Printing fabrication of large-area non-fullerene organic solar cells

Conjugated backbone optimization of an all-fused-ring acceptor for efficient and stable organic solar cells

Three all-fused-ring acceptors with different conjugated backbone are designed as acceptor materials for organic solar cells. It is found that the horizontally extended conjugation of all-fused-ring acceptors leads to better photovoltaic performance compared to the vertically extended analogue. The results provide a guideline for designing high-performance and stable all-fused-ring acceptor materials.

A theoretical investigation for improving the performance of non-fullerene organic solar cells through side-chain engineering of BTR non-fused-ring electron acceptors

In the current quantum chemical study, indacenodithiophene donor core-based the end-capped alterations of the reference chromophore BTR drafted eight A2-A1-D-A1-A2 type small non-fullerene acceptors. All the computational simulations were executed under MPW1PW91/6-31G (d, p) level of DFT. The UV-Vis absorption, open circuit voltage, electron affinity, ionization potential, the density of states, reorganization energy, orbital analysis, and non-covalent interactions were studied and compared with BTR. Several molecules of our modeled series BT1-BT8 have shown distinctive features that are better than those of the BTR. The open circuit voltage (VOC) of BT5 has a favorable impact, allowing it to replace BTR in the field of organic solar cells. The charge carrier motilities for proposed molecules generated extraordinary findings when matched to the reference one (BTR). Further charge transmission was confirmed by creating the complex with a PM6 donor molecule. The remarkable dipole moment contributes to the formation of non-covalent bond interactions with chloroform, resulting in superior charge mobility. Based on these findings, it can be said that every tailored molecule has the potential to surpass chromophore molecule (BTR) in OSCs. So, all tailored molecules may enhance the efficiency of photovoltaic cells due to the involvement of potent terminal electron-capturing acceptor2 moieties. Considering these obtained results, these newly presented molecules can be regarded for developing efficient solar devices in the future.

Unveiling the Impact of Light-Induced Acceptor-Generated ROS on Device Stability in Organic Photovoltaics

The intrinsic stability of the acceptor is a crucial component of the photovoltaic device stability. In this study, we investigated the efficiency and stability of the nonfused-ring acceptors LC8 and BC8 under indoor light conditions. Interestingly, we found that devices based on BC8 with terminal side chains exhibited a higher indoor efficiency and stability. Through accelerated aging experiments, we discovered that the acceptors generate singlet oxygen under light exposure with BC8 demonstrating lower levels of ROS compared to LC8. We attribute this difference to the modulation of the acceptor aggregation orientation. Furthermore, the generated reactive oxygen species (ROS) further deteriorate the acceptor structure, and this phenomenon is also observed in high-efficiency acceptor structures, such as Y6. Our research reveals important mechanisms of acceptor photo-oxidation processes, providing a theoretical basis for enhancing the intrinsic stability of acceptors.

Modular slot-die coater for in situ grazing-incidence x-ray scattering experiments on thin films

Multimodal in situ experiments during slot-die coating of thin films pioneer the way to kinetic studies on thin-film formation. They establish a powerful tool to understand and optimize the formation and properties of thin-film devices, e.g., solar cells, sensors, or LED films. Thin-film research benefits from time-resolved grazing-incidence wide- and small-angle x-ray scattering (GIWAXS/GISAXS) with a sub-second resolution to reveal the evolution of crystal structure, texture, and morphology during the deposition process. Simultaneously investigating optical properties by in situ photoluminescence measurements complements in-depth kinetic studies focusing on a comprehensive understanding of the triangular interdependency of processing, structure, and function for a roll-to-roll compatible, scalable thin-film deposition process. Here, we introduce a modular slot-die coater specially designed for in situ GIWAXS/GISAXS measurements and applicable to various ink systems. With a design for quick assembly, the slot-die coater permits the reproducible and comparable fabrication of thin films in the lab and at the synchrotron using the very same hardware components, as demonstrated in this work by experiments performed at Deutsches Elektronen-Synchrotron (DESY). Simultaneous to GIWAXS/GISAXS, photoluminescence measurements probe optoelectronic properties in situ during thin-film formation. An environmental chamber allows to control the atmosphere inside the coater. Modular construction and lightweight design make the coater mobile, easy to transport, quickly extendable, and adaptable to new beamline environments.

