Electrolyte-based Dye-sensitized Solar Cells Research Articles

How to choose proper electron acceptor groups for highly efficient copper electrolyte-based dye-sensitized solar cells?

A better understanding of electron-accepting groups (EAGs) is important for the development of potentially efficient dyes. Density functional theory (DFT) and time-dependent DFT were employed in this study to investigate a variety of dyes derived from XY1b (11.8 %) in conjunction with prominent EAGs including 2-cyano-3-phenylacrylic acid (CPA), 2-cyano-acrylic acid (CA), and benzoic acid (BA). Various critical parameters pertaining to short-circuit current density (Jsc) and open-circuit photovoltage (Voc) were calculated, including light-harvesting ability, conduction band energy shift, dye-[Cu(tmby)2]2+ interaction, dye aggregation, and charge recombination, in order to illustrate the advantages and limitations of these EAGs. The findings indicate that dyes based on CA demonstrate a redshifted absorption spectrum, stronger electronic coupling with TiO2 conduction band, extended excited state lifetime, and enhanced dye regeneration driving force, resulting in higher Jsc compared to CPA and BA-based dyes. Regarding Voc, CA-based dyes show an increased conduction band energy shift due to their larger vertical dipole moment and reduced charge recombination with [Cu(tmby)2]2+. Additionally, it is suggested that future studies on structure–property relationships should prioritize identifying the optimal dye conformation, as it significantly influences adsorption configuration and vertical dipole moment. Overall, among the commonly utilized EAGs, CA stands out for its ability to enhance Jsc, Voc, and adsorption stability over CPA and BA-based dyes.

Alkyl effects on charge recombination in copper electrolyte-based dye-sensitized solar cells: Insights for targeted molecular design towards high performance

Two quinoxaline dyes utilized in copper-electrolyte-based dye-sensitized solar cells (Cu-DSSCs) are theoretically investigated to analyze the impact of alkyl chains on dye performance. The investigation shows that ZS4, known for its record efficiency of up to 13.2 %, exhibits higher electron coupling and fewer binding sites for dye-[Cu(tmby)2]2+ interaction compared to ZS5. Contrary to common belief, alkyl chains are found to not only provide shielding but also hinder the interaction between dye and [Cu(tmby)2]2+ by influencing the optimal conformation of dyes, thereby impeding the charge recombination process. It is crucial to consider the influence of alkyl chains on dye conformation when discussing the relationship between dye structure and performance, rather than oversimplifying it as often done traditionally. Building on these findings, eight dyes are strategically designed by adjusting the position of the alkyl chain to further decrease charge recombination compared to ZS4. Theoretical evaluation of these dyes reveals that changing the alkyl chain on the nitrogen atom from 2-ethylhexyl (ZS4) to 1-hexylheptyl (D3-2) not only reduces the charge recombination rate but also enhances light harvesting ability. Therefore, D3-2 shows potential as a candidate for experimental synthesis of high-performance Cu-DSSCs with improved efficiency.

Study of KOH as alkali for enhancing performance of photo-galvanic cell in transparent cylindrical cell design

Photo-galvanic cells are liquid electrolyte-based dye-sensitized solar cells. Chemically, the dye/pigment photo-sensitizer, reductant, surfactant, and alkali materials are the main fabrication components of these cells. Most dye/pigment materials are more soluble and stable at high pH. The pH of Potassium hydroxide (an alkali of plant nutrient ‘potassium’ element) is very high. Therefore, Potassium hydroxide is supposed to be the best eco-friendly and effective alkali medium for photogalvanics. As far as alkali is concerned, NaOH has been exploited extensively in photo-galvanics. Although, the NaOH-based photo-galvanics show good electrical output, it is plagued with some drawbacks like shorter shelf life, high cost, unsafe for skin, low conductivity, low water solubility, etc. Therefore, in the present research, the KOH has been exploited as an alkali material for harvesting solar energy using the Sunset Yellow FCF dye sensitizer-Ascorbic acid reductant-CTAB surfactant cylindrical cell designed photo-galvanic system.In the present study, the observed optimum cell performance is as follows-open-circuit potential 777 mV, maximum current 25000 μA, short-circuit current 5600 μA, power 733.6 μW, fill factor 0.16, and efficiency is 19.77 % at pH 14.30. The Sunset Yellow FCF dye shows very high photostability and photo-absorption with KOH alkali. The power storage capacity is sufficiently robust, as the cell is capable of supplying power at its ∼36.16 % capacity after a very long time of 24 h. The KOH-Sunset Yellow FCF dye sensitizer-Ascorbic acid reductant-CTAB surfactant photo-galvanics in the present study show improved results over the reported results for the NaOH-Sunset Yellow FCF dye sensitizer-Ascorbic acid reductant-CTAB surfactant photo-galvanics. The reasons for the good photo-galvanics with KOH alkali may be attributed to some peculiar chemical and physical properties of KOH vis-à-vis the chemical and physical properties of NaOH.

