Active Layer Of Solar Cell Research Articles

Energy Level Modification with Carbon Dot Interlayers Enables Efficient Perovskite Solar Cells and Quantum Dot Based Light‐Emitting Diodes

AbstractControlling the transport and minimizing charge carrier trapping at interfaces is crucial for the performance of various optoelectronic devices. Here, how electronic properties of stable, abundant, and easy‐to‐synthesized carbon dots (CDs) are controlled via the surface chemistry through a chosen ratio of their precursors citric acid and ethylenediamine are demonstrated. This allows to adjust the work function of indium tin oxide (ITO) films over the broad range of 1.57 eV, through deposition of thin CD layers. CD modifiers with abundant amine groups reduce the ITO work function from 4.64 to 3.42 eV, while those with abundant carboxyl groups increase it to 4.99 eV. Using CDs to modify interfaces between metal oxide (SnO2 and ZnO) films and active layers of solar cells and light‐emitting diodes (LEDs) allows to significantly improve their performance. Power conversion efficiency of CH3NH3PbI3 perovskite solar cells increases from 17.3% to 19.5%; the external quantum efficiency of CsPbI3 perovskite quantum dot LEDs increases from 4.8% to 10.3%; and that of CdSe/ZnS quantum dot LEDs increases from 8.1% to 21.9%. As CD films are easily fabricated in air by solution processing, the approach paves the way to a simplified manufacturing of large‐area and low‐cost optoelectronic devices.

Air-processed active-layer of organic solar cells investigated by conducting AFM for precise defect detection.

Atmospheric processing of organic solar cells (OSCs) has already emerged and will be a challenge to emulate with the existing market leaders in terms of overall cost reduction and large scale production. However, the presence of defects in the active layer of OSC needs to be identified effectively to minimize the performance degradation involved. In this work, conventional bulk-heterojunction (BHJ) OSCs are fabricated entirely in air having an efficiency (η) up to 4.0% using P3HT and PC61BM as the donor and acceptor, respectively. The devices have exhibited reasonable degradation of performance parameters with aging time and uninterrupted illumination during characterization in ambient air. This visible degradation was as expected because of environmental oxygen and moisture penetration into the photoactive layer through the defects, which can be prevented by immediate encapsulation. Conducting AFM is utilized here to visualize these defects more prominently, which are impossible to see in typical AFM topography. Overall, significant development of atmospheric processing of BHJ OSCs is made, and performance stability is also studied to bring down the fabrication costs in the near future.

Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells.

Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers.

Using Solubility Parameters to Model More Environmentally Friendly Solvent Blends for Organic Solar Cell Active Layers.

To facilitate industrial applications, as well as for environmental and health purposes, there is a need to find less hazardous solvents for processing the photoactive layer of organic solar cells. As there are vast amounts of possibilities to combine organic solvents and solutes, it is of high importance to find paths to discriminate among the solution chemistry possibilities on a theoretical basis. Using Hansen solubility parameters (HSP) offers such a path. We report on some examples of solvent blends that have been found by modelling HSP for an electron donor polymer (TQ1) and an electron acceptor polymer (N2200) to match solvent blends of less hazardous solvents than those commonly used. After the theoretical screening procedure, solubility tests were performed to determine the HSP parameters relevant for the TQ1:N2200 pair in the calculated solvent blends. Finally, thin solid films were prepared by spin-coating from the solvent blends that turned out to be good solvents to the donor-acceptor pair. Our results show that the blend film morphology prepared in this way is similar to those obtained from chloroform solutions.

Narrow Emission from Rb3Sb2I9 Nanoparticles

AbstractMetal halide perovskites have gained attention for their optoelectronic properties and are employed as the active layer in solar cells, light‐emitting diodes, and photodetectors. However, the use of lead in the best‐performing perovskite devices may limit their wider application. Prior reports of lead‐free perovskite nanoparticles have exhibited linewidths more than twice as wide as their lead‐halide counterparts, limiting their attainable color gamut. Here the solution synthesis of lead‐free Rb3Sb2I9 nanoplatelets and single crystals is reported; the single crystals exhibit broad (full‐width at half‐maximum (FWHM) = 75 nm) photoluminescence centered at 635 nm, while the nanoplatelets exhibit narrow emission (FWHM = 21 nm) at 512 nm. The photoluminescence quantum yield of both the single crystals and nanoplatelets is low and the present demonstration of the narrowest emission among all lead‐free perovskites reported to date motivates further study of how these and related materials can achieve further‐enhanced brightness.

