LAUSR

Evening out the heat The conversion of precursors into the active layer of perovskite solar cells normally occurs by heating the underlying substrate. Conversion tends to occur near the top of the film, where solvent is lost, and unwanted preheating of reactants occurs near the substrate before the reaction. Li et al. show that the use of a surrounding heat transfer oil (anisole) leads to more rapid and even heating, removes solvent, and avoids air and water contamination effects. The larger grains and more uniform films led a much greater retention of efficiency in moving from small-area to large-area devices. Science, abh3884, this issue p. 561 Liquid medium annealing creates a robust microenvironment and constant heat field to fabricate durable perovskite solar cells. Solution processing of semiconductors is highly promising for the high-throughput production of cost-effective electronics and optoelectronics. Although hybrid perovskites have potential in various device applications, challenges remain in the development of high-quality materials with simultaneously improved processing reproducibility and scalability. Here, we report a liquid medium annealing (LMA) technology that creates a robust chemical environment and constant heating field to modulate crystal growth over the entire film. Our method produces films with high crystallinity, fewer defects, desired stoichiometry, and overall film homogeneity. The resulting perovskite solar cells (PSCs) yield a stabilized power output of 24.04% (certified 23.7%, 0.08 cm2) and maintain 95% of their initial power conversion efficiency (PCE) after 2000 hours of operation. In addition, the 1-cm2 PSCs exhibit a stabilized power output of 23.15% (certified PCE 22.3%) and keep 90% of their initial PCE after 1120 hours of operation, which illustrates their feasibility for scalable fabrication. LMA is less climate dependent and produces devices in-house with negligible performance variance year round. This method thus opens a new and effective avenue to improving the quality of perovskite films and photovoltaic devices in a scalable and reproducible manner.