Towards the environmentally friendly solution processing of metal halide perovskite technology

Metal halide perovskite materials have demonstrated unique properties for applications in optoelectrical devices such as solar cells, light-emitting diodes and photodetectors. The unprecedented world-record energy conversion efficiency of over 25% achieved with solution-processed perovskite solar cells is escalating research towards the commercialisation of the perovskite materials. Nevertheless, the use of large amounts of hazardous and carcinogenic solvents such as N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and skin-penetrating dimethyl sulfoxide (DMSO) in the current perovskite synthesis protocols are limited for the commercial uptake of perovskite technology as these detrimental solvents can cause environmental, health and safety issues. Therefore, the development of alternative environmentally-friendly, green solvents for the synthesis of perovskite materials including thin films, nanocrystals or single-crystals with desirable properties is critical for the commercialisation of perovskite technologies. In this review, we summarize the research progress of solution-processable perovskite material using low-toxic and green solvent alternatives. We discuss the fundamental properties that need to be considered in screening solvents for the solution processing of metal halide perovskites. By carefully analysing the common features of solvents and anti-solvent systems that have been reported for making perovskite precursor inks for applications in solar cells and light-emitting diodes, we provide insight into the relationship between the solvent molecular ligand – properties of perovskite materials – device performance. We discuss the advantages and challenges of each type of green solvent based on their performance in metal halide perovskite technology, effects on the environment, human health and safety, aiming to provide guidelines towards green metal halide perovskite technology.