Optical simulation and geometrical optimization of P3HT/GaAs nanowire hybrid solar cells for maximal photocurrent generation via enhanced light absorption

The implications of using the combination of inorganic and organic materials in the active layer of solar cells have motivated researchers to find a new pathway for flexible, low cost, and highly efficient future generation solar cells. III-V material based nanowires (NWs) with subwavelength scale diameters have shown excellent light harvesting and charge transport properties and can be easily combined with organic polymer materials and thin substrates to design hybrid solar cells (HSCs). To obtain optimum design requirements for GaAs nanowire array (NWA) HSCs, an optical simulation of poly(3-hexylthiophene) P3HT/ GaAs (NWA) hybrid solar cell is investigated using finite-difference-time-domain (FDTD) method. In comparison to planar substrate, P3HT coated NWA have shown superior optical properties owing to its intrinsic anti-reflection, broad absorption spectra, and efficient excitation of resonance modes. A steady improvement in light absorption of P3HT/GaAs NWA HSCs is observed as the polymer coating thickness increased up to a certain limit and beyond which there is a significant degradation in the exciton generation. The geometrical parameters like diameter (D) of NW and filling ratio or periodicity are also optimized to achieve superior light absorption and maximum short circuit current density (Jsc). Under AM1.5G illumination, maximum photocurrent obtained for optimized structure with conformal coating of P3HT is almost 12% and 15% higher than its fully infiltrated and uncoated counterparts respectively

The Thermomechanical Properties of Thermally Evaporated Bismuth Triiodide Thin Films

Bismuth triiodide (BiI3) has been studied in recent years with the aim of developing lead-free semiconductors for photovoltaics. It has also appeared in X-ray detectors due to the high density of the Bismuth element. This material is attractive as an active layer in solar cells, or may be feasible for conversion into perovskite-like material (MA3Bi2I9), being also suitable for photovoltaic applications. In this study, we report on the thermomechanical properties (stress, hardness, coefficient of thermal expansion, and biaxial and reduced Young’s moduli) of BiI3 thin films deposited by thermal evaporation. The stress was determined as a function of temperature, adopting the thermally induced bending technique, which allowed us to extract the coefficient of thermal expansion (31 × 10−6 °C−1) and Young’s biaxial modulus (19.6 GPa) for the films. Nanohardness (~0.76 GPa) and a reduced Young’s modulus of 27.1 GPa were determined through nanoindentation measurements.

The power conversion efficiency optimization of the solar cells by doping of (Au:Ag) nanoparticles into P3HT:PCBM active layer prepared with chlorobenzene and chloroform solvents

We report to enhance the power conversion efficiency of organic solar cells by embedding of (Au:Ag) nanoparticles (NPs) into P3HT:PCBM active layer of the organic solar cells. Furthermore, the effect of solvents based on chlorobenzene and chloroform on the P3HT:PCBM active layer has been investigated for comparison. As known, the performance of organic solar cells based on the blend of regioregular P3HT:PCBM is strongly influenced by blend composition. For this purpose, ITO/PEDOT:PSS/P3HT:PCBM/(Au:Ag)NPs/LiF/Al quaternary hybrid solar cells were fabricated. Absorption, AFM, SEM and XRD measurements of the quaternary hydride active layers prepared with chlorobenzene (CB) and chloroform (CF) solvents were obtained. The optical energy band gap of the hybrid active layer was calculated. The highest PCE values were obtained for 1.2% Au: 0.3% Ag NPs ratios and the study has been focused on these values. (Au:Ag) NPs in the active layer increased the power conversion efficiency (PCE) of the device from 2.11% to 3.29% and to 2.27% for prepared with CB and CF solvents, respectively. This increase was explained by the scatter of the incident light from the NPs and an enhancement of light absorption in the active layer of the solar cell, increasing the optical path distance.

Multiscale modeling of active layer of hybrid organic-inorganic solar cells for photovoltaic applications by means of density functional theory and integral equation theory of molecular liquids

Photovoltaic devices convert solar energy into electricity and are promising candidates to reduce carbon emission while providing an alternative way to meet increasing demand in energy consumption. In recent years, organic or hybrid organic-inorganic photovoltaic devices demonstrate steady increase in performance and stability and a promising tendency toward the low production cost. To make them attractive for commercial production, however, a deep understanding and ability to predict physical, chemical and electrochemical processes occurring in photovoltaic conversion layer is needed. Here, we present multiscale modeling of electronic and structural properties of hybrid organic-inorganic perovskites (OIP) of the type CH3NH3PbX3, X = Br, Cl, I, in contact with organic molecules of P3BT, P3HT, or SQ02, including adsorption on inorganic substrates of TiO2. Our methodology is based on Density Functional Theory (DFT) and integral equation theory of molecular liquids in the Reference Interaction Site Model (RISM). We apply it to study the photovoltaic thin film nanomorphology and determine the key factors affecting the performance of OIP-based bulk heterojunction solar cells through their influence on charge separation, charge transport and recombination losses in donor-acceptor blends. These factors include chemical composition of heterojunctions and mutual orientation of molecules on the border of the donor-acceptor or donor-acceptor-substrate systems. Since the formation of thin active layer of solar cells occurs in fluidic phase, we also provide a detailed microscopic insight into the organization of solvent molecules in the solvation shell structure and their contribution to the solvation thermodynamics. In total, these properties define charge transfer processes from donor to acceptor and are utilized in development of new generation organic and hybrid organic-inorganic solar cells. The calculated nanoscale morphologies serve as a guide in rational design of organic or hybrid photovoltaics.

