Green solvents for organic electronics processing

Since the use of solvents is ubiquitous in many industrial processes, the organic semiconductor industry, among others, is compelled to develop more sustainable fabrication processes, mainly because of the current regulatory requirements spelling out the need to avoid harmful solvents. The companies’ growing attitude toward sustainability, and the cost–benefits related to solvent storage/disposal, further contributes to strengthen the driving force toward the replacement of traditional solvents with reasonably benign counterparts by comparison. Nevertheless, in the case of organic-based device processing, chlorinated and/or aromatic hydrocarbon solvents are currently the preferred option, since they exhibit structural similarities with organic semiconductors and therefore excellent solvent ability, along with adequate viscosity, vapor pressure, and high boiling point. However, they pose critical issues for human health and the environment. In this chapter, we dive into the most relevant efforts to process semiconductive small molecule and polymers for applications in organic photovoltaics and thin-film transistors from solvents with green credentials, without compromising the semiconductor performance. Solvents are categorized into (1) protics, (2) ethers, (3) esters and carbonates, and (4) dipolar aprotics. Particularly, the different approaches developed to prepare stable solutions/dispersion of semiconducting materials in green solvents are discussed—including materials structure modification and various nanoparticle production techniques. In addition, a survey and a brief discussion of the corresponding devices performance, also in comparison with the conventionally processed counterparts, are given. The chapter aims to provide both evidence that material-green solvent combinations are possible, and grounds for the development of more sustainable organic electronic technologies abiding by relevant legislation.