Fabrication Of Organic Solar Cells Research Articles

Introduction of Water Treatment in Slot‐Die Coated Organic Solar Cells to Improve Device Performance and Stability

AbstractRecent advances in the development of organic solar cells (OSCs) have produced power conversion efficiency (PCE) of over 19%. Various studies have been conducted on scalable coating methods that are compatible with large‐area production of organic photovoltaic modules. However, it is still difficult to control the bulk heterojunction (BHJ) morphology of the active layer during large‐scale fabrication of OSCs. This study reports a morphology‐controllable strategy in OSCs using water treatment (WT) in the stirring process of the active solution, thus resulting in vortex agitation. The effects of WT and water injection volume are investigated based on three reference cells for the optimization of small‐ and large‐area devices, and the physicochemical and optical properties of the films are compared with those without WT. The thin films with WT exhibit a smoother morphology than those without WT, indicating well‐dispersed donor–acceptor phases. Therefore, enhanced efficiencies of the films are achieved via WT. Furthermore, large‐area solar cell modules with a total effective area of 10 cm2 are fabricated, and they exhibit superior PCEs as high as 11.92% (H‐NF‐DIW10), indicating that the WT method is a simple and effective strategy to fabricate large‐area organic photovoltaic modules.

Microfluidics: Continuous‐Flow Synthesis of Nanoparticle Dispersions for the Fabrication of Organic Solar Cells

AbstractState‐of‐the‐art solvents for the fabrication of organic solar cells are mostly toxic or hazardous. First attempts to deposit light‐harvesting layers from aqueous or alcoholic nanoparticle dispersions instead have been successful on laboratory scale, enabling future eco‐friendly production of organic solar cells. In this work, a scalable high‐throughput continuous‐flow microfluidic system is employed to synthesize surfactant‐free organic semiconductor dispersions by nanoprecipitation. By adjusting the differential speed of the syringe pumps, the concentration of the initial solute and the irradiation of the microfluidic chip, the synthesis can be controlled for tailored dispersion concentrations and nanoparticle sizes. The resulting dispersions are highly reproducible, and the semiconductor inks are stable for at least one year. The synthesis of the dispersions is exemplified on a polymer/fullerene combination with large‐scale availability.

Natural Product Betulin‐Based Insulating Polymer Filler in Organic Solar Cells

Introduction of filler materials into organic solar cells (OSCs) are a promising strategy to improve device performance and thermal/mechanical stability. However, the complex interactions between the state‐of‐the‐art OSC materials and filler require careful selection of filler materials and OSC fabrication to achieve lower cost and improved performance. In this work, the introduction of a natural product betulin‐based insulating polymer as filler in various OSCs is investigated. Donor–acceptor–insulator ternary OSCs are developed with improved open‐circuit voltage (Voc) due to decreased trap‐assisted recombination. Furthermore, filler‐induced vertical phase separation due to mismatched surface energy can strongly affect charge collection at the bottom interface and limit the filler ratio. A quasi‐bilayer strategy is used in all‐polymer systems to circumvent this problem. Herein, the variety of filler materials in OSCs to biomass is broadened, and the filler strategy is made a feasible and promising strategy toward highly efficient, eco, and low‐cost OSCs.

Organic Solar Cells: Electrostatic Stabilization of Organic Semiconductor Nanoparticle Dispersions by Electrical Doping

AbstractOrganic semiconductor nanoparticle dispersions are electrostatically stabilized with the p‐doping agent 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), omitting the need for surfactants. Smallest amounts of F4TCNQ stabilize poly(3‐hexylthiophene) dispersions and reduce the size of the nanoparticles significantly. The concept is then readily transferred to synthesize dispersions from a choice of light‐harvesting benzodithiophene‐based copolymers. Dispersions from the corresponding polymer:fullerene blends are used to fabricate organic solar cells (OSCs). In contrast to the widely used stabilizing surfactants, small amounts of F4TCNQ show no detrimental effect on the device performance. This concept paves the way for the eco‐friendly fabrication of OSCs from nanoparticle dispersions of high‐efficiency light‐harvesting semiconductors by eliminating environmentally hazardous solvents from the deposition process.

