Application In Photovoltaic Cells Research Articles

Integration of Photovoltaic Cells in Solar Drying Systems

Photovoltaic (PV) cells have not been sufficiently used in drying processes in the past, particularly for solar drying, due to their high price and low efficiency. This is now changing due to the important scientific and technological recent developments in the PV field. An increase in the number of published scientific works related to the integration of PV cells is clearly visible. It is revealed that PV cells are integrated in drying systems for two essential reasons. The first relates to their use as a part of the solar collector (generally solar air collector), which permits an improvement of their low efficiency. As a result, and in most of the studied cases, the total solar collector efficiency has reached 70%. The second reason relates to the recycling of the electrical energy consumed by other drying system components such as fans. The recycled electrical energy was directly used for instant energy consumption or stored in batteries. The main application of PV cells is their use in direct- and indirect-type forced convection dryers, generally for food and herb drying. In a study case, an economic analysis has shown that payback is dependent on the ratio of the PV cell surface to the total solar collector surface, with the possibility of an optimum payback in less than one year. In another study case, an additional heat pump significantly improved the performance of the photovoltaic–thermal (PV/T) solar dryer, reaching an efficiency of 70%. A proper design of solar drying plays an important role in attaining optimum results. In this case, particular care is given to the design of solar dryers with a detailed presentation of the influence of the different parameters such as the surface of the PV cell, geographical location, and materials used. For most of the presented systems, efficiency is calculated after application of the heat and mass balance for each solar dryer compound.

Novel Cyclopentadithiophene‐Based D–A Copolymers for Organic Photovoltaic Cell Applications

Here, the synthesis, characterization, and photovoltaic properties of four new donor–acceptor copolymers are reported. These copolymers are based on 4,4‐difluoro‐cyclopenta[2,1‐b:3,4‐b′] dithiophene as an acceptor unit and various donor moieties: 4,4‐dialkyl derivatives of 4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene and its silicon analog, dithieno[3,2‐b:2′,3′‐d]‐silol. These copolymers have an almost identical bandgap of 1.7 eV and have a HOMO energy level that varies from −5.34 to −5.73 eV. DSC and X‐ray diffraction (XRD) investigations reveal that linear octyl substituents promote the formation of ordered layered structures, while branched 2‐ethylhexyl substituents lead to amorphous materials. Polymer solar cells based on these copolymers as donor and PC61BM as acceptor components yield a power conversion efficiency of 2.4%. image

A Novel Method for Preparing Vertically Aligned CdS Nanorod Arrays and Its Application in Photovoltaic Cells with P3HT Fibers

Vertically aligned cadmium sulfide (CdS) nanorod arrays were prepared through a novel thermal annealing route. By embedding the as-prepared CdS nanorod arrays into the poly(3-hexylthiophene) (P3HT) nanofiber (NF) matrix, the photovoltaic devices were fabricated with the structure of ITO/PEDOT:PSS/CdS arrays/P3HT NF/Au. The device performance was highly dependent on the P3HT NF layer thickness in this structure, and a power conversion efficiency (PCE) of 0.23 % was obtained for optimal P3HT NF layer thickness of 150 nm. In addition, much higher PCE of 0.84 % was achieved after post-annealing. The significantly improved photovoltaic performance may be caused by the increased interfacial areas between P3HT NFs and CdS nanorods for efficient charge separation, as well as the decreased inter-nanocrystal distance caused by insulating organic ligands after the annealing treatment. The results demonstrate a promising inorganic–organic hybrid photovoltaic structure with vertically aligned CdS nanorods arrays.

