Abstract
Since the 2012 breakthroughs(1-3), it is now very much accepted that halide perovskite solar cells may have a strong practical impact in next-generation solar cells. The most efficient solar cells are using Pb-based halide perovskites. The presence of Pb in these devices, however, has caused some concerns due to the high perceived toxicity of Pb, which may slow down or even hinder the pace of commercialization. Therefore, the science community has been searching for lower-toxicity perovskite-type materials as a back-up strategy. The community is paying significant attention to Pb-free materials and has achieved promising results albeit not yet approaching the spectacular performance of APbI(3) materials. In this comment, we summarize the present status and future prospects for Pb-free perovskite materials and their devices.