Application In Photovoltaic Cells Research Articles

Rational Design and Construction of Well-Organized Macro-Mesoporous SiO2/TiO2 Nanostructure toward Robust High-Performance Self-Cleaning Antireflective Thin Films

Antireflection (AR) thin films on optical substrates are of great significance in high-performance optoelectronic devices. Here, we present a rational design and construction of well-organized macro-mesoporous nanostructure toward robust high-performance self-cleaning antireflective thin films on the basis of effective medium theory and finite difference time domain (FDTD) simulations that combine the optical design principle. A hierarchical macro-mesoporous SiO2 thin film with very high porosity and gradient refractive indexes works as a λ/4-wavelength AR layer and significantly suppresses the reflection in the range from 350 to 1200 nm. Even after dip-coating a layer of high refractive index TiO2 nanocrystals, the nanostructured thin film still exhibits broadband AR properties which are much superior to conventional flat SiO2/TiO2 thin films, especially in the range of 350-500 nm. In addition, the obtained thin film exhibits photocatalytic self-cleaning and durable superhydrophilicity. The advantages brought by the well-organized macro-mesoporous structure are also testified through comparing to the solely mesoporous SiO2/TiO2 film counterpart. Moreover, the pencil hardness test and sandpaper abrasion test show favorable robustness and functional durability of the thin film, which make it extremely attractive for practical applications in optical devices, display devices, and photovoltaic cells.

Metal Phthalocyanine Derivative Nanocrystals: Color-controlled and Transparent Dispersions by a One-pot UV-assisted Synthetic Process

Metal phthalocyanines (PCs) and their derivatives (PCDs) have been considered for applications in color filters, photovoltaic cells, and photodynamic therapy, owing to their unique optical properti...

Electrochemical and spectroscopic characterization of poly (bithiophene + 2-methylfuran) copolymer

In this work, Poly(bithiophene + 2-methylfuran) copolymer was successfully synthetized by an electrochemical polymerization of two monomers, bithiophene and 2-methylfuran in acetonitrile containing lithium perchlorate. The obtained copolymer was characterized via cyclic voltammetry, impedance spectroscopy, UV–visible, scanning electron microscope, conductivity and photocurrent measurements. The cyclic voltammetry study showed two redox couples characteristic of Poly (bithiophene + 2-methylfuran) copolymer. The impedance spectroscopy study revealed that the resistance of the copolymer film increases with the addition of 2-methylfuran. The photocurrent measurement showed good photoelectrochemical properties, making this copolymer an ideal candidate for photovoltaic cell applications.

Boron Subphthalocyanines, Boron Subnaphthalocyanines and Silicon Phthalocyanines As Non-Fullerene Electron Accepting Materials in Organic Photovoltaics (and Tetrabenzocorroles as Complimentary Electron Donating Materials)

