Using a new solution chemistry, researchers have made mixed tin-lead perovskite solar cells more efficient. They demonstrated this by using their improved films to produce two kinds of tandem (dual material) solar cells - one with an efficiency up to 25%. Solar cells that use perovskite are attractive because perovskite materials are cheap to produce and simple to manufacture. Many research efforts related to perovskites have focused on lead-based perovskites, often adding tin to absorb a larger fraction of the solar spectrum. At present, though, mixed tin-lead (Sn-Pb) perovskites have achieved power conversion efficiencies of about 18%, which is lower than their pure Pb-based perovskite counterparts. Despite several strategies explored recently to improve the performance of Sn-Pb-based perovskite solar cells (PSC), the tandem PSC performance has lagged behind its Pb counterparts. In a new effort to improve Sn-Pb-based perovskites' ability to harvest light, Jinhui Tong and colleagues used guanidiinium thocyanate (GuaSCN) to enhance the structural and optoelectronic properties of tin-lead mixed perovskite films. This boosted carrier lifetimes (or energy capturing abilities) to more than a 1 microsecond, among other enhancements. Tong and colleagues applied the films to fabricate all-perovskite tandem solar cells that showed efficiencies of up to 25%, in one case. In the final test of cells they built, more than 88% of the initial efficiency was maintained after 100 hours of continuous operation.