Stacked graphene–TiO2 photoanode via electrospray deposition for highly efficient dye-sensitized solar cells

A series of TiO₂–graphene stacked photoanodes for dye-sensitized solar cells (DSSCs) were fabricated by electrospray (E-spray) deposition. Among devices incorporating single graphene layer with different deposition times, device with 1 min graphene deposition gave the best performance. For multi-graphene-layer involved devices, best result was obtained with 3 layers of graphene. The working principles were analyzed by scanning electron microscopy, transmittance spectra, electrochemical impedance spectroscopy and incident-photo-conversion efficiency data. We found that although graphene layers incorporated in TiO₂ photoanode slightly decreased dye adsorption, they were able to significantly improve the electron transport, and the charge recombination at the interfaces of TiO₂/dye and TiO₂/electrolyte were greatly suppressed, leading to dramatic improvement in power conversion efficiency. When inserting three layers of pure graphene into the TiO₂ photoanode, high efficiency of 8.9% was obtained, constituting an over 23.6% improvement. Further increasing graphene layers to five, although electron lifetimes is the longest, both the largest charge transfer resistance and the least amount of the dye loading lead to the lowest device efficiency. Our work demonstrated, that pure graphene layer can be successfully incorporated into TiO₂ photoanode by E-spray method with easiness of thickness control and the photoanode with graphene/TiO₂ alternatively layered structure is an excellent candidate for DSSCs.     

An Effective Approach for High‐Efficiency Photoelectrochemical Solar Cells by Using Bifunctional DNA Molecules Modified Photoanode

This paper firstly reports the effect of deoxyribonucleic acid (DNA) molecules extracted from chickpea and wheat plants on the injection/recombination of photogenerated electrons and sensitizing ability of dye‐sensitized solar cells (DSSCs). These high‐yield DNA molecules are applied as both linker bridging unit as well as thin tunneling barrier (TTB) at titanium dioxide (TiO₂ )/dye interface, to build up high‐efficient DSSCs. With its favorable energy levels, effective linker bridging role, and double helix structure, bifunctional DNA modifier shows an efficient electron injection, suppressed charge recombination, longer electron lifetime, and higher light harvesting efficiency, which leads to higher photovoltaic performance. In particular, a photoconversion efficiency (PCE) of 9.23% is achieved by the binary chickpea and wheat DNA‐modified TiO₂ (CW@TiO₂) photoanode. Furthermore, time‐resolved fluorescence spectroscopy measurements confirm a better electron transfer kinetics for DNA‐modified TiO₂ photoanodes, implying a higher electron transfer rate (k_ET). This work highlights a great contribution for the photoanodes that are linked with DNA molecule, which act as both bridging unit and TTB to control the charge recombination and injection dynamics, and hence, boost the photovoltaic performance in the DSSCs.     

Effect of seed layer on the growth of rutile TiO2 nanorod arrays and their performance in dye-sensitized solar cells

In order to improve the performance of TiO₂ photoanode-based dye sensitized solar cells (DSSCs), rutile TiO₂ nanorod arrays (NRAs) were grown on SnO₂:F (FTO) conductive glass coated with TiO₂ seed layer by a hydrothermal method. The TiO₂ seed layer was obtained by spin-coating titanium tetraisopropoxide (TTIP) isopropanol solution with concentration in the range of 0~0.075 M. Then the effect of the thin TiO₂ seed layer on the crystal structure and surface morphology of TiO₂ NRAs and the photoelectric conversion properties of the corresponding DSSCs were investigated. It is found that TiO₂ NRAs are vertically oriented, about 1.7 μm long and the average diameter is about 35 nm for the samples derived from TTIP in the range of 0.005~0.05 M, which are more uniform and better separated from each other than those without TiO₂ seed layer (average diameter 35~85 nm). The photoelectric conversion efficiency of DSSCs based on TiO₂ NRAs with TiO₂ seed layer is larger than that without TiO₂ seed layer. Typically, the energy efficiency of DSSCs obtained from the seed solution of 0.025 M TTIP is 1.47%, about 1.8 times greater than that without TiO₂ seed layer. The performance improvement is attributed to the thinner, denser and better oriented NRAs grown on seeded-FTO substrate absorbing more dye and suppressing charge recombination at the FTO substrate/electrolyte interface.     

