Showing papers on "Heterojunction published in 2011"
TL;DR: In this paper, a heterojunction electrode was fabricated by layer-by-layer deposition of WO3 and BiVO4 on a conducting glass, and investigated for photoelectrochemical water oxidation under simulated solar light.
Abstract: Heterojunction electrodes were fabricated by layer-by-layer deposition of WO3 and BiVO4 on a conducting glass, and investigated for photoelectrochemical water oxidation under simulated solar light. The electrode with the optimal composition of four layers of WO3 covered by a single layer of BiVO4 showed enhanced photoactivity by 74% relative to bare WO3 and 730% relative to bare BiVO4. According to the flat band potential and optical band gap measurements, both semiconductors can absorb visible light and have band edge positions that allow the transfer of photoelectrons from BiVO4 to WO3. The electrochemical impedance spectroscopy revealed poor charge transfer characteristics of BiVO4, which accounts for the low photoactivity of bare BiVO4. The measurements of the incident photon-to-current conversion efficiency spectra showed that the heterojunction electrode utilized effectively light up to 540 nm covering absorption by both WO3 and BiVO4 layers. Thus, in heterojunction electrodes, the photogenerated electrons in BiVO4 are transferred to WO3 layers with good charge transport characteristics and contribute to the high photoactivity. They combine merits of the two semiconductors, i.e. excellent charge transport characteristics of WO3 and good light absorption capability of BiVO4 for enhanced photoactivity.
1,023 citations
TL;DR: Compared to planar WO(3)/BiVO(4) heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, it is believed, to the high surface area and improved separation of the photogenerated charge at the WO (3)/BiVO (4) interface.
Abstract: We report on a novel heterojunction WO3/BiVO4 photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO3 nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO4 layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO3/BiVO4 heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO3/BiVO4 interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.
939 citations
TL;DR: The major classes of molecular donors have been reported in the literature in the past several years and highlights some of key considerations in molecular heterojunction design compared to polymer-based bulk heterojunctions as mentioned in this paper.
Abstract: Although most research in the field of organic bulk heterojunction solar cells has focused on combinations of a p-type conducting polymer as a donor and a fullerene-based acceptor, recent work has demonstrated the viability of solution-processed heterojunctions composed entirely of molecular solids. Molecular solids offer potential advantages over conjugated polymer systems in terms of easier purification, amenability to mass-scale production and better batch-to-batch reproducibility. This article reviews the major classes of molecular donors that have been reported in the literature in the past several years and highlights some of key considerations in molecular heterojunction design compared to polymer-based bulk heterojunctions.
925 citations
TL;DR: It is shown, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO3 (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades.
Abstract: As silicon is the basis of conventional electronics, so strontium titanate (SrTiO(3)) is the foundation of the emerging field of oxide electronics. SrTiO(3) is the preferred template for the creation of exotic, two-dimensional (2D) phases of electron matter at oxide interfaces that have metal-insulator transitions, superconductivity or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs), which is crucial to understanding their remarkable properties, remains elusive. Here we show, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO(3) (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades. This 2DEG is confined within a region of about five unit cells and has a sheet carrier density of ∼0.33 electrons per square lattice parameter. The electronic structure consists of multiple subbands of heavy and light electrons. The similarity of this 2DEG to those reported in SrTiO(3)-based heterostructures and field-effect transistors suggests that different forms of electron confinement at the surface of SrTiO(3) lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO(3)-based devices and a novel means of generating 2DEGs at the surfaces of transition-metal oxides.
594 citations
TL;DR: It is proposed that the enhanced photoelectrochemical activity of the composite electrode for water photooxidation results, at least in part, from reduced recombination losses because of the formation of a Schottky-type heterojunction.
Abstract: Transient absorption spectroscopy was used to probe the dynamics of photogenerated charge carriers in α-Fe2O3/CoOx nanocomposite photoelectrodes for water splitting. The addition of cobalt-based electrocatalysts was observed to increase the lifetime of photogenerated holes in the photoelectrode by more than 3 orders of magnitude without the application of electrical bias. We therefore propose that the enhanced photoelectrochemical activity of the composite electrode for water photooxidation results, at least in part, from reduced recombination losses because of the formation of a Schottky-type heterojunction.
528 citations
TL;DR: These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer, and likely most polymer/fullerene systems, in OPV devices.
