Sb2(SxSe1−x)3 sensitized solar cells prepared by solution deposition methods

Solid state semiconductor sensitized solar cells are a very active research subject in emerging photovoltaic technologies. In this work, heterojunctions of antimony sulfide-selenide (Sb₂(S_xSe_1−x)₃) solid solution as the absorbing material and cadmium sulfide coated titanium dioxide (TiO₂/CdS) as the electron conductor have been developed with solution deposition methods such as spin-coating, successive ionic layer adsorption and reaction (SILAR), and chemical bath deposition. In particular, CdS has been deposited on mesoporous TiO₂ layers by SILAR deposition, followed by the chemical deposition of Sb₂(S_xSe_1−x)₃. It was found that by increasing the number of CdS SILAR deposition, both the open circuit voltage V_oc and the short circuit current density J_sc of the Sb₂(S_xSe_1−x)₃ sensitized solar cells had been increased from 153 to 434 mV and 0.77–9.73 mA/cm², respectively. This improvement was attributed to the fact that the presence of the CdS on TiO₂ surface reduces the formation of undesired Sb₂O₃ and promotes a better nucleation of the Sb₂(S_xSe_1−x)₃ during the chemical bath deposition. The best result was obtained for the solar cell with 30 cycles of CdS which produced a V_oc of 434 mV, a J_sc of 9.73 mA/cm², and a power conversion efficiency of 1.69% under AM1.5 G solar radiation.     

Structural and optical properties of CdS/PEO nanocomposite solid films

In this paper solution mixing and casting of Cd(NO₃)₂·4H₂O and poly(ethylene oxide) (PEO) at different molar ratios (1:100–1:600) followed by hydrogen sulfide treatment were employed to fabricate solid films of cadmium sulfide (CdS)/polyethylene oxide (PEO) nanocomposites. The nanocomposites were found to exhibit uniform distribution of CdS nanoparticles in the polymer matrix without any additional capping agent. Systematic investigations on the role of PEO on the optical properties of CdS are presented. The optical properties of the composites examined by UV–vis absorption spectroscopy show that the band gap of CdS nanoparticles increases from 2.45 eV to 2.54 eV with decreasing concentration of CdS in PEO films. X-ray diffraction pattern shows the broadening in shape of the PEO peaks which is induced by the CdS particles in PEO matrix. The CdS particle sizes ranging from 10 to 20 nm are clearly seen in a transmission electron microscope (TEM). The X-ray photoelectron spectroscopic studies (XPS) also confirm the presence of CdS in PEO. Fourier transform infrared spectroscopy studies using attenuated total reflectance (FTIR-ATR) indicate the influence of Cd²⁺ ion on C–O–C stretching in PEO and confirm the presence of CdS nanoparticles within PEO. Photoluminescence spectroscopy (PL) shows the broad emission due to the presence of surface trapped carrier states.     

Enhanced photocatalytic performance of platinized CdS/TiO2 by optimizing calcination temperature of TiO2 nanotubes

TiO₂ nanotubes were prepared by hydrothermal treatment of TiO₂ powder in NaOH aqueous solution and then calcined at various temperatures. The post-calcination treated TiO₂ nanotubes were decorated with CdS by wetness impregnation and subsequently sulfurization to fabricate CdS/TiO₂ composites. The photocatalytic performance of CdS/TiO₂ composites toward hydrogen production from water splitting was investigated. The results show that the calcination temperature of TiO₂ nanotubes has a significant effect on the photocatalytic performance of CdS/TiO₂. With the increase of calcination temperature from 300 to 500 °C, the crystallinity of TiO₂ nanotubes is increased resulting in the enhanced photocatalytic performance of CdS/TiO₂. When the calcination temperature is higher than 500 °C, TiO₂ nanotubes gradually transform into nanorods and finally completely collapse, which leads to the decrease of photocatalytic performance of CdS/TiO₂. The CdS/TiO₂ composite with TiO₂ nanotubes calcined at 500 °C exhibits the highest hydrogen evolution rate, which could be attributed to its 1 D nanotubular structure and good crystallinity.     

