High-performance Dye-sensitized Solar Cells Research Articles

Nitrogen and sulfur co-doped porous carbon obtained from direct carbonization of a renewable biomass for counter electrode of efficient dye-sensitized solar cells

It is highly necessary to fabricate cost-effective counter electrode for promoting the development and practical deployment of dye-sensitized solar cells (DSSCs). Herein, nitrogen and sulfur co-doped porous carbon (NSPC) is prepared through directly carbonizing a renewable biomass, Eupatorium fortunei Turcz., and used as an alternative to expensive Pt to fabricate low-cost counter electrode for high-performance DSSCs. Scanning electron microscopy and N2 adsorption analyses demonstrate that the obtained carbon sample displays a hierarchical pore structure containing macropore channels and well-developed mesopores formed on the wall of macropore channels. X-ray photoelectron spectroscopy measurements suggest that nitrogen and sulfur atoms are doped in the framework of as-prepared carbon sample. These favorable characteristics endow the obtained NSPC counter electrode with a superior electrocatalytic performance. Consequently, the assembled DSSC with NSPC counter electrode shows an efficiency of 8.25%, nearly matching the efficiency of the cell with conventional Pt counter electrode.

Oxygen enriched PAni-based counter electrode network toward efficient dye-sensitized solar cells (DSSCs)

Dye-sensitized solar cells (DSSCs) have great potential as a renewable energy technology assisting combat climate change due to its low cost, adaptability, and sustainability. Oxygen plasma ion doping is a promising strategy to improve the capacity of a low-cost, platinum-free counter-electrodes (CEs) to absorb photons and drive high-performance DSSCs via generating an abundance of active absorption sites. In this instance, novel PAni–ZnO (PZ) composite layers were designed as a CE material and received various in-situ oxygen plasma dosages, including 0, 2, 4, 6, 8, and 10 min, to improve their physiochemical and microstructural feature for the first time, to the best of our knowledge. Physical evaluations of the microstructure, porosity, morphology, contact angle, roughness, electrical, and optical, electrochemical impedance spectroscopy (EIS) features of CEs were conducted in along with an evaluation of J–V variables. Compared to pristine CE substance, the surface nature of the modified hybrids was gradually enhanced as the plasma level rose, reaching an optimum after 8 min (i.e. 0.2 µm for average pore size and average roughness Ra = 7.21 µm). Expanded plasma treatment doses also improved PV cell performance even further: after 4 min at a plasma level, η = 5.41% was obtained, and after 6 min in a oxygen plasma environment, η = 5.81% was obtained. Mixing high energetic plasma ions increased the mobility of charge carriers in PAni composites along with lowered charge carrier recombination through generating an environment that was conducive to charge dissociation. Therefore, longer lifespans and more effective charge transfer inside the photovoltaic cell as a consequence of the increased mobility less resistive losses. In this respect, following 8 min of plasma surface modification of the PZ CE, the optimized efficiency of 6.31% and Jsc of 15.6 mA/cm2 were obtained. The improvement in efficiency equated to a proportion growth of 77% versus a pristine one. This gain was explained by the reality that suffusing a quantity of oxygen plasma free radicals into the PAni system developed continuous channels that enabled the mixture to move electrons more rapidly, hence raising the photovoltaic efficiency. Overall, this study highlights the advantages of regulating heteroatom species and their co-doping, offering a new perspective for the application of heteroatom-doped CE in DSSCs.

Anion Effect on the CuII-Neocuproine Mediator and Its Electrocatalysts for Dye-Sensitized Solar Cells: Polymeric Chalcogenides of PEDOT-PEDTT and [Ag2(SePh)2]n.