Abstract: PTB7 semiconducting copolymer comprising thieno[3,4-b]thiophene and benzodithiophene alternating repeat units set a historic record of solar energy conversion efficiency (7.4%) in polymer/fullerene bulk heterojunction solar cells. To further improve solar cell performance, a thorough understanding of structure-property relationships associated with PTB7/fullerene and related organic photovoltaic (OPV) devices is crucial. Traditionally, OPV active layers are viewed as an interpenetrating network of pure polymers and fullerenes with discrete interfaces. Here we show that the active layer of PTB7/fullerene OPV devices in fact involves hierarchical nanomorphologies ranging from several nanometers of crystallites to tens of nanometers of nanocrystallite aggregates in PTB7-rich and fullerene-rich domains, themselves hundreds of nanometers in size. These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer, and likely most polymer/fullerene systems, in OPV devices.
428 citations
TL;DR: If the MEG efficiency can be further enhanced and charge separation and transport can be optimized within QD films, then QD solar cells can lead to third-generation solar energy conversion technologies.
Abstract: Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by utilizing the excess energy in the absorbed photons. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron–phonon coupling that cools hot excitons in bulk semiconductors. However, variations in the reported enhanced quantum yields (QYs) have led to disagreements over the role that quantum confinement plays. The enhanced yield of excitons per absorbed photon is deduced from a dynamical signature in the transient absorption or transient photoluminescence and is ascribed to the creation of biexcitons. Extraneous effects such as photocharging are partially responsible for the observed variations. When these extraneous effects are reduced, the MEG efficiency, defined in terms of the number of additional electron–hole pairs produced per additional band gap of photon excitation, is about two times bet...
418 citations
TL;DR: A supramolecular self-assembly approach is used to make a nanotubular heterojunction of two strategically designed molecular graphenes that displayed characteristic excitation energy transfer and charge transport properties not present in a mixture of the corresponding homotropically assembled nanotubes.
Abstract: One-dimensionally connected organic nanostructures with dissimilar semiconducting properties are expected to provide a reliable platform in understanding the behaviors of photocarriers, which are important for the development of efficient photon-to-electrical energy conversion systems Although bottom-up supramolecular approaches are considered promising for the realization of such nanoscale heterojunctions, the dynamic nature of molecular assembly is problematic We report a semiconducting nanoscale organic heterojunction, demonstrated by stepwise nanotubular coassembly of two strategically designed molecular graphenes The dissimilar nanotubular segments, thus connected noncovalently, were electronically communicable with one another over the heterojunction interface and displayed characteristic excitation energy transfer and charge transport properties not present in a mixture of the corresponding homotropically assembled nanotubes
353 citations
TL;DR: It is predicted that LaAuO(3) bilayers have a topologically non-trivial energy gap of about 0.15 eV, which is sufficiently large to realize the quantum spin Hall effect at room temperature.
Abstract: Topological insulators are a class of materials with an unusual band structure that makes them metallic at the surface and insulating in the bulk. Okamoto and co-workers use electronic structure calculations to predict a new family of possible topological insulators based on transition-metal oxides.
340 citations
01 Dec 2011
TL;DR: In this paper, the steepest sub-threshold swing (SS < 60mV/decade) was achieved in a III-V TFET by using thin gate oxide, heterojunction engineering and high source doping.
Abstract: This work demonstrates the steepest subthreshold swing (SS < 60mV/decade) ever reported in a III–V Tunneling Field Effect Transistor (TFET) by using thin gate oxide, heterojunction engineering and high source doping. Owing to a lower source-to-channel tunnel barrier height, heterojunction III–V TFETs demonstrate steeper subthreshold swing (SS) at a given drain current (I D ) and improved drive current compared to the homojunction III–V TFETs. Electrical oxide thickness (EOT) scaling and increased source doping in tandem with tunnel barrier height reduction are shown to greatly improve the SS of the III–V TFETs and increase I D by more than 20X.