CdS and PbS quantum dots co-sensitized TiO2 nanorod arrays with improved performance for solar cells application

In this paper, we report a novel CdS and PbS quantum dots (QDs) co-sensitized TiO₂ nanorod arrays photoelectrode for quantum dots sensitized solar cells (QDSSCs). TiO₂ film consisting of free-standing single crystal nanorods with several microns high and 90–100 nm in diameter were deposited on a conducting glass (SnO₂:FTO) substrate by hydrothermal method. Then CdS/PbS QDs were deposited in turn on TiO₂ nanorods by facile SILAR technique. The FTO/TiO₂/CdS/PbS, used as photoelectrode in QDSSCs, produced a light to electric power conversion efficiency (Eff) of 2.0% under AM 1.5 illumination (100% sun), which shows the best power conversion efficiency compared with single CdS or PbS sensitized QDSSCs. One dimension TiO₂ nanorod provides continuous charge carrier transport pathways without dead ends. The stepwise structure of the band edges favored the electron injection and the hole-recovery for both CdS and PbS layers in photoelectrode, which may gave a high electric power conversion efficiency. The facile preparation and low cost nature of the proposed method and structure make it has a bright application prospects in photovoltaic areas in the future.     

Improved performance of nanoporous TiO2 film in dye-sensitized solar cells via ZrCl4 and TiCl4 surface co-modifications

In this study, nanoporous TiO₂ films were modified by a dip-coating process using a mixture aqueous solution of ZrCl₄ and TiCl₄ followed by calcination to prepare a photoanode for dye-sensitized solar cells. Compared with the control film modified with 0.04 mol L⁻¹ TiCl₄, the power conversion efficiency of the TiO₂ film modified with a mixed solution of 0.05 mol L⁻¹ ZrCl₄ and 0.04 mol L⁻¹ TiCl₄, was 18.67% higher because of the improved short circuit current (J_sc) and open circuit voltage (V_oc). The improvement in J_sc was due to the suppression of charge recombination, which was demonstrated by a series of measurements, including electrochemical impedance spectroscopy, monochromatic incident photon-to-electron conversion efficiency spectroscopy, and the open-circuit voltage decay technique. The Mott-Schottky measurement results indicated that the negative shift of a flat band led to the increased V_oc.     

Binder-free MWCNT/TiO2 multilayer nanocomposite as an efficient thin interfacial layer for photoanode of dye sensitized solar cell

Multiwalled carbon nanotube/TiO₂ multilayer nanocomposite was successfully deposited on the fluorine-doped tin oxide (FTO) glass via layer-by-layer assembly technique to modify interfacial contact between the FTO surface and nanocrystalline TiO₂ layer as well as carbon nanotube/TiO₂ contacts in photoanode of dye sensitized solar cell. Using this approach, binder-free interfacial thin film was developed with nonagglomerated, well-dispersed MWCNTs on FTO and into TiO₂ matrix and with maximum covering of TiO₂ nanoparticles on MWCNTs. Introduction of MWCNTs/TiO₂ interfacial layer into the TiO₂ photoanode increased short circuit current density (J_sc) from 11.90 to 17.25 mA/cm² and open circuit voltage (V_oc) from 730 mV to 755 mV, whereas there was no notable change in the fill factor (FF). Consequently, power conversion efficiency (η) was enhanced from 5.32% to 7.53%, yielding a 41.5% enhancement. The results suggest that our simple strategy can integrate reduction of back electron reaction at FTO/TiO₂ interface with the effective charge transport ability of carbon nanotubes and possessing high surface area for efficient dye loading.     

Improved electrodeposition of CdS layers in presence of activating H2SeO3 microadditive

