TiO2 Solar Cells Research Articles

Pyrazine-Based Aromatic Dyes as Novel Photosensitizers with Improved Conduction Band and Photovoltaic Features: DFT Insights for Efficient Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have garnered significant attention due to their exceptional ability to convert solar energy into electricity at a relatively low cost. Novel organic photosensitizers (FZB1-FZB9) from the pyrazine-based aromatic dye (E)-3-(5-(2,3-bis(40-(diphenylamino)-[1,10-biphenyl]-4-yl)-7 (trifluoromethyl)quinoxalin-5-yl)thiophen-2-yl)-2-cyanoacrylic acid (TPPF) have been quantum chemically modeled for their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). The electrochemical and photovoltaic features of modeled dyes are investigated by performing DFT insights, i.e. FMOs, absorption maxima, DOS, TDM, NBO, exciton and binding energy, radiative lifetime analysis (ꚍ), electron-injection (Δ G inject ) and regeneration analysis ( Δ G dye regen )@TiO2. FMO analysis confirmed the better electron injection as HOMO of designed dyes was found to be more positive than redox potential I/I3 (-4.8 eV), and the LUMO appeared more negative than the conduction band of TiO2 (-4.0 eV). The modeled photosensitizers exhibited red shift λmax from 338-494 nm with a lower energy gap from 5.62 eV in FZB (R) to 5.17 eV in FZB9. Bridging modification reduces the exciton and binding energy for designed dye FZB9 and FZB7 compared to reference FZB. The designed dyes appeared with a lower radiative lifetime of up to 1.32 than the reference dye of 1.63, better light harvesting efficiency (LHE), and the highest NBO charge on bridges of designed photosensitizers for enhanced light emitting efficiency. The investigated dyes exhibited more negative values for electron injection, i.e. −0.003 and the highest values of dye regeneration ( Δ G regedye regen ) up to 11.717, which unveils innovative and effective injection of electrons toward semiconductor TiO2. Among all dyes, FZB8 proved best with the novel bridging modification that enables quick charge transfer as exhibited the lowest gap (5.17 eV), lowest excitation energy, better LHE, highest charge on LUMO and more negative electron injection (Δ G inject ) . The outcomes of this computational study confirmed that this research established a new benchmark for achieving novel and efficient photosensitizers, thus recommending them for future DSSC applications.

High Electronic Coupling between Cu Complexes and Oxidized Dyes Confirmed by Measurements of Driving Force Dependent Regeneration Kinetics in Minimal Electrolyte System.

We confirm fast regeneration kinetics between copper complexes and oxidized organic dyes and the major contribution of electronic coupling (HDA). The highest efficiency of dye-sensitized TiO2 solar cells has been shown by employing Cu complex redox couples. Various groups have reported a fast regeneration rate of oxidized dyes by Cu complexes giving a low driving force attributed to low reorganization energy (λ), but the effect of HDA has not been evaluated. The values of HDA and λ can be derived from driving force dependent transient absorption (TA) measurements. However, analyzing TA decay using Cu complexes is not trivial because accelerated recombination by the presence of Cu2+ complexes and biphasic TA decay often complicates the analysis. Here we employ 16 Cu1+ and Co2+ complexes and two dyes. To simplify the system, i.e., making a minimal electrolyte system, Cu2+ and Co3+ complexes and a common additive of 4-tert-butylpyridine are not used. From the driving force dependent TA decays of oxidized dyes by both Cu1+ and Co2+ complexes, λ for the combination of the Cu complexes and dyes is found to be about 0.15 eV lower than that of Co complexes. Approximately 3 to 5 times higher HDA values of Cu complexes than those of Co complexes are obtained, which is the dominant factor for faster rates. The values vary with the structure of the molecules, showing the possibility of increasing the HDA values further. The higher HDA values of a Cu complex than that of a Co complex are also reproduced by quantum chemical calculations.

Study of chlorophyll dye from peppermint (mentha spicata) used as a sensitizer in TiO2 solar cells

Abstract Chlorophyll from peppermint (mentha spicata) was evaluated as a natural dye sensitizer in TiO2 solar cells. The final photoconversion efficiency depended on the solvent used as chlorophyll dispersant and the technique used to sensitize the mesoporous TiO2 film. Evaluated sensitization techniques included pipetting, immersion, and electrophoresis. Best solar cell performance was obtained using methanol as solvent simultaneously with electrophoresis. A short circuit current density (J sc) of 0.174 mA/cm2 and an open circuit voltage (V oc) of 0.508 V were obtained. The photoconversion efficiency reached 0.39 %. However, sensitizing by the pipetting technique allowed a photoconversion efficiency of 0.35 % with better reproducibility.

