ElectroGreen^® Solvent Systems for Energy Materials and Advanced Polymers

Abstract

ElectroGreen^®, a group of solvent systems with firm specifications targeting electronic and energy applications, represents a significant advancement in promoting Green Chemistry within materials science. As the field increasingly prioritizes environmentally responsible practices, ElectroGreen^® offers a high-performance alternative for dissolving and processing functional materials and advanced polymers. It’s proven effectiveness in applications such as perovskite solar cells (PSC) and batteries underscores its versatility and relevance in next-generation energy technologies. By combining reduced environmental impact with excellent processing capabilities, ElectroGreen^® supports the transition towards more sustainable research and manufacturing, making it an essential tool for innovation in materials science.

Section Overview

• Introduction
• Environmental and Regulatory Benefits of ElectroGreen^® Solvents
• Chemical Properties and Composition of ElectroGreen^® Solvents
• Performance for Perovskite Solar Cells (PSC) and Precursors
• Performance for Battery Materials
• Performance for Polymer Dissolution in Solar and Battery Applications
• Conclusion
• Appendix
• Featured Products
• Related Products

Introduction

The global shift towards renewable energy technologies and advanced functional materials has positioned material science as a critical driver of innovation. As researchers and manufacturers strive for greener production pathways and improved environmental stewardship, the solvents employed across materials processing - from perovskite solar cells (PSCs) to lithium-ion batteries and organic electronics - are coming under increasing scrutiny for their environmental, health, and safety (EHS) impacts.

A wide variety of organic solvents are routinely used in these sectors due to their essential roles in precursor dissolution, surface cleaning, film deposition, or binder dispersion. As summarized in Table 1, many of these solvents - including dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), cyclohexanone, and chloroform - are critical for solution processing of solar cells and batteries.

However, their intrinsic properties lead to significant hazard classifications under CLP. Under the REACH regulation, NMP, DMF, and DMAc are listed in the candidate list of substances of very high concern for authorization due to their reproductive toxicity (Repr. 1B).¹ These solvents are flagged as high-risk (red category) in both the CHEM21 solvent selection guide and the GSK solvent sustainability guide.^2-3 Likewise, non-polar solvents derived from fossil resources - such as toluene and xylene - remain widely used in organic photovoltaics (OPV) formulations, hole transport layers, or coating processes, yet present neurotoxicity, and high volatile organic compounds (VOC) emissions that lead to regulatory activities to control potential risks from their use. Toluene and xylene, for instance, are associated with acute and chronic central nervous system (CNS) effects and are among the solvents most tightly regulated for workplace exposure. Chloroform and dichloromethane (DCM), though useful in processing fullerene derivatives or stripping polymers, are classified as suspected carcinogens (H351) and present severe inhalation risks. Furthermore, many of these solvents - such as tetrahydrofuran (THF), methyl isobutyl ketone (MIBK), methyl amyl ketone (MAK), and methyl ethyl ketone (MEK) - are highly flammable, volatile, and require stringent handling protocols.

Even some of the more routinely used solvents - acetone, isopropanol (IPA), and methanol - employed for cleaning or ink dilution, contribute to VOC load, flammability hazards, and toxicological risk.

Many commonly used solvents are hazardous, exhibit high energy recovery demands, and regulatory restrictions that undermine their long-term suitability. These concerns have catalyzed the search for greener, safer alternatives that maintain process performance while minimizing hazard.

To support this transition, Merck has introduced ElectroGreen^® solvents⁴, a proprietary blend of bio-based and low-toxic components optimized for solar cell, battery, and polymer processing applications. ElectroGreen^® solvents align with Green Chemistry principles⁵ and major solvent assessment frameworks, offering strong solvency with lower environmental and occupational hazards.

Environmental and Regulatory Benefits of ElectroGreen^® Solvents

ElectroGreen^® solvents by Merck are a bio-based option tailored for electronic and energy applications over conventional solvents. These solvents are derived from renewable, bio-based feedstocks - such as corn and sugar beets - verified by Carbon-14 (C-14) and ASTM D6866-16 analyses, which reduces reliance on fossil resources. Designed for low toxicity and minimal VOC emissions, ElectroGreen^® products enable safer handling, often without the need for fume hoods, and improves indoor air quality in laboratories and cleanrooms. The solvents also demonstrate excellent performance in dissolving active materials while maintaining stringent purity standards (e.g., <0.05% acidity, <1 ppm metallic impurities), making them suitable for high-performance electronics and energy applications. By aligning with the 12 Principles of Green Chemistry and solvent assessment frameworks such as CHEM21² and the GSK Solvent Sustainability Guide³, ElectroGreen^® products support process efficiency, waste reduction, and safer work environments (Table 2a). They represent compelling alternatives to hazardous solvents such as NMP, toluene, DMF, including the readily adoptable ElectroGreen^® demonstrated alternatives for PSC6 and battery, helping research and manufacturing organizations meet both technical demands and sustainability targets.

