Sensitizers For DSSCs Research Articles

Beyond SM315: A Comprehensive Analysis of Power Conversion Efficiency in Tailored Donor–Acceptor Porphyrin Sensitizers for DSSCs

Beyond SM315: A Comprehensive Analysis of Power Conversion Efficiency in Tailored Donor–Acceptor Porphyrin Sensitizers for DSSCs

Betanin dye extracted from ayrampo (Opuntia soehrensii) seeds to develop dye-sensitized solar cells.

Pigments extracted from ayrampo seeds of the Peruvian-native prickly pear (Opuntia soehrensii) were used in dye-sensitized solar cells with promising efficiencies. The performance of the solar cells was then improved via the addition of citric acid to stabilise the photosensitive dye, and an efficiency of 1.41% was achieved with current output remaining stable after 7 days. Upon testing in low-light conditions, the solar conversion efficiency of devices increased to 4%. This paper not only highlights the potential of natural sensitizers in DSSCs but also shows that simple extraction and gentle handling methods can contribute to the device performance.

Syntheses, characterization, crystal structures and applications as sensitizers in solar cells of novel heteroleptic Cu(I) complexes containing nitrile-substituted 2,2'-bipyridyl ligands.

Two novel Cu(I) tetradentate heteroleptic complexes, including nitrile-substituted bipyridines that can be anchored to semiconductor surfaces to be assembled in DSSCs, were synthesized and characterized by spectroscopic and electrochemical techniques. The crystal structures of both species were determined by X-ray diffraction. Results from DFT and TD-DFT calculations were found to be consistent with the experimental data. Emission at room temperature was observed for both complexes in the solid state, making them promising alternatives for the development of light-emitting diodes. We report for the first time the experimental evidence of photovoltaic conversion devices formed by Cu(I) complexes anchored to a TiO2 surface by means of nitrile groups present in substituted bipyridines, and subsequently tested as sensitizers for DSSCs, obtaining efficiency values for light to electrical energy conversion similar to those previously reported for analogous complexes with anchoring carboxylic groups.

Theoretical investigation of the effect of changing the auxiliary acceptor on the performance of organic D-A'-A dyes used as sensitizers in DSSCs.

Dye-sensitized solar cells (DSSCs) have displayed huge potential in inexpensive, efficient, and clean solar energy technology. In this work, seven new dyes with the structure D-A'-A were designed in which the thiophene in the reference dye was replaced by auxiliary acceptors (A'). These dyes consist mainly of a pyranylidene-based electron donor D and the cyanoacrylic acid moiety as acceptor A. A computational investigation was carried out on the effect of various auxiliary acceptors A' on the efficiency of D-A'-A dyes in isolation and after binding to the semiconductor TiO2. Optimized structures, geometrical, optoelectronic, and photovoltaic parameters were calculated to predict promising dyes for potential use as solar cell sensitizers, including band gap (Egap), natural bond orbital (NBO) analysis, nonlinear optical properties (NLO), UV-Vis absorption spectra, maximum absorption wavelength (λmax), reorganization energy (λtotal), light-harvesting efficiency (LHE), electron injection driving force (ΔGinject) and open-circuit photovoltage (VOC). The results of this study revealed that all designed dyes, compared to the reference dye, are characterized by small Egap and λtotal values as well as large λmax, in addition to significant NLO properties and large adsorption energy (Eads). Therefore, all studied dyes can be used as sensitizers in DSSC. Using Density Functional Theory (DFT) approaches with the B3LYP functional and the 6-31G(d,p) basis set, all ground state geometries of the isolated dyes were fully optimized. Time-Dependent Density Functional Theory (TD-DFT) method using the CAM-B3LYP/6-31G(d,p)/IEF-PCM level was applied to simulate the UV-visible absorption properties. All isolated dye calculations were performed using the Gaussian 09 software package. DFT calculations have been carried out with the DMol3 package included in Materials Studio for simulating the adsorption of the investigated dyestuff on the TiO2 surface of anatase (101), using the generalized gradient corrected approximation (GGA) approach of the Perdew-Burke-Ernzerhof (PBE) functional with the basic set of digital double polarisation (DNP). To study the optical performance of dye@TiO2 the PBE/DNP method present in DMol3 was applied.