A bacteriorhodopsin-based biohybrid solar cell using carbon-based electrolyte and cathode components

There is currently a high demand for energy production worldwide, mainly producing renewable and sustainable energy. Bio-sensitized solar cells (BSCs) are an excellent option in this field due to their optical and photoelectrical properties developed in recent years. One of the biosensitizers that shows promise in simplicity, stability and quantum efficiency is bacteriorhodopsin (bR), a photoactive, retinal-containing membrane protein. In the present work, we have utilized a mutant of bR, D96N, in a photoanode-sensitized TiO2 solar cell, integrating low-cost, carbon-based components, including a cathode composed of PEDOT (poly(3,4-ethylenedioxythiophene) functionalized with multi-walled carbon nanotubes (CNT) and a hydroquinone/benzoquinone (HQ/BQ) redox electrolyte. The photoanode and cathode were characterized morphologically and chemically (SEM, TEM, and Raman). The electrochemical performance of the bR-BSCs was investigated using linear sweep voltammetry (LSV), open circuit potential decay (VOC), and impedance spectroscopic analysis (EIS). The champion device yielded a current density (JSC) of 1.0 mA/cm2, VOC of −669 mV, a fill factor of ~24 %, and a power conversion efficiency (PCE) of 0.16 %. This bR device is one of the first bio-based solar cells utilizing carbon-based alternatives for the photoanode, cathode, and electrolyte. This may decrease the cost and significantly improve the device's sustainability.

UV-robust and efficient perovskite solar cells enabled by interfacial photocatalysis suppression and defect passivation

A UV absorber, 4,4′-oxybisbenzoic acid, was first utilized as a modification layer between TiO2 and perovskite solar cells. An impressive stability under extreme UV irradiation was achieved, and a PCE of up to 22.14% was obtained.

Twenty-Two Percent Efficient Pb-Free All-Perovskite Tandem Solar Cells Using SCAPS-1D

Herein, we reported the simulation study of lead (Pb)-free all-perovskite tandem solar cells using SCAPS-1D. Tandem solar cells are comprised of two different cells which are known as the top cell and the bottom cell. We simulated tandem solar cells using methyl ammonium germanium iodide (MAGeI3) as the top subcell absorber layer due to its wide band gap of 1.9 eV. Further, FA0.75MA0.25Sn0.25Ge0.5I3 = FAMASnGeI3 was used as the bottom subcell absorber layer due to its narrow band gap of 1.4 eV. The tandem solar cells were simulated with MAGeI3 as the top cell and FAMASnGeI3 as the bottom subcell using SCAPS-1D. Various electro-transport layers (ETLs) i.e., titanium dioxide, tin oxide, zinc oxide, tungsten trioxide, and zinc selenide, were used to examine the impact of ETL on the efficiency of tandem solar cells. The observations revealed that TiO2 and ZnSe have more suitable band alignment and better charge-extraction/transfer properties. A reasonably improved efficiency of 23.18% and 22.4% have been achieved for TiO2 and ZnSe layer-based tandem solar cells, respectively.

Nature of the Ultrafast Interligands Electron Transfers in Dye-Sensitized Solar Cells.

Charge-transfer dynamics and interligand electron transfer (ILET) phenomena play a pivotal role in dye-sensitizers, mostly represented by the Ru-based polypyridyl complexes, for TiO2 and ZnO-based solar cells. Starting from metal-to-ligand charge-transfer (MLCT) excited states, charge dynamics and ILET can influence the overall device efficiency. In this letter, we focus on N34- dye ( [Ru(dcbpy)2(NCS)2]4-, dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) to provide a first direct observation with high time resolution (<20 fs) of the ultrafast electron exchange between bpy-like ligands. ILET is observed in water solution after photoexcitation in the ∼400 nm MLCT band, and assessment of its ultrafast time-scale is here given through a real-time electronic dynamics simulation on the basis of state-of-the-art electronic structure methods. Indirect effects of water at finite temperature are also disentangled by investigating the system in a symmetric gas-phase structure. As main result, remarkably, the ILET mechanism appears to be based upon a purely electronic evolution among the dense, experimentally accessible, MLCT excited states manifold at ∼400 nm, which rules out nuclear-electronic couplings and proves further the importance of the dense electronic manifold in improving the efficiency of dye sensitizers in solar cell devices.