The synthetical methodology for the [Cu(dmp)2]2+/1+ (dmp = 2,9-dimethyl-1,10-phenanthroline; neocuproine) complexes has been systematically investigated by using various copper precursors, including CuCl2, Cu(NO3)2, and Cu(ClO4)2. After an anion exchange to trifluoromethanesulfonimide (TFSI), the tetra-coordinated CuII(dmp)2(TFSI)2-Cu(ClO4)2 (7.43%) outperformed the penta-coordinated CuII(dmp)2(TFSI)(NO3)-Cu(NO3)2 (4.30%) and CuII(dmp)2(TFSI)(Cl)-CuCl2. Polymeric chalcogenides, including a conducting copolymeric electrode of PEDOT-PEDTT [PEDOT = poly(3,4-ethylenedioxythiophene); PEDTT = poly(3,4-ethylenedithiothiophene)] and a coordination polymeric electrode of silver bezeneselenolate ([Ag2(SePh)2]n; mithrene), are introduced as the electrocatalysts for [Cu(dmp)2]2+/1+ for the first time. After optimization, dye-sensitized solar cells (DSSCs) based on carbon cloth (CC)/AgSePh-30 (10.18%) showed superior electrocatalytic ability compared to the benchmark CC/Pt (7.43%) due to numerous active sites provided by electron-donating Se atoms, high film roughness, and bottom-up 2D charge transfer routes. The DSSC based on CC/PEDTT-50 (10.38%) also outperformed CC/Pt due to numerous active sites provided by electron-donating S atoms and proper energy band structure. This work sheds light on the future design and synthesis in Cu-complex mediators and functional polymeric chalcogenides for high-performance DSSCs.

Investigate the utilization of novel natural photosensitizers for the performance of dye-sensitized solar cells (DSSCs)

Dye-sensitized solar cells (DSSCs) offer a promising route for sustainable energy conversion, with natural photosensitizers emerging as attractive alternatives to conventional synthetic dyes due to their abundant resources, cost-effectiveness, and eco-friendly materials. However, the efficiency of DSSC utilizing natural photosensitizer remains low. In this study, we investigate the utilization of novel natural photosensitizers extracted from gambier leaves, gambier branches, cinnamon, and petiole of tectona leaves, which contain flavonoids/tannins, chlorophyll, and anthocyanins, aiming to achieve high-performance DSSCs. Five different solvents—ethanol, isopropanol, distilled water, methanol, and Zamzam water—are explored to optimize the extraction process of the natural dyes. The doctor blade technique is employed to coat TiO2 nanomaterials onto ITO glass substrates. UV–Vis spectrophotometry and FTIR spectroscopy are used to characterize the optical properties and structural composition of the dyes, revealing that flavonoid/tannin groups are the primary compounds responsible for light harvesting. The DSSC performance is evaluated under a 30 W lamp, adjusted to light intensity of 10 mW/cm2. As a result, the DSSCs using gambier leaf extract as photosensitizer demonstrate the highest recorded efficiency of 4.71 %, with a Jsc of 2.95 mAcm−2 and a Voc of 0.64 V. These findings contribute to advancing DSSC technology by leveraging the potential of natural photosensitizers for sustainable energy conversion applications.

Study of photosensitizer dyes for high-performance dye-sensitized solar cells application: A computational investigation

Dye-sensitized solar cells (DSSCs) offer a promising, cost-effective alternative to conventional photovoltaic systems. Organic sensitizers, capable of capturing a broad spectrum of sunlight, are key components in DSSCs, but their development and testing are often time-consuming and expensive. Quantum chemical calculations, specifically Density Functional Theory (DFT), have emerged as valuable tools to evaluate potential dye candidates, streamlining the design process and reducing costs. This study investigated the molecular structures and photophysical properties of three common dye classes used in high-performance DSSCs: natural pigments, anthocyanidin pigments, and squaraine dyes. Employing DFT and time-dependent DFT (TD-DFT) at the B3LYP/6–31G level, key parameters such as the HOMO-LUMO energy gap, free energy differences for electron injection and dye regeneration, short-circuit current density, total reorganization energy, and open-circuit voltage were analyzed. Additionally, maximum absorption wavelengths and oscillator strength values were calculated. Our findings provide valuable insights into the optical and electrical properties of these natural dyes, aiding DSSC manufacturers in selecting optimal sensitizers. This research highlights the potential of computational methods in accelerating dye development and improving the overall efficiency of DSSC technology.

