Robot-Based High-Throughput Engineering of Alcoholic Polymer: Fullerene Nanoparticle Inks for an Eco-Friendly Processing of Organic Solar Cells

Performance and optimization study of selected 4-terminal tandem solar cells

Tandem solar cells owing to their layered structure in which each sub-cell utilizes a certain part of the solar spectrum with reduced thermal losses, are promising applicants to promote the power conversion efficiency beyond the Shockley-Queisser limit of single-junction solar cells. This study delves into the performance and optimization of 4-terminal organic/silicon tandem solar cells through numerical simulations using SCAPS-1D software. The tandem architecture combining organic, perovskite, and silicon materials, shows potential in enhancing light absorption across the solar spectrum with complementary absorption spectra. Through innovative material exploration, optimization techniques are explored to advance the performance boundaries of organic/silicon tandem solar cells. The study employs the Beer-Lambert law to assess the impact of varied physical parameters on tandem solar cell efficiency, aiming to propose optimal configurations. Results indicate a maximum efficiency of 25.86% with P3HT:PC70BM organic active layer (150 nm thickness) and 36.8% with Cs2AgBi0.75Sb0.25Br6 active layer (400 nm thickness) in the studied 4-terminal tandem structures. These findings offer valuable insights into the complex physics of these tandem solar cells, for developing high-performance and commercially practical photovoltaic devices.

Green-Processed Non-Fullerene Organic Solar Cells Based on Y-Series Acceptors

The development of environmentally friendly and sustainable processes for the production of high-performance organic solar cells (OSCs) has become a critical research area. Currently, Y-series electron acceptors are widely used in high-performance OSCs, achieving power conversion efficiencies above 19%. However, these acceptors have large fused conjugated backbones that are well-soluble in halogenated solvents, such as chloroform and chlorobenzene, but have poor solubility in non-halogenated green solvents. To overcome this challenge, recent studies have focused on developing green-processed OSCs that use non-chlorinated and non-aromatic solvents to dissolve bulk-heterojunction photoactive layers based on Y-series electron acceptors, enabling environmentally friendly fabrication. In this comprehensive review, an overview of recent progress in green-processed OSCs based on Y-series acceptors is provided, covering the determination of Hansen solubility parameters, the use of non-chlorinated solvents, and the dispersion of conjugated nanoparticles in water/alcohol. It is hoped that the timely review will inspire researchers to develop new ideas and approaches in this important field, ultimately leading to the practical application of OSCs.

Sub-4 nm mapping of donor-acceptor organic semiconductor nanoparticle composition

We report, for the first time, sub-4 nm mapping of donor : acceptor nanoparticle composition in eco-friendly colloidal dispersions for organic electronics. Low energy scanning transmission electron microscopy (STEM) energy dispersive X-ray spectroscopy (EDX) mapping has revealed the internal morphology of organic semiconductor donor : acceptor blend nanoparticles at the sub-4 nm level. A unique element was available for utilisation as a fingerprint element to differentiate donor from acceptor material in each blend system. Si was used to map the location of donor polymer PTzBI-Si in PTzBI-Si:N2200 nanoparticles, and S (in addition to N) was used to map donor polymer TQ1 in TQ1:PC₇₁BM nanoparticles. For select material blends, synchrotron-based scanning transmission X-ray microscopy (STXM), was demonstrated to remain as the superior chemical contrast technique for mapping organic donor : acceptor morphology, including for material combinations lacking a unique fingerprint element (e.g. PTQ10:Y6), or systems where the unique element is in a terminal functional group (unsaturated, dangling bonds) and can hence be easily damaged under the electron beam, e.g. F on PTQ10 donor polymer in the PTQ10:IDIC donor : acceptor blend. We provide both qualitative and quantitative compositional mapping of organic semiconductor nanoparticles with STEM EDX, with sub-domains resolved in nanoparticles as small as 30 nm in diameter. The sub-4 nm mapping technology reported here shows great promise for the optimisation of organic semiconductor blends for applications in organic electronics (solar cells and bioelectronics) and photocatalysis, and has further applications in organic core-shell nanomedicines.

