Metal halide perovskites, as a novel class of semiconductor optoelectronic materials, combine the excellent optoelectronic properties of inorganic semiconductors with the advantages of low-cost, printable fabrication typical of organic semiconductors, making them a cutting-edge research focus in the field of semiconductor optoelectronic devices. In recent years, significant progress has been made in perovskite solar cell research: the efficiency of single-junction cells has reached 27%, module efficiency at the square-meter scale has exceeded 18%, laboratory-tested stability has achieved 10 000 h, extrapolated stability has reached several tens of thousands of hours, and GW-scale production lines have been preliminarily established. Perovskite-based tandem cells are flourishing, with perovskite/crystalline silicon tandem efficiency approaching 35%. Wafer-sized perovskite/silicon tandems have already surpassed the efficiency of single-junction silicon cells, while important advancements have also been made in perovskite/perovskite, perovskite/organic, and perovskite/copper indium gallium selenide (CIGS) tandem cells. From these progresses, we fully believe perovskite solar cells is very promising photovoltaic technology.

In this special topic, we organized a Special Issue to summarize updated progresses in perovskite solar cells, and we are grateful to invite 12 researchers who are working in perovskite solar cells to summarize recent important progresses, contribute their research results or highlight recent outstanding work in perovskite solar cells. Specifically, we have 4 reviews, including the flexible perovskite solar cells and its potential application in aerospace^[1], integrated perovskite-organic solar cells^[2], NiO_x for perovskite solar cells^[3], and high performance perovskite material FAPbI₃^[4], in addition, 5 research papers covering perovskite/perovskite tandem solar cells^[5], lead free perovskite solar cells^[6], passivation and additive for enhancing device performance^[7−9]. We also invited two highlights, one is perovskite/silicon tandem^[10], which is one of the most important topic now in photovoltaic technology, not only the researchers in university or institute working in this topic, a lot of leading silicon companies are immerging into this hot area; the other one is the homogenizing of perovskite^[11], which should be the next critical strategy for further improving the efficiency and also the stability of perovskite solar cells. Last but not at least, a comment paper is about Interface energetics in organic and perovskite semiconductor solar cells^[12]. We sincerely hope that the readers working in this hot area could benefit a lot from the published papers in this Special Issue.