Chemical Properties and Composition of ElectroGreen^® Solvents

ElectroGreen^® products offer high chemical purity, low residue upon evaporation, minimal metal and water content, and reduced acidity, making them ideal for sensitive electronic processes. Each variant in the ElectroGreen^® range serves as a substitute for a traditional solvent such as acetone, isopropyl alcohol, toluene, and NMP, with tailored evaporation rates and solubility parameters to match performance needs (Table 2b). By combining superior functionality, ElectroGreen^® solvent blends provide a smart, safer, and more sustainable alternative for modern electronic manufacturing.

The Green Index (GI)^3,7 evaluates solvents on toxicity, volatility and environmental performance, identifying safer alternatives in Green Chemistry based on frameworks like the GSK Solvent Sustainability Guide. Scores range from 0 to 10, with values (≥7) indicating environmentally preferred solvents that are low in toxicity and regulatory concerns. In the context of ElectroGreen^® solvent blends, GI values help identify components that adhere to Green Chemistry principles, promoting safer and more sustainable formulations.

Equally important in solvent design are the Hansen Solubility Parameters (HSPs), which quantify the intermolecular interactions between solvents and solutes. These parameters - dispersion (δD), polar (δP), and hydrogen bonding (δH) - enable formulators to predict solubility and compatibility, ensuring that bio-based solvents in ElectroGreen^® blends can effectively replace traditional solvents without compromising performance.

The careful selection of components based on both GI and HSP values allows Merck’s ElectroGreen^® line to meet the dual goals of environmental responsibility and high technical performance.

Performance for Perovskite Solar Cells (PSC) and Precursors

In perovskite solar cell (PSC, Figure 1) fabrication, solvents like DMF and DMSO are commonly used to dissolve perovskite precursors and facilitate crystal film formation. However, as discussed, their toxicity, hygroscopicity, and environmental impact pose significant limitations to scale-up and commercial viability.^8,9 Recent studies⁹ have demonstrated that partial substitution of DMF with solvent blends such as ElectroGreen^® blends - comprising of ethanol, ethyl lactate, and ethyl acetate - can maintain comparable power conversion efficiencies (PCEs) while reducing DMF usage by up to 50%, thereby enhancing environmental safety and scalability.

Organic Halides: Organic quaternary halides such as methylammonium iodide (MAI), methylammonium bromide (MABr), and formamidinium iodide (FAI) are essential precursors in the synthesis of ABX₃-type perovskite solar cells, making their solubility just as critical as that of inorganic halides. We conducted a solubility screening of these quaternary salts across ten different ElectroGreen^® solvents. The results, compiled in a substrate-versus-concentration table (Table 3a), highlight that all ElectroGreen^® solvents exhibit solubility at room temperature for organic halides. The observed concentrations are adequate for typical perovskite formation processes.

Inorganic Halides: Similarly, inorganic halides such as PbI₂, PbBr₂, and CsI are also key precursors in perovskite solar cell fabrication. Their solubility plays a vital role in the successful formation of the ABX₃ perovskite structure. We performed a solubility screening of these inorganic halides in the same set of 8 ElectroGreen^® solvents. The results, organized in a substrate-versus-concentration format, revealed that the ElectroGreen^® NMP-substitute 929662 stands out as effective solvent (Table 3a.), demonstrating good solubility for these halides on heating up to 80 °C. These concentrations are sufficient for typical ABX₃ perovskite preparation, reinforcing the suitability of these solvents for both organic and inorganic precursors.⁶

Lead-Based Perovskites: Extending this study, we also evaluated the solubility of complete lead-based perovskite compounds such as MAPbI₃, MAPbBr₃, and CsPbI₃ at concentrations ranging from 0.5 M to 1 M. These were tested across the same eight ElectroGreen^® solvents. The findings indicate that the ElectroGreen^® NMP substitute type-2 (929662) is an effective solvent for dissolving these perovskites upon heating, making it a promising candidate for solution-based perovskite processing (Table 3b). For detailed information on the experiments, please refer to the appendix of this application note.¹⁰

