CdS Deposition Research Articles

Structural, Morphological, and Optical Properties of TiO2/CdS Core-Shell System Prepared by Two Method for Photoelectrocatalytic Application

Abstract The present study utilized the hydrothermal technique to carry out the deposition of films of TiO2. The deposition of CdS on the TiO2 films was accomplished using the chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods. The morphological and structural characteristics of the TiO2/CdS thin films were investigated using a combination of XRD, SEM, EDX, and AFM techniques. Additionally, the optical properties of the nanostructures were examined using UV-Visible and PL spectroscopic techniques. The X-Ray Diffraction pattern of all TiO2 films revealed the formation of the anatase phase. The CdS present in the Ti/TiO2/CdS samples exhibited a hexagonal structure. The hydrothermal technique employed in the preparation of the TiO2 thin films resulted in the formation of nanofiber morphology, which was evident from the SEM images. The absorption edge data for the TiO2/CdS films demonstrated a shift towards the visible region, indicating a decrease in the bandgap as compared to the TiO2 nanostructure. Significantly improved photoelectrocatalytic performance was observed in the Ti/TiO2/CdS samples prepared using the CBD method, surpassing that of the Ti/TiO2/CdS samples prepared using the SILAR method.

Application of AgInSe2 nanoparticles to boost the power conversion efficiency of CdS QDs-sensitized solar cells

In this study, bandgap engineering was utilized to assess the efficiency of photoanodes incorporating CdS nanocrystals and AgInSe2 (AISe) quantum dots (QDs) in quantum dot-sensitized solar cells (QDSSCs). Initially, the deposition of CdS(Xc) nanocrystal layers on a TiO2 substrate was tested using the SILAR method with varying cycles (X = 1–6). Optical transmission analysis revealed a redshift in the absorption edge and reduced transmission with an increasing number of cycles. J-V analysis of TiO2 NCs/CdS(Xc) photoanodes identified cycle X = 5 as optimal. The short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF) and maximum power conversion efficiency (PCE) were 15.5 mA/cm2, 614 mV, 40 %, and 3.76 %, respectively. Subsequently, pre-synthesized AISe QDs were deposited on TiO2 nanocrystals/CdS(Xc) photoanodes, exhibiting a single absorption edge with a bandgap energy of 2.19 eV for all photoanodes. The TiO2 NCs/CdS(5c)/AISe/ZnS photoanode showed an increase in Jsc and efficiency, reaching 17.25 mA/cm2 and 4.27 %, respectively. Utilizing sub-micron-sized TiO2 hollow spheres (HSs) as a light-scattering layer further enhanced light absorption and performance. It was demonstrated that this approach increased the photovoltaic parameters to a Jsc of 19.12 mA/cm2, FF of 43 %, and an overall efficiency of 4.75 %.

Construction of CdS/ZnO/TiO2 ternary heterojunction with hierarchical structure as photo-anode for enhancing photo-electrochemical performance

Composition and microstructure expert a significant impact on the photoelectric properties of the photo-anode. In this work, CdS/TiO2 and CdS/ZnO/TiO2 heterojunction materials were prepared using a simple and low-cost hydrothermal method. Their microstructure, crystallinity, elemental presence state and photoelectron-chemical performance of the heterojunction materials were investigated by SEM, XRD, XPS and Electrochemical workstation. The hydrothermal growth time of CdS has a significant impact on the structure and performance of heterojunctions. As the CdS deposition time increase, the photocurrent density of CdS/TiO2 shows a trend of first increasing and then decreasing. We optimized the process parameters of CdS/TiO2, and the optimal growth time for CdS is 6h. The transient photocurrent density value of CdS/TiO2 heterojunction is 0.15 mA/cm2. Depositing ZnO onto TiO2 to construct a hierarchical ZnO/TiO2 heterojunction can improve light absorption and accelerate carrier separation efficiency. The photoelectric performance of CdS/ZnO/TiO2 was compared with CdS/TiO2 and pure TiO2. The photocurrent density of CdS/ZnO/TiO2 is 1.5 mA/cm2, which is significantly larger than that of pure TiO2 and CdS/TiO2. This is due to the formation of a heterojunction between TiO2 and ZnO, which promotes the separation of carriers and ultimately improves the photoelectric performance of the CdS/ZnO/TiO2 ternary heterojunction. The fabricated CdS/ZnO/TiO2 heterojunction showed high photocurrent, which indicated a new candidate for photoelectric device.

