Improvement Of Photovoltaic Performance Research Articles

Improvement in photovoltaic performance of TiO2 nanoparticles by decoration of graphene nanosheets with spherical TiO2 nanoparticles

The comparative photovoltaic (PV) response was investigated for two architectures, indium tin oxide (ITO)/TiO2 nanoparticles/Al and ITO/graphene-TiO2 nanocomposite/Al. The graphene nanosheets used in this work was synthesized by electrochemical exfoliation, whereas TiO2 nanoparticles by using the co-precipitation method. The ex-situ approach was adopted for preparation of nanocomposite. The performance of graphene/TiO2 nanocomposite shows much higher power conversion efficiency and incident photon conversion efficiency than that of TiO2 nanoparticles. Power conversion efficiency of graphene/TiO2 nanocomposite was about 3 times higher than that of pure TiO2 nanoparticles.

Improvement of photovoltaic performance by substituent effect of donor and acceptor structure of TPA-based dye-sensitized solar cells.

We report a computational study of a series of organic dyes built with triphenylamine (TPA) as an electron donor group. We designed a set of six dyes called (TPA-n, where n = 0-5). In order to enhance the electron-injection process, the electron-donor effect of some specific substituent was studied. Thus, we gave insights into the rational design of organic TPA-based chromophores for use in dye-sensitized solar cells (DSSCs). In addition, we report the HOMO, LUMO, the calculated excited state oxidized potential E(dye*)(eV) and the free energy change for electron-injection ΔGinject(eV), and the UV-visible absorption bands for TPA-n dyes by a time-dependent density functional theory (TDDFT) procedure at the B3LYP and CAM-B3LYP levels with solvent effect. The results demonstrate that the introduction of the electron-acceptor groups produces an intramolecular charge transfer showing a shift of the absorption wavelengths of TPA-n under studies. Graphical Abstract Several organic dyes TPA-n with different donors and acceptors are modeled. A strong conjugation acrros the donor and anchoring groips (TPA-n) bas been studied. Candidate TPA-3 shows a promising results.

New String Reconfiguration Technique for Residential Photovoltaic System Generation Enhancement

Improvement of photovoltaic (PV) power plant performance under partial shading conditions aiming to increase electrical energy generation is in the focus of this research. This paper p ...

Precision and mirror micro-grinding of micro-lens array on macro-freeform glass substrate for micro-photovoltaic performances

A hybrid of micro-lens array and freeform surface produces a novel micro-optic and micro-photovoltaic behaviors, but it is difficult to control both micro-form and macro-form accuracies in micro-machining of brittle photovoltaic glass. Hence, a ductile micro-grinding is proposed to replicate the precision-trued diamond wheel V-tip on macro-freeform glass substrate of solar cell. The objective is to understand the formation mechanism of accurate micro-lens array on freeform glass surface for photovoltaic application. First, the micro-optic properties of freeform micro-lens array were analyzed with regard to micro- and macro-shapes. Second, the precision and mirror micro-grinding along with the form errors of freeform micro-lens array was observed on the base of the transfer from brittle-mode removal to ductile-mode removal. Finally, the photovoltaic properties were experimentally measured. It is shown that the freeform micro-lens array increases luminous flux by 53.8–54.5 % compared with the plane and micro-lens array. The micro-form accuracy and the micro-structure mirror are dominated by micro-meter-scale diamond wheel V-tip with accurate wheel V-tip profile and integrated micro-grains protrusion, respectively. The novel measuring model of freeform micro-lens array may be used to evaluate and control the curved micro-form accuracy. The freeform micro-lens array contributes to the improvement of photovoltaic performance in scattered light illumination.

Electrospun TiC embedded CNFs as a low cost platinum-free counter electrode for dye-sensitized solar cell

Generally, platinum (Pt) is used as a counter electrode (CE) for triiodide (I3−) reduction in the electrolyte solution of dye-sensitized solar cell (DSSC). Unfortunately, the high cost and scarcity of Pt make the limitation for large scale production of DSSCs. Hence, to replace Pt, we have prepared the titanium carbide (TiC) embedded carbon nanofibers (CNFs) by a facile electrospinning technique and used as a low cost alternative CE for DSSCs. The TiC embedded CNFs are found to have an enhanced electrocatalytic activity towards the I3– to iodide (I–) reduction and lower charge transfer resistance. The photovoltaic performance shows that the DSSC fabricated using TiC (10wt%) embedded CNFs as CE has very closer photo-conversion efficiency than std. Pt. This is attributed to the synergistic effect of TiC with larger electrocatalytic surface area of CNFs which plays a substantial part in the improvement of photovoltaic performance of DSSC.