Bio-cellulose-derived rGO-supported SmCoO3 hybrid composite photoanode for high performance dye-sensitized solar cells

Bio-cellulose-derived rGO-supported SmCoO3 hybrid composite photoanode for high performance dye-sensitized solar cells

Synergistic Co-sensitization: Unlocking the potential of carbohydrazide chromophores and metal complexes for high-performance dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have emerged as a promising alternative to traditional silicon-based photovoltaic devices due to their low-cost fabrication and tunable optical properties. One effective strategy to improve the light-harvesting capabilities of DSSCs is co-sensitization, which involves combining multiple dyes with complementary absorption properties. In this study, we report the co-sensitization of carbohydrazide-based organic chromophores, namely MRK-1–2, with a benchmark metal-complex dye (black dye) to enhance the photovoltaic performance of DSSCs. The synthesis of MRK-1–2 sensitizers is described, and their photophysical properties are thoroughly analyzed. The absorption spectra of the co-sensitizers revealed distinct absorption bands associated with intramolecular charge transfer and localized aromatic π-π* transitions. Sensitization by MRK-1–2 resulted in photovoltaic efficiencies ranging between 5.02–5.88 %. The ternary co-sensitization system of carbohydrazide-based chromophores (MRK-1–2 + black dye) showed promising potential for enhancing the short-circuit current density (JSC) (20.32–21.45 mA/cm2), open-circuit voltage VOC (691–729 mV), and overall power conversion efficiency (PCE) (9.52–9.90 %). This significant improvement in photovoltaic performance is attributed to the complementary light-harvesting abilities of the co-sensitizers, leading to enhanced light absorption and efficient charge separation and injection processes. The superior performance, with a (PCE) of up to 9.90 %, can be attributed to complementary light absorption, efficient charge injection facilitated by the carboxylic acid moiety in MRK-2, and suppressed charge recombination within the co-sensitized system. The findings of this study will contribute to the advancement of DSSC technologies and bring us closer to sustainable and renewable energy solutions.

Influence of the Selenophene Auxiliary Acceptor in Porphyrin Sensitizers for High-Performance Dye-Sensitized Solar Cells

Influence of the Selenophene Auxiliary Acceptor in Porphyrin Sensitizers for High-Performance Dye-Sensitized Solar Cells

Graphene oxide-titanium oxide-polyaniline hybrid materials for high-performance dye-sensitized solar cells

A new solar cell that comprises a graphene oxide and titanium oxide nanoparticle (NP) composite with graphitized polyaniline (PANI) has been tested in polymer solar cells (PSCs). In this study, a series of conjugated polymers were synthesized and evaluated as the absorber and hole-transport layer materials in organic solar cells, demonstrating the significant impact of the chemical structure of the polymers on solar cell performance. The incorporation of graphene oxide (GOX) and titanium oxide TiO2 NP in conjugated polymers, particularly when graphitized within the PANI layer, led to improved open-circuit voltages compared to structurally similar polymers without NP. The morphology of the composite films was analyzed and related to the photovoltaic performance of polymers synthesized with polyaniline PANI-base and PANI-salt. Optimal NP addition in PANI-salt, PANI-base, PANI-base-TiO2, and PANI-base-GOX resulted in open-circuit voltages and efficiencies of 433 mV and 3.67%, 250 mV and 0.595%, 310 mV and 1.358%, and 520 mV and 2.366%, respectively. This study underscores the importance of polymer film uniformity in the performance of PSCs, with the highest efficiency obtained using a conjugated polymer with the best PANI-salt and PANI-base-GOX films. The research sheds light on the relationship between polymer structure and device photovoltaic performance, which is crucial for the design of new polymeric materials for efficient use and stable OSCs and PSCs.

Nickel selenide embedded polyaniline nanofibers as a counter electrode for high-performance dye-sensitized solar cell

We report an innovative approach involving the hydrothermal synthesis of nickel selenide (NiSe) nanoparticles, which were subsequently embedded onto polyaniline (PANI) nanofibers through ultrasonic mixing at a weight ratio of 1:1 (NiSe to PANI). The physico-chemical properties of the prepared PANI nanofibers, NiSe nanoparticles and NiSe/PANI nanofibers composite were confirmed by XRD, FTIR and Raman spectroscopy studies. Their morphological and structural analysis confirmed that there is no alteration found when NiSe is decorated onto PANI nanofibers surface. This composite material serves as a proficient counter electrode (CE) in dye-sensitized solar cell (DSSC). The electrochemical analyses revealed that NiSe/PANI nanofibers composite CE showed an excellent electrocatalytic activity towards the redox electrolyte than the pristine PANI and pristine NiSe. Further, NiSe/PANI nanofibers composite based DSSC was fabricated and its photoconversion efficiency was found to be 8.46%, which is higher than that of the pristine Pt, PANI and NiSe based CEs. Therefore, NiSe decorated PANI nanofibers composite possibly employed as an alternate CE for DSSC.

