Improvement In Light Harvesting Efficiency Research Articles

CdS/CdSe/PbS quantum dots sensitized TiO2 eggshell hollow microspheres photoanode to boost photocurrent and power conversion efficiency of QDSSC

Light harvesting plays crucial role for high photovoltaic performance of quantum dots sensitized solar cell (QDSSC). However, there are still issues need to be tackled, such as enlarging light response range and enhancing light scattering capability. In this work, TiO2 eggshell hollow microspheres (EHMS) were synthesized by carbonaceous microspheres (CMS) template method and co-sensitized by CdS/CdSe/PbS quantum dots (QDs) for application in QDSSC. Compared with QDSSC based on TiO2 nanoparticles (NP) and TiO2 hollow microspheres (HMS), the TiO2 EHMS based QDSSC showed a remarkable increase of short-circuit current density (Jsc) to 24.81 mA cm−2 with a power conversion efficiency (PCE) of 4.07 %. Photoelectrochemical analysis of QDSSC indicate that CdS/CdSe/PbS QDs can enlarge the light response range, and the TiO2 EHMS improve the light scattering, leading to the improvement of light harvesting efficiency. Charges dynamics tests results proved that a larger charges recombination resistance at photoanode/electrolyte interface and longer electron lifetime can be achieved with TiO2 EHMS, contributing to the boost of Jsc. The presented study introduces a simple strategy for researchers interested in designing photoanode for various photoelectrochemical applications.

Building triple shelled ZnO hollow microspheres decorated TiO2 nanotree to boost light harvesting and reduced charges recombination in dye sensitized solar cell

It is well known that the microstructure of photoanode materials has direct influence on light harvesting and charges recombination in dye sensitized solar cells (DSSC). However, design of photoanode materials for efficient light harvesting and electron transport is still in challenge. Therefore, we developed a hierarchical microstructure of multi shelled ZnO hollow microspheres (MS ZnO HMS) decorated TiO2 nanotree (NT) for DSSCs application with aim to take advantages of enhanced light scattering and enlarged specific area offered by MS ZnO HMS and reduced charges recombination provide by TiO2 NT. The morphology, microstructure and crystalline of ZnO HMS and TiO2 NT have been characterized by SEM, TEM and XRD, confirming the successful building of MS ZnO HMS decorated TiO2 NT. I–V tests show that significant enhancement of short-circuit current density (Jsc) can be achieved by controlling shell numbers of MS ZnO HMS and combining MS ZnO HMS with TiO2 NT. As a result, the triple shelled ZnO HMS (TS ZnO HMS) decorated TiO2 NT (TS ZnO HMS/TiO2 NT) improve the power conversion efficiency (PCE) to 7.40%, which is 138% and 40% higher than DSSCs based on TiO2 NT (3.11%) and TS ZnO HMS (5.27%). IPCE, OCVD and EIS measurements indicate that the combination of TS ZnO HMS with TiO2 NT contribute to the improvement of light harvesting efficiency and prolonging of electron lifetime.

One-pot controlled microwave synthesis of Broadband-light absorbing irregular gold nanoparticles for solar cell application

Improvement of light-harvesting efficiency using the localized surface plasmon resonance (LSPR) from the metals nanoparticles (MNPs) is a promising approach to boost the efficiency of the solar energy conversion systems. To attain the narrowband SPR, synthesis of the monodisperse MNPs with particular shapes and sizes is cumbersome and has great importance for (surface-enhanced Raman spectroscopy) SERS application. Contrary, broadband SPR is prominent for solar cell applications to absorb maximum sunlight from the solar spectrum. Incorporating polydisperse MNPs of mixed shapes and sizes is a unique approach to realizing the broadband SPR for solar cell application. However, the synthesis of polydisperse MNPs with good reproducibility is challenging. To address this issue, we report facile one-pot microwave synthesis of mixed shapes and sizes of Au nanoparticles (Au-Mx), possessing broadband SPR with decent reproducibility. Microwave-assisted uniform heating provides the control over the reaction parameter to produce identical SPR. Further, the light-harvesting ability of the Au-Mx is demonstrated by incorporating ∼ 1% of Au-Mx in photoanode while fabricating the dye-sensitized solar cells (DSSCs). The photoconversion efficiency (PCE) of the Au-Mx loaded DSSCs improved by ∼ 30% compared to the reference devices, indicating the effective utilization of broadband SPR for efficient charge generation in plasmonic devices.

