The emergence of metal-free molecular perovskites: challenges and opportunities

Perovskite materials are increasingly important in a variety of optoelectronic applications. Some of these functional materials also exhibit ferroelectric properties, making them promising in memory elements, sensors, and energy technologies. While they exhibit extraordinary performances, their instabilities often hinder practical applications and toxic metal components cause environmental concerns. In the last few years, metal-free molecular perovskites (MOPs) have emerged, featuring ferroelectric properties that outperform conventional perovskite ferroelectrics while offering an environmentally friendly and costeffective alternative relevant to optoelectronics. We review the structural and optoelectronic characteristics of this new class of materials, as well as preparation techniques, with challenges and opportunities for future applications.