Influence of CdS sensitization on the photovoltaic performance of CdS:TiO2 solar cell

Influence of CdS sensitization on the photovoltaic performance of CdS:TiO2 solar cell

Photovoltaic study of TiO2 films sensitized with Cu2O and CdS QDs for applications in a solar cell

The effect of the Cu2O and CdS QD particles on the photoconversion efficiency of the TiO2 solar cell was analyzed. The Cu2O particles were synthesized using the chemical reduction method, and the CdS QDs were prepared using the SILAR method. The JV curves indicated that the photocurrent of the TiO2/ZnS solar cell was 0.04 ​mA/cm2, while the introduction of Cu2O particles in the TiO2/Cu2O/ZnS configuration showed that the cell exhibited a photocurrent forty times higher, of 1.82 ​mA/cm2. With the introduction of CdS QD in the following TiO2/Cu2O/CdS/ZnS and TiO2/CdS/ZnS/Cu2O solar cell configurations, the current increased to 5.34 ​mA/cm2 and 5.57 ​mA/cm2, respectively, being three times higher compared to TiO2/Cu2O/ZnS. Although the values of FF and Voc decreased in the TiO2 solar cells sensitized with Cu2O and CdS, probably due to the introduction of new defects, the photogenerated current increased significantly. These results lead to an improvement in photoconversion efficiency, η=0.38% for TiO2/Cu2O/CdS/ZnS and η ​= ​0.65% for TiO2/CdS/ZnS/Cu2O which is due to an increase in the absorption range. Cu2O particles contribute as a sensitizer probably improves the alignment of the conduction band between the different materials and the defect passivation effect of CdS on the surface of TiO2.

Designing All‐Inorganic EuO‐Sensitized TiO2 Solar Cell from 4f‐3d Composite Bandgap Structure

AbstractTiO2 dye‐sensitized solar cells (DSSCs) have blazed a new trail out of traditional silicon‐based photovoltaics. However, extensive applications of DSSCs are limited by the use of organic photosensitizers and liquid electrolytes, which raises strict requirements on dye synthesis and cell encapsulation. Considering the electron‐donating tendency and optical activity of Eu2+, EuO semiconductor is chosen as inorganic substitution of organic dyes based on Eu2+↔Eu3+ redox transition. Through first‐principle calculations, 4f‐3d composite bandgap is found in TiO2/EuO heterostructure, reducing the bandgap of pure TiO2 from 3.2 to 0.99 eV. This energy corresponds to near‐infrared photon and thus covers the whole range of visible light, which will significantly enhance the light‐absorption efficiency of TiO2. Similar electronic feature also appears in ATiO3 (A = Sr, Ba)/EuO interfaces. The bandgap value is critically dependent on bonding type and geometry structure of TiO6 octahedra at the interface. On this basis, all‐inorganic EuO‐sensitized TiO2 solar cell is theoretically designed, where EuO serves as photosensitizer to replace dye molecules and inject electrons into TiO2 anode under light excitation. This finding not only provides prospect for all‐inorganic DSSCs, but also sheds light on high‐efficiency TiO2‐based photocatalysis and EuO‐relevant spintronics with rich interfacial physics.

Influence of citric acid linker molecule on photovoltaic performance of CdS quantum dots-sensitized TiO2 solar cells

Influence of citric acid linker molecule on photovoltaic performance of CdS quantum dots-sensitized TiO2 solar cells

Magnesium-doped green solar cells using natural chromophores

The current study tested the hypothesis of whether specific metal doping may show synergy with plant chromophore-based solar cells using a titanium dioxide (TiO2) electrode. A natural dye-sensitized, magnesium-doped TiO2 solar cell was assembled using the methanol extract from various western African plants including Lawsonia inermis (henna). Mg2+–TiO2 nanoparticles were applied on fluorine-doped tin oxide (FTO) glass to serve as the photoanode of the solar cells with $$I^{ - } /I_{3}^{ - }$$ electrolyte. A surface-modified TiO2 photoanode was prepared through the immersion method using a selective dopant including magnesium and potash. An inductively coupled plasma-optical emission spectrophotometer (ICP-OES) was utilized to characterize the potash dopant for comparative analysis. Instrumental analysis including ultraviolet–visible spectroscopy (UV–Vis), infrared spectroscopy (IR), and gas chromatography and mass spectrometry (GC–MS) analysis were carried out to characterize the natural henna dye extracts. The photovoltaic performance including open-circuit voltage (Voc), short circuit current density (Jsc), current (I), and power output (P) was analyzed quantitatively. ICP-OES analysis demonstrated that potash contains a composite of 26 elemental metals with K and Na accounting for 72.2% (5192.2 mg/kg) and 9.5% (682.6 mg/kg), respectively. GC–MS analysis confirmed the presence of lawsone and tocopherol in henna extracts. Among the tested samples, the Mg-doped TiO2 group generated the highest improvement in Jsc, from 0.66 to 1.28 (mA/cm2), representing a 93% increase. Our experiments demonstrated that the presence of magnesium as a doping agent improves the photogenerated electron transport and the light-harvesting performance of the henna dye to increase the overall efficiency of light-to-electricity conversion of the photovoltaic cells.

