Solvent-free synthetic protocols for halide perovskites

Halide perovskites have been extensively researched in the past decade, and explored in fields stepping out from photovoltaics towards photothermal and thermoelectric energy conversion, light-emission, high-energy electromagnetic radiation detection, memristors/artificial synapses, ferroelectricity, etc. These frontier applications will fundamentally require a benign material platform of great sample quality but easy accessibility. Traditional synthesis of halide perovskites follows a wet chemistry route, that is, dissolving-precipitation through a solution medium. However, commonly used solvents are of high-cost, environmentally unfriendly, and have high treatment complexity and low post-processing convenience. Breakthroughs on solvent toxicity minimization or even solvent exemption can pave a new roadmap to future development of perovskite-based applications. In this work, we discuss new opportunities in solvent-free synthesis including newly researched vapor deposition and mechanochemical methods, as well as other potential insights in this direction.