336 citations
Book•
21 Mar 2011
TL;DR: In this article, the authors present a detailed history of the development of CdTe solar cells and their application in thin-films, including the development and performance analysis of the following technologies:
Abstract: Preface Symbols and Acronyms INTRODUCTION History of Cu(In,Ga)(S,Se), Solar Cells History of CdTe Solar Cells Prospects of Chalcogenide Photovoltaics THIN FILM HETEROSTRUCTURES Energies and Potentials Charge Densities and Fluxes Energy Band Diagrams Diode Currents Light Generated Currents Device Analysis and Parameters DESIGN RULES FOR HETEROSTRUCTURE SOLAR CELLS AND MODULES Absorber Bandgap Band Alignment Emitter Doping and Doping Ratio Fermi Level Pinning Absorber Doping Absorber Thickness Grain Boundaries Back Contact Barrier Buffer Thickness Front Surface Gradient Back Surface Gradients Monolithic Series Interconnection THIN FILM MATERIAL PROPERTIES AII-BVI Absorbers AI-BIII-C2VI Absorbers Buffer Layers Window Layers Interfaces THIN FILM TECHNOLOGY CdTe Cells and Modules Cu(In,Ga)(S,Se)2 Cells and Modules PHOTOVOLTAIC PROPERTIES OF STANDARD DEVICES CdTe Device Properties AI-BIII-C2VI Device Properties APPENDIX A: FREQUENTLY OBSERVED ANOMALIES JV Curves Colar Cell Parameters Diode Parameters Quantum Efficiency Transient Effects APPENDIX B: TABLES
TL;DR: Transient photovoltage and photocurrent decay measurements showed that the enhanced performance achieved with C220 partially stems from the high charge collection efficiency over a wide potential range.
Abstract: The high molar absorption coefficient organic D-pi-A dye C220 exhibits more than 6% certified electric power conversion efficiency at AM 1.5G solar irradiation (100 mW cm(-2)) in a solid-state dye sensitized solar cell using 2,2',7,7'-tetrakis(N,N-dimethoxyphenylamine)-9,9'-spirobi-fluorene (Spiro-MeOTAD) as the organic hole transporting material. This contributes to a new record (6.08% by NREL) for this type of sensitized heterojunction photovoltaic device. Efficient charge generation is proved by incident photon-to-current conversion efficiency spectra. Transient photovoltage and photocurrent decay measurements showed that the enhanced performance achieved with C220 partially stems from the high charge collection efficiency over a wide potential range.
TL;DR: The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of SrTiO(3) substrates play an important role.
Abstract: The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. Herein we show that metallic interfaces can be realized in SrTiO3-based heterostructures with various insulating overlayers of amorphous LaAlO3, SrTiO3, and yttria-stabilized zirconia films. On the other hand, samples of amorphous La7/8Sr1/8MnO3 films on SrTiO3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of SrTiO3 substrates play an important role.
TL;DR: The current-voltage characteristics of ZnO/PbS quantum dot (QD) solar cells show a QD size-dependent behavior resulting from a Schottky junction that forms at the back metal electrode opposing the desirable diode formed between theZnO and PbS QD layers.
Abstract: The current−voltage (J−V) characteristics of ZnO/PbS quantum dot (QD) solar cells show a QD size-dependent behavior resulting from a Schottky junction that forms at the back metal electrode opposing the desirable diode formed between the ZnO and PbS QD layers. We study a QD size-dependent roll-over effect that refers to the saturation of photocurrent in forward bias and crossover effect which occurs when the light and dark J−V curves intersect. We model the J−V characteristics with a main diode formed between the n-type ZnO nanocrystal (NC) layer and p-type PbS QD layer in series with a leaky Schottky-diode formed between PbS QD layer and metal contact. We show how the characteristics of the two diodes depend on QD size, metal work function, and PbS QD layer thickness, and we discuss how the presence of the back diode complicates finding an optimal layer thickness. Finally, we present Kelvin probe measurements to determine the Fermi level of the QD layers and discuss band alignment, Fermi-level pinning, a...
TL;DR: P3HT/PCBM bilayers are used as a model to investigate the interdiffusion of the components and its role in the development of the morphology and results indicated that one phase is an ordered P3HT domain and the other phase is the mixture of amorphous P3 HT and PCBM which is not consistent with a phase separation of the component by a spinodal decomposition mechanism.
Abstract: To better understand the physics of the photoactive layer in the organic photovoltaic devices, it is necessary to gain a quantitative understanding of the morphology and the manner in which it develops. A key element in the kinetics associated with the structure development is the interdiffusion of the components. To that end we used P3HT/PCBM bilayers as a model to investigate the interdiffusion of the components and its role in the development of the morphology. A detailed description of the diffusion behavior and the morphology developed from a layer of P3HT in contact with a layer of PCBM during thermal annealing is given. Amorphous P3HT and PCBM are shown to be highly miscible and PCBM can penetrate into the P3HT layer through the P3HT amorphous region and form the bulk heterojunction structure within a few seconds of annealing at 150 °C. The results indicated that one phase is an ordered P3HT domain and the other phase is the mixture of amorphous P3HT and PCBM which is not consistent with a phase separation of the components by a spinodal decomposition mechanism.
