Role of Co-Sensitizers in Dye-Sensitized Solar Cells

Unleashing synergistic co-sensitization of BOA dyes and Ru(ii) complexes for dye-sensitized solar cells: achieving remarkable efficiency exceeding 10% through comprehensive characterization, advanced modeling, and performance analysis

Dye-sensitized solar cells (DSSCs) have emerged as a promising alternative for renewable energy conversion. The synthesis and characterization of the 2-acetonitrile-benzoxazole (BOA) sensitizer MSW-1-4 are presented along with their chemical structures. Four new organic dyes, MSW-1 through MSW-4, were synthesized using BOA as the main building block, with different additional donor groups. The dyes were characterized and their photophysical and electrochemical properties were studied. Computational modeling using density functional theory (DFT) was performed to investigate their potential as sensitizers/co-sensitizers for photovoltaic applications. The modeling showed a distinct charge separation between the donor and acceptor parts of the molecules. For dye-sensitized solar cells, MSW-4 performed the best out of MSW-1-3 and was also better than the reference dye D-5. Moreover, MSW-3 was co-sensitized along with a typical highly efficient bipyridyl Ru(ii) sensitizer, N719, reference dye D-5, and metal-free dye MSW-4, to induce light harvesting over the expanded spectral region and hence improve the efficiency. Co-sensitizer (MSW-3 + N719) showed an improved efficiency of 10.20%. This outperformed a solar cell that used only N719 as the sensitizer, which had an efficiency of 7.50%. The appropriate combined dye loading of MSW-3 + N719 enabled good light harvesting and maximized the photoexcitation. The synergistic effect of using both MSW-3 and N719 as co-sensitizers led to enhanced solar cell performance compared with using N719 alone.

Optimizing photovoltaic performance of squaraine derivative dyes: a DFT study on different anchoring groups

In this study, we designed squaraine-based dyes with a 2-amino pyrrole donor unit and acene groups like anthracene and pentacene. These dyes incorporate three different electron-withdrawing groups - cyanoacrylate (A1), phosphonate (A2) and boronic acid (A3) - as linkers to the TiO2 semiconductor. The spectroscopic, electronic and photochemical properties of these compounds were investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) simulations. Compared to the squarylium dye, SQD, the UV-vis data indicate excellent absorption especially for pentacene-based dyes, which extended beyond 920 nm, enhancing the panchromatic effect. The calculated excited-state lifetimes of these dyes were notably longer than SQD, particularly for those containing pentacene and either A1 or A2 withdrawing groups, with lifetimes approximately four times longer. In contrast, boronic acid derivatives had shorter excited-state lifetimes, hindering charge transfer. Simulations suggest all sensitizers can inject electrons into TiO2 and be efficiently regenerated by electron transfer from the electrolyte. The best results were achieved with pentacene and A1 or A2 as linkers, notably A1 dyes achieve superior short circuit photocurrent, J sc, and power conversion efficiency, PCE, with over 50% improvement compared to SQD. Phosphonate derivatives exhibited the highest energy adsorption on TiO2 while still achieving significant open-circuit voltage, V oc, J sc, and PCE values. After surface adsorption, all dyes displayed efficient electron recovery, with HOMO levels significantly dropping below -4.8 eV. Our study demonstrates that computational design can significantly enhance experimental work, offering valuable insights to improve dye design and boost the performance of dye-sensitized solar cells.

Excited Charge Separation in a π-Interacting Phenothiazine-Zinc Porphyrin-Fullerene Donor-Acceptor Conjugate

We have designed, synthesized, and characterized a donor-acceptor triad, SPS-PPY-C60, that consists of a π-interacting phenothiazine-linked porphyrin as a donor and sensitizer and fullerene as an acceptor to seek charge separation upon photoexcitation. The optical absorption spectrum revealed red-shifted Soret and Q-bands of porphyrin due to charge transfer-type interactions involving the two ethynyl bridges carrying electron-rich and electron-poor substituents. The redox properties suggested that the phenothiazine-porphyrin part of the molecule is easier to oxidize and the fullerene part is easier to reduce. DFT calculations supported the redox properties wherein the electron density of the highest molecular orbital (HOMO) was distributed over the donor phenothiazine-porphyrin entity while the lowest unoccupied molecular orbital (LUMO) was distributed over the fullerene acceptor. TD-DFT studies suggested the involvement of both the S2 and S1 states in the charge transfer process. The steady-state emission spectrum, when excited either at porphyrin Soret or visible band absorption maxima, revealed quenched emission both in nonpolar and polar solvents, suggesting the occurrence of excited state events. Finally, femtosecond transient absorption spectral studies were performed to witness the charge separation by utilizing solvents of different polarities. The transient data was further analyzed by GloTarAn by fitting the data with appropriate models to describe photochemical events. From this, the average lifetime of the charge-separated state calculated was found to be 169 ps in benzonitrile, 319 ps in dichlorobenzene, 1.7 ns in toluene for Soret band excitation, and ∼320 ps for Q-band excitation in benzonitrile.