Vertically optimized phase separation with improved exciton diffusion enables efficient organic solar cells with thick active layers

The development of organic solar cells (OSCs) with thick active layers is of crucial importance for the roll-to-roll printing of large-area solar panels. Unfortunately, increasing the active layer thickness usually results in a significant reduction in efficiency. Herein, we fabricated efficient thick-film OSCs with an active layer consisting of one polymer donor and two non-fullerene acceptors. The two acceptors were found to possess enlarged exciton diffusion length in the mixed phase, which is beneficial to exciton generation and dissociation. Additionally, layer by layer approach was employed to optimize the vertical phase separation. Benefiting from the synergetic effects of enlarged exciton diffusion length and graded vertical phase separation, an efficiency of 17.31% (certified value of 16.9%) is obtained for the 300 nm-thick OSC, with a short-circuit current density of 28.36 mA cm−2, and a high fill factor of 73.0%. Moreover, the device with an active layer thickness of 500 nm also shows an efficiency of 15.21%. This work provides valuable insights into the fabrication of OSCs with thick active layers.

Low Cost Synthesis and Characterization of Donor P3HT Polymer for Fabrication of Organic Solar Cell

Over the years, the conjugated polymers acts as electron donor material in the active layer of Organic solar cells (OSCs). By altering means of doping, prepare a composite with suitable materials from Poly (p-phenylene vinylene) PPV polymer toPM6 polymer which gives Power conversion efficiency (PCE) can vary from ~ 2% to ~15%. But these are expensive, complicated synthetic procedure and less availability. To overcome this,the conjugated polymer Poly (3-Hexyl Thiophene)(P3HT) synthesized through oxidative coupling of 3-HT monomer and Ferric chloride (FeCl3) as an oxidant which is low cost, available and very easy method of synthesis. We investigated synthesized P3HT material that shows the Fourier Transform Infrared(FTIR) peaks shows that intramolecular interactions from thiophene ring, alkyl chain and polymer chain, FESEM Images reveals morphology consists of condensed layers in micrometer dimensions and Cyclic voltammetry studies gives oxidation and reduction potentials to promote the higher ionization potential of the compound to use as donor material in OSCs.

Gold(III) Porphyrin Was Used as an Electron Acceptor for Efficient Organic Solar Cells.

The widespread use of nonfullerene-based electron-accepting materials has triggered a rapid increase in the performance of organic photovoltaic devices. However, the number of efficient acceptor compounds available is rather limited, which hinders the discovery of new, high-performing donor:acceptor combinations. Here, we present a new, efficient electron-accepting compound based on a hitherto unexplored family of well-known molecules: gold porphyrins. The electronic properties of our electron-accepting gold porphyrin, named VC10, were studied by UV–Vis spectroscopy and by cyclic voltammetry (CV) , revealing two intense optical absorption bands at 500–600 and 700–920 nm and an optical bandgap of 1.39 eV. Blending VC10 with PTB7-Th, a donor polymer, which gives rise to an absorption band at 550–780 nm complementary to that of VC10, enables the fabrication of organic solar cells (OSCs) featuring a power conversion efficiency of 9.24% and an energy loss of 0.52 eV. Hence, this work establishes a new approach in the search for efficient acceptor molecules for solar cells and new guidelines for future photovoltaic material design.

