Materials For Photovoltaic Devices Research Articles

Optical spectrum of bottom-up graphene nanoribbons: towards efficient atom-thick excitonic solar cells

Recently, atomically well-defined cove-shaped graphene nanoribbons have been obtained using bottom-up synthesis. These nanoribbons have an optical gap in the visible range of the spectrum which make them candidates for donor materials in photovoltaic devices. From the atomistic point of view, their electronic and optical properties are not clearly understood. Therefore, in this work we carry out ab-initio density functional theory calculations combine with many-body perturbation formalism to study their electronic and optical properties. Through the comparison with experimental measurements, we show that an accurate description of the nanoribbon's optical properties requires the inclusion of electron-hole correlation effects. The energy, binding energy and the corresponding excitonic transitions involved are analyzed. We found that in contrast to zigzag graphene nanoribbons, the excitonic peaks in the absorption spectrum are a consequence of a group of transitions involving the first and second conduction and valence bands. Finally, we estimate some relevant optical properties that strengthen the potential of these nanoribbons for acting as a donor materials in photovoltaic.

Theoretical and X-ray diffraction studies of organic photovoltaic compounds

The electronic and structural properties of thiazolic ring derivatives were studied using density functional theory (DFT) and X-ray diffraction in terms of their application as organic semiconductor materials in photovoltaic devices. The B3LYP hybrid functional in combination with Pople type 6-31G(d) basis set with a polarization function was used in order to determine the optimized geometries and the electronic properties of the ground state, while transition energies and excited state properties were obtained from DFT with B3LYP/6-31G(d) calculation. The investigation of thiazolic derivatives formed by the arrangement of several monomeric units revealed that three-dimensional (3D) conjugated architectures present the best geometric and electronic characteristics for use as an organic semiconductor material. The highest occupied molecular orbital (HOMO) . lowest unoccupied molecular orbital (LUMO) energy gap was decreased in 3D structures that extend the absorption spectrum toward longer wavelengths, revealing a feasible intramolecular charge transfer process in these systems. All calculations in this work were performed using the Gaussian 03 W software package.

XRD Studies of Synthesized Bi2S3Crystalline Materials

Bismuth sulfide preparation and its x-ray diffraction studies are reported in this paper. The author have synthesized Bi2Sx (x = 3.15, 3.45) compound material with different sulfur content by conventional high temperature solid state solvothermal reaction of bismuth and sulfur which conforms that the (121) preferred orientation with crystallite size ~30 nm and splitting of peaks due to orthorhombic structure matches well with the standard data and demonstrate good crystalline quality and structural homogeneity of synthesized powder.This paper also describes the synthesis and x-ray diffraction studies of bismuth sulfide powder via versatile precipitation technique . Bismuth sulfide powder was synthesized using thiourea and sodium dodecyl sulfate or in absence of any surfactant maintained at 800C for 12 h keeping pH of solution constant at 1.4. Synthesized powder was characterized by x-ray diffraction technique which indicates that surfactants play major role in synthesis of bismuth sulfide that conforms the crystallite size ~35 nm. The employed solid state solvothermal technique played an important role to progress the homogeneous reaction and preparation of pure and fine bismuth sulfide powder. The possible application of this material in photovoltaic devices is suggested.

Arising applications of ferroelectric materials in photovoltaic devices

The ferroelectric-photovoltaic (FE-PV) device, in which a homogeneous ferroelectric material is used as a light absorbing layer, has been investigated during the past several decades with numerous ferroelectric oxides. The FE-PV effect is distinctly different from the typical photovoltaic (PV) effect in semiconductor p–n junctions in that the polarization electric field is the driving force for the photocurrent in FE-PV devices. In addition, the anomalous photovoltaic effect, in which the voltage output along the polarization direction can be significantly larger than the bandgap of the ferroelectric materials, has been frequently observed in FE-PV devices. However, a big challenge faced by the FE-PV devices is the very low photocurrent output. The research interest in FE-PV devices has been re-spurred by the recent discovery of above-bandgap photovoltage in materials with ferroelectric domain walls, electric switchable diodes and photovoltaic effects, tip-enhanced photovoltaic effects at the nanoscale, and new low-bandgap ferroelectric materials and device design. In this feature article, we reviewed the advance in understanding the mechanisms of the ferroelectric photovoltaic effects and recent progress in improving the photovoltaic device performance, including the emerging approaches of integrating the ferroelectric materials into organic heterojunction photovoltaic devices for very high efficiency PV devices.