Recent progress toward high-performance dye-sensitized solar cells: a review

Recent progress toward high-performance dye-sensitized solar cells: a review

N-doped lotus seedpods biocarbon hybridized with NiCo2S4 as counter electrodes for dye sensitized solar cells

A facile and green approach to composites containing nitrogen doped lotus seedpods biocarbon (NALC) and NiCo2S4 (NCS) is reported. The composites present excellent electrocatalytic activity for reduction from I3− to I− due to the synergistic effect between the nanocrystalline NCS and the NALC. Dye-sensitized solar cells (DSSCs) assembled with the as-prepared NALC@NCS counter electrodes (CEs) achieve impressive photovoltaic conversion efficiency (PCE) of 8.58%, which is higher than that by the same structured cell with Pt (7.85%) and NCS (7.53%) CEs. Compared with other NCS based CEs, the NALC@NCS CEs show good durability and stability, suggesting that combining nanocrystalline catalyst with biocarbon is beneficial to stimulate the synergistic effect, and is a feasible strategy to optimal CEs for high performance DSSCs. Low cost NALC@NCS composites developed in this work are environmentally friendly, stable and efficient, which are believed to be good candidates for Pt-free CE materials in DSSCs and electrocatalysis applications.

Recent advances in the approaches for improving the photovoltaic performance of porphyrin-based DSSCs.

Among other photovoltaic techniques including perovskite solar cells and organic solar cells, dye-sensitized solar cells (DSSCs) are considered to be a potential alternative to conventional silicon solar cells. Porphyrins are promising dyes with the properties of easy modification and superior light-harvesting capability. However, porphyrin dyes still suffer from a number of unfavorable aspects, which need to be addressed in order to improve the photovoltaic performance. This feature article briefly summarizes the recent progress in improving the Voc and Jsc of porphyrin-based DSSCs in terms of molecular engineering by modifying the porphyrin macrocycle, donor and acceptor moieties of the porphyrin dyes, coadsorption of the porphrin dyes with bulky coadsorbents like chenodeoxycholic acid (CDCA), and cosensitization of the porphyrin dyes with metal-free organic dyes. Notably, concerted companion (CC) dyes are described in detail, which have been constructed by linking a porphyrin dye subunit and a metal-free organic dye subunit with flexible alkoxy chains to achieve panchromatic absorption and concerted enhancement of Voc and Jsc. In one sentence, this article is expected to provide further insights into the development of high performance DSSCs through the design and syntheses of efficient porphyrin dyes and CC dyes in combination with device optimization to achieve simultaneously elevated Voc and Jsc, which may inspire and promote further progress in the commercialization of the DSSCs.

Synergism in carbon nanotubes and carbon-dots: counter electrode of a high-performance dye-sensitized solar cell.

Dye-sensitized solar cells (DSSCs) play a crucial role in the realm of renewable energy technology by converting solar energy into electrical energy in an efficient and cost-effective way. In the pursuit of improving the photoconversion efficiency (PCE) of DSSCs, this work aims at fabricating a new counter electrode (CE) using a binary composite of heteroatom-doped carbon dots (C-dots) and functionalized multi-walled carbon nanotubes (o-MWCNTs). We demonstrate that this binary composite exhibits superior performance to pristine o-MWCNTs, resulting in a remarkable enhancement in the PCE. The PCE of the o-MWCNT/C-dots composite was measured at an impressive 4.28%, significantly outperforming the pristine o-MWCNT electrode, which yielded an efficiency of 2.24%. The enhanced performance of the o-MWCNT/C-dots composite can be attributed to the synergistic effects of heteroatom-doped C-dots since their binding to the o-MWCNTs by activated oxygenic surface functional groups increases the surface area from 218 to 253 m2 g-1. This enhanced surface area results from the reduction of π-π stacking interactions of the individual tubes and production of a new hollow channel in the structure that provides an ideal scaffold for I2 adsorption and electron transfer. We demonstrate the role of C-dots on MWCNT's property modulation toward higher PCE by density functional theory (DFT) calculation and electrochemical analysis. Electron-excess N and S doped C-dots exhibit strong catalytic activity, allowing for rapid electron transfer processes in the CE-electrolyte surface via the donor acceptor mechanism, whereas electron-deficient B doped C-dots undermine the cell performance by forming a charge recombination trap at the CE surface. The synthesized composite has higher redox reversibility up to 100 CV cycles and chemical stability, studied by the post-performance material characterization. The findings offer a promising avenue for the development of high-performance DSSCs, which will help to promote sustainable and renewable energy technologies.