Mutual Diffusion of Model Acceptor/Donor Bilayers under Solvent Vapor Annealing as a Novel Route for Organic Solar Cell Fabrication

The fabrication of bulk heterojunction organic solar cells (OSCs) is primarily based on a phase demixing during solution deposition. This spontaneous process is triggered when, as a result of a decrease in the solvent concentration, interactions between donor and acceptor molecules begin to dominate. Herein, we present that interdiffusion of the same molecules is possible when a bilayers of donors and acceptors are exposed to solvent vapor. Poly(3-hexyl thiophene) (P3HT), and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) were used as donors and two types of fullerene derivatives were used as acceptors: phenyl-C61-butyric acid methyl ester (PC60BM) and phenyl-C71-butyric acid methyl ester (PC70BM), Secondary ion mass spectrometry depth profiling revealed that the interpenetration of donors and acceptors induced by solvent vapor annealing was dependent on solvent vapor and component compatibility. Exposure to chloroform vapor resulted in a complete intermixing of both components. The mutual mixing increased efficiency of inverted solar cells prepared by solvent vapor annealing of model donor/acceptor bilayers. These results provide a new means for mixing incompatible components for the fabrication of organic solar cells.

Recent Applications of Carbon Nanotubes in Organic Solar Cells.

In recent years, carbon-based materials, particularly carbon nanotubes (CNTs), have gained intensive research attention in the fabrication of organic solar cells (OSCs) due to their outstanding physicochemical properties, low-cost, environmental friendliness and the natural abundance of carbon. In this regard, the low sheet resistance and high optical transmittance of CNTs enables their application as alternative anodes to the widely used indium tin oxide (ITO), which is toxic, expensive and scarce. Also, the synergy between the large specific surface area and high electrical conductivity of CNTs provides both large donor-acceptor interfaces and conductive interpenetrating networks for exciton dissociation and charge carrier transport. Furthermore, the facile tunability of the energy levels of CNTs provides proper energy level alignment between the active layer and electrodes for effective extraction and transportation of charge carriers. In addition, the hydrophobic nature and high thermal conductivity of CNTs enables them to form protective layers that improve the moisture and thermal stability of OSCs, thereby prolonging the devices’ lifetime. Recently, the introduction of CNTs into OSCs produced a substantial increase in efficiency from ∼0.68 to above 14.00%. Thus, further optimization of the optoelectronic properties of CNTs can conceivably help OSCs to compete with silicon solar cells that have been commercialized. Therefore, this study presents the recent breakthroughs in efficiency and stability of OSCs, achieved mainly over 2018–2021 by incorporating CNTs into electrodes, active layers and charge transport layers. The challenges, advantages and recommendations for the fabrication of low-cost, highly efficient and sustainable next-generation OSCs are also discussed, to open up avenues for commercialization.

Eco-friendly fabrication of organic solar cells: electrostatic stabilization of surfactant-free organic nanoparticle dispersions by illumination.

Earlier reports have discussed the manifold opportunities that arise from the use of eco-friendly organic semiconductor dispersions as inks for printed electronics and, in particular, organic photovoltaics. To date, poly(3-hexylthiophene) (P3HT) plays an outstanding role since it has been the only organic semiconductor that formed nanoparticle dispersions with sufficient stability and concentration without the use of surfactants. This work elucidates the underlying mechanisms that lead to the formation of intrinsically stable P3HT dispersions and reveals prevailing electrostatic effects to rule the nanoparticle growth. The electrostatic dispersion stability can be enhanced by photo-generation of additional charges, depending on the light intensity and its wavelength. This facile, additive-free process provides a universal handle to also stabilize surfactant-free dispersions of other semiconducting polymers, which are frequently used to fabricate organic solar cells or other optoelectronic thin-film devices. The more generalized process understanding paves the way towards a universal synthesis route for organic nanoparticle dispersions.

A brief review of organic solar cells and materials involved in its fabrication

Organic solar cells are a futuristic system of power generation whose time has come. There is a looming threat of climate change which threatens life on earth as we know it. Also, fossil fuels will run out and will be exhausted in the not so near future. This will create a catastrophe of apocalyptic proportion and hence proper action needs to be taken in order to prevent this scenario from being a reality. An organic solar cell is an active area of research since the early 1970s and materials for the fabrication of organic solar cells are being developed for the past five decades. Both small molecule and polymeric materials have been developed for organic solar cell development. However, there is an issue of efficiency in the materials for organic solar cells. It has struggled to break the 5% energy efficiency barrier. This makes it a challenge for organic solar cells to be a viable option. However, even this is a considerable improvement from the initial 0.01% in the 1970s. Needless to say, a lot of research needs to be done in order to make a feasible organic solar cell a reality. This review looks at the different materials for organic solar cells and the disadvantages of organic solar cells.

