Gold nanomesh induced surface plasmon for photocurrent enhancement in a polymer solar cell

In this study, a gold (Au) nanomesh layer was manufactured on an ITO-coated glass substrate at room temperature. The Au nanomesh was used to induce surface plasmon resonance (SPR) to enhance the photocurrent of a polymer solar cell. The Au nanomesh was manufactured by lift-off on closely packed PS nanospheres (diameter ∼50 nm; density ∼10¹⁰/cm²). The PS nanospheres were fabricated by modified block copolymer nano-patterning on ITO. A transmittance-reflection-absorbance spectrum was used to explore the induced surface plasmon. An extinction peak was observed at ∼580 nm indicate the possibility of Au nanomesh induced surface plasmon resonance. The short-circuit current density of the polymer solar cell was enhanced from 7.02 to 14.2 mA/cm² by the addition of Au nanomesh. Consequently, the power conversion efficiency enhanced from 1.9% to 3.2%. By the normalized input photon-to-current conversion efficiency (IPCE) measurement, enhanced photocurrent conversion efficiency at approximately 580 nm was observed that coincided with the extinction spectrum, indicating that the surface plasmon enhanced the photocurrent.     

Effect of strong base addition to hole-collecting buffer layer in polymer solar cells

We report a brief study on the effect of strong base addition to the hole-collecting buffer layer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] on the performance of polymer solar cells made using blend films of poly(3-hexylthiophene) and soluble fullerene. A concentrated aqueous solution of sodium hydroxide (NaOH) was added to the PEDOT:PSS solution to decrease its acidity. The optical absorption spectra of modified buffer layers were measured to investigate the influence of NaOH addition on the spectral shape, while the surface of modified buffer layers was examined using atomic force microscopy. Results showed that the acidity of PEDOT:PSS solutions was remarkably reduced by adding the NaOH solution. However, the performance of solar cells was slightly degraded, which has been attributed to the decreased charge transportability as evidenced from the dark current-voltage characteristics.     

Long-lived bulk heterojunction solar cells fabricated with photo-oxidation resistant polymer

We report the fabrication of long-lived polymer solar cells using a new donor-acceptor type alternating copolymer, poly(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydroindeno[2,1-α]indene-2,7-diyl)-co-4,7-di-2-thienyl-2,1,3-benzothiadiazole (PININE-DTBT) in bulk heterojunction composites with the fullerene derivative [6,6]-phenyl C₇₀-butyricacidmethyl ester (PC₇₀BM). The PININE-DTBT:PC₇₀BM solar cells exhibit an extended device lifetime (as compared with other polymer systems) with a reasonable power conversion efficiency of ∼2.7% under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW/cm². The long-lived feature of the devices originates from the photo-oxidation resistant backbone unit and the deep HOMO (highest occupied molecular orbital) level of PININE-DTBT.     

Localized surface plasmon resonance enhanced organic solar cell with gold nanospheres

We use gold nanospheres (Au NSs) to improve the performance of polymer organic solar cells. Au NSs with a diameter of about 5 nm or 15 nm were doped into the buffer layer of organic solar cells. We attribute the efficiency improvement to the size-dependent localized surface plasmon resonance (LSPR) effect of Au NSs, which can enhance the light harvest ability of active layer around the Au NSs, and increase the probability of the exciton generation and dissociation. Our results show that solar cells doped with 15 nm-diameter Au NSs exhibit significant improvement of the efficiency (from 1.99% to 2.36%), while solar cells doped with only 5 nm-diameter Au NSs did not give obvious improvement of the performance.     

Effects of silver particles on the photovoltaic properties of dye-sensitized TiO2 thin films

To evaluate the possibility of using the plasmon resonance effect to enhance the efficiency of photochemical cells, cis-(SCN)₂Bis(2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) dye-sensitized cells were used to measure the photoresponse of TiO₂ film electrodes before and after deposition of Ag particles. The deposited Ag particles created a film with Ag islands. We found that the photoresponse in the visible region increased as the mass-equivalent Ag-island film thickness, t_Ag, increased to 3.3 nm, but decreased when t_Ag was further increased to 6 nm. On the other hand, compared with bare TiO₂ films, the photoresponse in the UV region decreased for any level of Ag islands. These results suggest that under proper conditions, enhancement of the optical absorption of the dye by the Ag plasmon resonance effect contributes to the photocurrent, and indicates the possibility of improving the energy conversion efficiency of photoelectrochemical cells with Ag-island films.     