Defects and Doping in Nanocrystalline Silicon-Germanium Devices

ABSTRACTNanocrystalline Silicon-Germanium (Si,Ge) is a potentially useful material for photovoltaic devices and photo-detectors. Its bandgap can be controlled across the entire bandgap region from that of Si to that of Ge by changing the alloy composition during growth. In this work, we study the fabrication and electronic properties of nanocrystalline devices grown using PECVD techniques. We discovered that upon adding Ge to Si during growth, the intrinsic layer changes from n-type to p-type. We can change it back to n-type by using ppm levels of phosphorus, and make reasonable quality devices when phosphine gas was added to the deposition mix. We also measured the defect density spectrum using capacitance frequency techniques, and find that defect density decreases systematically as more phosphine is added to the gas phase. We also find that the ratio of Germanium to Silicon in the solid phase is higher than the ratio in the gas phase.

Solution Synthesis and Reactivity of Colloidal Fe2GeS4: A Potential Candidate for Earth Abundant, Nanostructured Photovoltaics

Iron chalcogenides, in particular iron pyrite, have great potential to be useful materials for cost-effective thin film photovoltaics. However, the performance of pyrite as an absorber material in photovoltaic devices has fallen far short of the theoretical efficiency. A potential cause of this may be the instability of the pyrite phase. An alternate class of iron chalcogenides, Fe2MS4 (M = Ge, Si) has been proposed as a possible alternative to pyrite, yet has only been studied for interesting magnetic properties. Herein, we report the first solution synthesis of colloidal Fe2GeS4 and report the optical properties, reactivity, and potential for use as a photovoltaic material.

OCVD poly(3,4-ethylenedioxythiophene) conductivity and lifetime enhancement via acid rinse dopant exchange

Reduced sheet resistance and longer film stability of oCVD (oxidative chemical vapour deposition) PEDOT films were achieved by including a post-process acid rinse step in the production of the thin films. PEDOT films were rinsed in multiple concentrations of hydrobromic acid, sulfuric acid, and hydrochloric acid to test the effect of acid rinsing on sheet resistance, doping concentration, chemical composition, optical transmittance, and film morphology. XPS, FTIR, Raman spectroscopy, and XRD measurements were taken to determine the morphology and composition of the rinsed films. On average, rinsing films in HCl, HBr, and H2SO4 produced conductivity increases of 37%, 135%, and 117%. The dc to optical conductivity ratio, σdc/σop, was increased to 6, 12, and 10, for HCl, HBr, and H2SO4 rinsed films respectively as compared to σdc/σop = 4 for MeOH rinsed films. This study found evidence of dopant exchange within the films facilitated by the acid rinsing step, as well as complete removal of residual iron chloride oxidant. The acid rinse step also resulted in improved film conductivity stability at elevated temperatures. The XRD measurements in particular show signs of semi crystallinity in the PEDOT film after acid rinsing in comparison to an amorphous structure observed before this step. In this study, acid rinsing applied as a post-process step alters thin PEDOT films in ways that enhance their ability to function as electrode materials in photovoltaic devices.