Dye sensitized solar cell (DSC) based on reduced graphene oxide (rGO)-TiO2 nanocomposite photoelectrode and polyaniline (PANI) counter electrode

We report the successful application of reduced graphene oxide–titania (rGO–TiO2) nanocomposite as an efficient photoelectrode and an inexpensive polyaniline (PANI) synthesized by in-situ polymerization on graphite foam as a platinum substitute for tri-iodide reduction for dye‐sensitized solar cell (DSC). The bulk carrier concentration and conductivity of the PANI was measured to be 3.02x1017cm-3 and 4.89x10-1 W-1cm-1 respectively. Subsequently, three DSCs were assembled with rGO–TiO2 nanocomposite photoelectrode and PANI as counter electrode for one and the other two assembled using unmodified TiO2 photoelectrode with PANI and platinum as counter electrodes, respectively. The rGO loading allows more dye to be adsorbed due its large surface area thus improving the light harvesting efficiency (LHE). This improvement in LHE increases the short circuit current density (JSC). The JSC increase is more substantial compared to the reduction in VOC; thus, the increase in the efficiency of the cell with rGO-TiO2 nanocomposite electrode. The short circuit current density for the rGO-TiO2 DSC with PANI counter electrode is 0.45mAcm-2 while that for the unmodified TiO2 DSCs with PANI counter electrode and platinum counter electrode are 0.11mAcm-2 and 0.10 mAcm-2 respectively. This corresponds to 76% increase in the current density and it increases collection rate at the photoelectrode leading to enhanced power conversion efficiency of 0.13% compared with 0.04% and 0.02% for the DSCs assembled with unmodified TiO2 under full sunlight illumination (100 mW/cm2, AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduces the back electron transfer process. This represent 69% enhancement of energy conversion efficiency in the DSC consisting of rGO modified TiO2

Dye sensitized solar cell (DSC) based on reduced graphene oxide (rGO)-TiO2 nanocomposite photoelectrode and polyaniline (PANI) counter electrode

We report the successful application of reduced graphene oxide–titania (rGO–TiO2) nanocomposite as an efficient photoelectrode and an inexpensive polyaniline (PANI) synthesized by in-situ polymerization on graphite foam as a platinum substitute for tri-iodide reduction for dye‐sensitized solar cell (DSC). The bulk carrier concentration and conductivity of the PANI was measured to be 3.02x1017cm-3 and 4.89x10-1 W-1cm-1 respectively. Subsequently, three DSCs were assembled with rGO–TiO2 nanocomposite photoelectrode and PANI as counter electrode for one and the other two assembled using unmodified TiO2 photoelectrode with PANI and platinum as counter electrodes, respectively. The rGO loading allows more dye to be adsorbed due its large surface area thus improving the light harvesting efficiency (LHE). This improvement in LHE increases the short circuit current density (JSC). The JSC increase is more substantial compared to the reduction in VOC; thus, the increase in the efficiency of the cell with rGO-TiO2 nanocomposite electrode. The short circuit current density for the rGO-TiO2 DSC with PANI counter electrode is 0.45mAcm-2 while that for the unmodified TiO2 DSCs with PANI counter electrode and platinum counter electrode are 0.11mAcm-2 and 0.10 mAcm-2 respectively. This corresponds to 76% increase in the current density and it increases collection rate at the photoelectrode leading to enhanced power conversion efficiency of 0.13% compared with 0.04% and 0.02% for the DSCs assembled with unmodified TiO2 under full sunlight illumination (100 mW/cm2, AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduces the back electron transfer process. This represent 69% enhancement of energy conversion efficiency in the DSC consisting of rGO modified TiO2

Improvement of light-harvesting efficiency of amorphous silicon solar cell coated with silver nanoparticles anchored via (3-mercaptopropyl) trimethoxysilane

Owing to small size effect and large surface area, silver nanoparticles (Ag NPs) exhibit special physical properties and are widely used in different applications. One of the significant applications is that Ag NPs can be coated on the glass surface of solar cell to increase the light-harvesting efficiency of solar cell due to the plasmonic resonance and scattering effect. In this study, Ag NPs used for the coating of solar cells were synthesized via a chemical reduction method. The effect of the concentration of sodium borohydride (NaBH4) as reducing agent and 1-dodecanethiol (DDT) as capping agent on the size and shape of Ag NPs synthesized have been investigated. The synthesized Ag NPs were characterized using UV–vis spectroscopy, X-ray diffraction, energy-dispersive X-ray spectrometry and ATR-FTIR spectroscopy; while the particle size, morphology and topology of Ag NPs were examined by scanning electron microscopy and atomic force microscopy. By coating the glass surface of amorphous silicon solar cells with a uniform array of Ag NPs with the particle size of > 350 nm, a power conversion efficiency (PCE) enhancement of approximately 41% has been achieved. (3-mercaptopropyl) trimethoxysilane (MPTMS) was used as the adhesion promoter to anchor Ag NPs on the silicon surface of solar cells. With 7% of MPTMS, the array of Ag NPs formed on the glass surface was found being the most evenly distributed with a densely packed surface coverage, which resulted in 46% of PCE enhancement of the silicon solar cells.