Predicting the dye-sensitized solar cell performance of novel linear carbon chain-based dyes: insights from DFT simulations

In this paper, we employ density functional theory (DFT) simulations to predict the energy conversion efficiency of a novel class of organic dyes based on linear carbon chain (LCC) linkers for application in dye-sensitized solar cells (DSSCs). We investigate the role of the anchoring group, which serves as a bridge connecting the linker and the surface. Specifically, we compare the performance of cyanoacrylic acid, dyes PY-4N and PY-3N, with that of phosphonate derivatives, dyes PY-4NP and PY-3NP, wherein the carboxylic group of the cyanoacrylic moiety is replaced with phosphonic acid. The observed variations in the UV/VIS absorption spectra have a slight impact on the light harvesting efficiency (LHE). Based on the empirical parameters we have taken into account, the electron injection efficiency (Φinj) and electron collection efficiency (ηcoll) values do not impact the short-circuit current density (JSC) values of all the studied dyes. The open-circuit voltage (Voc) is theoretically predicted using the improved normal model (INM) method. Among the dyes, PY-4N and PY-3N demonstrate the highest Voc values. This can be attributed to a more favorable recombination rate value, which is related to the energy gap between the HOMO level of the dyes and the conduction band minimum (CBM) of the surface. Dyes PY-4N and PY-3N are predicted to demonstrate remarkably high photoelectric conversion efficiency (PCE) values of approximately 21.79% and 16.52%, respectively, and therefore, they are expected to be potential candidates as organic dyes for applications in DSSCs. It is worth noting that PY-4NP and PY-3NP exhibit strong adsorption energy on the surface and interesting PCE values of 11.66% and 8.29%, respectively. This opens up possibilities for their application in DSSCs either as standalone sensitizers or as co-sensitizers alongside metal-free organic dyes or organic-inorganic perovskite solar cells.

Computational study of linear carbon chain based organic dyes for dye sensitized solar cells

Spectroscopic, electronic and electron injection properties of a new class of linear carbon chain (LCC) based organic dyes have been investigated, by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT), for application in dye-sensitized solar cells (DSSCs). The photophysical properties of LCC-based dyes are tuned by changing the length of the linear carbon chain; UV/VIS absorption is red-shifted with increasing LCC length whereas oscillator strength and electron injection properties are reduced. Excellent nonlinear optical properties are predicted in particular for PY-N4 and PY-S4 dyes in the planar conformation. Results indicate that a LCC-bridge produces better results compared to benzene and thiophene bridges. Simulations of I--Dye@(TiO2)14 and Dye@(TiO2)14 anatase complexes indicate that designed dyes inject electrons efficiently into the TiO2 surface and can be regenerated by electron transfer from the electrolyte. Superior properties in terms of efficiency are shown by compounds with a pyrrole ring as the donor group and PY-3N is expected to be a promising candidate for applications, however all the investigated dyes could provide a good performance in solar energy conversion. Our study demonstrates that computational design can provide a significant contribution to experimental work; we expect this study will contribute to future developments to identify new and highly efficient sensitizers.

Solar energy conversion using first row d-block metal coordination compound sensitizers and redox mediators

The use of renewable energy is essential for the future of the Earth, and solar photons are the ultimate source of energy to satisfy the ever-increasing global energy demands. Photoconversion using dye-sensitized solar cells (DSCs) is becoming an established technology to contribute to the sustainable energy market, and among state-of-the art DSCs are those which rely on ruthenium(ii) sensitizers and the triiodide/iodide (I3 -/I-) redox mediator. Ruthenium is a critical raw material, and in this review, we focus on the use of coordination complexes of the more abundant first row d-block metals, in particular copper, iron and zinc, as dyes in DSCs. A major challenge in these DSCs is an enhancement of their photoconversion efficiencies (PCEs) which currently lag significantly behind those containing ruthenium-based dyes. The redox mediator in a DSC is responsible for regenerating the ground state of the dye. Although the I3 -/I- couple has become an established redox shuttle, it has disadvantages: its redox potential limits the values of the open-circuit voltage (V OC) in the DSC and its use creates a corrosive chemical environment within the DSC which impacts upon the long-term stability of the cells. First row d-block metal coordination compounds, especially those containing cobalt, and copper, have come to the fore in the development of alternative redox mediators and we detail the progress in this field over the last decade, with particular attention to Cu2+/Cu+ redox mediators which, when coupled with appropriate dyes, have achieved V OC values in excess of 1000 mV. We also draw attention to aspects of the recyclability of DSCs.