Synergistic effects of polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) blends in gel electrolytes for efficient and long-term stability in dye-sensitized solar cells (DSSCs)

In this work, the stability issues associated with liquid electrolyte-based dye-sensitized solar cells (DSSC) have been addressed by introducing polymer gel electrolytes. The synergistic combination of polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) has been achieved through solution blending. Ionic conductivity measurements, scanning electron microscopy, X-ray diffraction analysis, and Fourier transform infrared spectroscopy have been employed for analysis. Optimal cohesiveness was observed at PVP concentrations exceeding 40 %, with the best outcomes achieved at a 50 % PVDF-PVP weight ratio. The electrolyte solution, comprising the polymer blend, suitable solvents, and iodine-based salts, exhibits peak conductivity (2.33 mScm⁻1) at a 10 % salt content. DSSCs utilizing the PVDF & PVP polymer blend gel electrolytes demonstrate enhanced durability and maintained efficiency at 5.43 %, exhibiting only a modest 12 % reduction compared to liquid electrolyte counterparts. Over two weeks, the fabricated DSSCs exhibited consistent photovoltaic performance, while conventional cells experienced significant declines in short-circuit current (36 %) and open-circuit voltage (33.33 %). This study signifies a promising advancement in solar cell technology, showcasing improved stability and performance in DSSCs using conductive polymer blend gel electrolytes.

Efficient Solar Cells Based on Porphyrin and Concerted Companion Dyes Featuring Benzo 12-Crown-4 for Suppressing Charge Recombination and Enhancing Dye Loading.

In recent years, various porphyrin dyes have been designed to develop efficient dye-sensitized solar cells (DSSCs). Based on our previously reported porphyrin dye XW43, which contains a phenothiazine donor with two diethylene glycol (DEG)-derived substituents, we herein report a porphyrin dye XW89 by introducing a benzo 12-crown-4 (BCE) unit onto the N atom of the phenothiazine donor. On this basis, XW90 and XW91 have been synthesized by replacing a DEG chain in XW89 with two DEG chains and a 12-crown-4 unit, respectively. For iodine electrolyte-based DSSCs, dyes XW89-XW91 exhibit VOC values of 765-779 mV, higher than that of XW43 (755 mV), which may be related to the strong capability of the BCE group in binding Li+ and thus suppressing the downward shift of the TiO2 conduction band and interfacial charge recombination. Moreover, the smaller size of 12-crown-4 than the DEG unit enables higher adsorption amounts of the dyes than XW43, contributing to an enhanced JSC value. Due to the presence of two BCE units, dye XW91 exhibits the highest dye loading amount and JSC of 1.86 × 10-7 mol cm-2 and 19.79 mA cm-2, respectively, affording a high PCE of 11.1%. To further enhance the light-harvesting ability, a concerted companion (CC) dye XW92 has been constructed by linking the two subdye units corresponding to the porphyrin dye XW91 and an organic dye. As a result, XW92 affords an enhanced JSC and efficiency. Further coadsorption of XW92 with chenodeoxycholic acid achieved the highest efficiency of 12.1%. This work provides an effective approach for fabricating efficient DSSCs sensitized by porphyrin and CC dyes based on the introduction of crown ether units with smaller sizes and stronger Li+ affinities.