CdS thin films were deposited electrochemically onto indium tin oxide (ITO)/glass substrates from aqueous solutions containing 0.01 M CdCl₂, 0.05 M Na₂S₂O₃ and 0.02 M Edta-Na₂ at −1.2 mV versus saturated sulfate reference electrode. Depositions were carried out at various temperatures (20, 50 and 80 °С) and different pH (2.5, 3.5 and 4.5) in a three electrode electrochemical cell. All above mentioned electrochemical syntheses were reproduced in presence of H₂SeO₃ microadditive to compare resulted CdS layers. Electrodeposited CdS thin films were characterized by different instrumental techniques to know the influence of deposition conditions on the quality of the obtained layers. It was found that the presence of 0.05–0.5 mM of H₂SeO₃ in the electrolyte changes the mechanism of the CdS film formation that facilitates nucleation and a growth of a more dense and uniform polycrystalline CdS film. Addition of 0.5 mM of H₂SeO₃ into the initial solution allowed us to obtain nearly stoichiometric (sulfur content ~52 at%) CdS films at reduced temperature value of 50 °C vs. higher temperature values used in a conventional electrodeposition process of CdS layers. No Se-containing phases were detected by EDX, Raman and XRD analyses in the CdS films. The presence of H₂SeO₃ tends to rearrange polytype crystalline structure of CdS to more stable hexagonal structure. The band gap value of CdS was increased from 2.3 eV to 2.5 eV as a result of H₂SeO₃ addition.     

Enhance the performance of quantum dot-sensitized solar cell by manganese-doped ZnS films as a passivation layer

To make quantum dot-sensitized solar cells (QDSSCs) more attractive, it is necessary to achieve higher power conversion efficiency. A novel Mn-doped ZnS has been successfully fabricated on CdS/CdSe quantum dots (QDs) by simple successive ion layer adsorption and reaction (SILAR) technique. The Mn-doped ZnS is used as a passivation layer in the QDSSCs. The performance of the QDSSCs was examined in detail using sulfide/polysulfide electrolyte with a Pt or copper sulfide (CuS) counter electrode. Here we demonstrated, the fabricated Mn-doped ZnS QDs shows an improved V_oc (0.65 V) compared to bare ZnS QDs (0.60 V). The QDSSC based on a photoanode with Mn-doped ZnS (10 wt% of Zn) shows higher J_sc (15.32 mA cm⁻²) and power conversion efficiency (4.18%) compared to the bare ZnS photoanode (2.90%) under AM 1.5 G one sun illumination. We explore the reasons for this enhancement and demonstrated that it is caused by improved passivation of the ZnS surface by Mn ions, leading to a lower recombination of photo-injected electrons with the electrolyte. The effect of Cu ions in ZnS has been investigated by UV–Vis spectra and current density–voltage analysis.     

Fabrication of CdSe sensitized SnO2 nanofiber quantum dot solar cells

In the present study, we report a cost-effective quantum dot solar cells based on a combination of electrospinning and successive-ionic-layer-adsorption and reaction (SILAR) methods. CdSe nanocrystals are deposited on electrospun SnO₂ nanofibers by SILAR method using CdCl₂ as the cadmium source and Na₂Se as selenium source. The as-prepared materials are characterized by spectroscopy and microscopy. CdSe deposited SnO₂ electrodes are also characterized by spectroscopy and microscopy. Cells are fabricated with platinum (Pt)-sputtered FTO glasses used as the counter electrodes and polysulfide solution used as the electrolyte. The efficiency of the cells is studied for different number of SILAR cycles. Current density–voltage (J–V) measurements on a cell having CdSe deposition of 7 SILAR cycles and SnO₂ coating area 0.25 cm² showed an overall power conversion efficiency of 0.29 % with a photocurrent density (J_SC) of 5.32 mA cm⁻² and open circuit voltage (V_OC) of 0.23 V under standard 1 Sun illumination of 100 mWcm⁻² (AM 1.5 G conditions). This is improved by carefully coating SnO₂ film without losing the structures. Also ZnS passivation layer is coated to obtain an improved efficiency of 0.48% with J_SC of 4.68 mAcm⁻², and V_OC of 0.43 V.     

Comparative study between CBD and SILAR methods for deposited TiO2, CdS,and TiO2/CdS core-shell structure