Role of surface defects on the adsorption of poly(9-vinylcarbazole) on TiO2 using the monomer as a donor:acceptor model

Abstract In this report, we studied the interaction between 9-vinylcarbazole (VK) –i.e. the monomer of poly(9-vinylcarbazole) (PVK)- and a TiO2 (101) surface in order to shed some light in the interface phenomena of this promising fullerene-free donor:acceptor system as active layer for solar cells. Since the role of the TiO2 surface defects is the main concern of our study, we proceeded to simulate the adsorption of the molecule on TiO2 with oxygen or titanium atom vacancies and without any defect. All these systems were studied using First Principles calculations, utilizing Density Functional Theory (DFT). The adsorption energy of the VK monomer-TiO2 systems was favorable in all cases. The presence of vacancies in the TiO2 surface yielded modifications in the electronic properties: the difference between the LUMO level of VK and the conduction band of TiO2-O surface is only ~0.2 eV, thus allowing to infer a decrease in the energy barrier associated to the injection of electrons from VK monomer towards the TiO2-O surface. The charge density differences in all systems also revealed that the donor:acceptor model is plausible and concurs with previous results, suggesting promising features for potential application as a donor:acceptor systems in fullerene-free solar cells.

Optimization of rotation speed for CuSCN hole transport layer in perovskite solar cell using spin coating

Organometal lead halide has gained immense popularity as solar cell active layer due to their unique optical characteristic, low cost, and simple fabrication technique. Transport layer is important component to maximize overall performance of perovskite solar cell. Inorganic CuSCN have good transparency and high hole mobility as p-type transport layer for perovskite solar cell. In this work, we investigated the effect of rotational speed on spin coating to grow CuSCN thin film. Rotational speed is ranging from 1000 rpm to 4000 rpm. The best performing devices is when CuSCN layer deposited at 2000 rpm with VOC 0.96 V, ISC 5.29 mA, and FF 0.48.

The Influence of Embedded Plasmonic Nanostructures on the Optical Absorption of Perovskite Solar Cells

The interaction of light with plasmonic nanostructures can induce electric field intensity either around or at the surface of the nanostructures. The enhanced intensity of the electric field can increase the probability of light absorption in the active layer of solar cells. The absorption edge of perovskite solar cells (PSCs), which is almost 800 nm, can be raised to higher wavelengths with the help of plasmonic nanostructures due to their perfect photovoltaic characteristics. We placed plasmonic nanoparticles (NPs) with different radii (20–60 nm) within the bulk of the perovskite solar cell and found that the Au nanoparticles with a radius of 60 nm increased the absorption of the cell by 20% compared to the bare one without Au nanoparticles. By increasing the radius of the nanoparticles, the total absorption of the cell will increase because of the scattering enhancement. The results reveal that the best case is the PSC with the NP radius of 60 nm.

Present Research Progress of Sn Halide Perovskite Solar Cells

As a kind of photoelectric material with high performance, perovskite has drawn wide attention. Since its first application as active layer in solar cell in 2009, the efficiency of perovskite solar cell (PSC) has been raised from 3.8% to 23.3%. As the most efficient Pb-free PSC, Sn halide PSCs attract much attention recently. This review briefly introduces the principle of PSCs, summarizes the methods to improve Sn halide PSCs’ efficiency and makes some outlook of the future of this field.

Optical and structural properties of Cu2O thin film as active layer in solar cells prepared by DC reactive magnetron sputtering

Optical and structural properties of Cu2O thin film as active layer in solar cells prepared by DC reactive magnetron sputtering

Impedance analysis of perovskite solar cells: a case study

Metal halide perovskites are mixed electronic–ionic semiconductors with an extraordinarily rich optoelectronic behavior and the capability to function very efficiently as active layers in solar cells, with a record efficiency surpassing 23% nowadays.

Binary metal zinc-lead perovskite built-in air ambient: Towards lead-less and stable perovskite materials

Organo-metal halide perovskites are promising new-generation photovoltaic materials owing to their efficient electrical/optical characteristics. Despite having high efficiency, perovskites are toxic due to the presence of lead and instable in air ambient. Therefore, the toxicity and instability call for more efforts in this area. Here, methylammonium-zinc-lead iodide (MAZn0.2Pb0.8I3) is synthesized in air ambient as lead-less and more stable perovskite material for applying as the active layer of solar cells. 1.65 eV optical band gap and 51 nm minority carrier diffusion length (Ldiff) have been obtained with the help of UV–Visible spectroscopy (UV–Vis) and steady-state photocarrier grating (SSPG) technique respectively. Structural, chemical bonding and surface studies are done by X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR) and Field Emission Scanning Electron Microscope (FESEM) respectively. The sample has been stored in dark air ambient with average relative humidity of 45% at room temperature (27 °C) for 60 days and the properties of 60 days aged sample is investigated and compared with characteristics of 60 days aged MAPbI3. The results confirm MAZn0.2Pb0.8I3 is more stable than MAPbI3.