Interface Engineering for Highly Efficient Organic Solar Cells

Organic solar cells (OSCs) have made dramatic advancements during the past decades owing to the innovative material design and device structure optimization, with power conversion efficiencies surpassing 19% and 20% for single-junction and tandem devices, respectively. Interface engineering, by modifying interface properties between different layers for OSCs, has become a vital part to promote the device efficiency. It is essential to elucidate the intrinsic working mechanism of interface layers, as well as the related physical and chemical processes that manipulate device performance and long-term stability. In this article, the advances in interface engineering aimed to pursue high-performance OSCs are reviewed. The specific functions and corresponding design principles of interface layers are summarized first. Then, the anode interface layer, cathode interface layer in single-junction OSCs, and interconnecting layer of tandem devices are discussed in separate categories, and the interface engineering-related improvements on device efficiency and stability are analyzed. Finally, the challenges and prospects associated with application of interface engineering are discussed with the emphasis on large-area, high-performance, and low-cost device manufacturing.

Non-Covalent Interaction Enhancement on Active/Interfacial Layers via Two-Dimensional Vermiculite Doping for Efficient Organic Solar Cells

Interface modification plays an important role in improving the power conversion efficiency (PCE) of organic solar cells (OSCs). However, the low non-covalent interaction between the cathode interface layer (CIL) and nonfullerene acceptor (NFA) directly affects the charge collection of OSCs. Here, the non-covalent interaction between the CIL and NFA is enhanced by introducing the 2D vermiculite (VML) in the poly(9,9-bis(3'-(N,N-dimethyl)-Nethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) dibromide (PFN-Br) interface layer to form an efficient electron transport channel. As a result, the electron extraction efficiency from the active layer to the CIL is increased, and the PCE of OSCs based on PBDB-T:ITIC is boosted from 10.87% to 12.89%. In addition, the strategy of CIL doping VML is proven to be universal in different CIL materials, for which the PCE is boosted from 10.21% to 11.57% for OSCs based on PDINN and from 9.82% to 11.27% for OSCs based on PNDIT-F3N. The results provide a viable option for designing efficient CIL for high-performance non-fullerene OSCs, which may promote the commercialization of OSCs.

Solution Sequential Deposition Pseudo-Planar Heterojunction: An Efficient Strategy for State-of-Art Organic Solar Cells

Organic solar cells (OSCs) are considered as a promising new generation of clean energy. Bulk heterojunction (BHJ) structure has been widely employed in the active layer of efficient OSCs. However, precise regulation of morphology in BHJ is still challenging due to the competitive coupling between crystallization and phase separation. Recently, a novel pseudo-planar heterojunction (PPHJ) structure, prepared through solution sequential deposition, has attracted much attention. It is an easy-to-prepare structure in which the phase separation structures, interfaces, and molecular packing can be separately controlled. Employing PPHJ structure, the properties of OSCs, such as power conversion efficiency, stability, transparency, flexibility, and so on, are usually better than its BHJ counterpart. Hence, a comprehensive understanding of the film-forming process, morphology control, and device performance of PPHJ structure should be considered. In terms of the representative works about PPHJ, this review first introduces the fabrication process of active layers based on PPHJ structure. Second, the widely applied morphology control methods in PPHJ structure are summarized. Then, the influences of PPHJ structure on device performance and other property are reviewed, which largely expand its application. Finally, a brief prospect and development tendency of PPHJ devices are discussed with the consideration of their challenges.