TL;DR: It is demonstrated that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO(3) interlayer between the PbS colloidal quantum dot film and the top-contact anode.
Abstract: The ability to engineer interfacial energy offsets in photovoltaic devices is one of the keys to their optimization. Here, we demonstrate that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO3 interlayer between the PbS colloidal quantum dot film and the top-contact anode. Through a combination of current–voltage characterization, circuit modeling, Mott–Schottky analysis, and external quantum efficiency measurements performed with bottom- and top-illumination, these enhancements are shown to stem from the elimination of a reverse-bias Schottky diode present at the PbS/anode interface. The incorporation of the high-work-function MoO3 layer pins the Fermi level of the top contact, effectively decoupling the device performance from the work function of the anode and resulting in a high open-circuit voltage (0.59 ± 0.01 V) for a range of different anode materials. Corresponding increases in short-circuit current...
TL;DR: This work demonstrated that the organic-inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%.
Abstract: Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic–inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were cr...
TL;DR: In this paper, the effect of injection and extraction barriers on FHJ and BHJ organic solar cells is analyzed using drift-diffusion simulations, and the forward current is dominated by the choice of hole-transport layer (HTL) and as donor in vacuum-evaporated multilayer p-i-metal small-molecule solar cells.
Abstract: The effect of injection and extraction barriers on fl at heterojunction (FHJ) and bulk heterojunction (BHJ) organic solar cells is analyzed. The barriers are realized by a combination of p-type materials with HOMOs varying between ‐5.0 and ‐5.6 eV as hole-transport layer (HTL) and as donor in vacuum-evaporated multilayer p-i-metal small-molecule solar cells. The HTL/donor interface can be seen as a model for the infl uence of contacts in organic solar cells in general. Using drift-diffusion simulations we are well able to reproduce and explain the experimental I– V curves qualitatively. In FHJ solar cells the open-circuit voltage ( V oc ) is determined by the donor and is independent of the HTL. In BHJ solar cells, however, V oc decreases if injection barriers are present. This different behavior is caused by a blocking of the charge carriers at a spatially localized donor/acceptor heterojunction, which is only present in the FHJ solar cells. The forward current is dominated by the choice of HTL. An energy mismatch in the HOMOs leads to kinks in the I–V curves in the cases for which V oc is independent of the HTL.
TL;DR: This work fabricated bilayer organic photovoltaic devices with interfacial dipole moments that were selected to align the energy levels at the heterojunction using a simple film-transfer method.
Abstract: The energy-level alignment at the heterojunction critically influences the performance of organic photovoltaic devices. It is now shown that the surface dipole moments of individual organic semiconductor films can be tuned with surface-segregated monolayers before forming bilayer solar cells by a simple film-transfer method.
TL;DR: In this article, the authors demonstrate that the nonideality of the dark characteristics is determined by deeply trapped carriers in the transport-dominating constituent of the donor:acceptor blend, rather than a trap-assisted recombination mechanism.
Abstract: In organic bulk heterojunction solar cells, a deviation of the ideality factor of the dark current from unity is commonly put forward as evidence for the presence of trap-assisted recombination. We demonstrate that the non-ideality of the dark characteristics is determined by deeply trapped carriers in the transport-dominating constituent of the donor:acceptor blend, rather than a trap-assisted recombination mechanism. The light-intensity dependence of the open-circuit voltage confirms the absence of trap-assisted recombination and demonstrates that the dominant recombination mechanism in the investigated polymer:fullerene solar cells is bimolecular. © 2011 American Institute of Physics.
TL;DR: The n-type transition metal oxides (TMO) consisting of molybdenum oxide and vanadium oxide are used as an efficient hole extraction layer (HEL) in heterojunction ZnO/PbS quantum dot solar cells (QDSC) and a 4.4% NREL-certified device based on the MoO(x) HEL is reported with Al as the back contact material.
Abstract: The n-type transition metal oxides (TMO) consisting of molybdenum oxide (MoOx) and vanadium oxide (V2Ox) are used as an efficient hole extraction layer (HEL) in heterojunction ZnO/PbS quantum dot solar cells (QDSC). A 4.4% NREL-certified device based on the MoOx HEL is reported with Al as the back contact material, representing a more than 65% efficiency improvement compared with the case of Au contacting the PbS quantum dot (QD) layer directly. We find the acting mechanism of the hole extraction layer to be a dipole formed at the MoOx and PbS interface enhancing band bending to allow efficient hole extraction from the valence band of the PbS layer by MoOx. The carrier transport to the metal anode is likely enhanced through shallow gap states in the MoOx layer.