(Invited) CdS/Ti-Si-O Composite Photoanode for Photoelectrochemical Hydrogen Generation

Advancements in clean energy drive socio-economic development and foster a sustainable future by restructuring energy systems and promoting low-carbon development. In this paper, we presented a comprehensive investigation on the design and performance characterization of CdS/Ti-Si-O composite photoanodes for photoelectrochemical (PEC) hydrogen generation. Silicon-doped TiO2 nanotube arrays were fabricated through anodization of Ti-5Si alloy, followed by the deposition of CdS using the SILAR (successive ionic layer adsorption and reaction) process, resulting in nanostructured Ti-Si-O photoanodes modified with CdS. The composite photoanodes were characterized in terms of their composition, microstructure, optical properties and photoelectrochemical hydrogen production performance. The composite photoanodes revealed a notable enhancement in PEC hydrogen generation properties with a photocurrent density of 7.86 mA/cm2，which was 19.15 times and 9.59 times to those of the undoped TiO2 photoanode and Ti-Si-O photoanode, respectively. The Si-doping mechanism of the photoanodes was elucidated through Density Functional Theory (DFT) calculations. The synergistic combination of Si-doping and CdS modification represents a novel and promising approach for the design of efficient nanostructured photoanodes.

Photocatalytic reduction of aqueous carcinogenic pollutants on CdS-polymer nanocomposites

Water decontamination from the toxic effluents, for the safe use of human, is the hottest area of research nowadays. 4-nitrophenol and Cr(VI) are the two pollutants of high environmental concern due to their toxic and carcinogenic nature. Furthermore, their remediation is a laborious, time consuming and challenging task. In this context, photocatalysis is believed to be an efficient and safe remediation process, however, photocatalysts suffer from inferior stability and efficiency. Similar problems are also associated with CdS, which is considered a low cost and visible light absorbing material. To improve efficiency and stability of CdS, the CdS-polymer nanocomposites were prepared by the deposition of CdS on the polymeric beads (CS/PVA/TEOS) at ambient conditions. CdS-polymer nanocomposites were observed to be better photocatalysts under solar light than the bare CdS for the reduction of {4-nitrophenol and Cr(VI)} carcinogens. The photoreduction followed pseudo first order kinetics. Notably, the rate of photoreduction was observed to increase with an increase in the percentage of degree of deacetylation (DDA) of the chitosan polymer. Among the four synthesized catalysts, the B4/CdS presented the best catalytic efficiency: Cr(VI) reduced in 4 min with TOF = 6.4 × 10−3 mmol Cr(VI)/(mgcat.⋅min), ΔH# = 5.008 kJ/mol and ΔS# = - 0.856 kJ/mol.K and 4-NP in 8 min with TOF = 4.1 × 10−2 mmol 4-NP/(mgcat.⋅min), ΔS# = - 2.817 kJ/mol.K and enthalpy ΔH# = 14.26 kJ/mol. The effect of various parameters: temperature, pH and catalytic dose was also investigated to assess the optimal conditions for photocatalysis. It is anticipated that a unique combination of chitosan polymer and CdS might offer efficient adsorption and electron transfer, which ultimately triggered the reduction.

High performance NaNbO3/CdS/Bi2S3 ternary heterostructured photoelectrocatalysts for efficient OER activity

CdS and Bi2S3 decorated NaNbO3 samples were prepared by hydrothermal and linker assisted combinatory approach using oleic acid and starch as surface capping agents. Successful deposition of small sized and high surface area CdS and Bi2S3 over the smooth surface of large sized NaNbO3 was carried out. To prepare heterostructures of NaNbO3 different weight ratios of CdS and Bi2S3 were employed. The as-prepared heterostructures were subsequently characterized by X-ray diffraction (XRD), UV–visible diffused reflectance spectroscopy (DRS), Field Emission Scanning Electron Microscopy (FESEM), Brauner-Emmette-Teller (BET) surface area studies, and X-ray Photoelectron spectroscopy (XPS) studies. As-developed heterostructures were investigated as photoelectrocatalysts (PEC) for oxygen evolution reaction (OER) from water splitting reaction. From PEC OER investigations, it was observed that heterostructured sample (HS-2) with 10 wt % CdS and 5 wt% Bi2S3 show efficient and enhanced PEC OER activity as compared to the pristine parent compounds. The maximum current density of 11.9 mA/cm2 with low onset potential of 0.89 V and low tafel slope of 107 mV/day was observed in HS-2 sample under white light illumination. The efficient and enhanced activity was attributed to red shift in the absorption of NaNbO3 sample and efficient charge separation taking place due to deposition of CdS and Bi2S3 over the surface of NaNbO3.

