Over the past decade, perovskites have evolved into a promising technology, now with the ability to convert about 23% of sunlight into electricity, but work is still needed to make the devices durable enough for long-term use.   NREL’s unencapsulated solar cell—a cell used for testing that doesn’t have a protective barrier like glass between the cell’s conductive parts and the elements—held onto 94% of its starting efficiency after 1,000 hours of continuous use under ambient conditions, accord...