The effect of introducing a buffer layer to polymer solar cells on cell efficiency

The effect of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) as a buffer layer was investigated in polymer solar cells (PSCs). Four different types of PEDOT:PSS were used: PH, PH500 and their DMSO (dimethylsulfoxide)-doped counterparts. The efficiency of PSCs was independent of the electric conductivity of the buffer layer as a bulk property while it was significantly related to interfacial properties between the buffer layer and a bulk-heterojunction (BHJ) layer. The interfacial properties included charge transfer resistance (R_CT), hole mobility (μ_h) and contact angle (θ) of the solution of BHJ on the buffer layer. Lower R_CT, higher μ_h and smaller θ led to the higher fill factor (up to 72%), enabling highly efficient PSCs with efficiency (η)=4.25%.     

Preparation and characterization of nano-scale ZnO as a buffer layer for inkjet printing of silver cathode in polymer solar cells

Less-populated and well-isolated ZnO nanorods were prepared from a simple solution method by using polyethylene glycol (PEG) surfactant molecules. The structural and morphological information provided by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) demonstrated the high purity of the ZnO nanorods that were free from any unknown impurities. Furthermore, annealing treatment was used to increase the length of the ZnO nanorods further at an elevated temperature. This ZnO was used as a buffer layer for polymer solar cells (PSCs) in the device configuration of ITO/ PEDOT:PSS/P3HT-PCBM/ZnO/Ag, in which the Ag cathode was prepared by the inkjet printing method using silver ink. The present study discusses and compares the performance of the devices with and without the ZnO buffer layer.     

Anode engineering for photocurrent enhancement in a polymer solar cell and applied on plastic substrate

In this work, a multilayer structure, PEDOT:PSS/insulator/PEDOT:PSS (CIC), was designed and used as the anode in a polymer solar cell (PSC) to enhance the efficiency at low annealing temperature. The efficiency for PSC with CIC multilayers could increase around 22% as compared to the reference cell. The internal electrical field enhancement due to the effective work function increase by CIC multilayer was assumed and responded to efficiency enhancement. The work function of the multilayer anode structure was explored by an electrostatic force microscopy (EFM) analysis. The EFM result shows that the surface potential of PEDPT:PSS in CIC structure is around 0.6 V higher than PEDOT:PSS in reference structure, indicating a higher work function for PEDOT:PSS in multilayer structure. By the input photon-to-current conversion efficiency (IPCE) study, the major enhancement in photocurrent occurred at solar spectrum range of 400-650 nm. Further applied to plastic substrate, the PSC exhibits 9.2% enhancement in efficiency.     

Airbrush spray-coating of polymer bulk-heterojunction solar cells

We report on the fabrication of efficient polymer solar cells via airbrush coating as a promising method for low cost and large area production. We used a dual action airbrush for deposition of the active layer from a poly(3-hexylthiophene):[6,6]-Phenyl C61 butyric acid methyl-ester (P3HT:PCBM) blend dissolved in a co-solvent mixture. The resulting devices were measured under AM1.5G conditions and compared with spin-coated ones in air and nitrogen atmosphere. High power conversion efficiencies (η=4.1%) were obtained by optimizing the parameters of the spray system (i.e. film thickness, time of spray, distance between sample and airbrush, substrate temperature, etc.). The measurements also showed good repeatability and uniformity despite a relatively rougher surface.     

Efficiency enhancement of solar cells by luminescent up-conversion of sunlight

Significant improvements in the efficiency of solar cells by combination with luminescent up- or down-converters have recently been predicted theoretically. Here, we extend the theoretical analysis of the limiting efficiency of the up-conversion (UC)-system to realistic Airmass spectra and analyse the spectral robustness of the UC-system. We also present initial experimental results from prototypes involving bifacial silicon solar cells with UC-phosphors attached to the rear surface, and discuss the possibility of realizing efficient UC with low-band-gap solar cells in combination with a light emitting diode.     

Solar module using dye-sensitized solar cells with a polymer electrolyte

Dye-sensitized TiO₂ solar cells assembled with a polymer electrolyte were investigated, aiming at the construction of an 8 V solar module. The individual solar cells were assembled with 4.5 cm² active area and were characterized under outdoor conditions, exhibiting an average efficiency of 0.9% per cell (at 12:00 noon). The solar module was built by connecting 13 cells in series. The integrated average daily power was estimated to be 183 mW. The present paper discusses the performance of the individual cells and the module.     