The role of Na incorporation in the low-temperature processed CIGS thin film solar cells using post deposition treatment

Na incorporation is widely considered to play an important role in low-temperature processed Cu(In,Ga)Se2 (CIGS) solar cells. In this work, we used post deposition treatment (PDT) method for Na incorporation in CIGS films, which involved the deposition of a thin NaF layer accompanied by thermal annealing. It was found that thermal annealing drove the diffusion of Na into CIGS absorbers without causing loss of elements and change of crystallinity. The dependence of the photovoltaic performance and recombination of CIGS solar cells on the Na PDT temperature was investigated. Impedance spectroscopy and admittance spectroscopy were used to characterize the recombination and defects of CIGS solar cells. The results indicated that the CIGS solar cells with Na PDT exhibited significant improvement of photovoltaic performance compared to those with Na-free. The enhanced transport performances of Na-treated cells were attributed to the decreased space-charge region (SCR) recombination. Both Na-free and Na-treated at 300 °C CIGS devices showed a donor defect with activation energy of about 295 meV, while the Na-treated devices demonstrated lower density of states, which resulted in an improved Voc. A maximum conversion efficiency of 11.9% was achieved for CIGS solar cells with Na PDT temperature at 300 °C.

Fabrication of Novel High Potential Chromium-Doped TiO2 Nanoparticulate Electrode-based Dye-Sensitized Solar Cell (DSSC)

In the current study, pure TiO2 and Cr-doped TiO2 (Cr@TiO2) nanoparticles were synthesized via sol-gel method and the resulting materials were applied to prepare the porous TiO2 electrodes for dye-sensitized solar cells (DSSCs). It is hypothesized that the advantages of the doping of the metal ions into TiO2 lattice are the temporary rapping of the photogenerated electron-hole (charge carriers) by the metal dopants and the retarding charge recombination during electron migration from TiO2 to the electrode surface. Spectroscopic and microscopic findings showed that all the prepared samples consist of only anatse phase with average size of 10-15nm. In addition, relative to the bare TiO2, Cr@TiO2 absorption in visible light region was considerably improved due to the surface Plasmon phenomenon. Current-voltage (I-V) curves exhibited that the solar cells made of Cr@TiO2 nanoparticles results in higher photocurrent density than the cells made of bare TiO2. The large improvement of photovoltaic performance of the Cr-doped TiO2 cell stems from negative shift of TiO2 conduction band and retarding charge recombination. Finally, it is concluded that the proposed route in the current study is an effective way to enhance the energy conversion efficiency and overall performance of DSSC.

Improvement of photovoltaic performance and stability of AnE-PV:PCBM based organic solar cells using solution processed inverted geometry

Organic bulk heterojunction and inverted type solar cells were fabricated using AnE-PVstat:PCBM blends as photoactive layers. The device was inverted using thin films of TiO2 as hole blocking and electron conducting layers. The power conversion efficiency (PCE) of organic bulk heterojunction solar cells increased from 1.70% to 2.59% when inverted device configuration was used instead of regular organic bulk heterojunction solar cell configuration. Stability studies reveal that the inverted type devices are more stable than the herein investigated regular organic bulk heterojunction solar cells fabricated using AnE-PVstat:PCBM blends as photoactive layers.

Impact of alkoxyl tail of fullerene dyad acceptor on crystalline microstructure for efficient external treatment-free polymer solar cells with poly(3-hexylthiophene) as donor

A series of tri(alkoxyl)benzene-fullerene dyads(PCBB-Cn, n=4, 6, 8, 10, 12) with varied tri(alkoxyl) chain lengths was designed, synthesized and used as acceptor materials in polymer solar cells(PSCs). The five fullerene dyads possess similar absorption spectra in dilute solution, decreased glass-transition temperature(T-g and gradually elevated lowest unoccupied molecular orbital(LUMO) energy levels from -3.87 eV to -3.73 eV with the increase of the alkoxy chain length. In the fabrication of PSCs with poly(3-hexylthiophene)(P3HT) as donor and the fullerene dyads as acceptor, PCBB-Cn with longer tri(alkoxyl) chains and lower T-g can induce crystalline structure of P3HT during spin-coating the photoactive layer at room temperature and form nanoscale phase separated interpenetrating network of P3HT:PCBB-Cn blend films, which results in the improvement of photovoltaic performance of PSCs. A power conversion efficiency of 3.03% for the PSCs based on P3HT:PCBB-C10 was obtained without thermal annealing or solvent annealing. The thermal and solvent annealing-free fabrication using the fullerene dyads as acceptor is very important for the roll to roll production of PSCs with flexible large area.