For some time, our group has been focused on the design and synthesis of derivatives of boron subphthalocyanine (BsubPc) for application in organic electronics with a specific focus on organic photovoltaics and light emitting diodes; during this presentation however I will focus specifically on their application in organic photovoltaics. I will begin by focusing on our efforts with regards to synthetic variants of BsubPcs and their application in planar heterojunction organic photovoltaic cells (OPVs, organic solar cells, OSCs).[1,2] After summarizing this work, I will then outline our very recent results where we took BsubPc based planar heterojunction organic photovoltaic cells and put them on the roof of our building in downtown Toronto during the summers of 2015 and 2016 in the ambient environment. What we found was that when BsubPcs are applied as electron accepting materials they are remarkably stable and maintain a 4% PCE over time. On the flipside, when applied as electron donating materials the stability of the paired material, C60, fullerene, dictates the overall stability of the devices. Additionally we have used a novel method to map out the degradation pathway of the OPVs which will be described. We were able to ultimately form a structure property relationship to their stability in the ambient environment. In parallel we have also been exploring the concept of complementary absorption engineering by either the chemical modification of BsubPcs or by pairing BsubPcs with alternative materials having complementary absorption profiles. For example, we have recently shown that after firming up the chemical structure of phosphorus oxy tetrabenzotriazacorrole [POTbc, a phthalocyanine analogue] that the pairing of a BsubPc with yields a unique gray organic photovoltaic cell absorbing broadly across the visible spectrum. Our group’s has recently began the exploration of the bulk-heterojunction OPV space whereby BsubPcs are again electron accepting fullerene alternatives, although we are not the first to do so.[3,4] I will articulate our recent findings. We have also recently shown that structural analogs to BsubPcs, boron subnaphthalocyanines (BsubNcs) are actually a mixed alloy composition of chlorinated materials designated as Cl-ClnBsubNcs. After establishing the correlation of electrochemical characteristics and OPV performance for Cl-ClnBsubNc we have recently shown how phenoxylated versions of ClnBsubNc are also applicable in BHJ OPVs also as electron accepting materials. We have also explored the potential of chemistry variations to yield pure examples of BsubNcs. Time permitting this will be outlined along with electrochemical characterization. Finally, during last year’s meeting, I outlined how our group’s recent exploration of other p-block metal phthalocyanines (Pcs) yielded the conclusion that silicon phthalocyanines (SiPcs) can also be applied as fullerene alternatives/acceptors in organic photovoltaic cells. Our conclusion at the time was that phenoxylation enhances the performance of SiPcs as an electron transporting/accepting materials. Over the past year we have enhanced this conclusion and formed an initial structure property relationship that gives a road map to synthetic alternatives of SiPcs that may ultimately yield higher performing OPVs. The potential applications have also been expanded beyond SiPcs in PHJ OPVs whereby we have shown that they can be equally applied as electron accepting fullerene alternatives in the BHJ OPV space as well. I will outline this structure property relationship and our future work in this area. Coauthors and coinvestigators will be cited as appropriate throughout the presentation.

Concentrated solar light splitting using cold mirrors for photovoltaics and photonic hydrogen production applications

In this study, an experimental setup is constructed to investigate the utilization of solar light splitting mirrors in photovoltaic (PV) cell and photonic hydrogen production applications by varying the solar light intensity on the system components. In the experimental setup, the solar rays are split to be used by PV cells using six cold mirrors, and Fresnel lens are employed to concentrate the light for utilization. The experimental unit is modeled using the equivalent circuit diagram of the PV cell, and the results provided by the model are then compared with the ones obtained from the experiments. The PV module conversion efficiencies are comparatively illustrated for concentrated light and non-concentrated light together with and without solar light splitting. The lower wavelength of the spectrum is directed to a photoelectrochemical hydrogen production reactor which uses a copper oxide photocathode. It is derived from the results that, although solar light splitting significantly decreases the portion of wavelengths received by the PV panel, the total generated power can be increased or kept at same levels by concentrating the sun rays. The power output from the measured PV module increases to 6.75W from 3.50W, which yields a considerable rise in the efficiency from 6.7% to 13.2% under the concentrated and divided light spectrum, while approximately 19% of the entire spectrum energy is received by the PV module. The power obtained from the PV module is used electrify the PEM electrolyzer for further hydrogen production. The temperature levels on the surface of the PV panel reach considerably high values corresponding to approximately 125°C in some cases for a conventional PV module which then reduce the long-term stability of power generation. This is a challenge and requires cooling, utilization of high-temperature resistant materials in the PV module design, or employment of PV/T panels where the heat is extracted as a useful output or supplied to the PEM electrolyzer for heating the water before its disassociation which helps improve the performance.

