Perovskites hold a place of honor in the pantheon of much-heralded clean energy breakthroughs that have yet to actually arrive, alongside small modular nuclear reactors and solid-state batteries. In theory, these crystal structures could radically improve solar panels’ capabilities by absorbing wavelengths of light that conventional silicon cells can’t catch. But the stunning advances in R&D specimens have yet to infiltrate the cold, hard world of commercial solar manufacturing.