TiO₂, CdS, and TiO₂/CdS core–shell structures were deposited on fluorine-doped tin oxide (FTO)-coated glass substrate using chemical methods. TiO₂ thin films were prepared by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). SILAR was also utilized to deposit CdS film on TiO₂ thin film. The structural, surface morphology, and optical characteristics of FTO/TiO₂, FTO/CdS, and FTO/TiO₂/CdS core- shell structures were evaluated. The FTO/TiO₂ films produced by both methods conformed to anatase and rutile phase structures. Corresponding XRD pattern of the FTO/TiO₂/CdS sample exhibited one peak corresponding to hexagonal (101) for CdS. Scanning electron micrographs showed nanorod structures for the TiO₂ thin films deposited by CBD, contrary to the nanograin structure formed by SILAR. Optical results showed highly extended absorption edge to the visible region for the FTO/TiO₂/CdS structure deposited by the two methods. The TiO₂ thin films deposited by CBD exhibited higher absorption in the visible region than nanograined TiO₂ thin films deposited by SILAR because of the high surface area of the TiO₂ nanorod. Photoelectrochemical (PEC) properties of FTO/TiO₂, and FTO/TiO₂/CdS system were also examined. PEC behavior of FTO/TiO₂/CdS was compared with that of FTO/TiO₂ deposited by CBD and SILAR. The TiO₂ nanorod thin films deposited by CBD showed evidently enhanced PEC performance compared with nanograined TiO₂ thin films deposited by SILAR.     

Application research of CdS: Eu3+ quantum dots-sensitized TiO2 nanotube solar cells

Trivalent Eu³⁺-doped CdS quantum dot (CdS: Eu³⁺ QD)-sensitized TiO₂ nanotube arrays (TNTAs) solar cells are prepared by using the direct adsorption method. The influences of sensitization time, sensitization temperature, and Eu³⁺ ion concentrations are investigated systematically. The photo-current of the CdS: Eu³⁺ QDs/TiO₂ nanotubes appear at the main absorption region of 320–480 nm, and the maximum incident photon to the current conversion efficiency (IPCE) value is 21% at 430 nm when the sensitization condition is 4% doping Eu³⁺ concentration, 60 °C sensitization temperature, 8 h sensitization time. Compared with the un-doped CdS QD-sensitized TNTAs, the conversion efficiency and IPCE of CdS: Eu³⁺ QDs/TNTAs are two times and three times than that of un-doped CdS QDs sensitized TNTAs. This scenario exhibits the potential applications of rare earth elements in QD-sensitized solar cells.     

CdS amorphous thin films photochemical synthesis and optical characterization

Thin amorphous nanostructured CdS films were photochemically obtained via direct UV radiation (λ=254 nm) of complex Cd[(CH₃)₂CHCH₂CH₂OCS₂]₂ on Si(1 0 0) and ITO-covered glass substrate by spin coating. Thin cadmium xanthate complex films’ UV photolysis results in loss of all ligands from the coordination sphere. X-ray photoelectron spectra for as-deposited CdS thin films show the most representative signals of Cd 3d_5/2 located at 405 eV, Cd 3d_3/2 located at 412 eV and a small signal S 2p located at 162 eV. The surface morphology of the films was examined via atomic force microscopy. This can be described as a fibrous-type surface without structural order, which is characteristic of an amorphous deposit. The optical band gap value was 2.85 and 3.15±0.1 eV.     

Characterization of cadmium sulfide/titania heterostructure films by utilizing microstructure and optical characteristics

Engineering and controlling the bandgap of semiconducting metal oxide (TiO₂) to enhance photoactivity under visible light is challenging. Impact of the changing CdS thickness (50–150 nm) on the structure and optical properties of the CdS/TiO₂ heterostructure films (HSFs) which fabricated by pulsed laser deposition (PLD) was observed. XRD, FE-SEM, AFM, UV–vis and PL spectroscopy measurements were utilized to characterize structural and optical behaviors of the films. XRD measurement shows gradual increments of the lattice constants of the films with the increase of CdS thickness. The mean values of the calculated lattice constants and cell volume (V) were a=b=0.3785 nm, c=0.9475 nm and V=13.58 nm³ respectively. The average of crystallite sizes estimated for TiO₂ and CdS/TiO₂ at various CdS thickness is 12.20, 13.49, 24.24 and 43.10 nm. FESEM images prove the high quality nanocrystalline nature of the films without cracks and dislocation. The root means square roughness of the films was increased with the increase of CdS thickness as showed by AFM images. UV–vis measurement reveals an improvement in the optical absorbance of HSFs in the range of 380–550 nm due to presence of CdS. Interestingly, the PL intensity was enhanced by a factor of nineteen compare to pure TiO₂ attributed to the charge carrier recombination in the band gap. The current results suggest that possibility to improve the optical and structural properties of the TiO₂ films and also it possible to fabricate high quality CdS/TiO₂ HSFs by variation of the CdS thickness.     