Graphene nanosheets as counter electrode with phenoxazine dye for efficient dye sensitized solar cell

Efficient dye sensitized solar cells (DSSCs) are developed using phenoxazine (POZ) based organic dye (WS5) and graphene nanosheets (GNs) counter electrode (CE). Being organic, both these materials are used together to explore compatibility of organic materials in current DSSCs. Organic dye with POZ moiety is synthesized and graphene oxide nanosheets (GONs) are spin coated on FTO glass and thermally reduced afterwards. To increase the performance of WS5 through decreased dye aggregation, deoxycholic acid (DCA) is added to it. The results of adding DCA are observed and compared using UV–Vis spectroscopy, external quantum efficiency (EQE), electrochemical impedance spectroscopy (EIS) and photovoltaic conversion efficiency (PCE). Prepared organic dye based DSSC cell results in a high PCE of 6.61%. The optimized WS5 dye and GNs CE, shows PCE of 5.77% and the GNs CE compared to Pt CE results in almost identical charge transfer resistance value at the CE/electrolyte interface. Low cost of this designed organic dye and GNs and the PCE results indicate that this combination may result in the reduction of cost of current DSSCs and the realization that expensive and rare inorganic materials can be replaced with organic ones in future.     

Enhanced Performance of I2‐Free Solid‐State Dye‐Sensitized Solar Cells with Conductive Polymer up to 6.8%

An iodine‐free solid‐state dye‐sensitized solar cell (ssDSSC) is reported here, with 6.8% energy conversion efficiency—one of the highest yet reported for N719 dye—as a result of enhanced light harvesting from the increased transmittance of an organized mesoporous TiO₂ interfacial layer and the good hole conductivity of the solid‐state‐polymerized material. The organized mesoporous TiO₂ (OM‐TiO₂) interfacial layer is prepared on large‐area substrates by a sol‐gel process, and is confirmed by scanning electron microscopy (SEM) and grazing incidence small‐angle X‐ray scattering (GISAXS). A 550‐nm‐thick OM‐TiO₂ film coated on fluorine‐doped tin oxide (FTO) glass is highly transparent, resulting in transmittance increases of 8 and 4% compared to those of the bare FTO and conventional compact TiO₂ film on FTO, respectively. The high cell performance is achieved through careful control of the electrode/hole transport material (HTM) and nanocrystalline TiO₂/conductive glass interfaces, which affect the interfacial resistance of the cell. Furthermore, the transparent OM‐TiO₂ film, with its high porosity and good connectivity, exhibits improved cell performance due to increased transmittance in the visible light region, decreased interfacial resistance ( Ω ), and enhanced electron lifetime ( τ ). The cell performance also depends on the conductivity of HTMs, which indicates that both highly conductive HTM and the transparent OM‐TiO₂ film interface are crucial for obtaining high‐energy conversion efficiencies in I₂‐free ssDSSCs.     

Improved power conversion efficiency by insertion of RGO–TiO2 composite layer as optical spacer in polymer bulk heterojunction solar cells

We report that the power conversion efficiency (PCE) can be enhanced in polymer bulk heterojunction solar cells by inserting an interfacial electron transporting layer consisting of pristine TiO₂ or reduced graphene oxide–TiO₂ (RGO–TiO₂) between the active layer and cathode Al electrode. The enhancement in the PCE has been analyzed through the optical absorption, current–voltage characteristics under illumination and estimation of photo-induced charge carrier generation rate. It was found that either TiO₂ or RGO–TiO₂ interfacial layers improve the light harvesting, as well as the charge extraction efficiency, acting as a blocking layer for holes, and also reducing charge recombination. The combined enhancement in light harvesting property and charge collection efficiency improves the PCE of the organic solar cell up to 4.18% and 5.33% for TiO₂ and RGO–TiO₂ interfacial layer, respectively, as compared to a value of 3.26% for the polymer solar cell without interfacial layer.     