Non-fullerene acceptor IDIC based on indacinodithiophene used as an electron donor for organic solar cells: A computational study

In the present paper, a computational study was performed on a planar non-fullerene acceptor (A-D-A) type based on indacenodithiophene (noted IDIC) which is widely used in the fabrication of organic solar cells. The structural and optoelectronic properties were studied using the Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) approaches with different functionals, such as B3LYP, B3PW91, MPW1PW91. The optoelectronic properties such as HOMO and LUMO energy levels, energy gap, λmax were determined and compared with experimental results reported. Charge transfer properties were further characterized through Frontier Molecular Orbitals (FMOs) and Density of States (DOS). Transition density matrix (TDM) and hole&electron isosurface were used to illustrate the behavior of electronic excitation processes as well as the position of electron holes between the donor and acceptor units. In addition, the IDIC compound was tested as an electron donor with the fullerenes and their derivatives as electron acceptors (PCBM). Both electrochemical and photovoltaic properties were investigated and discussed in detailed. The theoretical results indicated that the B3LYP/6-31G(d,p) and its time-dependent counterpart TD-B3LYP/6-31G(d,p) methods are appropriate to predict the optoelectronic properties. The values of the open-circuit voltage (Voc) of IDIC with used acceptors range from 1.165 to 1.665 V. The results of this study showed the high potential of the IDIC compound for integratation into solar cells as an electron donor material and suggested the usefulness of studied materials as promising candidates for photovoltaics.

Influence of PEDOT:PSS Doping on the Performance of Organic Solar Cells

Fabrication of Organic Solar Cells (OSC) using PEDOT:PSS, has been focussed on the formation of the four-layered configuration of : ITO / PEDOT:PSS / P3TH:PC60 BM / LiF with Al metal layers its electrode. The active layer comprised P3TH:PC60 BM, where P3HT formed the donor and PC60 BM the acceptor components. Interestingly, it has been observed that the OSCs fabricated from ethylene glycol doped PEDOT:PSS depicted Power Conversion Efficiency (PCE) of about 2 times more than that of OSCs made from pure PEDOT:PSS. After optimizing process parameters(~ 16% of DMF, ~10% of DMSO, and ~ 12% EG in PEDOT:PSS) and continued loading of doped components, the conductivity reflected a decreasing trend. Such a phenomenon was attributed to an increasing distance between the successive conductive grain/domain, which has been explained based on Atomic Force Microscopy (AFM). Moreover, stress has been made on the inter-junction behavior of carrier transport, particularly the hole conduction mechanism. Further, the perovskite-based solar cell has been compared and discussed to understand material behavior and device performance better.

Fully vacuum-free large-area organic solar cell fabrication from polymer top electrode

Fully vacuum-free and solution-processed large-area organic solar cells (OSCs) were fabricated using a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) polymer top electrode. In addition, to evaluate the scalability of this polymer electrode toward large-scale modules, OSCs with various sized areas were fabricated, and their performance was compared with that of a metal top electrode. As a result, when we increased the area of the OSC from 0.4 to 1.6 cm2, the fill factor (FF) decreased from 40.5 % to 30.3 % and the corresponding photoconversion efficiency (PCE) decreased from 2.0 % to 1.4 % for an OSC with a polymer electrode. The FF decreased from 54.8 % to 44.1 % and essentially had no PCE degradation for the OSC with a metal electrode. Numerical calculations were also conducted to account for the FF and PCE degradation for both electrodes and to match the experimental data. Therefore, the lower FF and PCE of the OSC with a polymer electrode directly resulted from the higher sheet resistance of the polymer electrode and the corresponding higher series resistance.