Effect of reannealing temperature on characteristics of nanocrystalline Sn-doped In2O3thin films for organic photovoltaic cell applications

In this study, nanocrystalline Sn-doped In(2)O(3) (ITO) films were deposited by electron beam evaporation technique and were annealed in air atmosphere from 300°C to 500°C for 30 min. Then, the annealed ITO films in air at 450°C were reannealed in vacuum for 1 h at different temperatures from 300°C to 500°C. The effects of reannealing temperature on structural, electrical, and optical properties of the ITO films were investigated. Increasing reannealing temperature from 300°C to 500°C reduced sheet resistance of ITO thin films from 38 to 12(Ω/sq). The highest transparency over the visible wavelength region of spectrum (95%) was obtained for reannealed films at 450°C. The optimum reannealing temperature for these films is 450°C. Refractive index at 550 nm and porosity for ITO films reannealed at 450°C were 1.92% and 21.2%, respectively. The allowed direct bandgap at different reannealing temperature was evaluated to be in the range of 4.1-4.28 eV. X-ray diffraction results showed that the reannealed films were polycrystalline and a rise in grain size was observed in them. The average grain size in the films reannealed in vacuum at 450°C is about 48.6 nm. Atomic force microscope images indicated that the grain size and root-mean-square roughness films depend on the reannealing temperature. It has been found that reannealing temperature is a key factor in controlling the structural, electrical, and optical properties of ITO films. The power conversion efficiency of the device with ITO films reannealed at 450°C is 1.22% and it is about 58% higher than that of the device without it. This indicates that this film is a promising transparent electrode for organic photovoltaic cells.

Atomistic structures and phase transition of In2Se3 nanowires studied by DFT calculations and synchrotron radiation X-ray diffraction

In2Se3 has potential application in photovoltaic cell, solid-state batteries, phase change memories, and in the manufacture of detectors of ionizing radiation. Here we study the crystal structures and phase transition of In2Se3 by using DFT calculations. Crystal structures of In2Se3 include layered structures and vacancy-ordered-in-screw-form structures. Combining with SR-XRD techniques, our studies show that thermal annealing will merge the layer structures of In2Se3 and improves conductivity of In2Se3. Our results provide structural information for different phases and phase transition mechanism of In2Se3.

Tuning Photoinduced Intramolecular Electron Transfer by Electron Accepting and Donating Substituents in Oxazolones

The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31 + G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the π-electron mobility, however, the 3,5-dinitro substituent decreased the π-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the π-conjugated linker and may find applications in photovoltaic cells and light emitting diodes.

ITO-free photovoltaic cell utilizing a high-resolution silver grid current collecting layer

AbstractAn ITO-free transparent hybrid electrode based on an embedded high resolution current collecting silver grid (Ag-grid) in combination with solution processed high conductive PEDOT:PSS (PH1000) has been demonstrated for applications in organic photovoltaic cells. The high resolution embedded Ag-grid lends low shadow loss and gives rise to current collecting layers with good electrical conductivity. Sheet resistance of the hybrid electrode combining the high-resolution Ag-grid and the PH1000 reaches several Ohms per square. Solution-processed large area flexible polymer bulk-heterojunction (BHJ) photovoltaic cells are prepared from the Ag-grid/PH1000 hybrid electrode with a configuration of hybrid electrode/PEDOT:PSS-4083/P3HT:PCBB-C8/LiF/Al. A self-assembling fullerene derivative (PCBB-C8) is chosen as the acceptor, which induces the P3HT to form ordered active layer and hence avoids the annealing process on flexible PET substrates. Power conversion efficiency (PCE) of the resulting devices reaches 1.36%.

Efficiency enhancement of organic photovoltaic devices using a Sm:Al compound electrode

An effective cathode consisting of samarium (Sm) doped aluminum (Al) layer and a pure Al layer is reported for application in organic photovoltaic cells (OPVs). Standard copper phthalocyanine (CuPc)/C60 OPVs using this bilayer cathode show dramatically increased short-circuit current density and power conversion efficiency, which are 64% increased by employing a appropriate ratio of 1:3 of Sm:Al layer as compared with that of control devices with pure Al cathode. The photoelectric properties reveal that the improved efficiency is mainly related to the balance of the enhanced electron collection ability and the optimized optical reflection of a Sm doped Al layer.