Morphological Homogeneity and Interface Modification as Determinant Factors of the Efficiency and Stability for Upscaling Organic Solar Cell

Morphological homogeneity and interfacial traps are essential issues to achieve high-efficiency and stable large-area organic solar cells (OSCs). Herein, by the investigation of three quinoxaline-based acceptors, i.e., PM6:Qx-1, PM6:Qx-2, and PM6:Qx-p-4Cl, the performance degradation in up-scaling OSCs is explored. The inhomogeneous morphology in PM6:Qx-2 induces a nonuniform spatial distribution of charge generation, showing a rapid decline in efficiency and stability in large-area OSCs. In comparison, the homogeneous morphology in PM6:Qx-1 and PM6:Qx-p-4Cl alleviates the stability drop. When utilizing 2-phenylethylmercaptan to fill the interfacial traps, the stability drop disappears for PM6:Qx-1 and PM6:Qx-p-4Cl, while it persists for PM6:Qx-2. The PM6:Qx-1 large-are device yields a high efficiency of 13.47% and superior thermal stability (T80 = 2888 h). Consequently, the interface modification dominates the performance degradation of large-area devices with homogeneous morphology, while it cannot eliminate the traps in inhomogeneous film. These results provide a clear understanding of degradation mechanisms in upscaling devices.

A series of perylene diimide cathode interlayer materials for green solvent processing in conventional organic photovoltaics

Herein, we report on the design, synthesis, physical and chemical properties, and organic photovoltaic (OPV) device performance of four new cathode interlayer (CIL) materials based on bay N-annulated perylene diimides. Starting from the previously reported N-annulated perylene diimide (PDIN-H), the N-position was functionalized with a benzyl and pentafluorobenzyl group to make PDIN-B and PDIN-FB, respectively. Similarly, starting from the previously reported cyanated N-annulated perylene diimide (CN-PDIN-H), the N-position was functionalized with a benzyl and pentafluorobenzyl group to make CN-PDIN-B and CN-PDIN-FB, respectively. The materials exhibit solubility in the green solvent, ethyl acetate, and thus were processed into thin films using ethyl acetate as the solvent. The optoelectronic properties were assessed for both solution and film, and the electrochemical properties were probed in solution. To validate the potential as electron transporting layers, each film was used in conventional OPVs as the CIL with processing from ethyl acetate, while using a bulk heterojunction (BHJ) comprised of PM6:Y6. High power conversion efficiencies (PCEs) of 13% were achieved compared to control devices using the standard PFN-Br CIL.

Efficient and Stable Air-Processed Ternary Organic Solar Cells Incorporating Gallium-Porphyrin as an Electron Cascade Material

Two gallium porphyrins, a tetraphenyl GaCl porphyrin, termed as (TPP)GaCl, and an octaethylporphyrin GaCl porphyrin, termed as (OEP)GaCl, were synthesized to use as an electron cascade in ternary organic bulk heterojunction films. A perfect matching of both gallium porphyrins' energy levels with that of poly(3-hexylthiophene-2,5-diyl) (P3HT) or poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) polymer donor and the 6,6-phenyl C71 butyric acid methyl ester (PCBM) fullerene acceptor, forming an efficient cascade system that could facilitate electron transfer between donor and acceptor, was demonstrated. Therefore, ternary organic solar cells (OSCs) using the two porphyrins in various concentrations were fabricated where a performance enhancement was obtained. In particular, (TPP)GaCl-based ternary OSCs of low concentration (1:0.05 vv%) exhibited a ~17% increase in the power conversion efficiency (PCE) compared with the binary device due to improved exciton dissociation, electron transport and reduced recombination. On the other hand, ternary OSCs with a high concentration of (TPP)GaCl (1:0.1 vv%) and (OEP)GaCl (1:0.05 and 1:0.1 vv%) showed the poorest efficiencies due to very rough nanomorphology and suppressed crystallinity of ternary films when the GaCl porphyrin was introduced to the blend, as revealed from X-ray diffraction (XRD) and atomic force microscopy (AFM). The best performing devices also exhibited improved photostability when exposed to sunlight illumination for a period of 8 h than the binary OSCs, attributed to the suppressed photodegradation of the ternary (TPP)GaCl 1:0.05-based photoactive film.