Fabrication of TiO2 compact layer precursor at various reaction times for dye sensitized solar cells

A compact layer is used to increase the photoelectric conversion efficiency on DSSCs due to it can improve the transparent conduction oxides (TCOs) surface and prevent the electrolyte from directly contacting the ITO (Indium Tin Oxide) substrate. In this study, DSSCs with compact layer reacting for three hours are compared to those without compact layer, where the short-circuit current and solar energy conversion efficiency are improved by 22%, and 26%, respectively. Based on electrochemical impedance spectra (EIS) measurements, we clarify that the compact layer can decrease the charge interfacial resistance and the leakage current due to the fact that the dense TiO₂ nanoparticles can effectively prevent charge transport from the photoanode to the ITO substrate. We compared different reacting times for the formation of the compact layer, and showed that the quantum efficiency of DSSC is higher when a 3 h reacting time is adopted with respect to a 24 h processing time. A study of the various molar ratios of the precursor solution has been done. The data showed that the 1 M is the optimal molar ratio. We also studies the compact layer formation on FTO with respect to ITO, showing that the FTO substrate has higher photoelectric conversion efficiency.     

Silver-loaded anatase nanotubes dispersed plasmonic composite photoanode for dye-sensitized solar cells

In this article, a typical silver-loaded anatase TiO₂ nanotube (Ag-TNTs) was developed and assembled in DSSCs. By blending the Ag-TNTs and TiO₂ nanoparticles as the composite photoanode, this hybrid nanostructure exhibits a promising architecture for accelerating electron transport as well as enhancing dye adsorption. These nanotubes could provide direct charge transfer pathways and increase electrolyte penetration in comparison with the TiO₂ nanoparticles alone network. Moreover, the presence of the Ag nanoparticles could enhance the light harvesting efficiency and promote the charge separation, which further improves the performance of the DSSCs. The DSSC with metal-modified hybrid nanostructures has achieved an efficiency of 8.19% which is about 56% higher than DSSCs based on TiO₂ nanoparticles photoanode with 5.26%.     

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.     

Performance Enhancement of Tri‐Cation and Dual‐Anion Mixed Perovskite Solar Cells by Au@SiO2 Nanoparticles

Tri‐cation and dual‐anion mixed perovskites have been widely utilized in perovskite solar cell (PSC) applications due to their novel properties such as high absorption, high stability, and low cost. To commercialize the PSCs, further improving the device performance without detrimentally changing the device configuration is important at present. Herein, Au@SiO₂ nanoparticles (NPs) are introduced to modify the interface between mesoporous TiO₂ (mp‐TiO₂) and mixed perovskite with increased main photovoltaic parameters of the device, resulting in a ≈29% enhancement of power conversion efficiency (PCE) from 15.8% to 20.3%. The origins of the enhancement have been studied by exploring the optical absorption, optical power distribution, and charge carrier behaviors within the system. The small perturbation transient photovoltage measurement exhibits prolonged charge carrier lifetimes after the Au@SiO₂ NPs incorporation, and time of flight photoconductivity measurement shows that charge carrier mobilities of this system are also enhanced. These characteristics make metallic nanostructures a promising functional material in facile tuning of the charge carriers transport and further boosting the PCE of the PSCs.     

Low‐temperature flexible Ti/TiO2 photoanode for dye‐sensitized solar cells with binder‐free TiO2 paste

