investigation

Inspired by the successful application of heterocyclic components as robust anchoring groups in porphyrin dyes, we designed three novel organic analogues utilizing indenoperylene-based dye C275 as the skeleton prototype and three different heterocyclic units as anchoring groups in this research. In light of the theoretical studies on these three investigated dyes and the corresponding dye/(TiO2)38 compounds, two heterocyclic units (tropolone and 8-carboxylquinoline) were screened as alternative anchoring groups for dye-sensitized solar cells (DSCs). Especially, An1 and An2 dyes based on these two anchoring units show their remarkable performances in interfacial properties compared to those of C275 dye, involving larger conduction band CB up-shift (An1/(TiO2)38, ΔECB = 0.23eV and An2/(TiO2)38, ΔECB = 0.20eV) system, distinguished balance between the electron injection rate (An1/(TiO2)38, kinj = 8.71 × 1014 s−1 and An2/(TiO2)38, kinj = 8.52 × 1014 s−1) and electron–hole recombination (An1/(TiO2)38, krec = 1.63 × 107 s−1 and An2/(TiO2)38, krec = 2.75 × 107 s−1). Therefore, this work may be supplied several promising candidate for experimental synthesis in organic dye sensitized solar cells.

Theoretical study of triphenylamine-based organic dyes with mono-, di-, and tri-anchoring groups for dye-sensitized solar cells

Abstract In this report, DFT and TDDFT calculations used to explain the noticeable difference in the power conversion efficiencies (PCEs) of three reported triphenylamine-based organic dyes with mono-, di-, and tri-cyanoacrylic acid units as anchoring groups, and thiophene unit as π-bridges used as potential dyes in dye-sensitized solar cell applications. These dyes were showed the superiority of the multi-anchoring systems over the mono-anchoring system. The light was shed on the effect of various functionals, e.g., B3LYP, CAM-B3LYP, ωB 97 XD , M06, PBE0 and BHandHLYP on absorption spectra. The CAM-B3LYP functional was depicted the best among numerous adopted functionals which reproduced the experimental absorption data. The geometries, electronic structures and UV-Vis absorption spectra of the isolated dyes and their adsorbed dye@TiO2 complexes were calculated. The associated physical parameters that control the effectiveness of the cell, such as the light harvesting efficiency ( L H E ), hole and electron reorganization energies ( λ h o l e , and λ e l e ), and the driving force for electron injection ( Δ G i n j ) and dye regeneration ( Δ G r e g ) were computed and analyzed in order to determine their contributions to the open-circuit photovoltage ( V o c ) or the short-circuit photocurrent density ( J s c ), and correlate the structure with property. Also, charge transfer descriptors, such as the charge transfer distance ( D C T ), the amount of charge transferred ( q C T ), and dipole moment ( μ C T ) were investigated. The results reveal that the increasing of anchoring groups made significant influence on the PCE of the cells. The effect of mono-, di-, and tri-substituted anchored cyanoacrylic acid group(s) on the triphenylamine-TiO2 complexes has been explored on the frontier molecular orbitals, binding energies and absorption wavelengths. Among all the studied derivatives, electron injection energy barrier for TPA3T3A has been found the smallest which revealed that electron injection in this compound might be superior to other counterparts. Low-lying lowest unoccupied molecular orbital of TPA3T3A would favor it to stabilize thermodynamically. Moreover, TPA3T3A@TiO2 cluster was observed the most stable adsorption complex especially anchoring of TPA3T3A sensitizer at TiO2 cluster from B-side. Comprehensible intramolecular charge transfer has been observed from occupied to unoccupied molecular orbitals. The red shift in the absorption spectra has been perceived by increasing the number of anchoring groups, i.e., cyanoacrylic acid. The type-II band gap alignment between triphenylamine-based organic sensitizers and TiO2 is revealing that photovoltaic efficiency in these studied derivatives would be enhanced. Our quantum chemical analysis explored that these TPA derivatives especially tri-anchored dye would be proficient to be used in photovoltaic devices which would enhance the solar cell efficiency.

Synthesis of new di-anchoring organic sensitizer based on quinoxaline acceptor for dye-sensitized solar cells

New quinoxaline-based organic sensitizer bearing di-anchoring group for dye-sensitized solar cells (DSSCs) was synthesized from diethyl 4,5-diaminophthaltate, in which was prepared under mild condition by using Takehito’s method. The synthesized sensitizer was compared with mono-anchoring sensitizer through absorption spectra, emission spectra, J-V curve, and IPCE spectra, indicating the di-anchoring group leads to a noticeable improvement of Jsc value owing to more efficient intramolecular charge transfer and channel number increment.

Optical and Photovoltaic Properties of Thieno[3,2-b]thiophene-Based Push-Pull Organic Dyes with Different Anchoring Groups for Dye-Sensitized Solar Cells.

The effect of anchoring groups on the optical and electrochemical properties of triphenylamine-thienothiophenes, and on the photovoltaic performance of DSSCs photosensitized with the prepared dyes, was studied using newly synthesized compounds with cyanoacetic acid or rhodanine-3-acetic acid groups. Precursor aldehydes were synthesized through Suzuki cross-coupling, whereas Knoevenagel condensation of these with 2-cyanoacetic acid or rhodanine-3-acetic acid afforded the final push–pull dyes. A comprehensive photophysical study was performed in solution and in the solid state. The femtosecond time-resolved transient absorption spectra for the synthesized dyes were obtained following photoexcitation in solution and for the dyes adsorbed to TiO2 mesoporous films. Information on conformation, electronic structure, and electron distribution was obtained by density functional theory (DFT) and time-dependent DFT calculations. Triphenylamine–thienothiophene functionalized with a cyanoacetic acid anchoring group displayed the highest conversion efficiency (3.68%) as the dye sensitizer in nanocrystalline TiO2 solar cells. Coadsorption studies were performed for this dye with the ruthenium-based N719 dye, and they showed dye power conversion efficiencies enhanced by 20–64%. The best cell performance obtained with the coadsorbed N719 and cyanoacetic dye showed an efficiency of 6.05%.

Photovoltaic Properties and Long-Term Durability of Porphyrin-Sensitized Solar Cells with Silicon-Based Anchoring Groups.

Anchoring groups for dye-sensitized solar cells (DSSCs) play a decisive role in high-power conversion efficiency (η) and long-term cell durability. To date, a carboxylic acid is the most widely used anchoring group for DSSCs. However, the carboxylic acid tends to dissociate from a TiO2 surface during the cell operation as well as in the presence of water. Considering that the dye dissociation from TiO2 leads to a decrease in the cell performance, stable anchoring groups are highly desirable to achieve long-term durability of DSSCs toward their practical application. In this study, we designed and synthesized a series of porphyrin dyes with the triethoxysilyl anchoring groups, ZnPSi1, ZnPSi2, and ZnPSi3, to evaluate the effects of the silicon-based anchoring group on cell durability and photovoltaic properties. The DSSCs based on ZnPSi1, ZnPSi2, and ZnPSi3 exhibited moderate η-values of 2.2, 4.7, and 2.3%, respectively. It is noteworthy that the η-value of the DSSC based on ZnPSi2 (4.7%) is the highest among DSSCs based on porphyrin dyes with silicon-based anchoring groups. The moderate η-values are mainly attributed to the low charge collection efficiency originating from the low surface coverage and plausible tilted geometry of the dyes on TiO2. More importantly, we demonstrated that the DSSC based on ZnPSi2 revealed higher long-term cell durability under illumination than that based on reference porphyrin YD2-o-C8 having a conventional carboxylic acid anchoring group.