Impact of solvents on doctor blade coatings and bathocuproine cathode interlayer for large-area organic solar cell modules

Efforts to commercialize organic solar cells (OSCs) by developing roll-to-roll compatible modules have encountered challenges in optimizing printing processes to attain laboratory-level performance in fully printable OSC architectures. In this study, we present efficient OSC modules fabricated solely through printing methods. We systematically evaluated the impact of processing solvents on the morphology of crucial layers, such as the hole transport, photoactive, and electron transport layers, applied using the doctor blade coating method, with a particular focus on processability. Notably, deposition of charge transport layer using printing techniques is still a challenging task, mainly due to the hydrophobic characteristic of the organic photoactive layer. To overcome this issue, we investigated the solvent effect of a well-studied cathode interlayer, bathocuproine (BCP). We were able to form a uniform thin BCP film (∼10 nm) on a non-fullerene based organic photoactive layer using the doctor bladed coating method. Our results showed that the use of volatile alcohols in the BCP processing required a delicate balance between wettability and vaporization, which contrasted with the results for spin-coated films. These findings provide important insights into improving the efficiency of printing techniques for depositing charge transport layers. The fully printed OSC modules, featuring uniform and continuous BCP layer formation, achieved an impressive power conversion efficiency of 10.8% with a total area of 10.0 cm2 and a geometrical fill factor of 86.5%.

Star-shape non-fullerene acceptor featuring an aza-triangulene core for organic solar cells

We present the simple synthesis of a star-shape non-fullerene acceptor (NFA) for application in organic solar cells. This NFA possesses a D(A)3 structure in which the electron-donating core is an aza-triangulene unit and we report the first crystal structure for a star shape NFA based on this motive. We fully characterized this molecule's optoelectronic properties in solution and thin films, investigating its photovoltaic properties when blended with PTB7-Th as the electron donor component. We demonstrate that the aza-triangulene core leads to a strong absorption in the visible range with an absorption edge going from 700 nm in solution to above 850 nm in the solid state. The transport properties of the pristine molecule were investigated in field effect transistors (OFETs) and in blends with PTB7-Th following a Space-Charge-Limited Current (SCLC) protocol. We found that the mobility of electrons measured in films deposited from o-xylene and chlorobenzene are quite similar (up to 2.70 × 10-4 cm2 V-1 s-1) and that the values are not significantly modified by thermal annealing. The new NFA combined with PTB7-Th in the active layer of inverted solar cells leads to a power conversion efficiency of around 6.3% (active area 0.16 cm2) when processed from non-chlorinated solvents without thermal annealing. Thanks to impedance spectroscopy measurements performed on the solar cells, we show that the charge collection efficiency of the devices is limited by the transport properties rather than by recombination kinetics. Finally, we investigated the stability of this new NFA in various conditions and show that the star-shape molecule is more resistant against photolysis in the presence and absence of oxygen than ITIC.

Recent Advances in Carbon-Based Electrodes for Energy Storage and Conversion

Carbon-based nanomaterials, including graphene, fullerenes, and carbon nanotubes, are attracting significant attention as promising materials for next-generation energy storage and conversion applications. They possess unique physicochemical properties, such as structural stability and flexibility, high porosity, and tunable physicochemical features, which render them well suited in these hot research fields. Technological advances at atomic and electronic levels are crucial for developing more efficient and durable devices. This comprehensive review provides a state-of-the-art overview of these advanced carbon-based nanomaterials for various energy storage and conversion applications, focusing on supercapacitors, lithium as well as sodium-ion batteries, and hydrogen evolution reactions. Particular emphasis is placed on the strategies employed to enhance performance through nonmetallic elemental doping of N, B, S, and P in either individual doping or codoping, as well as structural modifications such as the creation of defect sites, edge functionalization, and inter-layer distance manipulation, aiming to provide the general guidelines for designing these devices by the above approaches to achieve optimal performance. Furthermore, this review delves into the challenges and future prospects for the advancement of carbon-based electrodes in energy storage and conversion.