HTL and ETL: In addition to the perovskite layer, the solubility of widely used HTL and ETL materials was evaluated in ElectroGreen^® solvents as part of internal R&D testing. Several HTL materials demonstrated improved solubility, particularly under mild heating, supporting their potential for greener solvent–based device fabrication. Notably, the HTL material SpiroMeoTAD (792071), Si-OMeTPA (913502) was processed using ElectroGreen^® solvents and has been successfully implemented in perovskite solar cells (Figure 1), as reported in Optical Materials^11a and ACS Energy Letters^11b, where they contributed to enhanced film uniformity and device stability. The findings suggest (Table 3b) that ElectroGreen^® solvents may offer a more sustainable and scalable alternative for processing both HTL and ETL layers in perovskite and other optoelectronic devices. This is further supported by their demonstrated utility in OLED fabrication for HAT-CN (926388)¹², where ElectroGreen^® solvents also enabled solubilization, however, a performance test was not conducted.

In addition to the well-established ElectroGreen^® NMP-type 1 and NMP-type 2 solvents, several other ElectroGreen^® variants demonstrate promising applicability in materials science, particularly in the fabrication and processing of PSC. For instance, ElectroGreen^® IPA substitute (929654), can be effectively employed as a cleaning solvent and anti-solvent during device fabrication.^13a Similarly, ElectroGreen^® substitute for toluene (929689) and xylene substitute (929700) can serve as solvents for P3HT, PCBM, and other donor–acceptor active layers commonly used in organic photovoltaics (OPVs), as well as anti-solvents in layered deposition techniques.^13b–c Further, ElectroGreen^® blends 929670 and 929735 are suitable candidates for use as solvents for hole transport layers (HTL) or anti-solvents and rinsing agents, which are critical in achieving uniform and defect-free film formation in PSC devices.^13d–f Additionally, the ElectroGreen^® MAK substitute (929727), can be tested for its potential in both HTL processing and interlayer rinsing, where slower evaporation kinetics are desirable for morphological control. Finally, ElectroGreen^® blend 929697, designed as a substitute for butyl cellosolve, holds promise as an additive or co-solvent in ink formulations and in the dispersion of polymeric binders and conductive additives for electrode fabrication.^13g–h

Performance for Battery Materials

In battery manufacturing, particularly in the formulation of cathode and anode slurries, solvents play a critical role in dispersing active materials and polymeric binders like PVDF or Styrene-Butadiene rubber (SBR). The most used solvents - such as DMF, NMP and DMAc - pose significant environmental and occupational safety risks. NMP is classified as a reproductive toxin and is restricted under EU REACH.^1b As a dipolar aprotic solvent, it is highly effective at dissolving PVDF, which is why it remains a mainstay in cathode slurry processing.¹⁴ Additionally, alternative ketone and ether-based solvents like MIBK, MAK, THF, and cyclohexanone are often flammable, volatile, or neurotoxic, adding to the hazard profile of battery manufacturing environments. Greener solvent strategies are increasingly focused on replacing these substances with safer, low-VOC alternatives that maintain binder compatibility while reducing energy and compliance burdens.

ElectroGreen^® products present a forward-looking solution tailored to these needs. Unlike traditional battery solvents, ElectroGreen^® blends are bio-based, derived from renewable feedstocks, and free from SVHC classification. Their low toxicity and lower vapor pressure reduce occupational exposure risks and eliminate the need for complex recovery infrastructure. NMP ElectroGreen^® solvent demonstrates strong solvency for PVDF and other binder systems, enabling their use in battery slurry processing without compromising electrode quality (see Figure 4 of the appendix). Their favorable evaporation behavior and low impurity levels support efficient coating and drying processes, while aligning with global green chemistry frameworks such as CHEM21 and GSK's solvent sustainability index. This can make ElectroGreen^® blends also here a practical and scalable drop-in alternative that not only addresses environmental and regulatory pressures but also enhances process efficiency and worker safety in the battery industry.