High performance dye-sensitized solar cells (DSSCs) achieved via electrophoretic technique by optimizing of photoelectrode properties

This paper describes a simple method utilizing electrophoretic deposition (EPD) of commercial P25 nanoparticles (NPs) films on fluoride-doped tin oxide (FTO) substrate. In this process, voltage and the number of deposition cycles are well controlled to achieve TiO₂ film thickness of around 1.5–26 μm, without any mechanical compression processing. The experimental results indicate that the TiO₂ film thickness plays an important role as the photoelectrode in DSSCs because it adsorbs a large number of dye molecules which are responsible for electrons supply. Furthermore, it was found that effects of the bulk traps and surface states within the TiO₂ films on the recombination of the photo-injected electrons (electron–hole pairs) strongly depend on the TiO₂ electrode annealing temperature. Finally, a DSSC with a 24 μm thick TiO₂ film and annealed at 500 °C produced the highest conversion efficiency (η=6.56%, I_SC=16.4, V_OC=0.72, FF=0.55) with an incident solar energy of 100 mW/cm².     

Development of SnS quantum dot solar cells by SILAR method

SnS quantum dot solar cell is fabricated by Successive Ionic Layer Adsorption and Reaction (SILAR) method. SnS layer is optimized by different SILAR cycles of deposition. The particle size increased with the increase in number of SILAR cycles. Cu₂S coated FTO is used as counter electrode against the conventional Platinum electrode. On comparison with a cell having a counter electrode–electrolyte combination of Platinum–Iodine, Cu₂S–polysulfide combination is found to improve both the short circuit current and fill factor of the solar cell. A maximum efficiency of 0.54% is obtained with an open circuit voltage of 311 mV and short circuit current density of 4.86 mA/cm².     

Solar Water Splitting by TiO2/CdS/Co–Pi Nanowire Array Photoanode Enhanced with Co–Pi as Hole Transfer Relay and CdS as Light Absorber

The cobalt phosphate water oxidation catalyst (Co–Pi WOC) stabilized, CdS sensitized TiO₂ nanowire arrays for nonsacrificial solar water splitting are reported. In this TiO₂/CdS/Co–Pi photoanode, the Co–Pi WOC acts as hole transfer relay to accelerate the surface water oxidation reaction, CdS serves as light absorber for wider solar spectra harvesting, and TiO₂ matrix provides direct pathway for electron transport. This triple TiO₂/CdS/Co–Pi hybrid photoanode exhibits much enhanced photocurrent density and negatively shifts in onset potential, resulting in 1.5 and 3.4 times improved photoconversion efficiency compared to the TiO₂/CdS and TiO₂ photoanode, respectively. More importantly, the TiO₂/CdS/Co–Pi shows significantly improved photoelectrochemical stability compared to the TiO₂/CdS electrode, with ≈72% of the initial photocurrent retained after 2 h irradiation. The reason for the promoted performance is discussed in detail based on electrochemical measurements. This work provides a new paradigm for designing 1D nanoframework/light absorber/WOC photoanode to simultaneously enhance light absorption, charge separation, and transport and surface water oxidation reaction for efficient and stable solar fuel production.     

Synthesis and characterization of TiO2-doped Polyaniline nanocomposites by chemical oxidation method

Polyaniline (PANI)/TiO₂ nanocomposite samples with various dopant percentages of TiO₂ were synthesized at room temperature using a chemical oxidative method. The samples were characterized by ultraviolet-visible spectrometer, Fourier transform infrared (FTIR) spectrometer, X-ray diffraction (XRD), scanning electron microscopy (SEM), EDAX and conductivity measurements. Incorporation of TiO₂ nanoparticles caused a slight red shift at 310 nm in the absorption spectra due to the interactions between the conjugated polymer chains and TiO₂ nanoparticles with π–π^? transition. FTIR confirmed the presence of TiO₂ in the molecular structure. In PANI/TiO₂ composites, two additional bands at 1623 cm^?1 and 1105 cm^?1 assigned to Ti–O and Ti–O^–C stretching modes were present. It can be concluded that Ti organic compounds are formed with an alignment structure of TiO₂ particles. XRD patterns revealed that, as the TiO₂ percentage was increased, the amorphous nature disappeared and the composites became more strongly oriented along the (1 1 0) direction, which showed the tetragonal structure of nanocrystalline TiO₂. SEM studies revealed the formation of uniform granular morphology with average grain size of 200 nm for (50%) PANI/TiO₂ nanocomposite samples.     