Selenophene-Containing Small-Molecule Donor with a Medium Band Gap Enables High-Efficiency Ternary Organic Solar Cells

To construct efficient donor:donor:acceptor (D1:D2:A)-type ternary devices, two new selenophene-containing small-molecule (SM) donors named FSBTSeEHR and FSBTSeHR have been designed and synthesized that show broader and red-shifted absorption spectra than the thiophene analogues. With the introduction of SM donors into the D18:CH-6F host system, enhanced light harvesting and charge transport were achieved, benefiting from more complementary absorptions and cascaded energy levels. Furthermore, the doping of the SM donor could effectively modulate the micromorphology and enable a more suitable phase separation size in the active layer. After systematic optimization, the FSBTSeEHR-based ternary organic solar cell (TOSC) exhibited an excellent power conversion efficiency (PCE) of 18.02% with a high open-circuit voltage (Voc) of 0.905 V, short-circuit current density (Jsc) of 26.41 mA cm-2, and fill factor (FF) of 0.754. By contrast, the FSBTSeHR counterpart showed a superior efficiency of 18.55% due to the higher Jsc (26.91 mA cm-2) and FF (0.761). The outstanding PCEs of D1:D2:A-type TOSCs based on our SM donors, FSBTSeEHR and FSBTSeHR, are significantly higher than those of the corresponding binary host system (16.86%) and among the highest values reported to date. This work demonstrates that D1:D2:A-type TOSCs have tremendous potential to achieve superior performances through elaborate design of the SM donor guest and reasonable combination of D and A ingredients.

High-efficiency organic solar cells processed from a real green solvent

The fabrication of organic solar cells (OSCs) depends heavily on the use of highly toxic chlorinated solvents, which are incompatible with industrial manufacturing. The reported alternative solvents such as non-halogenated aromatic hydrocarbons and cyclic ethers are also not really "green" according to the "Globally Harmonized System of Classification and Labelling of Chemicals" of the United Nations. Therefore, processing from real green solvents such as water, alcohols, or anisole will constitute a big breakthrough for OSCs. However, it is fundamentally challenging to obtain high-performance photovoltaic materials processable from these solvents. Herein, we propose the incorporation of a B-N covalent bond, which has a dipole moment of 1.84 Debye, into the conjugated backbone of polymer donors to fabricate high-efficiency OSCs from anisole, a real green and eco-compatible solvent recommended by the United Nations. Based on a newly developed B-N-based polymer, the OSCs with a record-high efficiency of 15.65% in the 0.04 cm² device and 14.01% in the 1.10 cm² device have thus been realized via real green processing.

Total Liquid Transfer with Enhanced Contact Line Slippage

A new surface treatment method is developed to achieve total liquid transfer. The transfer process of a liquid droplet is recorded through high-speed photography and analyzed via image analysis to investigate the hydrodynamic interactions. For a pristine PMMA surface, a viscous and viscoelastic liquid facilitates transfer by increased viscous and inertial forces and delayed liquid bridge breakage but is limited by slow contact line slippage. Hydrophobic surface treatments can increase contact line slippage and the receding angle to achieve transfer ratios up to 98%. However, pinning and contact angle hysteresis from surface roughness features limit liquid transfer, especially for smaller droplets and higher separation velocities. A lubricant-infused surface treatment with PDMS and a thin layer of less viscous silicone oil provides a smooth, homogeneous surface with fast slippage, low contact angle hysteresis, and only a slight oil wetting ridge. Liquid could then transfer at high ratios (∼99.9%), regardless of droplet size and separation velocity. Finally, complete transfer liquid from indented cells is demonstrated to show the potential of this surface modification method for gravure printing.