Performance for Polymer Dissolution in Solar and Battery Applications

Among polymers used in solar encapsulation and battery systems, polyvinylidene fluoride (PVDF) is a benchmark binder in lithium-ion batteries due to its excellent electrochemical stability, strong adhesion, and high dielectric strength. Its compatibility with NMP-type 2 ElectroGreen^® solvent 929662 allows for uniform electrode slurry formulation with optimized rheology, as confirmed through academic collaboration demonstrating PVDF dissolution in this solvent in laboratory-scale studies (see Figure 4 of the appendix). PVDF’s broader utility extends to polymer electrolytes, where it forms robust, ion-conductive matrices, as detailed in a study using PVDF-HFP-based membranes for solid-state lithium batteries.¹⁵

In flexible and high-capacity energy storage systems, polyurethane (PU) and thermoplastic polyurethane (TPU) are gaining traction due to their elasticity, moisture resistance, and processability at low temperatures. These properties are especially valuable in silicon-anode batteries and flexible electronics. Recent literature shows that CO₂-based TPU binders can even outperform PVDF in silicon-anode cells by mitigating volume expansion and improving mechanical stability.¹⁶ In-house R&D solubility tests at Merck have demonstrated that ElectroGreen^® blends exhibit excellent compatibility with PU, showing stable dissolution behavior comparable to that of conventional polar aprotic solvents. Additionally, PU and TPU are also gaining relevance in the solar sector as encapsulants, where their durability and mechanical flexibility make them suitable for harsh outdoor and flexible module applications. For example, PU-based encapsulants have shown promising performance in perovskite and organic photovoltaics, combining optical transparency with thermal and moisture stability.¹⁷

Meanwhile, the development of self-healing polymeric binders such as poly(acrylic acid)-poly(ethylene oxide) and poly(ether-thiourea) has demonstrated extended cycle life and mechanical resilience in silicon-based anodes, retaining >85% capacity after 200+ cycles.¹⁸ In parallel, aqueous binders like carboxymethyl cellulose (CMC), styrenebutadiene rubber (SBR), and polyacrylic acid (PAA) provide more sustainable, water-processable alternatives to NMP, addressing environmental and safety concerns without sacrificing electrochemical performance. For instance, CMC/SBR-based graphite and silicon anodes have demonstrated comparable or improved cycling stability and capacity retention versus PVDF systems under aqueous processing conditions.¹⁹

In photovoltaic encapsulation, ethylene vinyl acetate (EVA) remains dominant for its clarity and adhesion, yet its susceptibility to UV-induced degradation and acetic acid formation has driven the search for alternatives.²⁰ Thermoplastic polyolefins (TPO) and polyvinyl butyral (PVB) have emerged as durable alternatives for glass-glass PV modules, while silicone-based encapsulants (e.g., polydimethyl siloxane, PDMS) offer high UV stability and flexibility for wearable or curved PV systems.²¹

Given the evolving polymer landscape across solar and battery technologies, assessing the sustainability compatibility of critical polymers with Merck's ElectroGreen^® solvent systems is highly relevant. ElectroGreen^® blends, with their low toxicity, enable the possibility of more sustainable processing of PVDF, PU, TPU and other functional polymers - serving again as an alternative for toxic solvents like NMP. This positions ElectroGreen^® formulations as a pivotal enabler of performance-driven innovation across energy technologies.

Expanded polystyrene (EPS), a non-polar thermoplastic foam, is widely used in materials science for lightweight structural applications, thermal insulation, and packaging due to its closed-cell morphology, low density, and favorable mechanical behavior. EPS is readily soluble in organic solvents such as acetone, toluene, benzene, chloroform, xylene, and tetrahydrofuran (THF), owing to similar Hansen solubility parameters that effectively disrupt polymer chain interactions. A study by Garcia et al.²² systematically evaluated the dissolution of EPS in these solvents, including alternatives such as D-limonene and p-cymene, and confirmed effective solubility without molecular degradation of the polymer. Complementarily, Hattori et al.²³ reported that p-cymene could dissolve up to 212 g of EPS per 100 g solvent at 50 °C, showing that bio-based solvents can be potent and more sustainable alternatives to petroleum-based ones. Building on these insights, ElectroGreen^® solvents - notably, ethyl lactate–based blends such as, ElectroGreen^® Acetone substitute for electronics, bio-sourced 929670 - have demonstrated effective EPS solubilization, offering a lower-VOC alternative for electronics, coatings, and polymer processing applications (Figure 2).