Novel triphenylamine-based porphyrins: Synthesis, structural characterization, and theoretical investigation for dye-sensitized solar cell applications

In this work, we have synthesized a series of novel porphyrin derivatives, 8, 12, and 16 in high yields. The new porphyrin derivatives are equipped with different aromatic substituents at the peripheral position. The structures of the new compounds were confirmed by elemental and spectral analyses. Among these porphyrin structures, porphyrins 8, 12, and 16 were molecularly designed and synthesized based on triphenylamine (TPA), as the core donor (DTPA), linked to one, two, or three porphyrin (DPorph) moieties with different numbers of anchoring groups (AG) to generate: DTPA-π-DPorph-A(DE1), DTPA(π-DPorph-A)2(DE2) and DTPA(π-DPorph-A)3(DE3). The structural, electronic, and spectroscopic properties of the dyes have been obtained by using the density functional theory (DFT) and time-dependent-DFT calculations. Based on the DFT studies, porphyrins 8, 12, and 16 possess all thermodynamics requirements to be used for DSSCs as the HOMO values for these three porphyrins are greater than the electrolyte's redox potential (I−/I3−, -5.2 eV), while the LUMO level more negative than the conduction band of TiO2 (- 4.2 eV), which indicate that these structures are suitable as sensitizers in DSSCs. All proposed structures were estimated in the gaseous state based on their optimized ground state geometry to estimate their EHOMO, ELUMO, and HOMO-LUMO energy gaps. porphyrins 8, 12, and 16 electronic excitations were also probed using TD-DFT experiments, which were performed under the impact of time-dependent disturbances. The simulated absorption spectra of these structures revealed the porphyrins' typical Soret- and Q-bands. porphyrin 16 with tri-cyanoacrylic acid anchoring groups has a wider absorption spectrum than other porphyrins (8, 12), and their Soret- and Q-bands are red-shifted. As a final step, we analyzed and described the DSSC's performance using the concept of DFT reactivity indices. A more efficient DSSC can be built using this approach to correlate cell efficiency with molecular properties.

Involvement of halogen and polyaromatic substituents in chalcone derivatives as dye sensitizers in solar cell applications

Pyrenyl chalcones act as sensitizers in DSSCs due to their co-planar structures, head-to-tail architecture, small Eg and appropriate HOMO–LUMO levels.

New Carbazole-Based Sensitizers for p-Type DSSCs: Impact of the Position of Acceptor Units on Device Performance

We report the design, synthesis, and characterization of two new carbazole-based organic dyes PC1–2 as potential sensitizers for NiO-based p-type dye-sensitized solar cells (p-DSSCs). The D-A-π-A’ configured PC1 dye comprises a thienyl unit as a π-spacer and a malononitrile as an end-capping acceptor unit, whereas in PC2, the cyanovinylene group serves as an acceptor unit and a thienyl group acts as a donor unit in a D–A–D configuration. These molecules achieved excellent solubility due to their long-branched alkyl chains. The current work encompasses their structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies, establishing structure–property relationships. PC1–2 exhibit λabs and λemi in the range of 389–404 and 448–515 nm, respectively, with a band gap in the range of 2.88–2.92 eV. Electrochemical studies confirm the feasibility of electron injection, regeneration, and recombination. The introduction of an additional electron-withdrawing group (cyanovinylene group) on the dye PC1 skeleton endows it with a higher dye loading capacity, high hole injection, and a strengthened intramolecular charge transfer (ICT) effect, resulting in a redshifted ICT absorption with a higher molar extinction coefficient. Among the two new dyes, the device based on PC1 achieved the highest power conversion efficiency (PCE) of 0.027% with a short-circuit current density (JSC) of 1.29 mA·cm–2, open-circuit voltage (VOC) of 67 mV, and fill factor (FF) of 31%, whereas the device with dye PC2 performed less efficiently (PCE: 0.018%, JSC: 0.92 mA·cm–2, VOC: 68 mV, and FF: 30%). Conclusively, the study provides insights into the intricacies involved in the structural modification of carbazole-based p-type dyads for the development of highly efficient DSSCs.