Enhancement of Photo-Electrical Properties of CdS Thin Films: Effect of N2 Purging and N2 Annealing

The impact of N2 purging in the CdS deposition bath and subsequent N2 annealing is examined and contrasted with conventional CdS films, which were deposited without purging and annealed in ambient air. All films were fabricated using the chemical bath deposition method at a temperature of 80 °C on fluorine-doped tin oxide glass slides (FTO). N2 purged films were deposited by introducing nitrogen gas into the deposition bath throughout the CdS deposition process. Subsequently, both N2 purged and un-purged films underwent annealing at temperatures ranging from 100 to 500 °C for one hour, either in a nitrogen or ambient air environment. Photoelectrochemical (PEC) cell studies reveal that films subjected to both N2 purging and N2 annealing exhibit a notable enhancement of 37.5% and 27% in ISC (short-circuit current) and VOC (open-circuit voltage) values, accompanied by a 5% improvement in optical transmittance compared to conventional CdS thin films. The films annealed at 300 °C demonstrate the highest ISC, VOC, and VFB values, 55 μA, 0.475 V, and −675 mV, respectively. The improved optoelectrical properties in both N2-purged and N2-annealed films are attributed to their well-packed structure, enhanced interconnectivity, and a higher sulfur to cadmium ratio of 0.76 in the films.

Photoelectrochemical Properties and Characterization of CdS/CdSe Heterojunctions Obtained by CBD on ITO and p–Si Substrates

AbstractThis research investigates the optical, structural, electrical, and photoelectrochemical characteristics of CdS/CdSe heterojunctions formed on both ITO and p–Si substrates. The deposition of CdS and CdSe films was carried out using the chemical bath deposition method, which is economical and simple method. The optical, structural, and electrical properties of CdS/CdSe heterojunctions were analyzed through UV–Vis spectrometry, photoluminescence (PL) spectroscopy, field emission–scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), Raman spectroscopy, and Hall‐effect measurements. Furthermore, Mott–Schottky analysis was employed to investigate the electrochemical properties of the semiconductor CdS/CdSe heterojunctions on both ITO and p–Si substrates. Additionally, the photoelectrochemical investigations of CdS/CdSe heterojunctions on ITO and p–Si substrates were conducted by electrochemical analyses using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and photocurrent – time plots under both dark and illuminated conditions.

Rear Surface Passivation for Ink‐Based, Submicron CuIn(S, Se)2 Solar Cells

AbstractA N, N‐dimethylformamide and thiourea‐based route is developed to fabricate submicron (0.55 and 0.75 µm) thick CuIn(S,Se)2 (CISSe) thin films for photovoltaic applications, addressing challenges of material usage, throughput, and manufacturing costs. However, reducing the absorber film thickness below 1 µm in a regular CISSe solar cell decreases the device efficiency due to losses at the highly‐recombinative, and mediocre‐reflective Mo/CISSe rear interface. For the first time, to mitigate the rear recombination losses, a novel rear contacting structure involving a surface passivation layer and point contact openings is developed for solution processed CISSe films and demonstrated in tangible devices. An atomic layer deposited Al2O3 film is employed to passivate the Mo/CISSe rear surface while precipitates formed via chemical bath deposition of CdS are used to generate nanosized point openings. Consequently, Al2O3 passivated CISSe solar cells show an increase in the open‐circuit voltage (VOC) and short‐circuit current density when compared to reference cells with equivalent absorber thicknesses. Notably, a VOC increase of 59 mV contributes to active area efficiencies of 14.2% for rear passivated devices with 0.75 µm thick absorber layers, the highest reported value for submicron‐based solution processed, low bandgap CISSe solar cells.