Ti as Mediator in the Photoinduced Electron Transfer of Mixed-Metal NH2–UiO-66(Zr/Ti): Transient Absorption Spectroscopy Study and Application in Photovoltaic Cell

A series of mixed-metal NH2–UiO-66(Zr/Ti) with different percentages of exchanged Ti have been prepared and studied by transient absorption spectroscopy (TAS). The photogenerated transients from mixed NH2–UiO-66(Zr/Ti) exhibit at short time scales two defined absorption bands, evolving to a continuous absorption band expanding from 300 to 700 nm at longer time scales. The observed spectral changes are compatible with an initial formation of Ti3+–O–Zr4+ and its further transformation to Ti4+–O–Zr3+ via metal–metal electron exchange, thus providing support to the role of substituted Ti as mediator to facilitate electron transfer from excited ligand to the (Zr/Ti)6O4(OH)4 nodes in mixed NH2–UiO-66(Zr/Ti). The slow recombination of photogenerated electrons and holes in the mixed NH2–UiO-66(Zr/Ti) has been advantageously used for the construction of a photovoltaic cell fabricated with the mixed NH2–UiO-66(Zr/Ti), reaching a higher photon-to-current efficiency than NH2–UiO-66(Zr).

Good Dispersion of Large-Stokes-Shift Heterovalent-Doped CdX Quantum Dots into Bulk PMMA Matrix and Their Optical Properties Characterization

Dispersion of quantum dots (QDs) into a PMMA polymer matrix is promising for luminescent solar concentrator applications in improving the application of photovoltaic cells in both efficiency and flexibility. However, some problems like self-absorption of emitted light, drastic agglomeration, and the oxidation of QDs limit the application of it. Herein, we introduced heterovalent-doped CdX (X = S, Se):Ag (Cu) QDs with stable doped luminescence and large Stokes shift prepared by cation exchange strategy into a PMMA matrix, in which such good performances were kept after in situ polymerization. The UV–vis absorption and PL spectra comparison before and after polymerization confirmed this. The FT-IR, 1HNMR, XPS, and TG-DTA characterizations have been used to explore the interaction between QDs and the polymer matrix. The Stokes shift of them after dispersion in PMMA was larger than 0.9 ev, and the absolute quantum yields were more than 50% after dispersed in bulk PMMA. The luminescence collection behavior of the flexibly shaped centimeter-scale PMMA matrix confirmed their promising applications as a luminescent solar concentrator.

Terahertz emission and photoluminescence of silicon nanowires electrolessly etched on the surface of silicon (100), (110), and (111) substrates for photovoltaic cell applications

Silicon nanowires (SiNWs) were etched on Si (100), (110), and (111) substrates. Slanted nanowires with respect to the surface normal were produced on the Si (110) and (111) substrates, and vertical nanowires were produced on the Si (100) substrate. Photoluminescence spectroscopy exhibited luminescence lines attributed to oxide defects from the nanowires. A comparison of the transient photocurrent as measured using terahertz time-domain spectroscopy revealed an increase in the THz emission from the SiNWs on Si (110) substrate compared to those grown on (100) substrate. Reorienting the dipole moment by applying an external 650mT magnetic field suggested that the carrier transport was confined along the axis of the nanowires. Understanding the photocarrier and transport recombination properties in SiNWs may prove useful in the design considerations for future SiNW photovoltaic cell applications.

DFT/TD-DFT characterization of conjugational electronic structures and spectral properties of materials based on thieno[3,2-b][1]benzothiophene for organic photovoltaic and solar cell applications

In this work, a theoretical study on five organic π-conjugated molecules based on thieno[3,2-b][1]benzothiophene using together quantum methods, density functional theory (DFT) and its derivative time dependent-density functional theory (TD-DFT) is reported. Different electron side groups were introduced as a bridge to investigate their effects on the electronic structure; The HOMO, LUMO, chemical hardness (η), chemical potential (μ), electronegativity (χ), electrophilicity power (ω), reorganization energy total (λtotal), open circuit voltage (Voc), the gap energy and NBO analysis of these compounds have been reported and discussed in this paper. Thus, our aim is to explore their electronic and spectroscopic properties on the basis of the DFT quantum chemical calculations, and at the same time, we are interested to make an idea on the parameters influencing the photovoltaic efficiency toward a better understanding of the structure–property relationships. The calculated results of these compounds reveal that C4, C5, with thiophene and thienopyrazine as a bridge group respectively, can be used as a potential donor of electron in organic Bulk Heterojunction solar cells (BHJ), due to its best electronic and optical properties and good photovoltaic parameters. The study of electronic, optical and structural properties of these compounds could help to design more efficient functional photovoltaic organic materials.