All-Aqueous, Surfactant-Free, and pH-Driven Nanoformulation Methods of Dual-Responsive Polymer Nanoparticles and their Potential use as Nanocarriers of pH-Sensitive Drugs

All-aqueous, surfactant-free, and pH-driven nanoformulation methods to generate pH- and temperature-responsive polymer nanoparticles (NPs) are described. Copolymers comprising a poly(methyl methacrylate) (PMMA) backbone with a few units of 2-(dimethylamino)ethyl methacrylate (DMAEMA) are solubilized in acidic buffer (pH 2.0) to produce pH-sensitive NPs. Copolymers of different molar mass (2.3-11.5 kg mol^-1 ) and DMAEMA composition (7.3-14.2 mol%) are evaluated using a "conventional" pH-driven nanoformulation method (i.e., adding an aqueous polymer solution (acidic buffer) into an aqueous non-solvent (basic buffer)) and a robotized method for pH adjustment of polymer dispersions. Dynamic light scattering, zeta-potential (ζ), and sedimentation-diffusion analyses suggest the formation of dual-responsive NPs of tunable size (from 20 to 110 nm) being stable for at least 28 days in the pH and temperature intervals from 2.0 to 6.0 and 25 to 50 °C, respectively. Ultraviolet-visible spectroscopic experiments show that these NPs can act as nanocarriers for the pH-sensitive dipyridamole drug, expanding its bioavailability and potential controlled release as a function of pH and temperature. These approaches offer alternative strategies to prepare stimuli-responsive NPs, avoiding the use of harmful solvents and complex purification steps, and improving the availability of biocompatible polymer nanoformulations for specific controlled release of pH-sensitive cargos.

Water-Processed Organic Solar Cell with Efficiency Exceeding 11

Water processing is an ideal strategy for the ecofriendly fabrication of organic photovoltaics (OPVs) and exhibits a strong market-driven demand. Here, we report a state-of-the-art active material, namely PM6:BTP-eC9, for the synthesis of water-borne nanoparticle (NP) dispersion towards ecofriendly OPV fabrication. The surfactant-stripping technique, combined with a poloxamer, facilitates purification and eliminates excess surfactant in water-dispersed organic semiconducting NPs. The introduction of 1,8-diiodooctane (DIO) for the synthesis of surfactant-stripped NP (ssNP) further promotes a percolated microstructure of the polymer and NFA in each ssNP, yielding water-processed OPVs with a record efficiency of over 11%. The use of an additive during water-borne ssNP synthesis is a promising strategy for morphology optimization in NP OPVs. It is believed that the findings in this work will engender more research interest and effort relating to water-processing in preparation of the industrial production of OPVs.

Molecule-to-Material-to-Bio Nanoarchitectonics with Biomedical Fullerene Nanoparticles

Nanoarchitectonics integrates nanotechnology with various other fields, with the goal of creating functional material systems from nanoscale units such as atoms, molecules, and nanomaterials. The concept bears strong similarities to the processes and functions seen in biological systems. Therefore, it is natural for materials designed through nanoarchitectonics to truly shine in bio-related applications. In this review, we present an overview of recent work exemplifying how nanoarchitectonics relates to biology and how it is being applied in biomedical research. First, we present nanoscale interactions being studied in basic biology and how they parallel nanoarchitectonics concepts. Then, we overview the state-of-the-art in biomedical applications pursuant to the nanoarchitectonics framework. On this basis, we take a deep dive into a particular building-block material frequently seen in nanoarchitectonics approaches: fullerene. We take a closer look at recent research on fullerene nanoparticles, paying special attention to biomedical applications in biosensing, gene delivery, and radical scavenging. With these subjects, we aim to illustrate the power of nanomaterials and biomimetic nanoarchitectonics when applied to bio-related applications, and we offer some considerations for future perspectives.

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.

Surfactant Engineering and Its Role in Determining the Performance of Nanoparticulate Organic Photovoltaic Devices

The fabrication of organic photovoltaics (OPVs) from non-hazardous nanoparticulate (NP) inks offers considerable promise for the development of eco-friendly large-scale printed solar modules. However, the typical NP core-shell morphology (driven by the different donor/acceptor affinities for the surfactant used in NP synthesis) currently hinders the photovoltaic performance. As such, surfactant engineering offers an elegant approach to synthesizing a more optimal intermixed NP morphology and hence an improved photovoltaic performance. In this work, the morphology of conventional sodium dodecyl sulfate (SDS) and 2-(3-thienyl) ethyloxybutylsulfonate (TEBS)-stabilized poly(3-hexylthiophene) (P3HT) donor:phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) acceptor NPs is probed using scanning transmission X-ray microscopy, UV-vis spectroscopy, grazing-incidence X-ray diffraction, and scanning electron microscopy. While the SDS-stabilized NPs exhibit a size-independent core-shell morphology, this work reveals that TEBS-stabilized NPs deliver an intermixed morphology, the extent of which depends on the particle size. Consequently, by optimizing the TEBS-stabilized NP size and distribution, NP-OPV devices with a power conversion efficiency that is ∼50% higher on average than that of the corresponding SDS-based NP-OPV devices are produced.