Controlled synthesis of SnSxSe2-x thin films for solar energy water splitting

Earth-abundant and ecofriendly minerals SnSxSe2–x can be promising candidates for photoelectrochemical (PEC) cells because of their tunable band gaps and high absorption efficiency in the visible light range. In this paper, p type SnS thin films with sheet-like morphologies were successfully prepared by CBD method and then n-type SnSxSe2-x thin films were achieved by selenization annealing of SnS thin films. The physical properties and PEC performances of SnSxSe2-x thin films influenced by the annealing process were detailed studied. The photocurrent densities and stability of SnSxSe2-x films were further improved by the deposition of p-type CdS:Cu buffer layer. And the fabrication of FTO/SnSxSe2-x/CdS:Cu/TiO2/Pt photocathode improved the PEC performance further and the photocurrent as high as 10.5 mA/cm2 had been achieved. IPCE tests indicated that the FTO/SnSxSe2-x/CdS:Cu/TiO2/Pt structure achieved a power conversion efficiency of 31.3 %.

Rapid fabrication of fast response CdS/Si visible light photodetector: Influence of laser energy

In this article, a series of considerably fast response visible light photodetectors-based CdS nanostructure were fabricated via pulsed laser deposition (PLD) technique. Further, a detailed relation between the utilized laser energy during the nanostructured CdS deposition along with the photo-responsive characteristics of the projected devices was established. Particularly, higher laser energy resulted in augmented figure of merit wherein the photo-responsivity (R) increased from 32 to 54.8 mA/W upon increasing the applied laser energy from 140 to 220 mJ, respectively. The linear dynamic range (LDR) of the fabricated devices exhibited a pronounced laser energy linear dependency with maximum value of 20 dB at 220 mJ. In contrast, the optical power profile revealed an inverse correlation with the attained R, descending values from 68.5 mA/W at 6 mW/cm2 to 34.7 mA/W at 26 mW/cm2. Of the fabricated devices, photodetector attained using laser energy of 220 mJ resulted in response/recovery time of 179 and 161 ms, respectively. Despite the consistency and robustness of the proposed geometry, it represents a rapid framework for eco-friendly optoelectronic design.

Bulk Heterojunction Antimony Selenosulfide Thin‐Film Solar Cells with Efficient Charge Extraction and Suppressed Recombination

AbstractAs an emerging earth‐abundant light harvesting material, antimony selenosulfide (Sb2(S,Se)3) has received tremendous attention for photovoltaics. Manipulating the carrier separation and recombination processes is critical to achieve high device efficiency. Compared to the conventional planar heterojunction (PHJ), the bulk heterojunction (BHJ) configuration affords great potential to enable efficient charge extraction. In this work, BHJ Sb2(S,Se)3 solar cells are constructed based on CdS nanorod arrays (NRAs). Highly ordered CdS NRAs with appropriate nanorod lengths and diameters are obtained by regulating the growth environment and screening different substrates for CdS deposition. A low‐temperature oxygen doping strategy implemented on CdS NRAs is further developed to improve the optoelectronic and defect properties as well as form a favorable cascade band structure for CdS NRAs, so as to realize more efficient charge extraction and suppressed recombination at the heterointerface. As a result, the CdS NRAs‐based superstrated BHJ Sb2(S,Se)3 solar cell yields a considerable power conversion efficiency of 8.04%, outperforming that of the PHJ device. A careful comparative study of PHJ and BHJ based on electrostatic field simulations indicates that the BHJ allows more efficient charge extraction and transport. This work highlights the great potential of BHJ configuration for constructing high‐performance antimony chalcogenide solar cells.

Photoelectrochemical hydrogen generation with CdS/Ti–Si–O composite photoanode

CdS/TiO2 composite photoanode has attracted great attention due to its favorable electronic and optical properties. In this work, nanostructured Si-doped TiO2 photoanodes modified with CdS were fabricated through anodization of Ti–5Si alloy and depositing CdS by successive ionic layer adsorption and reaction (SILAR) process. The composition and morphology, optical properties and photoelectrochemical (PEC) performance of the composite photoanodes were investigated. The CdS/600-TiSiO composite photoanode with donor density of 2.2 × 1019 cm−3 and flat-band potential of −0.215 V exhibited excellent PEC hydrogen generation properties with remarkable photocurrent density (7.86 mA cm−2 at 0 V vs Ag/AgCl), which was 19.15 times and 9.59 times to that of undoped TiO2 photoanode and Ti–Si–O photoanode, respectively. The joint employment of Si-doping and CdS deposition provided an effective method to prepare excellent photocatalysts for PEC hydrogen generation.