Sensitizers designed toward efficient intramolecular charge separation for p-type dye-sensitized solar cells

Effective charge separation is demonstrated as one of the rational design strategies for organic sensitizers of both n-type and p-type dye-sensitized solar cells. Herein, we report the design and synthesis of novel D-A dye cTPAPh-NO2 and D-A1-A2 dye cTPABT-PyCN2 using triphenylamine as the donor, di-carboxylic acid group as anchoring group. Photophysical and electrochemical properties of both dyes were investigated to discuss the effect of anchoring group and molecular structure on the photophysical processes and charge separation feature of the sensitizers. For D-A dyes, the attachment of carboxyl groups reduces both the light harvesting and intramolecular charge separation ability of cTPAPh-NO2. In comparison, cTPABT-PyCN2 exhibits weak fluorescence and efficient intramolecular charge separation characteristics. Exceeding 80% of cTPABT-PyCN2 singlets decays via intramolecular electron transfer from the first acceptor to the dicyanovinyl pyrimidine. Finally, these synthesis dyes were used as sensitizers in p-type DSSCs and cTPABT-PyCN2 showed the overall power conversion efficiency of 0.103%, which is comparable to that of reported dyes. The results demonstrate that D-A1-A2 structure can be a promising strategy to design p-type sensitizers with effective charge separation characteristics.

Theoretical exploration of 1,3-Indanedione as electron acceptor-cum-anchoring group for designing sensitizers towards DSSC applications

The present work highlights the DFT and TD-DFT calculations of a few organic sensitizers designed based on a new electron-acceptor, 1,3-indanedione, which is a well-known electron-acceptor for designing new electron donor–acceptor molecules. Nine organic sensitizers (GR1-9) have been designed based on a modified 1,3-indanedione electron-acceptor and conventional electron-donor moieties. Optimization studies reveal that all dyes have twisted configurations, and therefore, the aggregation on the TiO2 semiconductor is expected to be less. GR2 dye shows the smallest energy gap, 2.43 eV, as compared to others which indicates an effective electronic excitation and injection. The dyes’ energy levels are compatible with the conduction band of TiO2 and redox potentials of the redox couple. Thermodynamic parameters indicate that the GR1, GR2, and GR5 dyes regenerate at a faster rate as compared to the other dyes. Further, NBO calculations demonstrate the dipolar nature of the designed molecules. Electronic spectra of dyes were red-shifted by 18–29 nm in acetonitrile solvent, which shifts further towards red-region upon adsorbing on to titania. The absorption spectrum of the GR1@TiO2 system shows a remarkable shift, 92 nm, and extends to the NIR region. The electron density of LUMO and LUMO + 1 is majorly confined to TiO2 moiety upon binding, which indicates complete electron donation from dye to the TiO2. Overall, our studies reveal that the 1,3-indanedione skeleton has the potential to serve as an electron-acceptor in designing new organic sensitizers for DSSCs. Therefore by conjugating conventional electron-donors with the 1,3-indanedione electron-acceptor, a new class of organic sensitizers can perhaps be synthesized for DSSC applications.

Double Fence Porphyrins that are Compatible with Cobalt(II/III) Electrolyte for High-Efficiency Dye-Sensitized Solar Cells.

A series of new double fence porphyrin dyes bJS1-bJS3, with eight long alkoxyl chains attached to four β-phenyl groups, have been designed and synthesized. The single fence meso-substituted counterparts mJS1-mJS3 were also prepared as reference dyes. Dyes bJS1-bJS3 and mJS1-mJS3 exhibit power conversion efficiencies of 8.03-10.69 % and 2.33-6.69 %, respectively. Based on photovoltaic studies, the remarkable cell performance of double fence porphyrin sensitizers can be attributed to reduced dye aggregation and a decreased charge-recombination rate. Notably, porphyrins bJS2 and bJS3 exhibit better efficiency than the benchmark YD2-o-C8 (9.83 % in this work), demonstrating that the double fence structure is a promising design strategy for efficient porphyrin sensitizers in high-performance DSSCs.

β-Functionalized push–pull opp-dibenzoporphyrins as sensitizers for dye-sensitized solar cells: the push group effect

β-Functionalized push–pull opp-dibenzoporphyrins with different donor groups were designed and synthesized, showing a significant push–pull effect. High power conversion efficiencies were achieved with these sensitizers in DSSCs.

Structural features of indoline donors in D–A-π-A type organic sensitizers for dye-sensitized solar cells

Novel D–A-π-A organic sensitizers for DSSCs based on benzothiadiazole internal acceptor (A) and N-substituted indolines fused with cyclopentane or cyclohexane as donor (D) with the best PCE of 5.8% were reported.

