The technology still has a way to go because the cells must become more efficient to prove cost-effective, but their promise is big: solar cells that could become a part of any glass or plastic surface. They could sit, invisibly, atop a smartphone’s display, allowing the phone to charge itself under natural or artificial light. And if the process became part of glass and window manufacturing, homes and skyscrapers could draw power from the sun without the spatial and aesthetic limits of current, opaque solar panels.