Recent advances in non-fullerene organic photovoltaics enabled by green solvent processing

Solution-processed organic photovoltaic (OPV) as a new energy device has attracted much attention due to its huge potential in future commercial manufacturing. However, so far, most of the studies on high-performance OPV have been treated with halogenated solvents. Halogenated solvents not only pollute the environment, but are also harmful to human health, which will negatively affect the large-scale production of OPV in the future. Therefore, it is urgent to develop low-toxic or non-toxic non-halogen solvent-processable OPV. Compared with conventional fullerene OPVs, non-fullerene OPVs exist with stronger absorption, better-matched energy levels and lower energy loss. Processing photoactive layers with non-fullerenes as the acceptor material has broad potential advantages in non-halogenated solvents. This review introduces the research progress of non-fullerene OPV treated by three different kinds of green solvents as the non-halogenated and aromatic solvent, the non-halogenated and non-aromatic solvent, alcohol and water. Furthermore, the effects of different optimization strategies on the photoelectric performance and stability of non-fullerene OPV are analyzed in detail. The current optimization strategy can increase the power conversion efficiency of non-fullerene OPV processed with non-halogen solvents up to 17.33%, which is close to the performance of processing with halogen-containing solvents. Finally, the commercial potential of non-halogen solvent processing OPVs is discussed. The green solvent processing of non-fullerene-based OPVs will become a key development direction for the future of the OPV industry.

Advanced Control of Drug Delivery for In Vivo Health Applications via Highly Biocompatible Self-Assembled Organic Nanoparticles

The use of nanostructured materials for targeted and controlled delivery of bioactive molecules is an attractive alternative to conventional drug administration protocols, enabling selective targeting of diseased cells, lower administered dosages, and reduced systemic side effects. Although a variety of nanocarriers have been investigated in recent years, electroactive organic polymer nanoparticles present several exciting advantages. Here we demonstrate that thin films created from nanoparticles synthesized from violanthrone-79, an n-type semiconducting organic material, can incorporate and release dexamethasone in vitro in a highly controlled manner. By systematically altering the nanoparticle formation chemistry, we successfully tailored the size of the nanoparticles between 30 and 145 nm to control the initial amount of drug loaded into the organic particles. The biocompatibility of the different particles was tested using live/dead assays of dorsal root ganglion neurons isolated and cultured from mice, revealing that elevated levels of the sodium dodecyl sulfate surfactant used to create the smaller nanoparticles are cytotoxic; however, cell survival rates in nanoparticles larger than 45 nm exceed 86% and promote neurite growth and elongation. By manipulating the electrical stimulus applied to the electroactive nanoparticle films, we show an accelerated rate of drug release in comparison to passive release in aqueous media. Furthermore, pulsing the electrical stimulus was successfully used to selectively switch the accelerated release rate on and off. By combining the tuning of drug loading (through tailored nanoparticle synthesis) and drug release rate (through electrical stimulus protocols), we demonstrate a highly advanced control of drug delivery dosage in a biocompatible delivery vehicle. This work highlights the significant potential of electroactive organic nanoparticles for implantable devices that can deliver corticosteroids directly to the nervous system for the treatment of inflammation associated with neurological disorders, presenting a translatable pathway toward precision nanomedicine approaches for other drugs and diseases.

Preparation, Physical Properties, and Applications of Water-Based Functional Polymer Inks

In this study, water-based functional polymer inks are prepared using different solvent displacement methods, in particular, polymer functional inks based on semiconducting polymer poly(3-hexylthiophene) and the ferroelectric polymer poly(vinylidene fluoride) and its copolymers with trifluoroethylene. The nanoparticles that are included in the inks are prepared by miniemulsion, as well as flash and dialysis nanoprecipitation techniques and we discuss the properties of the inks obtained by each technique. Finally, an example of the functionality of a semiconducting/ferroelectric polymer coating prepared from water-based inks is presented.