Conclusion

ElectroGreen^® solvent blends are designed to support more sustainable materials processing by offering alternatives to conventional hazardous solvents used in energy and polymer applications. They are formulated from bio-based components and are aligned with recognized sustainability frameworks such as CHEM21 and the GSK solvent guide. These solvent systems aim to provide safe options for processing perovskite solar cells, battery slurries, and functional polymers, while maintaining essential properties like solubility, volatility, and purity.

Although broad-scale performance validation of ElectroGreen^® products is still ongoing, initial data are promising. One peer-reviewed study has demonstrated that ElectroGreen^® type blends can partially substitute toxic solvents like DMF in perovskite solar cell fabrication while maintaining comparable device performance. In parallel, internal laboratory studies and academic collaborations have shown effective dissolution of key materials such as PVDF and lead halide perovskites in ElectroGreen^® NMP-type substitutes, further supporting their potential for enabling greener manufacturing pathways.

While more comprehensive device-level studies are needed to fully benchmark performance against industry standards, the early solubility, compatibility, and formulation behavior observed across a wide range of advanced materials strongly suggest that ElectroGreen^® solvents are well-positioned as more sustainable alternatives. As research and validation efforts expand, ElectroGreen^® products stand to play a central role in the transition toward safer, more environmentally responsible practices across solar, battery, and polymer processing domains.

Appendix:

General Experimental Information: Perovskite Solar Cells

A precursor solution for methylammonium lead iodide (MAPbI₃) perovskite was prepared by combining lead iodide  (PbI₂) 900168 and methylammonium iodide (MAI, CH₃NH₃I) 901434 in a glass vial under a nitrogen atmosphere. The halide precursors were mixed in a 1:1 molar ratio using 1 mL of ElectroGreen^® NMP substitute type-2 929662. At room temperature (25–30 °C), the organic halide (MAI) was fully soluble, while the inorganic halide (PbI₂) exhibited partial solubility.

The mixture was subsequently heated in a preheated oil bath at 80–85 °C for 15 minutes. Upon heating, an instantaneous reaction occurred, yielding a clear yellow solution indicative of successful perovskite precursor formation (Figure 3).

Other salts were investigated under the same/similar conditions.

Concentration-Dependent Observations:

• 0.5 M: The solution remained visually stable for up to 24 hours, with minor sedimentation observed. This suggests the onset of spontaneous crystallization in the absence of external triggers such as coating or condensation.
• 0.75 M: Phase separation was evident after overnight storage, with the formation of two distinct layers and visible precipitation. This behavior indicates increased nucleation or solubility limits being approached at higher concentrations.
• 1.0 M: The solubility of PbI₂ was insufficient at this concentration, resulting in significant solid residue and incomplete dissolution.

General Experimental Information: Battery Materials

Preparation of PVDF Solution in NMP Type-2 ElectroGreen^® Solvent (10% w/v)

A 10% w/v solution of poly(vinylidene fluoride) (PVDF) was prepared by dissolving 1.0 g of PVDF powder 182702 in 10 mL of ElectroGreen^® NMP substitute type-2 (929662). The process was conducted under a nitrogen atmosphere using a Carousel Core+ stirring hotplate system equipped with a 25 mL borosilicate glass tube sealed with a Teflon screw cap. A magnetic stir bar was placed at the base of the vessel, which was mounted on a height-adjustable jack stand. Chiller lines were connected to the system via inlet and outlet ports to regulate temperature flow.

The ElectroGreen^® solvent (10 mL) was added gradually in portions to the test tube containing 1.0 g of PVDF while stirring at approximately 350 rpm at room temperature (27–30 °C). The dispersion was stirred for 15 minutes under nitrogen, yielding a thick, sticky material that indicated swelling and partial solvation of the polymer (Figure 4).

Subsequently, the hotplate was set to 75 °C, and the heating was initiated to reach the desired temperature within 15 minutes. The solution was maintained at 75 °C for 2 hours under continuous stirring. Over time, the PVDF fully dissolved in the NMP type-2 solvent, resulting in a clear light brown solution.

The magnetic bar stirring continued as the system gradually cooled to room temperature, completing the dissolution and equilibration process.

Conclusion: A homogeneous, clear brown solution of PVDF in ElectroGreen^® NMP type-2 solvent was achieved at a 10% w/v concentration. The solution demonstrated excellent film-forming potential and remained stable under ambient conditions.