Effect of TiO2 Particle Size on the Performance of Flexible Dye Sensitized Solar Cells

The size TiO2 nanoparticles was controlled by changing the concentration of titanium tetraisopropanolate (TTIP) and utilized as light scattering particles in the efficient flexible photoelectrodes for flexible dye sensitized solar cells (DSSCs). The flexible photoelectrodes were prepared by TiO2 nanoparticles (-25 nm) paste with different concentrations of ethanolic TTIP solution. The addition of TTIP produced the bigger TiO2 nanoparticles, which significantly enhanced the dye absorption of flexible TiO2 photoelectrode. The fabricated flexible DSSCs showed the reasonable conversion efficiency of 2.50% with short circuit current (J(sc)) of 6.3 mA/cm2, open circuit voltage (V(oc)) of 0.720 V and fill factor (FF) of 0.55. The improvement in photovoltaic performance with 25 wt% TTIP might due to uniform distribution of small TiO2 nanoparticles over the big particles to lead the enhancement in the surface area, resulting in the high dye absorption and light harvesting efficiency.

Linking Group Influences Charge Separation and Recombination in All‐Conjugated Block Copolymer Photovoltaics

All‐conjugated block copolymers bring together hole‐ and electron‐conductive polymers and can be used as the active layer of solution‐processed photovoltaic devices, but it remains unclear how molecular structure, morphology, and electronic properties influence performance. Here, the role of the chemical linker is investigated through analysis of two donor–linker–acceptor block copolymers that differ in the chemistry of the linking group. Device studies show that power conversion efficiencies differ by a factor of 40 between the two polymers, and ultrafast transient absorption measurements reveal charge separation only in block copolymers that contain a wide bandgap monomer at the donor–acceptor interface. Optical measurements reveal the formation of a low‐energy excited state when donor and acceptor blocks are directly linked without this wide bandgap monomer. For both samples studied, it is found that the rate of charge recombination in these systems is faster than in poly­mer–polymer and polymer–fullerene blends. This work demonstrates that the linking group chemistry influences charge separation in all‐conjugated block copolymer systems, and further improvement of photovoltaic performance may be possible through optimization of the linking group. These results also suggest that all‐conjugated block copolymers can be used as model systems for the donor–acceptor interface in bulk heterojunction blends.

High Efficiency Millimeter-Scale Crystalline Perovskite Solar Cells

Current state-of-the-art photovoltaics utilize high purity single-crystal semiconductors grown by sophisticated, high temperature crystal-growth processes. Alternative emerging solar cell technologies based on solution-processed materials promise to deliver power at lower cost, but so far have had limited success due to the presence of defects in the bulk and at the grain boundaries. Improving the crystal size and quality of solution-processed films could lead to unprecedented improvements in photovoltaic performance. However, large-scale crystal growth is challenging in solution-based deposition where molecular kinetics are limited by the low processing temperature. Here, for the first time we demonstrate organometallic perovskites thin-films composed of extra-ordinarily large crystalline grains (1-2 mm), fabricated using a new processing technique. The increase in the grain-size directly correlates to a dramatic increase in the efficiency, as a direct consequence of increased charge carrier mobility and reduction in defect densities. Our measured efficiency values approach ~18%, which is among the highest reported. These devices are extremely robust, exhibiting no degradation with voltage sweep direction or the rate at which the voltage was scanned. We anticipate that this technique for growing high quality large-area crystals at low temperature with low defect concentration will be universally applicable to a wide variety of other material systems thus providing a solution to a long-standing scientific challenge of overcoming polydispersity, defects and grain boundary recombination in solution-processed thin-films. From the perspective of the global photovoltaics community, these results are expected to lead the field towards the synthesis of wafer-scale crystalline perovskites necessary for the fabrication of high-efficiency single-junction and hybrid (semiconductor and perovskite) tandem planar cells. In addition, I will also discuss design principles that govern the photostability in these systems.