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se2Photovoltaic Cell Applications with Optimized Absorber Thickness

Absorber layer thickness gradient in Cu(In1−xGax)Se2(CIGS) based solar cells and several substitutes for typical cadmium sulfide (CdS) buffer layers, such as ZnS, ZnO, ZnS(O,OH), Zn1−xSnxOy(ZTO), ZnSe, and In2S3, have been analyzed by a device emulation program and tool (ADEPT 2.1) to determine optimum efficiency. As a reference type, the CIGS cell with CdS buffer provides a theoretical efficiency of 23.23% when the optimum absorber layer thickness was determined as 1.6 μm. It is also observed that this highly efficient CIGS cell would have an absorber layer thickness between 1 μm and 2 μm whereas the optimum buffer layer thickness would be within the range of 0.04–0.06 μm. Among all the cells with various buffer layers, the best energy conversion efficiency of 24.62% has been achieved for the ZnO buffer layer based cell. The simulation results with ZnS and ZnO based buffer layer materials instead of using CdS indicate that the cell performance would be better than that of the CdS buffer layer based cell. Although the cells with ZnS(O,OH), ZTO, ZnSe, and In2S3buffer layers provide slightly lower efficiencies than that of the CdS buffer based cell, the use of these materials would not be deleterious for the environment because of their non-carcinogenic and non-toxic nature.

Low band-gap conjugated polymer based on diketopyrrolopyrrole units and its application in organic photovoltaic cells

A new conjugated polymer utilizing diketopyrrolopyrrole (DPP) and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) units as the backbone framework was designed, synthesized, and applied in polymer solar cells.

Efficient organic photovoltaic cells on a single layer graphene transparent conductive electrode using MoOx as an interfacial layer.

The large surface roughness, low work function and high cost of transparent electrodes using multilayer graphene films can limit their application in organic photovoltaic (OPV) cells. Here, we develop single layer graphene (SLG) films as transparent anodes for OPV cells that contain light-absorbing layers comprised of the evaporable molecular organic semiconductor materials, zinc phthalocyanine (ZnPc)/fullerene (C60), as well as a molybdenum oxide (MoOx) interfacial layer. In addition to an increase in the optical transmittance, the SLG anodes had a significant decrease in surface roughness compared to two and four layer graphene (TLG and FLG) anodes fabricated by multiple transfer and stacking of SLGs. Importantly, the introduction of a MoOx interfacial layer not only reduced the energy barrier between the graphene anode and the active layer, but also decreased the resistance of the SLG by nearly ten times. The OPV cells with the structure of polyethylene terephthalate/SLG/MoOx/CuI/ZnPc/C60/bathocuproine/Al were flexible, and had a power conversion efficiency of up to 0.84%, which was only 17.6% lower than the devices with an equivalent structure but prepared on commercial indium tin oxide anodes. Furthermore, the devices with the SLG anode were 50% and 86.7% higher in efficiency than the cells with the TLG and FLG anodes. These results show the potential of SLG electrodes for flexible and wearable OPV cells as well as other organic optoelectronic devices.

Optical properties of (TiO<SUB align="right">2)<SUB align="right">1-x(CuO)<SUB align="right">x pseudo binary oxides thin films prepared by spray pyrolysis technique

The pseudo binary oxide thin films were prepared by spray pyrolysis technique on cleaned quartz and silicon substrates at a substrate temperature of 350°C. The X-ray diffraction reveals that the obtained films show anatase phase and mixed phase of copper titanium oxide (Cu3TiO4) for TiO2-CuO films. The surface morphology as observed from SEM image shows spherical grains and rough surface structure of TiO2-CuO films. The EDAX provides the chemical elemental analysis, which reveals that with increase of CuO oxygen weight percentage found to decrease. In an optical study the transmittance and reflectance spectra were recorded in normal incidence by UV-Visible spectrophotometry in the wave length range 350-1200 nm. Using these optical data estimated the thickness, refractive index, and extinction coefficient, real and imaginary parts of dielectric constants of the TiO2-CuO films. It is observed that, with the increase in molar fraction there is variation of the optical parameter, which may be attributed to the mixed phase formation in the films as well as the formation of defects. The increasing Cu contents estimated energy band gap decreases and grain size decreases which leads to decreasing surface resistivity; hence TiO2-CuO films are further used for photovoltaic cell application.