TL;DR: Energy band alignments between CdS and Cu2ZnSn(SxSe1−x)4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry as discussed by the authors.
Abstract: Energy band alignments between CdS and Cu2ZnSn(SxSe1−x)4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes.
TL;DR: In this paper, the surface properties of metal oxide photocatalysts are investigated and the importance of surface charge separation and charge trapping at the surface leads to new concepts for engineering surface properties with potentially increased photocatalysis activity.
Abstract: Many metal oxide photocatalysts exhibit strong variations in their photocatalytic activities as a function of their crystallographic surface orientation. In this Perspective possible fundamental reasons for the surface dependent photocatalytic properties are discussed. The majority of the data imply that the differing surface activities for photo-oxidation and -reduction reactions are mainly a consequence of electron and hole diffusion towards different surfaces. This is either due to directional charge carrier diffusion as a result of bulk anisotropies or it is a consequence of differing band bending (or flat band potentials) at the interface of the photocatalyst with its environment. Although the fundamental reason for the surface electronic structure must lie in the surface structure, no correlation between surface chemical properties and photochemical properties has yet been unambiguously determined. The importance of surface charge separation and charge trapping at the surface leads to new concepts for engineering surface properties with potentially increased photocatalytic activity. Consequently, enhancement can be achieved by synthesizing photocatalyst powders that expose surfaces with ‘naturally’ higher photoactivity; or in a proposed approach by modifying surfaces selectively with special surface phases or monolayer heterostructures that enhance charge separation at the surface. In addition, special surface phases with a narrowed band gap may enable visible light activity of otherwise only UV active bulk materials.
TL;DR: In this article, H2 plasma treatments are used during film deposition to improve the passivation of the a-Si:H layers, and 4 cm2 heterojunction solar cells were produced with industry compatible processes, yielding open-circuit voltages up to 725 mV and aperture area efficiencies up to 21%.
Abstract: Silicon heterojunction solar cells have high open-circuit voltages thanks to excellent passivation of the wafer surfaces by thin intrinsic amorphous silicon (a-Si:H) layers deposited by plasma-enhanced chemical vapor deposition. We show a dramatic improvement in passivation when H2 plasma treatments are used during film deposition. Although the bulk of the a-Si:H layers is slightly more disordered after H2 treatment, the hydrogenation of the wafer/film interface is nevertheless improved with as-deposited layers. Employing H2 treatments, 4 cm2 heterojunction solar cells were produced with industry-compatible processes, yielding open-circuit voltages up to 725 mV and aperture area efficiencies up to 21%.
TL;DR: In this article, the formation of heterojunction structure in the V2O5−BiVO4 composite plays an important role in the kinetic behaviors (including separation, transport, and recombination) of photogenerated charges.
Abstract: Macroporous V2O5−BiVO4 composites with a heterojunction structure have been successfully synthesized under the assistance of colloidal carbon spheres. X-ray diffraction, Raman, and X-ray photoelectron spectroscopies reveal that the as-prepared composites are composed of monoclinic BiVO4 and orthorhombic V2O5. The behavior of photogenerated charges in V2O5, BiVO4, and the V2O5−BiVO4 composite have been investigated through surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV) techniques. It is demonstrated that the formation of heterojunction structure in the V2O5−BiVO4 composite plays an important role in the kinetic behaviors (including separation, transport, and recombination) of photogenerated charges. The heterojunction greatly increases the separation extent and the lifetime of the photogenerated charges in the composites.
TL;DR: In this paper, an n-ZO thin-film layer, prepared with an appropriate thickness by low damage deposition, on high quality Cu2O sheets produced by the thermal oxidization of copper sheets, optimal thickness ranges from 30 to 50 nm.
Abstract: High conversion efficiencies were achieved in low cost n–p heterojunction oxide solar cells with an Al-doped ZnO (AZO)/non-doped ZnO (ZO)/Cu2O structure. This achievement was made possible by the formation of an n-ZO thin-film layer, prepared with an appropriate thickness by low damage deposition, on high quality Cu2O sheets produced by the thermal oxidization of copper sheets: n-ZO thin film optimal thickness ranges from 30 to 50 nm. Photovoltaic characteristics such as an open circuit voltage of 0.69 V, a fill factor of 0.55 and a conversion efficiency of 3.83% were attained under simulated AM1.5G solar illumination.