Bismuth‐doped Cu(In,Ga)Se2 absorber prepared by multi‐layer precursor method and its solar cell

AbstractBismuth (Bi)‐doped Cu(In,Ga)Se2 (CIGS) films were prepared by the so‐called “multi‐layer precursor method”, obtained by depositing them onto Bi layers with various thicknesses on Mo‐coated soda‐lime glass (SLG) substrates. Material composition (Cu, In, Ga, and Se) profiles of the CIGS films are almost identical, whereas sodium (Na) is reduced, when Bi thickness is increased. Moreover, the incorporation of Bi into the CIGS film is enhanced with thicker Bi layer. With Bi thickness from 0 to 70 nm, the 2.4‐μm‐thick CIGS absorbers demonstrate the increase in CIGS grain size, carrier lifetime, and carrier concentration, thus improving their cell performances, especially open‐circuit voltage (VOC). With further increase in Bi thickness of above 70 nm, the CIGS films show the deterioration of CIGS film quality owing to the formation of Bi compounds such as Bi, BiSe, and Bi4Se3. Consequently, Bi‐doped CIGS absorber with thickness of 2.4 μm, prepared with the 70‐nm‐thick Bi layer on Mo‐coated SLG substrate, gives rise to the improvement of photovoltaic performances, especially VOC. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical Study on the Rational Design of Cyano-Substituted P3HT Materials for OSCs: Substitution Effect on the Improvement of Photovoltaic Performance

Calculations have been made regarding the strong electron-withdrawing cyano (−CN) group, which was introduced onto the backbone of poly(3-hexylthiophene) (P3HT), as an effective way to improve the parameters essential for the photovoltaic performance of organic solar cells (OSCs). The substitution effect on the optical and photovoltaic properties of various CN-substituted P3HT are comprehensively investigated by means of density functional theory and molecular dynamics simulation. The results of theoretical modeling indicate that the direct introduction of strong electron-withdrawing group −CN onto the backbone of P3HT, can not only significantly reduce the HOMO level of polymer which leads to increased open circuit voltage (VOC) in solar cells, but also exhibit red-shifted absorption spectra and increased hole mobility, which might lead to the enhancement of the short circuit current (JSC) and the fill factor (FF) in comparison to pristine P3HT and fluorine (F)-substituted P3HT. These results provide a fundamental understanding of how different electron-withdrawing groups influence the photophysical, electrochemical, and optoelectronic properties of conjugated polymers and potentially provide useful information for better design strategy for OSCs.

Overpotential modification at the MoS2 counter electrode/electrolyte interfaces by thermal annealing resulting improvement in photovoltaic performance of dye-sensitized solar cells

The application of molybdenum sulfide (MoS2) to dye-sensitized solar cells (DSSCs) as a counter electrode (CE) has been reported. However, CE possessing both high electrical conductivity and excellent electrocatalytic activity is indispensable for DSSCs and it is still unclear how much of power conversion efficiency increase in the present case is due to each of these two components. The effect of thermal annealing on the MoS2 counter electrode in DSSCs is investigated. The experimental results revealed that the MoS2 crystallinity influences on the power conversion efficiency by controlling the overpotential for an electron transferring from the MoS2 CE to the electrolyte that serves to change the short circuit current. This understanding can provide guidance for the development of highly efficient DSSCs with platinum-free CEs.

Enhanced Power Conversion Efficiency of P3HT : PC71BM Bulk Heterojunction Polymer Solar Cells by Doping a High-Mobility Small Organic Molecule

The effect of molecular doping with TIPS-pentacene on the photovoltaic performance of polymer solar cells (PSCs) with a structure of ITO/ZnO/poly(3-hexylthiophene-2,5-diyl) (P3HT) : [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) : TIPS-pentacene/MoOx/Ag was systematically investigated by adjusting TIPS-pentacene doping ratios ranged from 0.3 to 1.2 wt%. The device with 0.6 wt% TIPS-pentacene exhibited the enhanced short-circuit current and fill factor by 1.23 mA/cm2and 7.8%, respectively, resulting in a maximum power conversion efficiency of 4.13%, which is one-third higher than that of the undoped one. The photovoltaic performance improvement was mainly due to the balanced charge carrier mobility, enhanced crystallinity, and matched cascade energy level alignment in TIPS-pentacene doped active layer, resulting in the efficient charge separation, transport, and collection.