Nano gold-coated surface patterned mesoporous titanium tin oxide sol–gel thin film: fabrication, optical and photoelectrochemical properties

Nano noble metal coating on surface patterned mesoporous semiconductor thin film can play an important role in enhancing visible light harvesting efficiency (LHE) towards improvement in photoelectrochemical (PEC) activity of the material. In this work, one-dimensional (1D) and two-dimensional (2D) mesoscale surface patterns have been created on sol–gel-based titanium tin oxide (TSO) nanostructured thin film on pure silica/indium tin oxide-coated glass by soft lithography. The TSO film matrix is observed to be mesoporous and semicrystalline as evidenced from the structural characterization by transmission electron microscopy and measurement of atmospheric ellipso-porosimetry, respectively. The 2D patterned film exhibits maximum LHE value in visible wavelength region. Further film surface modification has been carried out by depositing nano Au coating onto the bare patterned TSO films by a low temperature solution technique. Under visible light, a significant improvement in PEC activity is found and the gold-coated patterned 2D film shows higher visible LHE as well as >2.7 times higher photocurrent density than bare 2D film. This facile fabrication strategy can create an avenue toward improvement in LHE vis-a-vis the PEC activity of mesoporous mixed metal oxide semiconductor thin film.

The effect of silver nanoparticles/graphene-coupled TiO2 beads photocatalyst on the photoconversion efficiency of photoelectrochemical hydrogen production

In this work, a novel configuration of the photoelectrochemical hydrogen production device is demonstrated. It is based on TiO2 beads as the primary photoanode material with the addition of a heterostructure of silver nanoparticles/graphene. The heterostructure not only caters to a great improvement in light harvesting efficiency (LHE) but also enhances the charge collection efficiency. For LHE, the optimized cell based on TiO2 beads/Ag/graphene shows a 47% gain as compared to the cell having a photoanode of commercial P25 TiO2 powders. For the charge collection efficiency, there is a pronounced improvement of an impressive value of 856%. The reason for the improvement in light absorption is attributed to either the light scattering of TiO2 beads or the surface plasmonic resonance on the Ag nanoparticles/graphene. The photoconversion efficiency (PCE) of the resulting cells is also presented and discussed. The PCE of the TiO2 beads/Ag/graphene cell is approximately 2.5 times than that of pure P25 cell.

Comparative study on effect of titania morphology for light harvesting and scattering of DSSCs: Mesoporous nanoparticles, microspheres, and dandelion‐like particles

The light scattering and harvesting effects in dye‐sensitized solar cells (DSSCs) is studied by controlling morphology, phase composition, and thickness of monolayer and double‐layer TiO2 photoanode electrodes. The starting materials for preparation of TiO2 cells, including 25 nm mesoporous anatase nanoparticles, 200 nm anatase microspheres, 10 µm dandelion‐like rutile particles and 40 nm nanoparticles containing 80% anatase‐20% rutile, are synthesized by evaporation‐induced self‐assembly, sol‐gel, and hydrothermal processes. It was found that the mesoporous anatase nanoparticles may improve light harvesting and dye‐sensitization due to their high surface area and small particle size, whereas the microspheres and dandelion‐like particles can enhance light scattering effect. The improvement of light harvesting efficiency is obtained by controlling the microstructure and thickness of photoanode electrode to increase dye adsorption. This is achieved by preparation of high surface area TiO2 monolayer film with optimum thickness and good connections between the particles using mesoporous anatase nanoparticles. The influence of film's thickness on photovoltaic characteristics of monolayer DSSCs shows that the optimal thickness around 30 μm results in the highest cell efficiency of 6.31%. The enhancement of light scattering is acheieved by design of a proper scattering layer with desired morphology and phase composition. The dye loading property of the scattering layer is also considered simultaneously. The photovoltaic characteristics of double‐layer DSSCs, with total thickness of 30 µm, reveal that the cell efficiency enhances up to 7.54 and 8.91% using a mixture of dandelion‐like particles and mesoporous nanoparticles and microspheres and mesoporous nanoparticles, respectively. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1818–1826, 2016