Energy transfer in hybrid optoelectronic structures between perovskite nanocrystals and an organic matrix

Solution-processed hybrid perovskite materials are attracting considerable attention as active layers of solar cells and hybrid light-emitting diodes (LEDs). Introducing perovskite CsPbBr3 nanocrystals (NCs) into light-emitting polymer (MEH-PPV) matrix can improve the processability and stability of such hybrid LEDs. In this work we investigate experimentally and consider theoretically the nonradiative excitation energy transfer from perovskite CsPbBr3 NCs to organic conjugated polymer MEH-PPV matrix along with experimental investigation of optical properties of such MEH-PPV:CsPbBr3 hybrid thin film structures. The theoretical analysis is carried out based on the Förster theory. The relative photoluminescence (PL) intensity of the MEH-PPV matrix is calculated as a function of the embed CsPbBr3 NC concentration. The decrease of the PL intensity with the increase of the CsPbBr3 NC concentration is found both theoretically and experimentally. It was found that the PL decay obtained experimentally is stronger with respect to that found theoretically. The reasons for the quantitative distinctions between the experimental data and as a result of the theoretical consideration are discussed.

Novel design of plasmonic and dielectric antireflection coatings to enhance the efficiency of perovskite solar cells

Recently, nanostructured plasmonic antireflection coatings emerge as a solution to minimize reflection in solar cells over a wideband. However, metals have large light absorption coefficient, making this solution non-reliable for efficient large-scale production. On the other hand, all dielectric antireflection coatings are considered as promising alternative due to the lower losses and easier assembly, especially for third generation photovoltaics such as perovskite solar cells. Herein, we report a first principles methodology for selecting and comparing optimally nanostructured antireflective coatings for enhancing the efficiency of perovskite solar cells based on Mie theory. The first part of the method includes studying absorption and scattering cross sections of five nanostructures and identifying the role of magnetic and electric dipoles. Accordingly, dimensions of each nanostructure that maximizes light coupling to the solar cell active layer was identified. The second part comprises the study of the coupling effect between closed nanostructures. Using three-dimensional finite element method optical and electrical model, periodicity and dimensions of the proposed nanostructures with the highest generated photocurrent were identified. The results showed 15% enhancement in short circuit current (Jsc) over the entire wavelength band, and up to 27% in narrow band spectrum compared to planar perovskite solar cells.

Alkyl Branching Position in Diketopyrrolopyrrole Polymers: Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells

Diketopyrrolopyrrole (DPP)-based donor–acceptor copolymers have gained a significant amount of research interest in the organic electronics community because of their high charge carrier mobilities in organic field-effect transistors (OFETs) and their ability to harvest near-infrared (NIR) photons in solar cells. In this study, we have synthesized four DPP-based donor–acceptor copolymers with variations in the donor unit and the branching point of the solubilizing alkyl chains (at the second or sixth carbon position). Grazing incidence wide-angle X-ray scattering (GIWAXS) results suggest that moving the branching point further away from the polymer backbone increases the tendency for aggregation and yields polymer phases with a higher degree of crystallinity (DoC). The polymers were blended with PC70BM and used as active layers in solar cells. A careful analysis of the energetics of the neat polymer and blend films reveals that the charge-transfer state energy (ECT) of the blend films lies exceptionally c...

In-Plane Pathways Facilitate Out-of-Plane Charge Transport in Organic Solar Cell Active Layers

Solution-processed organic bulk heterojunctions are promising for enabling low-cost, lightweight, and mechanically flexible solar cells. While the nanostructured interpenetrating donor–acceptor morphology in bulk heterojunctions leads to efficient charge photogeneration, the locally varying composition, crystallinity, and electrical connectivity result in a complex landscape for charge transport. This work examines the structural features that govern out-of-plane charge transport in a high-performance small molecule:fullerene organic photovoltaic system, 7,7-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b]dithiophene-2,6-diyl)bis(6-fluoro-4-(5-hexyl-[2,2-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole) (p-DTS(FBTTh2)2) blended with phenyl-C71-butyric acid methyl ester (PC71BM). Active layer composition and degree of donor–acceptor phase separation were systematically varied and characterized electrically by conductive atomic-force-microscope-based charge carrier mobility mapping and structurally by grazing incid...