1-D photonic crystals for photovoltaics

The paper presents the theoretical analysis of photonic structures with 1-D photonic crystals on both sides of the slab glass and the results of experimental research. Within the scope of theoretical analysis, using the 2x2 transfer matrix method, we have determined the spectral reflectivity and transmittance characteristics, and basing on the said characteristics, we have determined the influence of the number of bilayers on the maximum reflectivity and on the width of the main reflectivity peak. For the structure with four bilayers (SiO2/TiO2) we have obtained the maximum reflectivity of 0.933 for the wavelength λr = 505nm and full width at half maximum of the main reflectivity peak of FWHM=185nm.   Full Text: PDF References T.M.Razykov, C.S.Ferekides, D.Morel, E.Stefanakos, H.S.Ullal, H.M.Upadhyaya,"Solar photovoltaic electricity: Current status and future prospects", Sol. Energy 85, 1580 (2011)[CrossRef] B. Parida, S. Iniyanb, R. Goic,"A review of solar photovoltaic technologies", [CrossRef] Organic electronics, edited by Hagen Klauk, (Weinheim, WILEY-VCH Verlag GmbH & Co.KGaA,. 2006) E. Gondek, I.V.Kityk, A.Danel,"Some anthracene derivatives with N,N-dimethylamine moieties as materials for photovoltaic devices", [CrossRef] E.Gondek, Y.Djaoued, J.Robichaud, P.Karasiński, I.V.Kityk, A.Danel, K.J.Plucinski,"Influence of TiO2 nanoparticles on the photovoltaic efficiency of the ITO/PEDOT:PSS/fluorine copolymers/polythiophene: TiO2/Al architecture", J. Mater. Sci.: Mater Electron[CrossRef] R.Signerski, G.Jarosz,"Effect of buffer layers on performance of organic photovoltaic devices based on copper phthalocyanine-perylene dye heterojunction", Opto-Electron. Rev. 19, 468 (2011)[CrossRef] A.G.Imenes, D.R.Mills,"Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review", Sol. Energy Mater. Sol. Cells 84, 19 (2004)[CrossRef] A.Zhedi,"Review of modelling details in relation to low-concentration solar concentrating photovoltaic", Ren. Sust. Energy Rev 15, 1609 (2011)[CrossRef] B.C.Rowan, L.R.Wilson, B.S.Richards,"Advanced Material Concepts for Luminescent Solar Concentrators", [CrossRef] R.M.Almeida, L.M.Fortes, M.C.Gonçalves,"Sol–gel derived photonic bandgap coatings for solar control", Opt. Mater. 33, 1867 (2011)[CrossRef] E. Yablonovitch,"Inhibited Spontaneous Emission in Solid-State Physics and Electronics", Phys. Rev. Lett. 58, 2059 (1987)[CrossRef] G.V.Morozov, F.Placido, D.W.L.Sprung,"Absorptive photonic crystals in 1D", J. Opt. 13, 035102 (2011)[CrossRef] P.Karasiński, "Influence of aging and annealing on the properties of silica films produced with sol-gel method", Opt. Appl. 36, 389 (2006) P.Karasiński, E.Gondek, S.Drewniak, I.V.Kityk,"Nano-sized blue spectral shift in sol–gel derived mesoporous titania films", J. Sol Gel Sci. Techn. 61, 355 (2012)[CrossRef]

ChemInform Abstract: Colloidal CIGS and CZTS Nanocrystals: A Precursor Route to Printed Photovoltaics

AbstractReview: CIGS: Cu(In1‐xGax)Se2, CZTS: Cu2ZnSnS4; 63 refs.

ChemInform Abstract: Thieno[3,4‐b]pyrazines and Their Applications to Low Band Gap Organic Materials

AbstractReview: 100 refs.

Colloidal CIGS and CZTS nanocrystals: A precursor route to printed photovoltaics

This review article summarizes our research focused on Cu(In1–xGax)Se2 (CIGS) nanocrystals, including their synthesis and implementation as the active light absorbing material in photovoltaic devices (PVs). CIGS PV layers are typically made using a high temperature (>450°C) process in which Cu, In and Ga are sequentially or co-evaporated and selenized. We have sought to use CIGS nanocrystals synthesized with the desired stoichiometry to deposit PV device layers without high temperature processing. This approach, using spray deposition of the CIGS light absorber layers, without high temperature selenization, has enabled up to 3.1% power conversion efficiency under AM 1.5 solar illumination. Although the device efficiency is too low for commercialization, these devices provide a proof-of-concept that solution-deposited CIGS nanocrystal films can function in PV devices, enabling unconventional device architectures and materials combinations, including the use of flexible, inexpensive and light-weight plastic substrates.