Efficiency enhancement by mixed cation effect in dye-sensitized solar cells with a PVdF based gel polymer electrolyte

This paper reports the effect of using a mixed iodide salt system with two dissimilar cations to enhance the efficiency of dye-sensitized solar cells made with polyvinylidenefluoride (PVdF) based gel electrolyte. Instead of a single iodide salt, a mixture of potassium iodide (KI) with a small K⁺ cation and tetrapropylammonium iodide (Pr₄NI) with a bulky Pr₄N⁺ cation were used to provide the required iodide ion conductivity. Solar cells of configuration FTO/TiO₂/Dye/electrolyte/Pt/FTO were fabricated using a mesoporous TiO₂ electrode sensitized with a Ruthenium dye (N719). With identical electrolyte compositions, the cells with KI and Pr₄NI alone gave efficiencies of 2.37% and 2.90% respectively. The cell with the mixed iodide system, KI:Pr₄NI = 16.6:83.4 (% weight ratio), however, showed an enhanced efficiency of 3.92% with a short circuit current density of 9.16 mA cm⁻², open circuit voltage of 674.4 mV and a fill factor of 63.4%.     

Stability/degradation of polymer solar cells

Polymer and organic solar cells degrade during illumination and in the dark. This is in contrast to photovoltaics based on inorganic semiconductors such as silicon. Long operational lifetimes of solar cell devices are required in real-life application and the understanding and alleviation of the degradation phenomena are a prerequisite for successful application of this new and promising technology. In this review, the current understanding of stability/degradation in organic and polymer solar cell devices is presented and the methods for studying and elucidating degradation are discussed. Methods for enhancing the stability through the choice of better active materials, encapsulation, application of getter materials and UV-filters are also discussed.     

Efficiency enhancement of the poly-silicon solar cell using self-assembled dielectric nanoparticles

In this study, silica nanospheres dispersed in a surfactant solution were spin-coated on commercially available silicon solar cells to form colloidal crystals on the surface. This self-assembled nanoparticle layer served as an anti-reflection (AR) layer for solar cell devices. The self-assembled layer exhibits excellent anti-reflection properties in the UV and NIR wavelength regions, and the reflectance spectra match the theoretical prediction done using the rigorous coupled-wave analysis model. We also showed that the overall conversion efficiency of polycrystalline Si solar cells coated with the silica nanospheres was increased from 11% to 12.3% when using optimized spin-coating parameters and nanoparticle concentrations.     

Multiparametric optimization of polymer solar cells: A route to reproducible high efficiency

We carried out a detailed optimization of P3HT:PCBM polymer solar cells by variation of blending ratio, film thickness and annealing conditions. From our studies it became evident that the film thickness and the fullerene concentration are mutually dependent parameters, what the overall performance concerns. In detail, we revealed a clear relationship between film thickness, PCBM concentration and the blend film morphology. We varied the PCBM concentration in our polymer solar cells between 25% and 50%, and found the best results for 33.3% of PCBM. In this case, the optimum between competing processes like effective charge carrier separation and percolation path establishment was realized. In thicker films, the growth of PCBM aggregates via phase separation leads to formation of percolation paths and therefore improves the photocurrent. In contrast, for thinner films a high PCBM concentration is favourable to achieve optimal efficiencies.     

Heteropolyacid-impregnated PVDF as a solid polymer electrolyte for dye-sensitized solar cells

Heteropolyacid (HPA)-impregnated polyvinylidene fluoride (PVDF) with iodine/iodide was prepared as a new polymer electrolyte for bio-mimicking natural photosynthesis. With this new polymer electrolyte, dye-sensitized solar cell was fabricated using N3 dye-adsorbed over TiO₂ nanoparticles (photoanode) and conducting carbon cement coated on conducting glass (photocathode). The fabricated cell generates high open circuit voltage (V_OC 426 mV) and short circuit current (I_SC 3.90 mA) upon illumination with visible light. It is also demonstrated that the polymer electrolytes prevent the back-electron transfer reactions taking place in dye-sensitized hetero-junctions and are highly promising for solar energy conversion to electricity.     