Theoretical design and characterization of D-A1-A based organic dyes for efficient DSSC by altering promising acceptor (A1) moiety

The electronic, optical and photovoltaic properties of dyes can be readily tuned by modifying the structure. Herein, the thieno[2,3-b]indole (Thi)-based molecules derived from dye NTU-2 (D-A1-A) have been designed by substituting BT by DPP(O), DPP(S), QuT and BBT units and dicyanovinylene by cyanoacetic acid. Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the regulation effect of acceptor groups on designed compounds was theoretically investigated. Indeed, in this context, the effects of various acceptor groups (A1) in D-A1-A dyes before and after binding to (TiO2)8 cluster on the electron injection have been studied. The optimized structures, electronic parameters, FMOs, NBO, PDOS analysis, the absorption spectra, and ICT parameters were evaluated to predict the suitable candidates for DSSC device. Our investigations reveal that all designed compounds have not only a significant λmax in the range of 593−824 nm, with a bandgap in the order, 2.31−1.56 eV, larger adsorption energies (Eads) and lower Λtotal, but also large light harvesting efficiency (LHE) and significant intramolecular charge transfer (ICT) properties compared to dye R. Accordingly, these theoretical calculations can provide an efficient strategy to design new promising sensitizers for DSSCs.

Novel organic dyes for dye-sensitized solar cells based on 1-(2-ethylhexyl)pyrrole as a π-bridge

Three novel organic dyes coded as FWD9, FWD10 and FHD7 with different donors were reported in this work. Their molecular structures were fully characterized and photophysical/electrochemical properties as well as performances as sensitizers for DSSCs were scrutinized in detail. By the adoption of 1-(2-ethylhexyl)pyrrole moiety, dye aggregation was efficiently suppressed and better power conversion efficiencies were observed for all the three dyes compared with the addition of coadsorbent chenodeoxycholic acid. FWD9 with bis(4-styryl)phenyl amino donor exhibited the best power conversion efficiency to be 5.80% among the three dyes, while the Jsc to be 13.95 mA cm−2, Voc to be 0.66 V and FF to be 0.63, and it was unnecessary to add adsorbent to suppress the dye aggregation.

Tailoring dual-channel anchorable organic sensitizers with indolo[2,3-b]quinoxaline moieties: Correlation between structure and DSSC performance

Two new metal-free heteroaromatic organic dyes, FS13 and FS14, with D-D|A-(π-A)2 structural configuration were tailored and synthesized as effective dual-channel anchorable sensitizers in DSSCs. The new entities consist of indolo[2,3-b]quinoxaline (IQ) as the constructing unit containing merged donor–acceptor system (D|A) connected to two cyanoacetic acids as anchoring groups via phenylene as π-linker at 2- and 3- positions of IQ rings. Their experimental properties together with theoretical modeling using density functional theory (DFT) are studied to understand their achievability as feasible sensitizers. The photovoltaic performance and charge transfer properties were assessed with illumination condition as 1.5 AM standard. The DFT study revealed that the isodensity of FS13 and FS14 has been slightly shifted towards di-anchors compared to the mono-anchoring FS08, leading to more distinguished charge separation; however, the closely paralleled anchoring branches bring out high spatial hindrance, turning into the less conjugated system and the lower photocurrent. For the study of co-sensitization effect employing dual-channel dyes with HD-2 ruthenium sensitizer, FS14 displayed the most positive co-sensitization effect and enhanced the overall efficiency by 9.2% from 7.50% to 8.67%. For both novel dyes, the considerably improved photovoltage and fill factor are ascribed to the improved coverage percentage on TiO2 surface and the enhancement of dye anti-aggregation and charge recombination resistance, which in turn corroborates the superior affinity of di-anchors. Furthermore, the dark current resistance estimated from impedance graphs employing co-sensitization methodology coincided with the observed photovoltage, indicating the enormous potential of di-anchoring dyes in ameliorating the photovoltaic performance.

The effect of group-substitution on the sensitization properties of alkynylrhenium(I) tricarbonyl diimine complexes adsorbed to TiO2(101) film surface: a theoretical study.