A new method for improving the performance of dye sensitized solar cell using macro-porous silicon as photoanode

This paper presents a novel method to improve the function of dye-sensitized solar cell (DSSC). The pro- posed method includes use of macro-porous silicon (PSi) as a photoanode for DSSC. The photoanode, PSi, was fabri- cated by a simple electrochemical anodization process. The effects of the obtained PSi-based photoanode on the DSSC performance are investigated by using photocurrent-volt- age, UV-visible spectroscopy, and reflectance spec- troscopy measurements. The results show that the macro- porous structure in the PSi-based photoanode not only increases internal surface area in the photoanode, but also functions as an anti-reflective/light-trapping layer. Macro- porous structure leads to the both enhancement of pho- toanode dye loading capacity and increasing the optical path length of the incident light inside the photoanode. This way, macro-porous structure plays an important role in the improvement of light harvesting efficiency. The optimal power conversion efficiency of 3.56 and 3.93 % (spin coated and sputtered TiO2 respectively) is obtained from the PSi-based DSSC, with 58 and 75 % improvement in the efficiency as compared to a fabricated conventional DSSC. The measurement results suggest that exploiting PSi in the structure of photoanode raises hopes for low-cost and high- performance production of hybrid Si/dye solar cells in the future.

Facile Synthesis of ZnO@TiO2 Core‐Shell Nanorod Thin Films for Dye‐Sensitized Solar Cells

ZnO nanorod thin films grown on fluorine‐doped tin oxide (FTO) glasses have been synthesized via facile thermal evaporation. To optimize the performance of dye‐sensitized solar cells (DSSCs), we fabricated ZnO@TiO2 core‐shell composite by a simple dip‐coating method immersed in the mixed solution of Ti(OC4H9) and ethanol. Results of solar cell testing showed that ZnO@TiO2 core‐shell nanorod thin films on FTO significantly increased open circuit voltage (from 0.47 V to 0.53 V), short circuit current (from 10.78 mA/cm2 to 13.98 mA/cm2), and fill factor (from 51% to 55%). The photoelectric conversion efficiency (PEC) increased from 3.3% for bare ZnO DSSCs to 4.85% for ZnO@TiO2 core‐shell structured DSSCs. This is mainly ascribed to the improvement in light harvesting efficiency, electron transfer, and the effective suppression of charge recombination.

Improvement of light-harvesting efficiency in dye-sensitized solar cells using silica beads embedded in a TiO2 nanoporous structure

The effect of various materials of the spherical scattering centre in a TiO2 nanoporous structure in dye-sensitized solar cells (DSSCs) was investigated by both theoretical simulation and experiment. Three materials, titania, electrolyte and silica, were investigated using the Mie Theory, in which the concepts of volume total cross section and solar spectrum were accommodated for better accuracy. Of those materials, silica was chosen in this study due to its perfectly transparent nature, easy size controllability and perfectly spherical shape, which make silica most suitable for understanding the scattering effect with a simple optical approach. The validity was proved by experiment with various sizes of silica beads (0.3, 0.6, 0.9, 1.2, 1.5 µm) embedded in DSSCs; experiments revealed the same trend as did the simulation. The overall efficiency of the DSSCs was increased by 20.4% using 300 nm diameter silica beads. The efficiency versus bead size had a peak with beads of 300 nm diameter and decreased as the bead size increased. This study showed that silica could be a good candidate for scattering particles in DSSCs. Furthermore, this study could be considered a valuable reference for further investigations of scattering phenomena by small spherical particles or arbitrary shape of particles in DSSCs.

Significant Efficiency Improvement of the Black Dye-Sensitized Solar Cell through Protonation of TiO2 Films

This paper describes the influence of acid pretreatment ofTiO2 mesoporous films prior to dye sensitization on the performance of dye-sensitized solar cells based on [(C4H9)4N]3[Ru(Htcterpy)(NCS)3] (tcterpy = 4,4',4"-tricarboxy- 2,2',2"-terpyridine), the so-called black dye. The HCl pretreatment caused an increase in overall efficiency by 8%, with a major contribution from photocurrent improvement. It is speculated, from the analysis of incident photon-to-electron conversion efficiency, UV-vis absorption spectra, redox properties of the dye and TiO2, and the impedance spectra of the dye-sensitized solar cells, that photocurrent enhancement is attributed to the increases in electron injection and/or charge collection efficiency besides the improvement of light harvesting efficiency upon HCl pretreatment. Open-circuit photovoltage (V(oc)) remained almost unchanged in the case of significant positive shift of flat band potential for TiO2 upon HCl pretreatment. The suppression of electron transfer from conduction band electrons to the I3- ions in the electrolyte upon HCl pretreatment, reflected by the increased resistance at the TiO2/dye/electrolyte interface and reduced dark current, resulted in a V(oc) gain, which compensated the V(oc) loss due to the positive shift of the flat band. Using the HCl pretreatment approach, 10.5% of overall efficiency with the black dye was obtained under illumination of simulated AM 1.5 solar light (100 mW cm(-2)) using an antireflection film on the cell surface.