Natural Saccharum officinarum (sugarcane) juice assisted TiO2 nanoparticle synthesis for high performance dye-sensitized solar cell

Green chemistry technologies are perceived to be more straightforward, sustainable and cost-effective and therefore explored extensively in recent years. A range of natural reducing and capping agents, viz. proteins, enzymes, and phytochemicals have been used to synthesize TiO2 nanoparticles. The capping agents are vital in stabilizing nanoparticles, avoiding their over-growth and aggregation during synthesis. In this work, green synthesis of TiO2 has been carried out through the sol-gel method using Saccharum officinarum (sugarcane) juice as a capping agent. The optical properties, morphology, size, and porosity of the synthesized TiO2 were characterized by UV, FT-IR, XRD, TEM, and BET respectively. The XRD pattern and TEM confirmed the anatase phase and particle size, while BET revealed surface area and pore sizes. Under irradiance of 100 mWcm−2 light intensity, the photoelectric conversion efficiency using capped TiO2 sensitized with N719 dye was observed to 3.65 %, much enhanced compared to the efficiency 0.69 % observed with the un-capped TiO2. The present study successfully demonstrated that sugarcane phytochemicals have the potential to improve dye-sensitized solar cell (DSSC) efficiency via inducing capping during nucleation in TiO2 synthesis.

Experimental and computational investigation of multi-walled carbon nanotubes decorated by Co–Ni–Se@MoSe2 core–shell as a sustainable counter electrode for dye-sensitized solar cells

The development of a highly active, long-lasting, and cost-effective electrocatalyst as an alternative to platinum (Pt) is a vital issue for the commercialization of dye-sensitized solar cells (DSSCs). Herein, Co–Ni–Se@MoSe2 core–shell structures decorated on multi-walled carbon nanotubes (MWCNTs) were synthesized for the first time by the hydrothermal and probe-sonication methods. The electrochemical performance of this composite was examined using electrochemical measurement techniques. The results showed improved properties and better electrochemical activities of the Co–Ni–Se@MoSe2@MWCNTs than Pt and other counter electrodes (CEs) for the triiodide reduction and exhibit good electrochemical stability in iodine-based electrolytes. The power conversion efficiency of DSSCs based on Co–Ni–Se@MoSe2@MWCNTs CE reaches 9.43%, significantly superior to that with Co–Ni–Se@MoSe2 core–shell (8.13%), Pt CE (7.44%), and other CEs. The notable performance is attributed to the synergistic effect between Co–Ni–Se@MoSe2 and MWCNTs. As a result, the transfer of electrons to the active site is promoted, the agglomeration of Co–Ni–Se@MoSe2 is hampered, and more active sites are available. Density functional theory calculations revealed that I2 adsorption on MoSe2 surfaces facilitated the generation of I− ions, which played a critical role in enhancing the reaction efficiency. Therefore, the Co–Ni–Se@MoSe2@MWCNTs composite is a promising candidate for use in high-performance DSSCs.

Synergistic Effect of Size-Tailored Structural Engineering and Postinterface Modification for Highly Efficient and Stable Dye-Sensitized Solar Cells.