Synthesis of high quality PbS colloidal quantum dots by ultrasonic bath as photosensitizers in a TiO2 solar cell

We report a novel and simple method for the synthesis of high quality PbS colloidal quantum dots (CQDs) by controlled precipitation between Pb2+ cations and S2− anions inside aqueous nanodroplets that are generated by an ultrasonic bath operated at 35 ​kHz frequency. The synthesized PbS CQDs have cubic crystal structure with an average particle size of 6.8 ​nm, a size dispersion of 15% and an optical band gap of 0.72 ​eV. PbS CQDs were deposited uniformly by electrophoretic method on a TiO2 photoelectrode applying 200 ​V for 60 ​min and used as photosensitizers in a TiO2 solar cell. Their photovoltaic parameters were studied under 1 sun illumination. Remarkably, we obtain power conversion efficiencies similar to those found in TiO2 sensitized solar cells made with high quality PbS CQDs synthesized by hot injection method.

Identification of the loss mechanisms in TiO2 and ZnO solar cells based on blue, piperidinyl-substituted, mono-anhydride perylene dyes

While perylene dyes have suitable properties for dye-sensitized solar cells (DSSCs), the performance has been limited by various factors that are not fully understood yet. We prepared DSSCs based on mesoporous TiO2 and ZnO with three blue piperidinyl-substituted perylene derivatives and three different electrolyte solutions. The perylene dyes have different non-conjugated side units and HOMO levels, and the anchoring group is a mono-anhydride moiety that would provide better compatibility with ZnO. Using current - voltage characteristics, incident and absorbed photon-to-electron conversion efficiency measurements (IPCE/APCE), stepped light induced transient measurements, and transient absorption spectroscopy (TAS), the limiting processes governing the solar cell performance are analyzed. With TiO2, weak electronic coupling between the dye and TiO2 appears to limit the injection efficiency, while for ZnO, the coupling seems stronger resulting in higher injection yield and higher APCE. The HOMO levels and structural differences of the dyes have only a minor impact on the reduction kinetics of oxidized dyes. DFT calculations illustrate that the HOMO and LUMO of the dye are spatially not well separated. This probably leads to a short-excited state lifetime, resulting in the relatively low APCE values. The TA measurements of the cells with and without redox couple show similar decays, suggesting the oxidized dyes in the solar cells are reduced not only by redox couple but also by electrons from TiO2 and ZnO, further decreasing the conversion efficiency. These results suggest the design rules to be followed for the successful implementation of all-organic perylene-based dyes for DSSCs.

Efficient dye-sensitized solar cell based on a new porphyrin complex as an inorganic photosensitizer

The synthesis of new porphyrin complexes that can absorb light in a broad range of the spectrum is very important for getting a high efficiency in dye-sensitized solar cells. The primary reason for using these complexes is good photophysical characteristic like good absorption and high quantum efficiency. Most of the metal porphyrin shows good photophysical characteristics with changing their ligands. In this work, the synthesis of a new Zn-porphyrin complex, that has a good spectral and electrochemical characteristic, is reported. Then, this complex is used as a dye in dye-sensitized solar cells, using titanium dioxide as a semiconductor. The application of this complex in a dye-sensitized nanocrystalline TiO2 solar cell has indicated a short circuit density of 11.60 mA, an open circuit potential of 0.65 V with an overall efficiency of 5.33%. The overall conversion efficiency of this system is due to the efficient electron injection into the conduction band during light absorption. In this work, the synthesis of a new Zn-porphyrin complex, together with its spectral and electrochemical properties, is described. The application of this complex in a dye-sensitized nanocrystalline TiO2 solar cell indicated a short circuit density of 11.60 mA, an open circuit potential of 0.65V with an overall efficiency of 5.33%.