Performance analysis of aqueous Al-ion electrolyte based dye sensitized solar cell

Photovoltaic performance of the aqueous Al-ion electrolyte-based dye-sensitized solar cells (DSSCs) was investigated by varying the aluminium nitrate concentration, ranging from 0.02 to 0.1 M and using Eosin-Y (EY) sensitized antimony-doped tin oxide (ATO) photoanode with platinum (Pt) as counter electrode. Photoconversion efficiency (PCE) peaks for 0.1 M using the source of 100 mW cm−2 with AM 1.5G (standard) solar simulator under ambient condition, photocurrent density (JSC) reaches 3.76 mA/cm2 and efficiency (PCE, η) 3.17%. Most of the work that exist in literature with (K, Na, Co, Li, etc. based) aqueous electrolyte quoted the maximum efficiency 1.55% whereas, the present work with pure aqueous Al-ion electrolyte gives 50% of higher efficiency over the quoted value. Moreover compared to the undoped tin oxide photoanode, this work with Sb doped tin oxide shows an enhancement of efficiency about 80%.

Understanding Mass Transport in Copper Electrolyte-Based Dye-Sensitized Solar Cells

Understanding Mass Transport in Copper Electrolyte-Based Dye-Sensitized Solar Cells

Designing highly effective mesoporous Carbon-based counter electrodes for liquid Electrolyte-based and Quasi-solid Dye-sensitized solar cells

In this study, nitrogen-doped mesoporous carbon (NMC) and boron-doped mesoporous carbon (BMC) are synthesized and used as Pt-free counter electrode (CE) materials for dye-sensitized solar cells (DSCs). The optimized NMC and BMC CEs exhibit significantly higher catalytic activities than the pristine mesoporous carbon (MC). The I-/I3- in acetonitrile liquid electrolyte-based DSCs have power conversion efficiencies (PCE) of 7.20% with the NMC CE and 7.15% with the BMC CE, which are significantly higher than that obtained using the MC CE (5.88%). This is attributed to the improved effective catalytic active sites and the enhanced electrical conductivities of the NMC and BMC CEs. When Pt with trace amounts (0.1 wt%) is loaded on NMC, the liquid DSCs using Pt/NMC composite CEs yield PCE values of 8.31% and 9.92%, respectively, under 1.0 Sun and 0.1 Sun illumination. The Pt/NMC CE is further employed in quasi-solid DSCs, which also give a high PCE of 8.15% under 1.0 Sun illumination. A flexible Pt/NMC CE is also prepared on indium tin oxide-polyethylene naphthalate (ITO-PEN) substrate, and the generated liquid DSCs show a PCE of 6.92%. This work provides a feasible path to enhance the catalytic activity of the MC CE in DSCs.

Organosoluble, esterified starch as quasi-solid biopolymer electrolyte in dye-sensitized solar cell

Fabrication of quasi-solid state polymer electrolytes are recently being endorsed by electrochemists due to its superior electrical and physical properties. With the aspiration to develop a sustainable electrolyte component, this study is a novel attempt to fabricate quasi-solid electrolyte based on esterified starch. Potato starch was chemically modified via simple phthaloylation method. The resulting amorphous, hydrophobic starch derivative was used as a polymer base to prepare cost effective thermoplastic gel electrolytes via incorporation of propylene carbonate, dimethylformamide and lithium iodide. Fourier transform infrared spectroscopy and X-ray diffraction characterizations verified the impact of phthaloylation and plasticization in suppressing the crystallinity and hydrophilicity of starch. The biopolymer gel with 40 wt.% LiI recorded the highest room temperature ionic conductivity of 4.82 mS cm−1. The sample with highest ionic conductivity recorded the best efficiency of 3.56%, which is one of the highest values for starch electrolyte-based dye-sensitized solar cells (DSSC). The optimized efficiency indicate that starch-based electrolyte has good prospects for fabrication of quasi-solid DSSC.