Surfactant-treated graphene oxide in organic solvents and its application in photovoltaic cells

In this paper, a simple and non-poisonous “surfactant treatment” method to prepare graphene oxide (GO) in organic solvents with good dispersibility was presented. As the surfactant molecules, didodecyldimethyla-mmonium bromide (DDAB) was attached onto the GO sheets via ionic interactions by mild sonication, the obtained GO:DDAB nanocomposites were then blended into copolymer Poly(3-hexylthiophene-2,5-diyl) (P3HT) [6,6]:-Phenyl C61 butyric acid methyl ester (PC61BM) as the active layer to fabricate bulk-heterojunction (BHJ) organic solar cells ITO/PEDOT:PSS/P3HT:PC61BM:(GO:DDAB)/Ca/Al. The concentration of GO:DDAB in the active layer, a maximum power conversion efficiency (PCE) of 3.67% was obtained by blending 0.5 mg/mL GO:DDAB in the active layer, showing an efficiency increment of 13.35% as compared with that of the control device without doping GO:DDAB. The optimized OPVs with PTB7:PC71BM by adding GO:DDAB shows the PCE of 7.96%. Therefore, it paves a way to get high efficiency organic photovoltaic cells by directly blending surfactant-treated graphene oxide in organic solvent.

Synthesis of Carbazole Based Co-polymers Containing Thienothiophene and Benzothiadiazole Units in a Direct Arylation Scheme

The photovoltaic effect can be used to harvest energy from sunlight, enabling a cleaner approach to generating energy. Organic photovoltaics based on polymers are an attractive replacement of expensive, high energy consuming silicon solar cells. However, the limitations of efficiency have prevented industrial application, and polymer-based solar cells remain uncompetitive. Thus, optimisation of efficiency is required before potential application of these devices. In this work, the polymers were synthesised by direct arylation, in order to investigate its suitability for application in photovoltaic cell. Morphological, spectroscopic and charge-transport measurements are used to investigate the influence of either the dithienyl or thienothiophene moieties on the structure and photophysical properties of the copolymer rationalise the solar cell characteristics. The polymers obtained were characterised using 1H-NMR, 13C-NMR, IR, UV and thermal gravimetric analysis. The absorption spectral, thermal, electrochemical and photovoltaic properties of the random copolymers were investigated. Finally, a new series of carbazole-based dithienyl or thienothiophene polymers was successfully synthesised and characterised.

Blends of poly(3-alkylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester for organic photovoltaic cell applications: Multi-scale modeling approach

The interface-to-volume ratio of the structure and the transport property of the charge careers are the two main factors affecting the photovoltaic cell performance. In this study, the blends of poly(3-alkylthiophene) (P3AT) (A denotes H, N, and D for hexyl, nonyl, and dodecyl, respectively) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are investigated to understand the effect of the variation of molecular structure of the thiophene-based polymer in the active layer on the two main factors. First, we develop well-designed coarse-grained models to efficiently describe P3AT-PCBM systems. Next, the coarse-grained molecular dynamics simulations are performed to investigate the structural properties of three coarse-grained active layer systems, P3AT-PCBM. We conclude from our simulated analysis that the P3HT-PCBM system will provide the structurally optimized condition for the best photovoltaic cell performance. This is evidenced by two observations: (1) P3HT exhibits a good contact with PCBM in molecular level and (2) the P3HT-PCBM system forms a well-organized molecular network in each of the electron donor and accepter phases.