Dependence of needle architecture and chemical composition on canopy light availability in three North American Pinus species with contrasting needle length.

Morphology and chemical composition of needles of shade-intolerant southern conifers (Pinus palustris Mill. (mean needle length +/- SD = 29.1 +/- 4.1 cm), P. taeda L. (12.3 +/- 2.9 cm) and P. virginiana Mill. (5.1 +/- 0.8 cm)) were studied to test the hypothesis that foliage acclimation potential to canopy light gradients is generally low for shade-intolerant species, and in particular, because of mechanical limitations, in species with longer needles. Plasticity for each needle variable was defined as the slope of the foliar characteristic versus irradiance relationship. A novel geometrical model for needle area and volume calculation was employed for the three-needled species P. palustris and P. taeda. Needle thickness (T) strongly increased, but width (W) was less variable with increasing daily integrated quantum flux density averaged over the season (Q(int)), resulting in changes in cross-sectional needle shape that were manifested in a positive relationship between the total to projected needle area ratio (A(T)/A(P)) and Q(int) in the three-needled species. In contrast, cross-sectional needle geometry was only slightly modified by irradiance in the two-needled conifer P. virginiana. Needle dry mass per unit total needle area (M(T)) was positively related to Q(int) in all species, leading to greater foliar nitrogen contents per unit area at higher irradiances. Separate examination of the components of M(T) (density (D) and the volume (V) to A(T) ratio; M(T) = DV/A(T)) indicated that the positive effect of light on M(T) resulted solely from increases in V/A(T), i.e., from increases in the thickness of foliage elements. Foliar chlorophyll content per unit mass increased with increasing Q(int), allowing an improvement in light-harvesting efficiency in low light. The variables characterizing needle material properties (D, the dry to fresh mass ratio, and needle carbon content per unit mass) were generally independent of Q(int), suggesting that needles were less stiff and had greater tip deflections under their own weight at lower irradiances because of smaller W and T. Comparisons with the literature revealed that plasticity in foliar characteristics tended to be lower in the studied shade- intolerant species than in shade-tolerant conifers, but plasticity among the investigated species was unaffected by needle length. However, we argue that, because of mechanical limitations, plastic changes in needle cross section in response to low irradiance may decrease rather than increase light-interception efficiency in long-needled species.

Functional responses of Acer species to two simulated forest gap environments: leaf-level properties and photosynthesis

Seedlings of eight forest maple (Acer L.) species were grown outdoors through a full season under two irradiation treatments: (a) “gap edge” with a photosynthetic photon flux density of 30 µmol m-2 s-1 and a red:far-red ratio of 0.55, and (b) “gap centre” with 400 µmol m-2 s-1 and a red:far-red ratio of 1.12. Area-based leaf nitrogen concentration was greater in gap centre-grown seedlings, whereas, except for A. saccharum, area-based chlorophyll (Chl) (a+b) was higher in gap edge-grown plants. There was also a significantly lower Chl a/b ratio in gap edge-grown plants. Maximum photosynthetic rate (P max ) was 60 % higher in the gap-centre treatment. These results are consistent with the functional expectation that shade-acclimated plants will increase their radiant-energy harvesting capacity as a result of limited photon input while gap-acclimated plants will operate more efficiently under bright irradiance by increasing their carboxylation capacity. This inverse relationship between the capacity of the light-harvesting component and the carboxylation component is, however, only partially supported by Chl fluorescence measurements of intact leaves. Compared to gap centre-grown plants, the lower total fluorescence quenching in gap edge-grown plants indicated a lower carboxylation capacity that was in accord with the observed P max . However, edge-grown seedlings did not show the expected improvement in light-harvesting efficiency and reduction in electron transport of photosystem 2 inferred from their marginally greater t1/2 and lower Fv/Fm, respectively. Hence while maples acclimated to different irradiation levels by adjusting leaf N and Chl contents, they showed limited acclimation potential at the photosystem level. Variations in the leaf traits examined had only minor effect on low irradiance photosynthesis and sunfleck utilization.