Binary Redox Couples for Highly Transparent and High-Voltage Dye-Sensitized Solar Cells

The conventional iodine-based (I−/I3 −) electrolyte used in dye-sensitized solar cells (DSSCs) presents several limitations, such as ∼30% absorption of visible light in the wavelength range of 300–500 nm and a large potential difference between the Fermi level of I−/I3 − and the HOMO level of the dye. This has a negative impact on the characteristics of DSSC such as transparency and open circuit voltage (Voc). In the present work, a series of transparent electrolytes are prepared using various additives such as I2, LiI, guanidine thiocyanate/guanidine nitrate (GuSCN/GuNO3), and Br2 to obtain highly transparent and high voltage DSSCs. The results demonstrate that the usage of the optimized electrolyte consisting of 0.003 M Br2, 0.01 M LiI, and 0.1 M GuNO3, with the binary redox couple (I−, Br−)/(I3 −, I2Br−), contributes to an ∼25% increase in transmittance compared to that of the conventional electrolyte, while the concentration of I3 − is significantly reduced. Furthermore, the downward shift in the Fermi level of the binary redox system is shown to provide an ∼100 mV enhancement in the Voc of the DSSC compared with that of the conventional electrolyte based DSSC. In addition, the devices with the optimized binary redox system achieve a power conversion efficiency of ∼7.94% which is closely comparable to the performance of conventional (I−/I3 −) electrolyte-based DSSCs. Thus, the present study could provide immense insights toward the fabrication of high-voltage and transparent DSSCs for the application in transparent photovoltaic windows. Furthermore, by using a binary redox electrolyte, the DSSCs that operative under a 2000 lux compact fluorescent lamp (CFL) were also successfully fabricated and yielded a promising efficiency of 23.6%.

Characteristics of ionic adsorption on silica nanoparticles and its impact on the long term stability of dye-sensitized solar cells

Quasi-solid electrolytes based on silica nanopowder are well known in literature and these electrolytes are able to match in performance with that of liquid electrolytes. However, contrasting results are observed in literature regarding stability of dye-sensitized solar cells (DSSCs) with most of the reported articles projecting silica-loaded quasi-solid electrolyte-based cells as a stable alternative to liquid electrolyte-based cells, while a few others contradicting the same. The present study demonstrates the effect of ageing under heat (60°C) and illumination on the performance of liquid electrolyte and silica-loaded electrolyte-based DSSCs. It has been observed that DSSC based on silica-loaded electrolyte are less stable than DSSC based on liquid electrolyte even though independent study on both electrolytes by thermal analysis shows silica-loaded electrolyte to be more stable than liquid electrolyte. Segregation of silica in electrolyte has been confirmed through cryo-field emission gun-scanning electron microscopy. Zeta potential measurements show that ions are desorbed from the surface of silica on ageing under heat and illumination.

Efficient Solar Cells Based on Concerted Companion Dyes Containing Two Complementary Components: An Alternative Approach for Cosensitization.

With the purpose to achieve panchromatic absorption for constructing efficient dye-sensitized solar cells (DSSCs), the cosensitization approach of using two dyes with complementary absorption has been developed with great success. However, this approach usually requires time-consuming optimization of a number of parameters for controlling the ratio and distribution of the two coadsorbed dyes on TiO2 film, which limits the potentials of this strategy. We herein report an alternative approach for developing efficient DSSCs by designing a class of "concerted companion dyes" with two complementary dye components linked covalently. Thus, a newly synthesized organic dye Z2 was linked to a recently reported doubly strapped porphyrin dye XW51 through flexible chains with various lengths to afford XW60-XW63. These dyes exhibit excellent absorption and efficiencies in the range of 8.8%-11.7%. Notably, upon coadsorption with chenodeoxycholic acid, XW61 affords an impressive efficiency of 12.4%, a record for iodine electrolyte-based DSSCs, to the best of our knowledge. In addition, these dyes also exhibit the advantages of easy cell fabrication, simple optimization, as well as excellent photostability.

Surface Carbon Shell-Functionalized ZrO2 as Nanofiller in Polymer Gel Electrolyte-Based Dye-Sensitized Solar Cells.