Photochemical Response of Commercial MOFs: Al2(BDC)3 and Its Use As Active Material in Photovoltaic Devices

The presence of organic linkers in MOFs allows introducing response in the solid upon chemical, electrochemical, or photochemical excitation of these units. In the present study, we report the intrinsic photoresponse of four commercially available MOFs as well as after incorporation of some organic guests. Laser flash photolysis measurements have allowed us to detect transient species upon irradiation of commercial Al2(BDC)3. The signal has been rationalized as derived from the photochemical generation of charge separated states. In contrast to Al2(BDC)3, the other three commercial MOFs tested did not exhibit any signal. The photoinduced charge separation in Al2(BDC)3 can be modulated by inclusion of organic guests that can act as traps of electrons or holes increasing the lifetime of charge separation. When the oxidation potential of the organic guest is low, as in the case of 1,4-phenylendiamine, PDA, we have been able to observe spontaneous charge separation even for Fe-BTC and Cu3(BTC)2. The basic und...

Quantum mechanical modelling and calculation of two-photon absorption properties of new class ‘Λ’-shaped conjugated molecules

Organic material with high intensity of two-photon absorption (TPA)-induced fluorescence can be used as the up-converter material for photovoltaic devices. In this work, quantum mechanics modelling techniques were applied to theoretically investigate one- and two-photon absorption properties of new ‘Λ’-shaped conjugated molecules. Fluorene and diphenylmethylene analogues as the π centres were chosen for building the π-conjugated bridges to connect the two types of strong electron donors, N,N-diphenylamino and carbazole groups. In these molecular structures, cyano and ketone groups were also selected to modify the π centres as electron acceptors. The TPA cross sections of these derivatives were calculated using two-state, three-state and sum-over-state models, respectively. Geometrical structures of these molecules were optimised using Hartree–Fock theory, and properties of excited states of these molecules were obtained based on configuration interaction with single excitations method. The effects of donor, acceptor and π centre on the TPA behaviours of these designed molecules were investigated. Several of these molecules have attractive TPA properties, which may have potential for photovoltaic device applications.

Thieno[3,4-b]pyrazines and their applications to low band gap organic materials

The application of fused-ring thieno[3,4-b]pyrazines in conjugated organic polymers has been found to be a powerful approach to the production of low band gap materials. While thieno[3,4-b]pyrazine-based materials date back to the early 1990s, significant advances in the preparation and scope of thieno[3,4-b]pyrazine-based materials have been reported in recent years, primarily in response to the increasing demand for reduced band gap materials in photovoltaic devices. In this review, we provide an overview of thieno[3,4-b]pyrazines and their application to conjugated materials, highlighting in particular the recent advances in the breadth of thieno[3,4-b]pyrazine building blocks and the promise of tuning materials to achieve optimal properties for specific applications.

Investigating morphology and electronic properties of self-assembled hybrid systems for solar cells

We investigate self-assembled network morphologies of hybrid materials and their application in solar cells. We show the use of a semiconducting functional block copolymer as a structure directing agent. The application of a functional block copolymer circumvents an additional filling step of the templated inorganic part with a hole conductor. Within a one-pot synthesis various morphologies adequate for active materials in photovoltaic devices are prepared. The solar cell performance was found to depend on the morphological design of the hybrid material since the formation of percolating networks is of general importance. Using conductive scanning force microscopy on a cross-section of a functional solar cell device, we proved that the titania in our system forms a percolating network. Measurements showed that percolation is not a limiting factor for the device performance. In combination with a functionalized titania-precursor, we were able to double the power conversion efficiency of our hybrid bulk heterojunction cells in comparison to our previous results.

Thiophene-based conjugated oligomers for organic solar cells

Owing to their efficient light harvesting, structural versatility and intrinsic charge transport behavior, thiophene-based π-conjugated systems have attracted much attention in developing high performance organic solar cells. In comparison to the relevant conjugated polymers that are used as active materials in photovoltaic devices, conjugated oligomers possess some critical advantages: (1) well-defined molecular structures lead to their synthetic reproducibility with high purity which is vital to obtain repeatable device performance; (2) crystalline features of oligomers favor the long range order in the solid state and benefit the charge carrier transport; (3) the devices can be readily fabricated by both solution-processable and vacuum-deposited techniques. In this feature article, thiophene-based conjugated oligomers with molecular architectures from 1D to 3D, which play an essential role in the device performance of organic solar cells, will be summarized. We aim to address the influence of the thiophene motifs on the electronic, optical and self-assembly properties of the materials, and eventually conclude the relationship between the molecular structures and photovoltaic properties.