An energy‐economical dye‐sensitized solar cell (DSSC) with highly flexible Ti/TiO₂ photoanode was developed through a low‐temperature process, using a binder‐free TiO₂ paste. Ti foils, coated with the binder‐free TiO₂ films were annealed at various temperature. Scanning electron microscopic (SEM) images of the films show uniform, mesoporous and crack‐free surface morphologies as well as interpenetrated TiO₂ network. DSSCs with binder‐free TiO₂ films annealed at 450, 350, 250 and 120°C show solar‐to‐electricity conversion efficiencies (η) of 4.33, 4.34, 3.72 and 3.40%, respectively, which are comparable to the efficiency of 4.56% obtained by using a paste with binder and annealing it at 450°C; this observation demonstrates the benefits of a binder‐free TiO₂ paste for the fabrication of energy‐fugal DSSCs. On the other hand, when organic binder was used in the TiO₂ paste for film preparation, a drastic deterioration in the cell performance with decreasing annealing temperature is noticed. Laser‐induced photo‐voltage transient technique is used to estimate the electron lifetime in various Ti/TiO₂ films. Electrochemical impedance spectroscopic (EIS) analysis shows that the lower the annealing temperature of the TiO₂ coated Ti foil, the larger the charge transfer resistance at the TiO₂/dye/electrolyte interface (R_ct2). Copyright © 2011 John Wiley & Sons, Ltd.     

Dye‐sensitized TiO2 solar cells based on nanocomposite photoanode containing plasma‐modified multi‐walled carbon nanotubes

A series of anatase TiO₂‐based nanocomposite incorporated with plasma‐modified multi‐walled carbon nanotubes (MWNTs) was prepared by physical blending and shows its capability for efficient electron transport when used as photoanode in dye‐sensitized solar cells (DSSCs). These MWNTs characterized with good dispersal performance were obtained by functionalization technique via in situ plasma treatment and subsequent grafting with maleic anhydride (MA) onto the external walls reported previously. Compared with the conventional DSSCs, the TiO₂ film with 1D carbon nanotubes possesses more outstanding ability to transport electrons injected from the excited dye within the device under illumination. As a result, at an optimum addition of 0.3 wt% MWNTs‐MA in TiO₂ matrix, the photocurrent–voltage (J–V) characteristics showed a significant increase in the short‐circuit photocurrent (J_sc) of 50%, leading to an increase in overall solar conversion efficiency by a factor of 1.5. Electrochemical impedance spectroscopy analyses reveal that the MWNTs‐MA/TiO₂ incur smaller resistances at the photoanode in assembled DSSCs when compared with those in the anatase titania DSSCs. These features suggest that the conducting properties of the MWNTs‐MA within the anodes are crucial for achieving a higher transport rate for photo‐induced electrons in TiO₂ layer by exhibiting lower resistance in the porous network and hence retard charge recombination that could result in poor conversion efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

Improving the Extraction of Photogenerated Electrons with SnO2 Nanocolloids for Efficient Planar Perovskite Solar Cells

Great attention to cost‐effective high‐efficiency solar power conversion of trihalide perovskite solar cells (PSCs) has been hovering at high levels in the recent 5 years. Among PSC devices, admittedly, TiO₂ is the most widely used electron transport layer (ETL); however, its low mobility which is even less than that of CH₃NH₃PbI₃ makes it not an ideal material. In principle, SnO₂ with higher electron mobility can be regarded as a positive alternative. Herein, a SnO₂ nanocolloid sol with ≈3 nm in size synthesized at 60 °C was spin‐coated onto the fuorine‐doped tin oxide (FTO) glass as the ETL of planar CH₃NH₃PbI₃ perovskite solar cells. TiCl₄ treatment of SnO₂‐coated FTO is found to improve crystallization and increase the surface coverage of perovskites, which plays a pivotal role in improving the power conversion efficiency (PCE). In this report, a champion efficiency of 14.69% (J_sc = 21.19 mA cm^?2, V_oc = 1023 mV, and FF = 0.678) is obtained with a metal mask at one sun illumination (AM 1.5G, 100 mW cm^?2). Compared to the typical TiO₂, the SnO₂ ETL efficiently facilitates the separation and transportation of photogenerated electrons/holes from the perovskite absorber, which results in a significant enhancement of photocurrent and PCE.     