We prepare dye-sensitized solar cells (DSSCs) fabricated with a poly (ethylene glycol) based polymer gel electrolytes (PGEs) incorporating surface carbon shell-functionalized ZrO2 nanoparticles (ZrO2-C) as nanofillers (NFs). ZrO2 are polymerized via atom transfer radical polymerization (ATRP) using poly (ethylene glycol) methyl ether methacrylate (POEM) as a scaffold to prepare the ZrO2-C through carbonization. The power conversion efficiency of DSSC with 12 wt% ZrO2-C/PGEs is 5.6%, exceeding that with PGEs (4.4%). The enhanced efficiency is attributed to Lewis acid-base interactions of ZrO2-C and poly (ethylene glycol), catalytic effect of the carbon shells of ZrO2-C, which results in reduced crystallinity, enhanced ion conductivity of electrolytes, decreased counterelectrode/electrolyte interfacial resistance, and improved charge transfer rate. These results demonstrate that ZrO2-C introduction to PGEs effectively improves the performance of DSSCs.

Stable and Efficient Organic Dye-Sensitized Solar Cell Based on Ionic Liquid Electrolyte

Summary Dye-sensitized solar cells (DSCs) for outdoor applications must show both high efficiency and long-term stability. Here we introduce a co-sensitized, ionic liquid electrolyte-based DSC meeting these requirements. A key feature of our embodiment is the concerted action of two judiciously designed organic dyes, whose co-adsorption at the surface of a mesoscopic TiO2 scaffold results in the formation of a compact and highly robust self-assembled monolayer, harvesting sunlight across the whole visible region and converting the photons into charges with near-unity quantum efficiency. Apart from producing a high photocurrent, the dense dye layer blocks the back electron transfer from TiO2 to the redox electrolyte, increasing the photovoltage. This allows for the first time to attain a solar to electric power-conversion efficiency of 10% with an ionic liquid-based DSC. Remarkably, the co-sensitized cell is stable under both full-sunlight soaking at 60°C and heat stress at 85°C for 1,000 hr.

Investigation on gel polymer electrolyte-based dye-sensitized solar cells using carbon nanotube

A new poly (acrylonitrile) (PAN)-based gel polymer electrolyte (GPE) is fabricated to study the effect of carbon nanotube (CNT) on dye-sensitized solar cell (DSSC) efficiency. The GPEs are examined using electrochemical impedance spectroscopy (EIS) to analyze ionic conductivity. A maximum of 4.45 mS cm−1 ionic conductivity is achieved at room temperature with incorporation of 11 wt.% CNT. Performance of DSSC is examined with a solar simulator, and the highest energy conversion efficiency of 8.87% is achieved with the addition of 11 wt.% CNT. All GPE samples are found to follow Arrhenius model with temperature-dependent ionic conductivity testing. Structural properties are also characterized by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy.

Molecular Engineering of Quinoxaline-Based D-A-π-A Organic Sensitizers: Taking the Merits of a Large and Rigid Auxiliary Acceptor.

The continuing efforts of creating novel D-A-π-A structured organic sensitizers with excellent optoelectronic properties have resulted in substantial improvement of power conversion efficiency (PCE) as well as stability of dye-sensitized solar cells (DSSCs). Here, we report a new molecular engineering strategy for enhancing optical gain and improving excited-state features in D-A-π-A structured organic sensitizers by improving the conjugation size and rigidity of the auxiliary acceptor functional group. A series of phenanthrene-fused-quinoxaline (PFQ)-based D-A-π-A organic sensitizers (WS-82, WS-83, and WS-84) are designed and synthesized for applications in DSSCs. Compared to 2,3-diphenylquinoxaline (DPQ)-based dye IQ-4, PFQ dyes show extended absorption spectra and improved open-circuit voltage performance. Upon a systematical engineering of alkyl chains and π-spacer structure, the unfavorable issues of PFQ dyes including low solubility and high energy barrier in intramolecular charge transition are successfully eliminated. When applied in iodine electrolyte-based DSSCs, the best performing PFQ dye WS-84 shows a PCE of 10.11%, which is much higher than that of our previous champion DPQ dye IQ-4 under the same conditions.

A novel carbon bead string cathode for dye-sensitized solar cells

In this study, a novel carbon bead string (CBS) is synthesized through a simple method, which is subsequently introduced into the dye-sensitized solar cells (DSCs) as a cathode catalyst. The resultant CBS cathode displays decent electro-catalytic activities for the traditional iodide redox couple (I3−/I−). More importantly, CBS cathode presents distinct superiorities when applied in an organic sulfide redox couple (T2/T−). T2/T− electrolyte-based DSCs with CBS cathode has resulted in a high power conversion efficiency (PCE) of 5.83%, which is much higher than that of Pt cathode-based counterpart (3.71%), demonstrating 57.1% of PCE improvement.