Exploring the potential of tetraazaacene derivatives as photovoltaic materials with enhanced photovoltaic parameters

AbstractA series of D‐π‐A type molecules have been designed for their potential use in organic photovoltaic devices. Photovoltaic and optoelectronic properties of newly designed molecules have been explored by comparing with a reference molecule R comprising of the central core (2,3,8,9‐tetrakis(thiophen‐2‐ylethynyl)‐5,7,10,12‐tetrakis((trimethylsilyl)ethynyl)pyrazino[2,3‐b]phenazine) and π‐bridge (thiophene). The end groups are (2‐(2‐ethylidene‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1 ylidene)malononitrile), (2‐ethylidenemalonitrile), (methyl 2‐cyanoacrylate) and (3‐methyl‐5‐methylene‐2‐thioxothiazolidin‐4‐one) in the newly designed molecules. Among the investigated molecules M1 and M2 exhibit a broad absorption range of 627 and 626 nm with respect to the reference. All the designed molecules exhibited a lower bandgap as compared to R which indicates a better transfer of electron density from highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO). The reorganization energy values show that all designed molecules have efficient charge transport capability. This study proves that end‐capped acceptor modification is an effective strategy for designing optimistic molecule for high performance future organic solar cells fabrication.

Solution processable graphene derivative used in a bilayer anode with conductive PEDOT:PSS on the non-fullerene PBDB-T:ITIC based organic solar cells

In this work, a semi-transparent, low-cost and easy processable graphene derivative and PH1000 (conductive PEDOT:PSS polymer) based bilayer anode, is presented as a sustainable potential alternative to ITO. The simple mechanical-synthesized graphene derivative was in aqueous-suspension processed (SPG) and drop-coated onto a common glass substrates. The SPG film presents a Raman intensity ratio (ID/IG) of 0.56 and a number of 7 sheets theoretically estimated. Modified PH1000 with dimethyl sulfoxide (DMSO) was spin-coated onto SPG layer. The bilayer anode (SPG/PH1000) exhibits a transmittance, roughness and resistance of 82% (550 nm), 9 nm and 226 Ω/sq, respectively. The bilayer alternative electrode is used in the manufacture of organic solar cells (OSCs) based on the non-fullerene PBDB-T:ITIC active layer. Average power conversion efficiency (PCE) of 8.3% (best 8.6%) is attained for control devices (using ITO as anode) and 4.0% (best 4.2%) for devices with the alternative SPG/PH1000 bilayer anode. For OSCs fabrication, a vacuum free deposited top electrode Field’s metal (FM, an eutectic alloy of Bi 32.5%, In 51% and Sn 16.5%, with a melting point above 62°C) was used.

Pyridine End-Capped Polymer to Stabilize Organic Nanoparticle Dispersions for Solar Cell Fabrication through Reversible Pyridinium Salt Formation.

Bulk-heterojunction nanoparticle dispersions in water or alcohol can be employed as eco-friendly inks for the fabrication of organic solar cells by printing or coating. However, one major drawback is the need for stabilizing surfactants, which facilitate nanoparticle formation but later hamper device performance. When surfactant-free dispersions are formulated, a strong limitation is imposed by the dispersion concentration due to the tendency of nanoparticles to aggregate. In this work, pyridine end-capped poly(3-hexylthiophene) (P3HT-Py) is synthesized and included as an additive for the stabilization of P3HT:indene-C60 bis-adduct (ICBA) nanoparticle dispersions. In the presence of acetic acid (AcOH), a surface-active pyridinium acetate end-capped P3HT ion pair, P3HT-PyH+AcO-, is formed which effectively stabilizes the dispersion and hence allows the formation of dispersions with smaller nanoparticle sizes and higher concentrations of up to 30 mg/mL in methanol. The dispersions exhibit an enhanced shelf-lifetime of at least 60 days at room temperature. After the deposition of light-harvesting layers from the nanoparticle dispersions, the ion-pair formation is reversed at elevated temperatures leading to regeneration of P3HT-Py and AcOH. The AcOH evaporates from the active layer, while the performance of the corresponding solar cells is not affected by the residual P3HT-Py in the devices. Enhanced nanoparticle stability is achieved with only 0.017 wt % pyridine in the P3HT/ICBA formulation.