Accelerating organic solar cell material's discovery: high-throughput screening and big data

The discovery of novel high-performing materials such as non-fullerene acceptors and low band gap donor polymers underlines the steady increase of record efficiencies in organic solar cells witnessed during the past years. Nowadays, the resulting catalogue of organic photovoltaic materials is becoming unaffordably vast to be evaluated following classical experimentation methodologies: their requirements in terms of human workforce time and resources are prohibitively high, which slows momentum to the evolution of the organic photovoltaic technology. As a result, high-throughput experimental and computational methodologies are fostered to leverage their inherently high exploratory paces and accelerate novel materials discovery. In this review, we present some of the computational (pre)screening approaches performed prior to experimentation to select the most promising molecular candidates from the available materials libraries or, alternatively, generate molecules beyond human intuition. Then, we outline the main high-throuhgput experimental screening and characterization approaches with application in organic solar cells, namely those based on lateral parametric gradients (measuring-intensive) and on automated device prototyping (fabrication-intensive). In both cases, experimental datasets are generated at unbeatable paces, which notably enhance big data readiness. Herein, machine-learning algorithms find a rewarding application niche to retrieve quantitative structure-activity relationships and extract molecular design rationale, which are expected to keep the material's discovery pace up in organic photovoltaics.

Review of Waterborne Organic Semiconductor Colloids for Photovoltaics

Development of carbon neutral and sustainable energy sources should be considered as a top priority solution for the growing worldwide energy demand. Photovoltaics are a strong candidate, more specifically, organic photovoltaics (OPV), enabling the design of flexible, lightweight, semitransparent, and low-cost solar cells. However, the active layer of OPV is, for now, mainly deposited from chlorinated solvents, harmful for the environment and for human health. Active layers processed from health and environmentally friendly solvents have over recent years formed a key focus topic of research, with the creation of aqueous dispersions of conjugated polymer nanoparticles arising. These nanoparticles are formed from organic semiconductors (molecules and macromolecules) initially designed for organic solvents. The topic of nanoparticle OPV has gradually garnered more attention, up to a point where in 2018 it was identified as a "trendsetting strategy" by leaders in the international OPV research community. Hence, this review has been prepared to provide a timely roadmap of the formation and application of aqueous nanoparticle dispersions of active layer components for OPV. We provide a thorough synopsis of recent developments in both nanoprecipitation and miniemulsion for preparing photovoltaic inks, facilitating readers in acquiring a deep understanding of the crucial synthesis parameters affecting particle size, colloidal concentration, ink stability, and more. This review also showcases the experimental levers for identifying and optimizing the internal donor-acceptor morphology of the nanoparticles, featuring cutting-edge X-ray spectromicroscopy measurements reported over the past decade. The different strategies to improve the incorporation of these inks into OPV devices and to increase their efficiency (to the current record of 7.5%) are reported, in addition to critical design choices of surfactant type and the advantages of single-component vs binary nanoparticle populations. The review naturally culminates by presenting the upscaling strategies in practice for this environmentally friendly and safer production of solar cells.

Eco-Friendly Polymer Solar Cells: Advances in Green-Solvent Processing and Material Design

Despite the recent breakthroughs of polymer solar cells (PSCs) exhibiting a power conversion efficiency of over 17%, toxic and hazardous organic solvents such as chloroform and chlorobenzene are still commonly used in their fabrication, which impedes the practical application of PSCs. Thus, the development of eco-friendly processing methods suitable for industrial-scale production is now considered an imperative research focus. This Review provides a roadmap for the design of efficient photoactive materials that are compatible with non-halogenated green solvents (e.g., xylenes, toluene, and tetrahydrofuran). We summarize the recent development of green processing solvents and the processing methods to match with the efficient photoactive materials used in non-fullerene solar cells. We further review progress in the use of more eco-friendly solvents (i.e., water or alcohol) for achieving truly sustainable and eco-friendly PSC fabrication. For example, the concept of water- or alcohol-dispersed nanoparticles made of conjugated materials is introduced. Also, recent important progress and strategies to develop water/alcohol-soluble photoactive materials that completely eliminate the use of conventional toxic solvents are discussed. Finally, we provide our perspectives on the challenges facing the current green processing methods and materials, such as large-area coating techniques and long-term stability. We believe this Review will inform the development of PSCs that are truly clean and renewable energy sources.

Progress in Stability of Organic Solar Cells

The organic solar cell (OSC) is a promising emerging low-cost thin film photovoltaics technology. The power conversion efficiency (PCE) of OSCs has overpassed 16% for single junction and 17% for organic-organic tandem solar cells with the development of low bandgap organic materials synthesis and device processing technology. The main barrier of commercial use of OSCs is the poor stability of devices. Herein, the factors limiting the stability of OSCs are summarized. The limiting stability factors are oxygen, water, irradiation, heating, metastable morphology, diffusion of electrodes and buffer layers materials, and mechanical stress. The recent progress in strategies to increase the stability of OSCs is surveyed, such as material design, device engineering of active layers, employing inverted geometry, optimizing buffer layers, using stable electrodes and encapsulation materials. The International Summit on Organic Photovoltaic Stability guidelines are also discussed. The potential research strategies to achieve the required device stability and efficiency are highlighted, rendering possible pathways to facilitate the viable commercialization of OSCs.