TL;DR: In this paper, a series of terminally dicyanovinyl (DCV)-substituted oligothiophenes, without solubilizing side chains synthesized via a novel convergent approach and their application as electron donors in vacuum-processed m-i p-type planar and p-i n-type bulk heterojunction organic solar cells is described.
Abstract: Efficient synthesis of a series of terminally dicyanovinyl (DCV)-substituted oligothiophenes, DCVnT 1–6, without solubilizing side chains synthesized via a novel convergent approach and their application as electron donors in vacuum-processed m-i-p-type planar and p-i-n-type bulk heterojunction organic solar cells is described. Purification of the products via gradient sublimation yields thermally highly stable organic semiconducting materials in single crystalline quality which allows for X-ray structure analysis. Important insights into the packing features and intermolecular interactions of these promising solar cell materials are provided. Optical absorption spectra and electrochemical properties of the oligomers are investigated and valuable structure–property relationships deduced. Photovoltaic devices incorporating DCVnTs 4–6 showed power conversion efficiencies up to 2.8% for planar and 5.2% for bulk heterojunction organic solar cells under full sun illumination (mismatch corrected simulated AM 1.5G sunlight). The 5.2% efficiency shown here represents one of the highest values ever reported for organic vacuum-deposited single heterojunction solar cells.
TL;DR: This work achieves 13.8% efficiency solar cells by combining carbon nanotubes and Si and doping with dilute HNO(3).
Abstract: Various approaches to improve the efficiency of solar cells have followed the integration of nanomaterials into Si-based photovoltaic devices. Here, we achieve 13.8% efficiency solar cells by combining carbon nanotubes and Si and doping with dilute HNO3. Acid infiltration of nanotube networks significantly boost the cell efficiency by reducing the internal resistance that improves fill factor and by forming photoelectrochemical units that enhance charge separation and transport. Compared to conventional Si cells, the fabrication process is greatly simplified, simply involving the transfer of a porous semiconductor-rich nanotube film onto an n-type crystalline Si wafer followed by acid infiltration.
TL;DR: In this paper, a review of colloidal quantum dot solar cells is presented, where the authors discuss the preparation methods, working concepts, advantages and disadvantages of different device architectures, including Schottky solar cells, depleted heterojunction solar cells and extremely thin absorber solar cells.
TL;DR: In this paper, two vacuum processed single heterojunction organic solar cells with complementary absorption are described and the construction and optimization of tandem solar cells based on the combination of these heterojunctions demonstrated.
Abstract: In this paper, two vacuum processed single heterojunction organic solar cells with complementary absorption are described and the construction and optimization of tandem solar cells based on the combination of these heterojunctions demonstrated. The red-absorbing heterojunction consists of C60 and a fluorinated zinc phthalocyanine derivative (F4-ZnPc) that leads to a 0.1–0.15 V higher open circuit voltage Voc than the commonly used ZnPc. The second heterojunction incorporates C60 and a dicyanovinyl-capped sexithiophene derivative (DCV6T) that mainly absorbs in the green. The combination of both heterojunctions into one tandem solar cell leads to an absorption over the whole visible range of the sun spectrum. Thickness variations of the transparent p-doped optical spacer between both subcells in the tandem solar cell is shown to lead to a significant change in short circuit current density jsc due to optical interference effects, whereas Voc and fill factor are hardly affected. The maximum efficiency η of about 5.6% is found for a spacer thickness of 150-165 nm. Based on the optimized 165nm thick spacer, effects of intensity and angle of illumination, and temperature on a tandem device are investigated. Variations in illumination intensity lead to a linear change in jsc over three orders of magnitude and a nearly constant η in the range of 30 to 310 mW cm−2. Despite the stacked heterojunctions, the performance of the tandem device is robust against different illumination angles: jsc and η closely follow a cosine behavior between 0° and 70°. Investigations of the temperature behavior of the tandem device show an increase in η of 0.016 percentage points per Kelvin between −20 °C and 25 °C followed by a plateau up to 50 °C. Finally, further optimization of the tandem stack results in a certified η of (6.07 ± 0.24)% on (1.9893 ± 0.0060)cm2 (Fraunhofer ISE), i.e., areas large enough to be of relevance for modules.