PV cells protection by using class PV fuses

During the last 50 years, the application of Photovoltaic cells (PV cells) has increased at a high speed. PV cells have special characteristics that require protective devices specifically designed for this application, among which the fuse presents optimum features. The main characteristics are: dc power generation, low short-circuit current and low X/R ratios, behavior influenced by temperature, etc. The most used gPV fuse specification is the new IEC 60269-6, that gives some rough guidelines. Also fuse manufacturers give "application rules" that have some inconsistencies and difficult the fuse selection. The need for more coordinated work between PV cells and fuses manufacturers is stressed, indicating the areas where this work is required.

Solution‐Processed Nickel Oxide Hole Transport Layers in High Efficiency Polymer Photovoltaic Cells

AbstractThe detailed characterization of solution‐derived nickel (II) oxide (NiO) hole‐transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported. The NiO precursor solution is examined in situ to determine the chemical species present. Coordination complexes of monoethanolamine (MEA) with Ni in ethanol thermally decompose to form non‐stoichiometric NiO. Specifically, the [Ni(MEA)2(OAc)]+ ion is found to be the most prevalent species in the precursor solution. The defect‐induced Ni3+ ion, which is present in non‐stoichiometric NiO and signifies the p‐type conduction of NiO, as well as the dipolar nickel oxyhydroxide (NiOOH) species are confirmed using X‐ray photoelectron spectroscopy. Bulk heterojunction (BHJ) solar cells with a polymer/fullerene photoactive layer blend composed of poly‐dithienogermole‐thienopyrrolodione (pDTG‐TPD) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) are fabricated using these solution‐processed NiO films. The resulting devices show an average power conversion efficiency (PCE) of 7.8%, which is a 15% improvement over devices utilizing a poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. The enhancement is due to the optical resonance in the solar cell and the hydrophobicity of NiO, which promotes a more homogeneous donor/acceptor morphology in the active layer at the NiO/BHJ interface. Finally, devices incorporating NiO as a HTL are more stable in air than devices using PEDOT:PSS.

FT-IR spectroscopic analyses of 2-(2-furanylmethylene) propanedinitrile

In the present work, a computational study for the optimized molecular structural parameters, thermo-chemical parameters, total dipole moment, HOMO–LUMO energy gap and a combined experimental and computational study for FT-IR spectra for 2-(2-furanylmethylene) propanedinitrile have been investigated using B3LYP utilizing 6-31G and 6-311G basis set. Our calculated results showed that the investigated compound possesses a dipole moment of 7.5D and HOMO–LUMO energy gap of 3.92eV using B3LYP/6-311G which indicates that our investigated compound is highly applicable for photovoltaic solar cell applications.

Solution-processable graphene oxide as an insulator layer for metal–insulator–semiconductor silicon solar cells

Development of a high quality but low cost insulating layer is important for its application in photovoltaic cells. In this work, solution processable graphene oxide (GO) thin films were first utilized as an insulating layer to construct MIS silicon solar cells. The efficient water-soluble GO nano-sheets with controlled thickness produced a good contact with the hydrophilic silicon surfaces. The average open circuit voltage (VOC) of the GO incorporated MIS silicon solar cell was increased by 0.2 V, while their power conversion efficiency (PCE) was demonstrated as 88% higher than that of the corresponding Schottky solar cells. The improvement of the device performance in the GO-based MIS silicon solar cell is attributed to the increased built-in potential as well as the reduced interface defect, resulting in reduced carrier recombination. The ability to establish a low-cost and solution-processable insulating layer will open the door for wide application in photovoltaic and other optoelectronic devices.