Post-polymerisation approaches for the rapid modification of conjugated polymer properties

Post-polymerisation functionalisation provides a facile and efficient way for the introduction of functional groups on the backbone of conjugated polymers. Using post-polymerisation functionalisation approaches, the polymer chain length is usually not affected, meaning that the resulting polymers only differ in their attached functional groups or side chains, which makes them particularly interesting for investigating the influence of the different groups on the polymer properties. For such functionalisations, highly efficient and selective reactions are needed to avoid the formation of complex mixtures or permanent defects in the polymer backbone. A variety of suitable synthetic approaches and reactions that fulfil these criteria have been identified and reported. In this review, a thorough overview is given of the post-polymerisation functionalisations reported to date, with the methods grouped based on the type of reaction used: cycloaddition, oxidation/reduction, nucleophilic aromatic substitution, or halogenation and subsequent cross-coupling reaction. Instead of modifications on the aliphatic side chains of the conjugated polymers, we focus on modifications directly on the conjugated backbones, as these have the most pronounced effect on the optical and electronic properties. Some of the discussed materials have been used in applications, ranging from solar cells to bioelectronics. By providing an overview of this versatile and expanding field for the first time, we showcase post-polymerisation functionalisation as an exciting pathway for the creation of new conjugated materials for a range of applications.

Toward high-performance organic photovoltaics: the new cooperation of sequential solution-processing and promising non-fullerene acceptors

Organic photovoltaics (OPVs) have long been a hot topic due to their light weight, low cost, and flexibility. Simple blend-based OPVs have sufficient donor/acceptor (D/A) interfaces and high exciton dissociation efficiency, which result in certified high power conversion efficiency (PCE) exceeding 18%. However, the difficult morphology control and poor device stability limit further progress toward higher PCE and future application. Sequential solution-processing with tunable vertical phase distribution, D/A interfaces, and charge transportation pathways not only benefit device stability but can also overcome the up-scaling challenge. In recent years, the development of non-fullerene acceptors (NFAs) has been very rapid, which is attributed to their tunable energy levels, bandgaps, planarity, and crystallinity. In this minireview, the opportunities for the cooperation of sequential solution-processing and NFAs are revealed based on their characteristics, such as diverse molecular shapes, abundant functional groups and heteroatoms, and various aggregation states for NFAs; independent active layer processing, controllable D/A interfaces, and excellent device stability for sequential solution-processing. Few but important existing examples are discussed to display the prospects of sequential solution-processed fullerene-free OPVs toward high PCE, good device stability, high semitransparency, and large-area industrial manufacture. Finally, some possible research directions are predicted and the main issues that need to be overcome are proposed for sequential solution-processed fullerene-free OPVs toward higher performance.

The principles, design and applications of fused-ring electron acceptors

Fused-ring electron acceptors (FREAs) have a donor-acceptor-donor structure comprising an electron-donating fused-ring core, electron-accepting end groups, π-bridges and side chains. FREAs possess beneficial features, such as feasibility to tailor their structures, high property tunability, strong visible and near-infrared light absorption and excellent n-type semiconducting characteristics. FREAs have initiated a revolution to the field of organic solar cells in recent years. FREA-based organic solar cells have achieved unprecedented efficiencies, over 20%, which breaks the theoretical efficiency limit of traditional fullerene acceptors (~13%), and boast potential operational lifetimes approaching 10 years. Based on the original studies of FREAs, a variety of new structures, mechanisms and applications have flourished. In this Review, we introduce the fundamental principles of FREAs, including their structures and inherent electronic and physical properties. Next, we discuss the way in which the properties of FREAs can be modulated through variations to the electronic structure or molecular packing. We then present the current applications and consider the future areas that may benefit from developments in FREAs. Finally, we conclude with the position of FREA chemistry, reflecting on the challenges and opportunities that may arise in the future of this burgeoning field.