Structure and Optical Properties of Cu (In0.7, Ga0.3) Se2 Absorbers on Copper Substrate for Photovoltaic Solar Cells Application

Polycrystalline thin films Cu (In0.7, Ga0.3) Se2 (CIGSe) were grown on copper foils at various cathodic potentials by using electrodeposition technique. Scanning electron microscopy (SEM) displays that average diameter of CIGSe grain increases from 0.1μm to 1μm when cathodic potential decreases. The structure and surface morphology were investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. This structure study shows that the thin films were well crystallized in chalcopyrite structure without unwanted secondary phase with preferred orientation along (112) plane. Energy-dispersive x-ray analysis (EDAX) confirms the existence of CIGSe single phase on copper substrate. AFM analysis indicated that the root mean square (RMS) roughness decreases from 64.2 to 27.4 when the potential deposition increases from −0.95V to −0.77V. Using Raman scattering spectroscopy, the A1 optical phonon mode was observed in 173cm−1 and two other weak peaks detected at 214cm−1 and 225cm−1 associated to the B2 and E modes of the CIGSe phase. Through spectroscopy ellipsometry (SE) analysis, three layer optical model was exploited to derive the optical properties and layer thickness of the CIGSe film by least-squares fitting the measured variation in polarization light versus the obtained microstructure.

Electrodeposition synthesis and characterization of In2S3 microspheres

Hollow microspheres of In2S3 of ~3μm in diameter were grown on the surface of thin films of the same material in a simple, fast and one step process by electrodeposition. Structural and morphological characterization as well as the composition of the films were investigated by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy, while optical characterization was done by ultraviolet-visible spectroscopy. According to our results, a mechanism for the formation of the spheres through the generation of hydrogen was proposed, and it was also found that In2S3 crystallized mainly in the β-In2S3 allotropic form in tetragonal and cubic structures. We found that the spheres were embedded in a nanostructured compact film of ~46nm of average grain diameter. On the other hand, voltammetry sweeps revealed that the films were stable in electrochemical environments and, therefore, a possible application in photovoltaic cells was investigated by measuring the photoelectrical response and testing the films in a photoelectrochemical cell. This last result evidenced that the films showed a fast and stable performance.

Synthesis of a BDT-based small-molecule acceptor with dye end groups for organic photovoltaic cell application

ABSTRACTAn acceptor-donor-acceptor (A–D–A)-type small molecule, BDT-IN, having a benzo[1,2-b:4,5-b']dithiophene (BDT) unit as its electron-donating core (D) and an 1,3-indanedione (IN) unit as its electron-withdrawing end group (A), was synthesized by Knoevenagel condensation. The BDT-IN film showed broader UV absorption with a greater red shift (λmax = 622 nm) than that of the BDT-IN solution (λmax = 570 nm). The organic photovoltaic cells were fabricated with an ITO/PEDOT:PSS/poly(3-hexylthiophene): BDT-IN/LiF/Al configuration, and showed a power conversion efficiency of 0.23%.

Realization of structural and optical properties of CdZnO composite coated films for photovoltaic cell applications

CdZnO composite coated films were deposited on glass substrate by screen printing method at the sintering temperature of 450°C and 550°C. The morphological and structural details of composite films were characterized by Scanning Electron microscope (SEM), Powder X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) techniques. Similarly, optical properties were analyzed by UV–vis and Photoluminescence (PL) spectroscopy. XRD patterns revealed increase in crystallite size with increasing sintering temperature. SEM images clearly show agglomeration and increase in the grain size of the nanoparticles in high temperature sintered film. Similarly, FTIR spectra exhibit a slight shift in peak positions and increase in intensity of peaks with increase in sintering temperature. The optical absorption measurements have been used to evaluate the values of refractive index, extinction coefficients of these direct- energy band gap semiconductor films with energy band gaps distributed in the range of ∼2.81eV at 450°C and ∼2.70eV at 550°C. The imaginary and real parts of dielectric constants are also calculated, while PL spectra showed band emission shifting towards the higher side (red shift) with increase in sintering temperature. These studies revealed that on increasing sintering temperature the crystallinity of the film improves with reduction in lattice deformations in such composite films.