Bioinspired,Stimuli‐Responsive,Multifunctional Superhydrophobic Surface with Directional Wetting,Adhesion, and Transport of Water

A novel smart stimuli responsive surface can be fabricated by the subsequent self‐assembly of the graphene monolayer and the TiO₂ nanofilm on various substrates, that is, fabrics, Si wafers, and polymer thin films. Multiscale application property can be achieved from the interfacial interaction between the hierarchical graphene/TiO₂ surface structure and the underlying substrate. The smart surface possesses superhydrophobic property as a result of its hierarchical micro‐ to nanoscale structural roughness. Upon manipulating the UV induced hydrophilic conversion of TiO₂ on graphene/TiO₂ surface, smart surface features, such as tunable adhesiveness, wettability, and directional water transport, can be easily obtained. The existence of graphene indeed enhances the electron–hole pair separation efficiency of the photo‐active TiO₂, as the time required for the TiO₂ superhydrophilic conversion is largely reduced. Multifunctional characteristics, such as gas sensing, droplet manipulation, and self‐cleaning, are achieved on the smart surface as a result of its robust superhydrophobicity, tunable wettability, and high photo‐catalytic activity. It is also revealed that the superhydrophilic conversion of TiO₂ is possibly caused by the atomic rearrangement of TiO₂ under UV radiation, as a structural transformation from {101} to {001} is observed after the UV treatment.     

Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells

A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoO_x) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased V_oc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased V_oc, a J_sc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoO_x layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoO_x interface is hence significantly retarded. The GO‐MoO_x device consequently shows significantly enhanced V_oc and J_sc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability.     

Metal–Organic Framework Derived Co3O4/TiO2/Si Heterostructured Nanorod Array Photoanodes for Efficient Photoelectrochemical Water Oxidation

A novel hierarchical structured photoanode based on metal–organic frameworks (MOFs)‐derived porous Co₃O₄‐modified TiO₂ nanorod array grown on Si (MOFs‐derived Co₃O₄/TiO₂/Si) is developed as photoanode for efficiently photoelectrochemical (PEC) water oxidation. The ternary Co₃O₄/TiO₂/Si heterojunction displays enhanced carrier separation performance and electron injection efficiency. In the ternary system, an abnormal type‐II heterojunction between TiO₂ and Si is introduced, because the conduction band and valence band position of Si are higher than those of TiO₂, the photogenerated electrons from TiO₂ will rapidly recombine with the photogenerated holes from Si, thus leading to an efficient separation of photogenerated electrons from Si/holes from TiO₂ at the TiO₂/Si interface, greatly improving the separation efficiency of photogenerated hole within TiO₂ and enhances the photogenerated electron injection efficiency in Si. While the MOFs‐derived Co₃O₄ obviously improves the optical‐response performance and surface water oxidation kinetics due to the large specific surface area and porous channel structure. Compared with MOFs‐derived Co₃O₄/TiO₂/FTO photoanode, the synergistic function in the MOFs‐derived Co₃O₄/TiO₂/Si NR photoanode brings greatly enhanced photoconversion efficiency of 0.54% (1.04 V vs reversible hydrogen electrode) and photocurrent density of 2.71 mA cm^?2 in alkaline electrolyte. This work provides promising methods for constructing high‐performance PEC water splitting photoanode based on MOFs‐derived materials.     

A Triphenylamine Dye Model for the Study of Intramolecular Energy Transfer and Charge Transfer in Dye‐Sensitized Solar Cells

A novel dye ( 2TPA‐R ), containing two triphenylamine (TPA) units connected by a vinyl group and rhodanine‐3‐acetic acid as the electron acceptor, is designed and synthesized successfully to reveal the working principles of organic dye in dye‐sensitized solar cells (DSSCs). 2TPA and TPA‐R , which consist of two TPA units connected by vinyl and a TPA unit linked with rhodanine‐3‐acetic acid, respectively, are also synthesized as references to study the intramolecular energy transfer (E_nT) and charge transfer (ICT) processes of 2TPA‐R in CH₂Cl₂ solution and on a TiO₂ surface. The results suggest that the intramolecular E_nT and ICT processes show a positive effect on the performance of DSSCs. However, the flexible structure and less‐adsorbed amount of dye on TiO₂ may make it difficult to improve the efficiency of DSSCs. This study on intramolecular E_nT and ICT processes acts as a guide for the design and synthesis of efficient organic dyes in the future.     