Green Inks for the Fabrication of Organic Solar Cells: A Case Study on PBDTTPD:PC61BM Bulk Heterojunctions

Nonhalogenated ecofriendly solvents are an important asset to avoid costly safety precautions during the fabrication of organic solar cells by printing. Yet, in the past, the quest for suitable nontoxic solvents has widely used empirical approaches. Herein, a comprehensive solubility study is rolled out embracing Hansen solubility parameters (HSPs), tailoring of binary solvents and rational choices of solvent additives, identifying ecofriendly solvents or solvent combinations for the deposition of poly‐benzodithophene‐thienopyrroledione (PBDTTPD)/fullerene thin‐film blends. A particular challenge is the low polymer solubility even in common halogenated solvents. Following the HSPs, initially, a list of suitable solvent candidates is identified which are tested toward their applicability in solar cell fabrication. Among the shortlisted solvents, significant differences between p‐xylene and o‐xylene are observed, which can be compensated using solvent additives. The ecofriendly green solvent eucalyptol in combination with benzaldehyde and p‐anisaldehyde in a ternary solvent mixture gives rise to decent solar cell performances. Solar cells are produced with power conversion efficiencies matching those conventionally fabricated from state‐of‐the‐art halogenated solvents comprising chlorobenzene and chloronaphthalene. Notably, the Hansen solubility approach provides an initial choice of solvents, but comes to its limits in predicting the best micromorphology formation, or if solvents react with the organic semiconductors.

Pressure and thermal annealing effects on the photoconversion efficiency of polymer solar cells

This paper presents the results of experimental and theoretical studies of the effects of pressure and thermal annealing on the photo-conversion efficiencies (PCEs) of polymer solar cells with active layers that consist of a mixture of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative (6,6)-phenyl-C61-butyric acid methyl ester. The PCEs of the solar cells increased from ∼2.3% (for the unannealed devices) to ∼3.7% for devices annealed at ∼150 °C. A further increase in thermal annealing temperatures (beyond 150 °C) resulted in lower PCEs. Further improvements in the PCEs (from ∼3.7% to ∼5.4%) were observed with pressure application between 0 and 8 MPa. However, a decrease in PCEs was observed for pressure application beyond 8 MPa. The improved performance associated with thermal annealing is attributed to changes in the active layer microstructure and texture, which also enhance the optical absorption, mobility, and lifetime of the optically excited charge carriers. The beneficial effects of applied pressure are attributed to the decreased interfacial surface contacts that are associated with pressure application. The implications of the results are then discussed for the design and fabrication of organic solar cells with improved PCEs.

Printable and Semitransparent Nonfullerene Organic Solar Modules over 30 cm2 Introducing an Energy-Level Controllable Hole Transport Layer.

For the commercialization of organic solar cells (OSCs), the fabrication of large-area modules via a solution process is important. The fabrication of OSCs via a solution process using a nonfullerene acceptor (NFA)-based photoactive layer is limited by the energetic mismatch and carrier recombination, reducing built-in potential and effective carriers. Herein, for the fabrication of high-performance NFA-based large-area OSCs and modules via a solution process, hybrid hole transport layers (h-HTLs) incorporating WO3 and MoO3 are developed. The high bond energies and electronegativities of W and Mo atoms afford changes in the electronic properties of the h-HTLs, which can allow easy control of the energy levels. The h-HTLs show matching energy levels that are suitable for both deep and low-lying highest occupied molecular orbital energy level systems with a stoichiometrically small amount of oxygen vacancies (forming W6+ and Mo6+ from the W5+ and Mo5+), affording high conductivity and good film forming properties. With the NFA-based photoactive layer, a large-area module fabricated via the all-printing process with an active area over 30 cm2 and a high power conversion efficiency (PCE) of 8.1% is obtained. Furthermore, with the h-HTL, the fabricated semitransparent module exhibits 7.2% of PCE and 22.3% of average visible transmittance with high transparency, indicating applicable various industrial potentials.