A flexible self-powered UV–Vis photodetector based on Successive Ionic Layer Adsorption and Reaction (SILAR) deposited CdS on asymmetric contacts

Self-powered photodetectors exhibiting broadband spectral responses have drawn significant attention owing to their zero-power consumption, high sensitivity, and enhanced light-matter interaction. However, considering the existing complex fabrication processes for self-powered devices, facile fabrication schemes that can be performed at room temperature and are scalable are highly desirable. This work demonstrates a metal-semiconductor-metal (MSM) based flexible, self-powered photodetector employing Successive Ionic Layer Adsorption and Reaction (SILAR) deposition of CdS directly on a paper substrate with interdigitated Asymmetric contacts, namely of pencil-drawn graphite and silver paste. Upon light illumination, a built-in field is generated due to the asymmetry in the fermi levels of the metal contacts, supporting efficient carrier separation. The as-fabricated device extends its absorbance from Ultraviolet (UV) to Visible (Vis) spectra, with the highest peak absorption around 520 nm. Further, the device exhibits a responsivity of 6.56 mA/W and 1500 mA/W and detectivity of 2.3 × 108 Jones and 5.66 × 1010 Jones when illuminated with Visible (intensity-0.0125 mW/cm2) and UV (intensity-2.50 mW/cm2) lights respectively. Without any external power, the device showed response times of 0.11 s and 1.42 s when subjected to UV and Vis irradiations. This detector also exhibited superior resistance to bending stress and retained its performance even after multiple bending cycles (∼1000). Hence, the facile, low-cost, and room-temperature SILAR deposition technique-assisted photodetector fabrication paves the way for developing other high-performance and flexible photodetectors for various optoelectronic applications.

Interface-Engineered Ni-Coated CdTe Heterojunction Photocathode for Enhanced Photoelectrochemical Hydrogen Evolution

Photoelectrochemical (PEC) water splitting for hydrogen production using the CdTe photocathode has attracted much interest due to its excellent sunlight absorption property and energy band structure. This work presents a study of engineered interfacial energetics of CdTe photocathodes by deposition of CdS, TiO2, and Ni layers. A heterostructure CdTe/CdS/TiO2/Ni photocathode was fabricated by depositing a 100-nm n-type CdS layer on a p-type CdTe surface, with 50 nm TiO2 as a protective layer and a 10 nm Ni layer as a co-catalyst. The CdTe/CdS/TiO2/Ni photocathode exhibits a high photocurrent density (Jph) of 8.16 mA/cm2 at 0 V versus reversible hydrogen electrode (VRHE) and a positive-shifted onset potential (Eonset) of 0.70 VRHE for PEC hydrogen evolution under 100 mW/cm2 AM1.5G illumination. We further demonstrate that the CdTe/CdS p-n junction promotes the separation of photogenerated carriers, the TiO2 layer protects the electrode from corrosion, and the Ni catalyst improves the charge transfer across the electrode/electrolyte interface. This work provides new insights for designing noble metal-free photocathodes toward solar hydrogen development.

Controllable and innovative preparation of Zn(O,S) buffer layers for CIGS thin film solar cells

The band gap of CdS (Eg = 2.4 eV) was narrow, which made it unable to transmit short-wave sunlight through the CIGS absorber layer. Zn(O,S) thin film, prepared by doping O into ZnS, had a wider band gap, and the raw material was green and non-toxic, making it suitable as a buffer layer for solar cells. However, CBD-Zn(O,S) usually takes longer than CdS deposition. In this work, By shortening the deposition time through the fast hydrolysis of TAA. Na3NTA was added in the solutions to improve the quality of Zn(O,S) thin films. The effect of Na3NTA concentration on the complex ion contents was investigated. When Na3NTA was added at a concentration of 0.04 M along with TAA (0.04 M), the film had a high T% of 88.6%, Eg of 3.76 eV, and a dense grain distribution. ZnS and ZnO grew at (111) and (100) crystals, respectively. Raman and XPS analyses showed the existence of Zn–S and Zn–O bonds, indicating the high crystalline quality of the Zn(O,S) thin films prepared with CBD. Finally, when the optimal concentrations of ZnSO4, NH4OH, Na3NTA, and TAA were 0.04 M, 0.48 M, 0.04 M, and 0.04 M, respectively, the prepared Zn(O,S) thin films could be used as a cadmium-free buffer layer for solar cells.