Ultrafast Discharge/Charge Rate and Robust Cycle Life for High‐Performance Energy Storage Using Ultrafine Nanocrystals on the Binder‐Free Porous Graphene Foam

A hierarchical architecture fabricated by integrating ultrafine titanium dioxide (TiO₂) nanocrystals with the binder‐free macroporous graphene (PG) network foam for high‐performance energy storage is demonstrated, where mesoporous open channels connected to the PG facilitate rapid ionic transfer during the Li‐ion insertion/extraction process. Moreover, the binder‐free conductive PG network in direct contact with a current collector provides ultrafast electronic transfer. This structure leads to unprecedented cycle stability, with the capacity preserved with nearly 100% Coulombic efficiency over 10 000 Li‐ion insertion/extraction cycles. Moreover, it is proven to be very stable while cycling 10 to 100‐fold longer compared to typical electrode structures for batteries. This facilitates ultrafast charge/discharge rate capability even at a high current rate giving a very short charge/discharge time of 40 s. Density functional theory calculations also clarify that Li ions migrate into the TiO₂–PG interface then stabilizing its binder‐free interface and that the Li ion diffusion occurs via a concerted mechanism, thus resulting in the ultrafast discharge/charge rate capability of the Li ions into ultrafine nanocrystals.     

Pulsed Laser Ablation Based Synthesis of PbS‐Quantum Dots‐Decorated One‐Dimensional Nanostructures and Their Direct Integration into Highly Efficient Nanohybrid Heterojunction‐Based Solar Cells

The pulsed laser deposition (PLD) technique is used for the direct fabrication of nanohybrid heterojunctions (NH‐HJs) solar cells exhibiting high PCE and excellent stability in air without any encapsulation and/or resorting to any surface treatment, ligand engineering and/or post‐synthesis processing. The NH‐HJs are achieved through the PLD‐based decoration of hydrothermally‐grown one‐dimensional TiO₂ nanorods (TiO₂‐NRs) by PbS quantum dots (PbS‐QDs). By optimizing both the amount of PbS‐QDs (via the number of laser ablation pulses) and the length of the TiO₂‐NRs, it is possible to achieve optimal NH‐HJs based PV devices with high power conversion efficiency (PCE) of 4.85%. This high PCE is found to occur for an optimal length of the NRs (≈290 nm) which coincides with the average penetration depth of PbS‐QDs into the porous TiO₂‐NRs matrix, leading thereby to the formation of the largest extent of NH‐HJs. Most importantly, the PCE of these novel devices is found to be fairly stable for several months under ambient air. The addition of single‐wall carbon nanotubes (SWCNTs) onto the TiO₂‐NRs prior to their decoration by PbS‐QDs is shown to further enhance their PCE to a value as high as 5.3%, because of additional light absorption and improved charge collection ensured by SWCNTs.     

A nanostructure-based counter electrode for dye-sensitized solar cells by assembly of silver nanoparticles

A nanostructure-based Pt counter electrode for dye-sensitized solar cells (DSSCs) is fabricated by assembly of silver nanoparticles on glass substrate and deposition of a thin Pt layer. This typical counter electrode has several unique behaviors such as good conductivity, quasi-uniform undulating morphology and high surface area. Studies indicate that the application of the FTO-free nanostructure-based Pt counter electrode in DSSCs can decrease the charge-transfer resistance of the Pt/electrolyte interface, enlarge the light pathway and enhance the light reabsorption superior to the devices with planar Pt counter electrode. In addition, theoretical analysis and experimental study demonstrate that the hot electrons injection effect caused by Localized Surface Plasmon Resonance effect of silver nanoparticles enhances the charge transport characteristic at the Pt/electrolyte interface, and this SPR effect makes the certain contributions on the enhancement of the photovoltaic performance of DSSCs. Compared to the DSSC with traditional planar counter electrode, the incident photon-to-current conversion efficiency, short-circuit current, and power conversion efficiency of DSSCs with nanoparticulate structure are increased by 1.117 times, 1.156 times, and 1.145 times, respectively; and the final power conversion efficiency (PCE) increases from 6.95% to 7.96%.