Electronic structure study using density functional theory in organic dendrimers

The electronic and structural properties of pyrrolic ring derivatives were studied using density functional theory (DFT) in terms of their application as organic semiconductor materials in photovoltaic devices. The B3LYP hybrid functional in combination with Pople type 6-31G(d) basis set with a polarization function was used in order to determine the optimized geometries and the electronic properties of the ground state, while transition energies and excited state properties were obtained from time-dependent (TD)-DFT with B3LYP/6-31G(d) calculation. The investigation of pyrrolic derivatives formed by the arrangement of several monomeric units revealed that three-dimensional (3D) conjugated architectures in which the combination of a triphenylamine (TPA) core with π-conjugated rings attached to the core, present the best geometric and electronic characteristics for use as an organic semiconductor material. The highest occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) energy gap was decreased in 3D-structures that extend the absorption spectrum toward longer wavelengths, revealing a feasible intramolecular charge transfer process in these systems. All calculations in this work were performed using the Gaussian 03 W software package.

Acetylene-Based Materials in Organic Photovoltaics

Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Organic photovoltaic systems hold the promise of a lightweight, flexible, cost-effective solar energy conversion platform, which could benefit from simple solution-processing of the active layer. The discovery of semiconductive polyacetylene by Heeger et al. in the late 1970s was a milestone towards the use of organic materials in electronics; the development of efficient protocols for the palladium catalyzed alkynylation reactions and the new conception of steric and conformational advantages of acetylenes have been recently focused the attention on conjugated triple-bond containing systems as a promising class of semiconductors for OPVs applications. We review here the most important and representative (poly)arylacetylenes that have been used in the field. A general introduction to (poly)arylacetylenes, and the most common synthetic approaches directed toward making these materials will be firstly given. After a brief discussion on working principles and critical parameters of OPVs, we will focus on molecular arylacetylenes, (co)polymers containing triple bonds, and metallopolyyne polymers as p-type semiconductor materials. The last section will deal with hybrids in which oligomeric/polymeric structures incorporating acetylenic linkages such as phenylene ethynylenes have been attached onto C60, and their use as the active materials in photovoltaic devices.

Trannulenes: a new class of photoactive materials for organic photovoltaic devices

We report the first large-scale preparation of fluorinated trannulene C60F15[C(COOMe)3]3 (TMCMT) and its application as a photoactive material in organic solar cells. Two types of photovoltaic devices were fabricated: bulk heterojunction cells comprising blends of TMCMT with a polyfluorene polymer and bilayer cells based on a planar heterojunction of TMCMT with a perylene diimide. Photoluminescence quenching studies suggested that a photoinduced electron transfer occurs from polyfluorene and perylenediimide to TMCMT, therefore it behaves as photoinduced electron acceptor. Both types of solar cells comprising TMCMT as photoactive material showed clear photovoltaic effects. This proves for the first time the feasibility of the previously anticipated idea of using trannulenes as light-harvesting materials in photovoltaic devices.

Some anthracene derivatives with N, N-dimethylamine moieties as materials for photovoltaic devices

Photovoltaic properties of novel composites consisting of poly(3-decylotiophene-4,5-diyl) PDT with doped anthracene dye chromophore were explored. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the composite were estimated by means of DFT B3LYP quantum chemical calculations. The open-circuit voltage was found to be enhanced with the increase of the chromophore state dipole moment, however short-circuit current is diminished. Despite the values of the quantum efficiencies not being too large (about 0.16–0.19%), the influence of the state dipole moments should be taken into account during the further research of materials with improved photovoltaic responses. One of possible mechanisms may be related to existence of trapping polaron states, which are directly related to the state dipole moments of the chromophore interacting with the dipole moments of the particular polymer chains.