Effect of auxiliary acceptor on D-π-A based porphyrin sensitizers for dye sensitized solar cells

Among the tetrapyrrolic class of compounds, porphyrin based sensitizers have attracted considerable attention due to their excellent performance in dye-sensitized solar cells (DSSCs). Herein, two new donor-[Formula: see text]-acceptor (D-[Formula: see text]-A) concept based porphyrin sensitizers having donor 3-ethynylphenothiazine tethered at meso- position, zinc porphyrin as [Formula: see text]-spacer and acceptor either 3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylic acid (LG22), and 3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)thiophene-2-yl)-2-cyanoacrylicacid (LG23) were designed and synthesized. Both sensitizers were characterized by various spectroscopic techniques and electrochemical methods. Optical, electrochemical and optimized studies suggest that these dyes are suitable for sensitization of nanocrystalline TiO2. The optimized device studies showed the power conversion efficiencies (PCE) of 1.86% and 1.37% for LG22 and LG23 dyes, respectively using [Formula: see text]/[Formula: see text] liquid redox shuttle. Finally, Charge Extraction (CE), Intensity Modulated Photovoltage Spectroscopy (IMVS), Intensity Modulated Photocurrent Spectroscopy (IMPS) and Open Circuit Voltage Decay (OCVD) measurements were adopted to understand in detail the electron transfer properties at various interfaces in a way to understand the performance limiting processes in these novel porphyrin sensitizers.

The influence of three diphenylpyran isomer co-sensitizers with different sterical structures on N719-based dye sensitized solar cells

Aiming to explore the relationship between the molecular structure and photovoltaic performance, three pyran isomer dyes DO, DM and DP were synthesized and applied as a co-sensitizer with N719 dye in dye-sensitized solar cells (DSCs). These sensitizers were investigated by theoretical calculation, UV-vis absorption spectroscopy and cyclic voltammetry measurement to understand their structure, optical and electrochemical properties. The DSC devices based on N719 and the co-sensitizers were characterized using I–V tests, incident photon-to-current conversion efficiency and electrochemical impedance spectroscopy measurements. As compared to the standard N719-based DSCs, the co-sensitization system of N719 and DM with the most sterical structure exhibited an enhancement of the power conversion efficiency (PCE) by 18% from 7.60% to 8.96%. Both the short-circuit photocurrent density (J_sc) and open-circuit voltage (V_oc) of the co-sensitized systems were increased resulting from the better maintained N719 dye loading amount on TiO₂ as well as the prevention of dye aggregation. Co-sensitization of the DO molecule with less steric hindrance reduced the desorbed N719 dye amount by half leading to a decline of the photo-harvesting ability and photocurrent generation in DSCs.

This work applied three isomers with different spatial geometries as co-sensitizers to enhance N719-based dye sensitized solar cells.

Bis(4′-tert-butylbiphenyl-4-yl)aniline (BBA)-substituted A3B zinc porphyrin as light harvesting material for conversion of light energy to electricity

Limited synthetic steps via low-cost starting materials are needed to develop large-scale light-active materials for efficient solar cells. Here, novel bis(4[Formula: see text]-tert-butylbiphenyl-4-yl)aniline (BBA) based A3B zinc porphyrin (GB) is synthesized and applied as a light harvesting/electron injection material in dye-sensitized solar cells. The GB sensitizer was characterized by various spectroscopic techniques and the optimized device shows [Formula: see text] of 10.98 ± 0.37 mA/cm2 and power conversion efficiency (PCE) of 3.34 ± 0.26%. In addition, performance is enhanced up to ∼3.9% by the addition of co-adsorbent 3a,7a-dihydroxy-5b-cholic acid (chenodeoxycholic acid, CDCA) to minimize [Formula: see text]-[Formula: see text] staking of the planar porphyrin macrocycles. These results demonstrate that novel broad-absorbing light-active material (GB) could be used for indoor solar panels.

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.

Research Progress on Photosensitizers for DSSC

Dye sensitized solar cells (DSSC) are considered one of the most promising photovoltaic technologies as an alternative to traditional silicon-based solar cells, for their compatibility with low-cost production methods, their peculiar optical and mechanical properties and the high indoor efficiency. Photosensitizers represent one of the most important components of a DSSC device and probably the most thoroughly investigated in the last twenty years, with thousands of dyes that have been proposed and tested for this kind of application. In this review we aimed to provide an overview of the three main classes of DSSC photosensitizers, namely ruthenium(II) polypyridyl complexes, Zn-porphyrin derivatives and metal-free organic dyes. After a brief introduction about the architecture and operational principles of a DSSC and the state of the art of the other main components of this type of device, we focused our discussion on photosensitizers. We have defined the numerous requirements DSSC photosensitizers should satisfy and have provided an overview of their historical development over the years; by examining specific dyes reported in the literature, we attempted to highlight the molecular design strategies that have been established for the optimization of their performance in real devices both in terms of efficiency (which recently reaches an outstanding 14.3%) and operational stability. Finally, we discussed, in the last section, the possible future developments of this intriguing technology.