Conformal coating of CdS onto flexible enokitake-like standing gold nanowire arrays for omnidirectional low-light-intensity photocatalysis

Nature’s photocatalysis system is typically flexible and can function with omnidirectional sunlight illumination (e.g. plant leaves), sometimes even under low-intensity sunlight conditions (e.g. seagrass). Previous research efforts have been mainly directed at designing photocatalysts in solutions or on rigid substrates with the aim of achieving high efficiency rather than mimicking the features of ubiquitous natural biosystems. Here we report on flexible artificial leaves by using elastomer-bonded, CdS-coated, enokitake-like gold nanowire (AuNW) arrays, which can perform model chemical reactions under omnidirectional light illumination and at a low light intensity of ∼1.2 mW/cm2 – about 1% of the sunlight energy at the sea surface level, which corresponds to the disphotic zone in the sea. The key attributes of our photocatalytic system include: (1) closely-packed, vertically aligned AuNWs offering high surface area and efficient light absorption; (2) the conformal and tunable deposition of CdS onto AuNWs enabling optimization of photocatalytic efficiency; (3) free-standing and flexible features allowing for a versatile design that mimics Nature’s photocatalytic process.

Synthesis and characterization by experimental and theory research suitable on the CdS and CdO materials

In this paper, we have compared and analyzed experimental and theoretical research on A2B6 types semiconductor materials CdS and CdO. The XRD spectra of the samples were examined using an atomic force microscope and X-ray diffraction microscopy. During film deposition, the temperature of the crucible with a source (CdS) varied in the range Tsourse ≈ 800 ÷ 850°C, and the substrate temperature was maintained within the range Tp ≈ 250 ÷ 270°C. In this case, to ensure the reproducibility of the structures, a shutter was used, with the help of which the CdS deposition time was set, which ensured that the film thickness was the same from experiment to experiment.

Deposition of CdS and ZnS directly on rGO via. an emulsion-solvothermal method for excellent photocatalytic activity and stability

Graphene was often employed as electron mediator between semiconductors in the heterogeneous materials to improve electron transfer and therefore enhance photocatalytic performance. Little reported synthesis method can guarantee the deposition of two different semiconductors directly on graphene. In this work, an emulsion-solvothermal method employing graphene oxide (GO) as surfactant was proposed to prepare CdS/reduced graphene oxide (rGO)/ZnS composites for accomplishing the direct contact of CdS and ZnS with rGO. The optimal composite CG0.5Z prepared via. emulsion-solvothermal method can produce H2O2 with the remarkable efficiency of 24.93 mM g−1 h−1 under visible light, and rapidly decompose tetracycline and RhB with the removal rate of 80.3% and 87.4%, respectively, after only 10 min irradiation, exhibiting superior photocatalytic activity to the material prepared via. conventional method. CG0.5Z also exhibited out-standing photocatalytic ability under real sunlight irradiation. The recycling experiments proved the excellent stability of the obtained ternary composite. The photoluminescence measurements, the time-resolved photoluminescence decay curves and Mott-Schottky plots further confirmed the more efficient electron-hole spatial separation and transfer in composite prepared through emulsion-solvothermal route, proving the emulsion-solvothermal synthesis is a better way to construct the rGO bridge between semiconductors. The possible degradation reaction pathways were also deduced based on the detected intermediate products.

TiO2/CdS/CdSe quantum dots co-sensitized solar cell with the staggered-gap (type-II) heterojunctions for the enhanced photovoltaic performance

The effect of co-sensitization and ZnS passivation on the photovoltaic performance of CdS quantum dot sensitized solar cells (QDSSCs) were investigated. The deposition of CdS, CdSe quantum dots (QD) and ZnS passivation on TiO2 photoanode was carried out by successive ionic layer adsorption and reaction (SILAR) method. CdS/CdSe co-sensitization developed two staggered type-II heterojunctions at TiO2/CdS and CdS/CdSe interfaces and resulted a cascade energy band structure. This suitable band alignment facilitated the double charge transfer mechanism at each heterojunction and transported the electrons easily into the photoanode. The narrow bandgap sensitizers CdS and CdSe significantly improved the potential utilization of solar spectrum with more charge carrier generation. ZnS passivation on QD surface suppressed electrode/electrolyte interfacial charge recombination and facilitated more electron injection from QDs into TiO2 photoanode. The EDAX elemental mapping results inferred that CdS, CdSe and ZnS have efficiently covered the TiO2 surface. TiO2/CdS and CdS/CdSe interfaces and the amorphous nature of ZnS could be verified with HRTEM images. Hence, the co-sensitization and surface passivation played a significant role to enhance the PCE of CdS QDSSC from 1.9% to 4.05%.