A series of dyes are designed by adding the different electron-donating (-CH3, -NH2, -OH) and electron-withdrawing groups (-Br, -Cl, -NO2) to the different ancillary ligands in the alkynylrhenium(I) tricarbonyl diimine complexes [Re(CO)3(N^N){C≡C-C6H4-CH=C(CN)(COOH)}], where N^N = 1,10-phenanthroline (phen)(1) and then investigated the sensitization properties of dyes linked to the TiO2(101) surface. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to study the electronic structure, frontier molecular orbitals, and absorption spectral properties. The effect of group-substitution on sensitization properties is obvious. When the dye molecules are combined with TiO2(101) surface, not only the absorptions of some sensitizers containing -CH3 or -OH groups have red shift but also the electrons can be directly injected into the TiO2 conduction band from the dye molecules compared with the parent molecular 1. The results indicate that the designed dyes containing electron-donating groups have smaller energy gaps, better light-harvesting efficiency, sufficient driving force, and higher charge transfer efficiency as appropriate dye sensitizers. We hope it can provide valuable hints so that we can design more efficient dye sensitizers in DSSCs.

Molecular engineering and synthesis of symmetric metal-free organic sensitizers with A-π-D-π-A architecture for DSSC applications: the effect of bridge unit

Herein, we report the design and synthesis of six symmetric metal-free organic sensitizers (llyu1a, llyu1b, llyu1c, llyu2a, llyu2b, and llyu2c) based on fluorene or dimethyl fluorene donors core carrying double acceptors. All these dyes were characterized using UV–Vis, ESI-MS, and 1HNMR. To study the influence of π-bridges on total solar-to-electric conversion efficiency (%η) for DSSCs, three different π-bridges thiophene, furane, or benzene were introduced into the sensitizers. Their device performances were studied and showed a distinctive difference in efficiency with a maximum of PCE of 2.35% (Jsc = 5.63 mA cm − 2, VOC = 0.60 V and FF = 70.00%) for dye llyu1a. Density functional theory (DFT) and time-dependent density functional theory calculations were used to probe the relationship between chemical structure, photophysical, and photoelectrochemical properties. DFT studies showed that the dihedral angle between thiophene and donor is 26.6°, indicating that the dyes bearing thiophene π-bridge possess more efficient photoexcitation compared to dyes bearing benzene π-bridge (36.6° for both llyu2c and llyu1c) and less aggregation than dyes bearing furane π-bridge (0° for llyu1b and llyu2b). This new finding of influence of π-bridges on total solar-to-electric conversion efficiency would open the door for the molecular engineering of better light harvesting and more efficient metal-free organic sensitizers for DSSCs.

DFT/TD-DFT study of novel T shaped phenothiazine-based organic dyes for dye-sensitized solar cells applications.

Five novel T shaped phenothiazine-based organic dyes DTTP1~5 with different spacers at N (10) position were designed. The geometries, electronic structures, absorption spectra, electron transfer and injection properties of these isolated dyes and dye/(TiO2)9 systems were investigated via density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculation. The optimized geometries indicate that these T shaped dyes show non-planar conformations, which are helpful in suppressing the close intermolecular π-π aggregation in device and enhancing thermal stability. The calculated results indicate that type of π-conjugated spacers can affect the molecular absorption spectra. Introduction of thiophene-benzothiadizole-thiophene unit as π-conjugated spacer can most effectively shift the light absorption to near infrared region and enhance the light harvesting efficiency (LHE). Moreover, it is found that these dyes show a good performance of electron injection and dye regeneration owing to the proper electron injection driving force (ΔGinject) and dye regeneration driving force (ΔGreg). The theoretical results reveal that these dyes could be used as potential sensitizers for DSSCs, and DTTP4 would be the most plausible sensitizer for high-efficiency DSSCs due to the narrow HOMO-LUMO energy gap (ΔH-L), broad absorption spectrum, high LHE value, and large dipole moment (μnormal).

Auxiliary donors for phenothiazine sensitizers for dye-sensitized solar cells – how important are they really?

A comprehensive study into auxiliary donors for phenothiazine sensitizers in DSSCs and a critical look at a remarkably efficient literature dye.

Improving the photovoltaic performance by employing alkyl chains perpendicular to the π-conjugated plane of an organic dye in dye-sensitized solar cells

We demonstrate that employing alkyl chains perpendicular to the π-conjugated plane is a promising strategy to construct efficient sensitizers for DSSCs.