Dye-sensitized solar cells based on electrospun polymer blends as electrolytes

We prepared electrospun polymer nanofibers by the electrospinning method and investigated about their applications to dye-sensitized solar cells (DSSCs). Electrospun poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) and PVDF-HFP/polystyrene (PS) blend nanofibers were prepared and examined the uptake, the ionic conductivity, and the porosity by impedance measurement and Scanning Electron Microscope (SEM). The best results of V_oc, J_sc, FF, and efficiency of the DSSC devices using the electrospun PVDF-HFP/PS(3:1) blend nanofibers were 0.76 V, 11.8 mA/cm², 0.66, and 5.75% under AM 1.5.     

Efficiency enhancement for bulk-heterojunction hybrid solar cells based on acid treated CdSe quantum dots and low bandgap polymer PCPDTBT

We report on the efficiency enhancement for bulk-heterojunction hybrid solar cells based on hexanoic acid treated trioctylphosphine/oleic acid-capped CdSe quantum dots (QDs) and low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) compared to devices based on poly(3-hexylthiophene) (P3HT). Photovoltaic devices with optimized polymer:QD weight ratio, photoactive film thickness, thermal annealing treatment, and cathode materials exhibited a power conversion efficiency of 2.7% after spectral mismatch correction, which is the highest reported value for spherical CdSe QD based photovoltaic devices. The efficiency enhancement is attributed to the surface treatment of the QDs together with the use of the low bandgap polymer PCPDTBT leading to an increased short-circuit current density due to additional light absorption between 650 and 850 nm. Our results suggest that the hexanoic acid treatment is generally applicable to various ligand-capped CdSe and confirm that low bandgap polymers with adequate HOMO and LUMO levels are promising to be incorporated into hybrid solar cells for further device performance improvement.     

Activation of inert Ag by nanoplasmonic synergy for enhanced hydrogen evolution reaction

The application of Ag as an electrocatalyst for hydrogen evolution reaction (HER), which holds promise to quench the worldwide thirst for clean energy source, is severely limited by its poor intrinsic activity. To address this issue, in the present contribution the Ag electrode is anodically etched, giving rise to the Ag nanocorals (NCs) consisted of closely interconnected Ag nanoparticles (NPs), between which the grain boundaries are flooded with coordinately unsaturated Ag atoms. Electrokinetic studies reveal that those under–coordinated Ag atoms stabilize the hydrogen intermediates bound to Ag NCs to facilitate the subsequent transfer of the hot electrons stemmed from the relaxation of the localized surface plasmon resonance (LSPR) of Ag NCs under visible and near–infrared (NIR) light illumination. As a result of such synergistic effect is HER over Ag NCs largely accelerated, resulting in the cathodic current density of 10 mA cm^?2 readily turned on at an early overpotential η = 156 mV with respect to those of additional Ag-based electrocatalysts reported in the literature. Such outperformance unambiguously highlights the strong prospect of Ag NCs as an alternative photoelectrocatalyst, which additionally takes advantage of the incident light to boost HER, to the state–of–the–art Pt electrocatalytic counterpart for solar fuel production.     

An innovative,high-efficiency silver/silica nanocomposites for direct absorption concentrating solar thermal power

Using of nanofluids in the concentrating direct absorption solar collectors has the potential of reducing thermal losses because of the excessive temperature of the absorbing surface in the conventional solar collectors. However, increasing the concentration ratio of solar radiation must be followed by increasing the volume fraction of the nanoparticles, which, in turn, has the drawbacks of increasing the settlement and agglomeration rates of the nanoparticles. In this study, we have suggested using the plasmonic nanofluids for volumetric absorption in the concentrated solar power applications because of the less volume fraction of the plasmonic nanoparticles that are required to harvest the concentrated solar radiation. The interaction of concentrated solar radiation with different morphologies of silver nanoparticles coated by silica shell has been computationally studied. Then, the finite element method has been implemented to determine the photo-thermal conversion efficiency for silver nanosphere and nanoplates with a silica shell. Silver nanoparticles coated by silica exhibit a promising potential because of their distinct characteristics. The silica shell is transparent to the visible and near-infrared radiation bands; it also consolidates the intensity of the localized plasmon resonance and so the absorption characteristics, besides its protective role. A high-efficiency low concentration nanofluid has been designed using blended morphologies of Ag nanospheres and nanoprisms with silica-coating–based nanofluid for full-spectrum absorption characteristics. The suggested nanofluid exhibits a promising performance at a volume fraction of 0.0075 wt% where the volumetric solar collector efficiency exceeds 75% under the solar concentration ratio of 50.