Platinum nanoparticle interlayer promoted improvement in photovoltaic performance of silicon/PEDOT:PSS hybrid solar cells

Inorganic–organic hybrid solar cells have attracted considerable interest in recent years for their low production cost, good mechanical flexibility and ease of processing of polymer films over a large area. Particularly, silicon/conducting polymer hybrid solar cells are extensively investigated and widely believed to be a low-cost alternative to the crystalline silicon solar cells. However, the power conversion efficiency of silicon/conducting polymer solar cells remains low in case hydrogen-terminated silicon is used. In this paper, we report that by introducing a platinum nanoparticle interlayer between the hydrogen-terminated silicon and the conducting polymer poly(3,4-ethylenedioxy thiophene):poly(styrene sulfonate), namely PEDOT:PSS, the power conversion efficiency of the resulting Si/PEDOT:PSS hybrid solar cells can be improved by a factor of 2–3. The possible mechanism responsible for the improvement has been investigated using different techniques including impedance spectroscopy, Mott–Schottky analysis and intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). The results show that with a platinum nanoparticle interlayer, both the series resistance and charge transport/transfer resistance of the Si/PEDOT:PSS hybrid solar cells are reduced leading to an increased short circuit current density, and the built-in voltage at the space charge region is raised facilitating electron-hole separation. Moreover, the lifetime of charge carriers in the Si/PEDOT:PSS solar cells is extended, namely, the recombination is effectively suppressed which also contributes to the improvement of photovoltaic performance.

Fused-Thiophene Based Materials for Organic Photovoltaics and Dye-Sensitized Solar Cells

Organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs) have drawn great interest from both academics and industry, due to the possibility of low-cost conversion of photovoltaic energy at reasonable efficiencies. This review focuses on recent progress in molecular engineering and technological aspects of fused-thiophene-based organic dye molecules for applications in solar cells. Particular attention has been paid to the design principles and stability of these dye molecules, as well as on the effects of various electrolyte systems for DSSCs. Importantly, it has been found that incorporation of a fused-thiophene unit into the sensitizer has several advantages, such as red-shift of the intramolecular charge transfer band, tuning of the frontier molecular energy level, and improvements in both photovoltaic performance and stability. This work also examines the correlation between the physical properties and placement of fused-thiophene in the molecular structure with regard to their performance in OPVs and DSSCs.

Subwavelength nanostructures integrated with polymer‐packaged iii–v solar cells for omnidirectional, broad‐spectrum improvement of photovoltaic performance

AbstractReduction in surface and interface reflectance via the integration of subwavelength nanostructures in flexible polymer packaging material combined with incorporation of dielectric nanoislands into a conventional two‐layer antireflection coating has been demonstrated, analyzed and optimized. Transmittance measurements of moth‐eye textured polymer packaging sheets with different tapered pillar heights fabricated by reactive‐ion etching and nanosphere lithography provide insights into the choice of the optimum nanostructure dimensions. Detailed computational modeling and simulations elucidate the physical nature of the antireflection performance of dielectric nanoisland structures integrated with a commercial two‐layer antireflection coating, and provide guidance for design of the nanoisland structure for optimum antireflection performance. Measurements show that the integration of appropriately designed nanostructures in both polymer packaging material and conventional antireflection layers enables substantial increases in external quantum efficiency (E.Q.E.) and short‐circuit current density (Jsc) over a broad range of incident angles, compared to structures with conventional bilayer antireflection coatings and unpatterned polymer packaging sheets. A 1.1× increase in Jsc, derived directly from E.Q.E. measurements, at normal incidence, increasing to 1.67× improvement at 80° angle of incidence, suggests that such an approach is promising for a variety of photovoltaic applications, particularly those where solar tracking is not feasible or practical. Copyright © 2014 John Wiley & Sons, Ltd.

Investigating the role of graphene in the photovoltaic performance improvement of dye-sensitized solar cell

This article compares and describes the photovoltaic performance of dye-sensitized solar cell (DSSC) consisting of platinum (Pt) and graphene-coupled-platinum based counter electrodes (CE). The power conversion efficiency of DSSC could be enhanced by 36% with multi-layer graphene flakes (MGF)/Pt CE as compared to Pt CE. Electrochemical impedance spectroscopy and cyclic voltammetry analysis show that DSSC with an MGF/Pt CE exhibits a higher electro-catalytic activity with lower series resistance. Two-diode model has been used to extract the recombination governing and the performance indicating parameters of a DSSC. An enhancement of ≈76% in short-circuit current of MGF/CE based DSSC, as compared to Pt CE, could be attributed to optical and catalytic properties of graphene. This study provides an insight into electronic transport mechanism of DSSC, which changes under the influence of highly catalytic materials such as graphene.