Despite significant progress in device performance, dye-sensitized solar cells (DSSCs) continue to fall short of their theoretical potential. Moreover, research in recent years needs to pay more attention to improving the device fabrication process. To achieve the theoretical efficiency limit, it is crucial to optimize the interface between the dye and TiO2 nanoparticles in the entire device stack. Our study indicates that optimizing the structure or size of the coadsorbents and implementing a monolayer adsorption process can be an effective strategy to reduce charge recombination and enhance light-harvesting properties. Our research aims to develop a surface-coating adsorbent plan that controls the TiO2 nanoparticle interface to achieve the radiative limit of power conversion efficiency (PCE). Specifically, we utilized 2-thiophenecarboxylic acid (THCA) or chenodeoxycholic acid (CDCA) as postinterfacial surface-coating adsorbents. Our results demonstrate that this approach effectively achieves the desired PCE limit. Combined with the coadsorbent structure engineering and interface optimization, the device increased the packing area on the TiO2 nanoparticles' surface, reaching an improved PCE of over 13.17% under simulated sunlight (1.5G), which is the highest efficiency of a porphyrin single dye-based DSSC. In particular, this practical approach was also applied to a large-area DSSC with an area of 3 cm2, yielding a remarkable PCE of 9.04%. Furthermore, when applied to a polymer gel electrolyte, this novel approach recorded the highest PCE of 11.16% with a long-term operational stability of up to 1000 h for the quasi-solid-state DSSCs. Our research findings provide a promising avenue for achieving high-performance DSSCs with ease of access and demonstrate practical applications as alternatives to conventional power sources.

Barium titanate perovskite nanoparticles integrated reduced graphene oxide nanocomposite photoanode for high performance dye-sensitized solar cell

Nanocomposites comprised of barium titanate perovskite nanoparticles decorated reduced graphene oxide (BaTiO3-RGO NC) were formed through facile hydrothermal method. X-ray diffractometer profile confirmed crystallite and tetragonal phase of BaTiO3. Identification of D and G bands in Raman investigation and XPS spectra disclosed existence of graphene in the prepared BaTiO3-RGO NC. FE-SEM examination indicates small sized BaTiO3 NPs are obviously decorated on the graphene sheets by strong binding forces between graphene and BaTiO3 NPs. Among graphene of different wt%, BaTiO3-RGO NC with 1.5 wt% showed lowest PL intensity, indicating effective reduction of photogenerated charge carrier recombination. Dye-sensitized solar cell fabricated using BaTiO3-RGO NC photoanode having 1.5 wt% graphene displays high efficiency of 4.93% associated with high photocurrent density.

A Theoretical Molecular Design of Acridine/Anthracene‐Polyoxometalate Hybrid Materials for Enhanced Dye‐Sensitized Solar Cells Performance

AbstractFour novel organoimido‐substituted hexamolybdate dyes featuring acridine/anthracene donors for dye‐sensitized solar cells (DSSCs) have been designed and studied using a combination of density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations. The energy levels of frontier molecular orbitals, absorption spectra with electronic transition characters, and photovoltaic parameters of dyes 1–4 were systematically evaluated. The results confirm the suitability of all the studied dyes for n‐type DSSCs. The investigated dyes could be introduced as an active co‐absorbent as well as main dye. All dyes showed remarkable reorganization energy for electron transport (λe) and hence increased electron transfer rate. Due to the strong absorption in the visible region, as well as high light harvesting efficiency (LHE), dye regeneration efficiency (DRE), and electron injection efficiency (Φinj), dyes 2 and 3 are the most promising candidates for high performance DSSC materials.

Performance Improvement of Dye-Sensitized Solar Cells Using a Combination of TiO<sub>2</sub> and ZnO as Photoanodes

TiO2 are usually used as photoanode to get high-performance dye-sensitized solar cells (DSSCs). TiO2 has good chemical stability, but still has poor electron mobility so that the DSSC efficiency is low. An alternative semiconductor metal-oxides such as ZnO currently are being explored due to ease of processing, higher electron mobility, interface band energetics, and can be utilized as photoanode also, but the chemical stability is low. Based on these facts, by combining the advantages of TiO2 and ZnO, the TiO2:ZnO composite can be an ideal material as a photoanode in DSSC. In this study, composite of TiO2:ZnO was synthesized using sol-gel method with ratio of TiO2 to ZnO were varied from 80:20, 60:40, 50:50, 40:60, and 20:80 in atomic percent. DSSCs were fabricated by coating the photoanode using screen-printing technique on a FTO-glass substrate. Composite of TiO2:ZnO photoanodes were then sensitized in a solution of N719 dye for several hours. Finally, the DSSCs were assembled and the power conversion efficiency was measured using an I–V measurement system. The highest power conversion efficiency of 2.30% was obtained from the cell fabricated with TiO2:ZnO (50:50) photoanode. This result indicated that the balanced composition allowed to increase Jsc along with reducing recombination process and retaining high dye-loading capability.