Application of a nanostructured, tri-layer TiO2 photoanode for efficiency enhancement in quasi-solid electrolyte-based dye-sensitized solar cells

A nanostructured, tri-layer TiO2 photoanode consisting of a rice grain-shaped (RG), electrospun TiO2 nanofiber layer (NF) sandwiched between two TiO2 nanoparticle (NP) layers has been successfully used for the efficiency enhancement in quasi-solid-state electrolyte-based dye-sensitized solar cells (DSSCs). A polyethylene oxide-based quasi-solid-state or gel electrolyte with binary iodide salts with optimized composition was employed as the electrolyte. The solar cell parameters of this DSSC were compared with DSSCs fabricated using conventional NP TiO2 photoanode. While the DSSCs fabricated with conventional NP photoanode showed an average efficiency of 5.76% with J sc of 12.12 mA cm−2 and V oc of 718.7 mV, the DSSCs fabricated with three-layer composite TiO2 nanostructured photoanode (TiO2 NP/RG/NP) showed an enhanced efficiency of 6.90% with J sc of 16.93 mA cm−2 and V oc of 672.3 mV. This shows that the three-layered composite photoanode with “rice grain-shaped” nanostructure is much superior to single-layered TiO2 nanoparticle photoanode prepared by conventional method and evidently contributes to the efficiency enhancement by enhanced light harvesting by scattering. Post-treatment of the three-layer photoanode with TiCl4 further enhanced the efficiency up to an impressive 7.30% which is among the highest for a quasi-solid-state DSSC.

Doping effect of aminopyridine analogous in supramolecular quasi-solid polymer electrolyte for DSSCs: improvement in ionic diffusion leading to superior efficiency

In the present work, hydroxy butyl methyl cellulose-based quasi-solid-state polymer gel electrolyte has been prepared by incorporating I−/I3 − couple in ethylene carbonate and propylene carbonate. This bare electrolyte’s properties have been investigated first time by additional doping of amino pyridine analogous moieties such as pyridin-4-amine, di(pyridin-4-yl)amine, and tri(pyridin-4-yl)amine moiety. Effect on ionic conductivity, triiodide diffusion, glass transition temperature, rheology, and photovoltaic performance in dye-sensitized solar cells (DSSC) was briefly evaluated. Addition of dopant creates amorphous loops in the gel matrix, and dopant has lone pair of electrons at the N of pyridile, which attracts the Li+ species of LiI making smooth and fast diffusion of triiodides. Tg and XRD characterizations were performed to prove the immense effect on physical properties. TPA-doped electrolyte shows 4.3 mS/cm conductivity and has explored 3.67% power conversion efficiency in DSSC with N719 sensitizer. This non-volatile type of electrolyte-based DSSCs performs efficiently up 600 h in one sun illumination.

Supramolecular Hemicage Cobalt Mediators for Dye-Sensitized Solar Cells.

A new class of dye-sensitized solar cells (DSSCs) using the hemicage cobalt-based mediator [Co(ttb)]2+/3+ with the highly preorganized hexadentate ligand 5,5'',5''''-((2,4,6-triethyl benzene-1,3,5-triyl)tris(ethane-2,1-diyl))tri-2,2'-bipyridine (ttb) has been fully investigated. The performances of DSSCs sensitized with organic D-π-A dyes utilizing either [Co(ttb)]2+/3+ or the conventional [Co(bpy)3 ]2+/3+ (bpy=2,2'-bipyridine) redox mediator are comparable under 1000 W m-2 AM 1.5 G illumination. However, the hemicage complexes exhibit exceptional stability under thermal and light stress. In particular, a 120-hour continuous light illumination stability test for DSSCs using [Co(ttb)]2+/3+ resulted in a 10 % increase in the performance, whereas a 40 % decrease in performance was found for [Co(bpy)3 ]2+/3+ electrolyte-based DSSCs under the same conditions. These results demonstrate the great promise of [Co(ttb)]2+/3+ complexes as redox mediators for efficient, cost-effective, large-scale DSSC devices.