Synthesis and some surface studies of laminated ZnO/TiO2 transparent bilayer by two-step growth

A laminated bilayer was prepared by first depositing titanium dioxide (TiO₂) nanocrystals on indium tin oxide (ITO) coated glass by a two-electrode cell. Zinc oxide (ZnO) thin film was thereafter deposited on the TiO₂ by two different techniques: electrochemical deposition and vacuum evaporation. The films were characterized by some surface probing techniques. Morphological study revealed that particle size of the TiO₂ underlayer increases between 110 and 138 nm with increase in deposition voltage. It also showed that ZnO thin film (overlayer) completely covered the underlying TiO₂ without chemical interaction between constituents of both layers. Cross-sectional FESEM study gave values of layered film thickness below 55 µm. Exhibition of strong diffraction peak at plane (121) indicated preference of TiO₂ film's growth orientation. It also suggested a feature of phase-pure brookite. Optical studies showed that each film exhibited strong absorption edge at λ=~330 nm and transmitted fairly across visible light region. Energy band gap lied between 3.24 and 3.43 eV. This study demonstrated successive layer deposition of transparent metal oxide structures from inorganic reagents. It also reaffirmed TiO₂ as a recipe for barrier layer that can hinder transition of holes from absorber to transparent front contact of nanostructured photonic devices.     

Unipolar nonvolatile memory devices with composites of poly(9-vinylcarbazole) and titanium dioxide nanoparticles

Organic-based devices with an 8 × 8 array structure using titanium dioxide nanoparticles (TiO₂ NPs) embedded in poly(9-vinylcarbazole) (PVK) film exhibited bistable resistance states and a unipolar nonvolatile memory effect. TiO₂ NPs were a key factor for realizing the bistability and the concentration of TiO₂ NPs influenced ON/OFF ratio. From electrical measurements, switching mechanism of PVK:TiO₂ NPs devices was closely associated with filamentary conduction model and it was found that the OFF state was dominated by thermally activated transport while the ON state followed tunneling transport. PVK:TiO₂ NPs memory devices in 8 × 8 array structure showed a uniform cell-to-cell switching, stable switching endurance, and a high retention time longer than 10⁴ s.     

Enhancement in the optical and electrical properties of CdS thin films through Ga and K co-doping

In the presented work, Ga-doped CdS and (Ga-K)-co-doped CdS thin films are grown on glass substrates at a temperature of 400 °C through spray pyrolysis. Influence of K-doping on structural, morphological, optical and electrical characteristics of CdS:Ga thin films are examined. K level is changed from 1 at% to 5 at% for CdS:Ga samples just as Ga concentration is fixed 2 at% for all CdS thin films. It is observed from the X-ray diffraction data that all the samples exhibit hexagonal structure and an increase level of K in Ga-doped CdS samples causes a degradation in the crystal quality. Energy-dispersive X-ray spectroscopy measurements illustrate that the best stoichiometric film is acquired when K content is 2 at% in Ga-doped CdS films. Optical transmission curves demonstrate that CdS:Ga thin films exhibit the best optical transparency in the visible range for 4 at% K content compared to other specimens. A widening in the optical bandgap is unveiled after K-dopings. It is obtained that maximum band gap value is found as 2.45 eV for 3 at%, 4 at% and 5 at%. K -dopings while Ga-doped CdS thin films display the band gap value of 2.43 eV. From photoluminescence measurements, the most intensified peak is observed in the deep level emission after incorporation of the 4 at% K atoms. As for electrical characterization results, the resistivity reduces and the carrier density improves with the increase of K concentration from 1 at% to 4 at%. Based on all the data, it can be deduced that 4 at% K-doped CdS:Ga thin films show the best optical and electrical behavior, which can be utilized for solar cell devices.