J-aggregation of a squaraine dye and its application in organic photovoltaic cells

In this paper, we investigated the aggregation behavior of a squaraine dye in solid films, as well as the effects on its optical and electrical properties. We observed a strong intermolecular interaction in thin films, which can be controlled via processing solvents. Two typical aggregation behaviors, i.e. H- and J- aggregation, can be selectively formed via the proper selection of solvents, resulting in a significant difference in material properties and the resultant photovoltaic performance. In addition to the monomer absorption between 600 nm and 700 nm, the H-aggregation mainly absorbs green light around 500–600 nm, while the J-aggregation shows a strong absorption in the near infrared range up to 850 nm. Therefore in squaraine/fullerene bi-layer hetero-junction photovoltaic cells, we demonstrated a significant contribution of J-aggregation to the photocurrent. Furthermore the J-aggregation films have a deeper ionization potential, most likely due to the intermolecular charge-transfer interaction, and thus gave rise to a larger open circuit voltage than those of the H-aggregation based devices. The J-aggregation formation shall be considered as an effective approach to tune the optical/electrical properties in organic optoelectronic devices.

Architecture of low dimensional nanostructures based on conjugated polymers

To date, the aggregated nanostructures of conjugated polymers have been actively investigated as active materials, displaying promising optical and electrical properties and as good candidates for developing potential applications in electronics, optics, photovoltaic cells, and biology. This paper presents a review of the works on low dimensional nanostructures (nanowires, nanotubes, nanobelts, and nanofibers) of π-conjugated polymers. The diverse preparation methods were discussed, including hard and soft template-assisted synthesis, electrospinning, nanolithography, self-assembly at interfaces, in solution and in solids, and other strategies. Their potential applications in the fields of light-emitting diodes, field emission devices, organic photovoltaics, sensors and nanoelectronics are shown.

Effects of Surfactant Concentration on the Microstructures of TiO<sub>2</sub> Hollow Spheres by Hydrothermal Method

TiO2 hollow spheres were prepared by hydrothermal method using CTAB, glucose and (NH4)2TiF6 as surfactant, template and titanium source, respectively. The microstructures of hollow spheres TiO2 were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR). The results showed the concentration of the CTAB obviously influenced the morphology of hollow spheres TiO2. This synthesis route may also extend to the preparation of hollow structures of other metal oxides. Because of the large specific surface area, porous structure, and good penetration, the hierarchical TiO2-derived hollow spheres may find great applications in catalysis, photovoltaic cells and high surface area electrodes.

Novel polythiophene derivatives functionalized with conjugated side-chain pendants comprising triphenylamine/carbazole moieties for photovoltaic cell applications

We synthesized a series of polythiophenes (PTs) featuring 2-ethylhexyl-substituted terthiophene (T) or quaterthiophene (BT) as the conjugated unit in the polymer backbone with pendant conjugated tert-butyl-substituted triphenylamine (tTPA)- or carbazole (tCz)-containing moieties as side chains, namely PTtTPA, PBTtTPA, PTtCz and PBTtCz. Incorporating T and BT moieties into the polymer backbone and attaching tTPA or tCz units promoted efficient conjugation within the extended conjugated frameworks of the polymers, resulting in lower band-gap energies and red-shifting of the maximal UV-Vis absorption wavelength. The higher electron-donating ability of tTPA resulted in broader absorption bands and lower band-gap energies of PTtTPA and PBTtTPA as compared with PTtCz and PBTtCz. Incorporation of the T and BT moieties into the polymer backbone enhanced the compatibility of PT and the fullerene derivative by reducing the side-chain density of PT, thus providing sufficient free volume for efficient incorporation of [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) into the polymer chains. Polymer solar cells (PSCs) were fabricated by spin-coating a blend of each PT with the fullerene derivative (PC61BM) as a composite film-type photoactive layer; PBTtTPA/PC61BM-based PSCs showed superior photovoltaic (PV) performance to PTtTPA/PC61BM-based PSCs in terms of conjugation and absorption band broadness. However, PBTtCz/PC61BM-based PSCs showed inferior PV performance to PTtCz/PC61BM-based PSCs. The lower HOMO level led to a higher open-circuit voltage (Voc; 0.74 V) and larger photo-energy conversion efficiency (η; 2.77%) of PTtCz/PC61BM-based PSCs.