High-Performance Organic Solar Modules via Bilayer-Merged-Annealing Assisted Blade Coating

Although encouraging progress is being made on spin-coated prototype cells, organic solar cells (OSCs) still face significant challenges, yet to be explored, for upscaling the multi-stacked photoactive layers in the construction of large-area modules. Herein, high-performance opaque and semitransparent organic solar modules are developed via a bilayer-merged-annealing (BMA)-assisted blade-coating strategy, achieving impressive efficiencies of 14.79% and 12.01% with respect to active area of 18.73 cm² , which represent the best organic solar minimodules so far. It is revealed that the BMA strategy effectively resolves the de-wetting issues between polar charge transport layer solution and non-polar bulk heterojunction blends, hence improving the film coverage, along with electronic and electric contacts of multi-stacked photoactive layers. As result, organic solar modules coated under ambient conditions successfully retain the high-efficiency of small-area cells upon 312 times area scaling-up. Overall, this work provides a facile and effective method to fabricate high-performance organic solar modules under ambient conditions.

High Sensitivity of Non-Fullerene Organic Solar Cells Morphology and Performance to a Processing Additive

Although solvent additives are used to optimize device performance in many novel non-fullerene acceptor (NFA) organic solar cells (OSCs), the effect of processing additives on OSC structures and functionalities can be difficult to predict. Here, two polymer-NFA OSCs with highly sensitive device performance and morphology to the most prevalent solvent additive chloronaphthalene (CN) are presented. Devices with 1% CN additive are found to nearly double device efficiencies to 10%. However, additive concentrations even slightly above optimum significantly hinder device performance due to formation of undesirable morphologies. A comprehensive analysis of device nanostructure shows that CN is critical to increasing crystallinity and optimizing phase separation up to the optimal concentration for suppressing charge recombination and maximizing performance. Here, domain purity and crystallinity are highly correlated with photocurrent and fill factors. However, this effect is in competition with uncontrolled crystallization of NFAs that occur at CN concentrations slightly above optimal. This study highlights how slight variations of solvent additives can impart detrimental effects to morphology and device performance of NFA OSCs. Therefore, successful scale-up processing of NFA-based OSCs will require extreme formulation control, a tuned NFA structure that resists runaway crystallization, or alternative methods such as additive-free fabrication.

Environmentally Friendly and Roll-Processed Flexible Organic Solar Cells Based on PM6:Y6

Organic Solar Cells (OSCs) have reached the highest efficiencies using lab-scale device manufacturing on active areas far below 0.1 cm2. The most used fabrication technique is spin-coating, which has poor potential for upscaling and substantial material waste. This tends to widen the so-called “lab-to-fab gap”, which is one of the most important challenges to make OSCs competitive. Other techniques such as blade or slot-die coating are much more suitable for roll-to-roll manufacturing, which is one of the advantages the technology presents due to the huge potential for fast and low-cost fabrication of flexible OSCs. However, only a few studies report solar cells using these fabrication techniques, especially applied on a roll-platform. Additionally, for environmentally friendly large area OSCs, inks based on non-hazardous solvent systems are needed. In this work, slot-die coating has been chosen to coat a PM6:Y6 active layer, using o-xylene, a more environmentally friendly alternative than halogenated solvents, and without additives. The optimal coating process is defined through fine-tuning of the coating parameters, such as the drying temperature and solution concentration. Moreover, ternary devices with PCBM, and fully printed devices are also fabricated. Power conversion efficiencies of 6.3% and 7.2% are achieved for binary PM6:Y6 and ternary PM6:Y6:PCBM devices measured with an aperture area of ∼0.4 cm2 (total device area ∼0.8 cm2).