Beyond Ternary OPV: High-Throughput Experimentation and Self-Driving Laboratories Optimize Multicomponent Systems

Fundamental advances to increase the efficiency as well as stability of organic photovoltaics (OPVs) are achieved by designing ternary blends, which represents a clear trend toward multicomponent active layer blends. The development of high-throughput and autonomous experimentation methods is reported for the effective optimization of multicomponent polymer blends for OPVs. A method for automated film formation enabling the fabrication of up to 6048 films per day is introduced. Equipping this automated experimentation platform with a Bayesian optimization, a self-driving laboratory is constructed that autonomously evaluates measurements to design and execute the next experiments. To demonstrate the potential of these methods, a 4D parameter space of quaternary OPV blends is mapped and optimized for photostability. While with conventional approaches, roughly 100 mg of material would be necessary, the robot-based platform can screen 2000 combinations with less than 10 mg, and machine-learning-enabled autonomous experimentation identifies stable compositions with less than 1 mg.

Manipulating nanoscale structure to control functionality in printed organic photovoltaic, transistor and bioelectronic devices

Printed electronics is simultaneously one of the most intensely studied emerging research areas in science and technology and one of the fastest growing commercial markets in the world today. For the past decade the potential for organic electronic (OE) materials to revolutionize this printed electronics space has been widely promoted. Such conviction in the potential of these carbon-based semiconducting materials arises from their ability to be dissolved in solution, and thus the exciting possibility of simply printing a range of multifunctional devices onto flexible substrates at high speeds for very low cost using standard roll-to-roll printing techniques. However, the transition from promising laboratory innovations to large scale prototypes requires precise control of nanoscale material and device structure across large areas during printing fabrication. Maintaining this nanoscale material control during printing presents a significant new challenge that demands the coupling of OE materials and devices with clever nanoscience fabrication approaches that are adapted to the limited thermodynamic levers available. In this review we present an update on the strategies and capabilities that are required in order to manipulate the nanoscale structure of large area printed organic photovoltaic (OPV), transistor and bioelectronics devices in order to control their device functionality. This discussion covers a range of efforts to manipulate the electroactive ink materials and their nanostructured assembly into devices, and also device processing strategies to tune the nanoscale material properties and assembly routes through printing fabrication. The review finishes by highlighting progress in printed OE devices that provide a feedback loop between laboratory nanoscience innovations and their feasibility in adapting to large scale printing fabrication. The ability to control material properties on the nanoscale whilst simultaneously printing functional devices on the square metre scale is prompting innovative developments in the targeted nanoscience required for OPV, transistor and biofunctional devices.

Aqueous-Soluble Naphthalene Diimide-Based Polymer Acceptors for Efficient and Air-Stable All-Polymer Solar Cells

Aqueous-processed all-polymer solar cells (aq-APSCs) are reported for the first time by developing a series of water/ethanol-soluble naphthalenediimide (NDI)-based polymer acceptors [P(NDIDEG-T), P(NDITEG-T), and P(NDITEG-T2)]. Polymer acceptors are designed by using the backbones of NDI-bithiophene and NDI-thiophene in combination with nonionic hydrophilic oligoethylene glycol (OEG) side chains that facilitate processability in water/ethanol mixtures. All three polymers exhibit sufficient solubility (20-50 mg mL^-1) in the aqueous medium. The P(NDIDEG-T) polymer with shorter OEG side chains is the most crystalline with the highest electron mobility, enabling the fabrication of efficient aq-APSCs with the maximum power conversion efficiency (PCE) of 2.15%. Furthermore, these aq-APSCs are fabricated under ambient atmosphere by taking advantage of the eco-friendly aqueous process and, importantly, the devices exhibit outstanding air-stability without any encapsulation, as evident by maintaining more than 90% of the initial PCE in the air after 4 days. According to a double cantilever beam test, the interfacial adhesion properties between the active layer and electron/hole transporting layers were remarkably improved by incorporating the hydrophilic OEG-attached photoactive layer, which hinders the delamination of the constituent layers and prevents the increase of series resistance, ultimately leading to enhanced durability under ambient conditions. The combination of increased device stability and minimal environmental impact of these aq-APSCs demonstrates them to be worthy candidates for continued development of scalable polymer solar cells.

Building intermixed donor–acceptor architectures for water-processable organic photovoltaics

Building intermixed donor–acceptor nanoparticle morphologies by utilising rapid miniemulsion dispersed phase solvent removal to disrupt self-assembly.