High performance broadband absorber in the visible band by engineered dispersion and geometry of a metal-dielectric-metal stack

We propose a nanostructured broadband absorber in the visible regime through designing the dispersion and geometry of a Cu/Si3N4/Cu stack. Two examples with nearly perfect absorption at different spectral ranges are designed based on the special dispersion relationship and fabricated using nanoimprint lithography. Experiments confirm an ultra flat average absorption greater than 80% from 400 nm to 700 nm. The robustness of the design with angle insensitive absorption characteristic is desirable for the applications in thin-film thermal emitters and photovoltaic cells.

Asymmetrical Interleaved DC/DC Switching Converters for Photovoltaic and Fuel Cell Applications—Part 1: Circuit Generation, Analysis and Design

A novel asymmetrical interleaved dc/dc switching converters family intended for photovoltaic and fuel cell applications is presented in this paper. The main requirements on such applications are small ripples in the generator and load, as well as high voltage conversion ratio. Therefore, interleaved structures and voltage multiplier cells have been asymmetrically combined to generate new converters, which inherently operate indiscontinuous conduction mode. The novel family is derived from boost, buck-boost and flyback-based structures. This converter family is analyzed to obtain the design equations and synthesize a design process based on the typical requirements of photovoltaic and fuel cell applications. Finally, the experimental results validate the characteristics and usefulness of the asymmetrical interleaved converter family.

A Versatile Approach to Organic Photovoltaics Evaluation Using White Light Pulse and Microwave Conductivity

State-of-the-art low band gap conjugated polymers have been investigated for application in organic photovoltaic cells (OPVs) to achieve efficient conversion of the wide spectrum of sunlight into electricity. A remarkable improvement in power conversion efficiency (PCE) has been achieved through the use of innovative materials and device structures. However, a reliable technique for the rapid screening of the materials and processes is a prerequisite toward faster development in this area. Here we report the realization of such a versatile evaluation technique for bulk heterojunction OPVs by the combination of time-resolved microwave conductivity (TRMC) and submicrosecond white light pulse from a Xe-flash lamp. Xe-flash TRMC allows examination of the OPV active layer without requiring fabrication of the actual device. The transient photoconductivity maxima, involving information on generation efficiency, mobility, and lifetime of charge carriers in four well-known low band gap polymers blended with phenyl-C(61)-butyric acid methyl ester (PCBM), were confirmed to universally correlate with the PCE divided by the open circuit voltage (PCE/V(oc)), offering a facile way to predict photovoltaic performance without device fabrication.

Power quality analysis for building integrated PV and micro wind turbine in New Zealand

World over, sustainability and carbon emissions are two major growing concerns. Energy efficiency and larger proportion of renewable energy integration are treated as two of the solutions for electricity sector by governments, utilities as well as large end users. Many different small-scale renewable generation technologies are being developed and tested for grid performance motivated by reducing transmission and distribution loss, reducing peak demand, maintaining security of supply, and a possible reduction in electricity charges [1]. It is foreseen that once small scale renewable generation cells become economically competitive, the growth of them in existing electricity networks could be dramatic. Many of the existing small scale renewable generation technologies rely on electronic inverter switching [2–4] at the integration point. Currently, due to the switching characteristics of inverters power quality could become a problem for end users and also impact on regulatory limits for distribution line utilities. The existing inverter technology application of micro wind turbine and solar photovoltaic cells is being currently deployed and assessed several distribution network utilities like Vector in New Zealand. In this paper the outcome of these trials are analysed in addition to proposing the modelling framework to quantify the power quality effect of small scale renewable generation cells. A practical and comprehensive way to assess the power quality impacts due to large scale integration of these new renewable generation devices is also presented. Software such as ATP-EMTP and DIgSILENT PowerFactory is used in this work to provide the platforms for assessment of an individual device and overall network effect, respectively.