3D Structural Optimization of Zinc Phthalocyanine-Based Sensitizers for Enhancement of Open-Circuit Voltage of Dye-Sensitized Solar Cells

We designed and synthesized two zinc phthalocyanine sensitizers (PcS27 and PcS28), substituted with branched or cyclic alkoxy chains, to investigate the structural effect of peripheral alkyl chains on the performance of dye-sensitized TiO2 solar cells. The bulky cyclic alkyl chains of PcS28 decreased the adsorption density of PcS28 on the TiO2 electrode, while the terminal branches of alkoxy chains of PcS27 did not influence the adsorption density in comparison to the previously published PcS20 with linear alkoxy chains. Under one sun conditions, PcS27 cells exhibited higher open-circuit voltage but a slightly lower energy conversion efficiency, 6.0% less than PcS20. These results suggest that the small alternation of alkoxy chains resulted in decreasing electron pushing ability of peripheral phenoxy units, giving lower short-circuit current.

Effect of PbS quantum dot-doped polysulfide nanofiber gel polymer electrolyte on efficiency enhancement in CdS quantum dot-sensitized TiO2 solar cells

Quantum dot-sensitized solar cells (QDSSCs) are among the most promising low cost third generation solar cells. Semiconductor quantum dots have unique properties such as high molar extinction coefficients, tunable energy gap by the quantum confinement effect and the ability of multiple exciton generation. In this study, stable CdS QDSSCs were fabricated by using polysulfide liquid electrolyte and also by using cellulose acetate nanofiber-based gel electrolyte. Incorporation of PbS Q dots to the liquid or gel electrolyte showed a significant enhancement in solar cell efficiency. Under the simulated light of 100 mW cm−1 the efficiency of the polysulfide liquid electrolyte based CdS QD solar cells increased from 1.19% to 1.51% and the efficiency of the nanofibre gel electrolyte based CdS QD solar cells increased from 0.94% to 1.46% due to the incorporation of 5% (wt/wt) PbS Q dots into the respective electrolytes. The efficiency increase has been attributed to the increase in short circuit photocurrent density due to increased sulfide ion (S2−) conductivity evidently caused by indirect ionic dissociation facilitated by PbS QDs.

Performance improvement of TiO2/CuO by increasing oxygen flow rates and substrate temperature using DC reactive magnetron sputtering method

In the present study, TiO2/CuO solar cells have been successfully fabricated for the first time using DC reactive magnetron sputtering for application in PV devices. To improve the performance of TiO2 and CuO solar cells, we increased the oxygen flow rates and substrate temperature during the deposition of TiO2 and CuO thin films compared with our previous work. The structural features by X-ray diffraction and energy-dispersive X-ray spectroscopy spectrum(s) with the atomic percent were analyzed. Next, scanning electron microscopy images with cross-sections were compared. Finally, current–voltage characteristics (I-V) capacitance–voltage (C-V) were determined. The PV parameters, open circuit voltage, short circuit current, fill factor, and efficiency, were then analyzed and compared. We observed a maximum efficiency of 0.24 % and an open circuit voltage of 0.14 V. To the best of our knowledge, we attained the fourth highest efficiency reported to date. The C-V and I-V characteristics were compared with theoretical calculations obtained with the solar cell capacitance simulator, SCAPS, program.

Performance Comparison of Low Cost TiO2 and ZnO Solar Cells Sensitized with Coumarin C343

Performance Comparison of Low Cost TiO2 and ZnO Solar Cells Sensitized with Coumarin C343

Photovoltaic and capacitance measurements of solar cells comprise of Al-doped CdS (QD) and hierarchical flower-like TiO2 nanostructured electrode

This work focuses on the performance of Al-doped CdS quantum dot (QD)/TiO2 solar cells. The devices were analyzed through current-voltage and capacitance-voltage measurements. It was observed from the analysis of absorption spectra that TiO2 nanowires improve the absorption of light of Al doped CdS QDs both in visible and near infrared (NIR) range. Current-voltage characteristics curve of Al doped CdS/TiO2 at different illuminations show that decrease in illumination (from 100 to 5 mW/cm2), affects the voltage and current correspondingly. Power-voltage curve at various intensities of light indicates that power of the solar cell increases with the increase of the bias voltage and reaches its maximum value at each value of light illumination intensity. The peak value of power at maximum illumination is 35 µW at 0.20 V and with decreasing illumination the peak value decreases. Capacitance-voltage measurements reveal that by increasing the bias voltage from −2.0 V to 0 V, the capacitance voltage indicates the rising trend. However, at 5 kHz and 10 kHz frequencies, it was observed that a marginal increase of capacitance was noticed with exceeding bias voltage. The results revealed that subsequent addition of the TiO2 nanowires significantly improved the output performance of QDSSC.