Next-generation solar cells made of super-thin films of semiconducting material hold promise because they’re relatively inexpensive and flexible enough to be applied just about anywhere.Researchers are working to dramatically increase the efficiency at which thin-film solar cells convert sunlight to electricity. But it’s a tough challenge, partly because a solar cell’s subsurface realm—where much of the energy-conversion action happens—is inaccessible to real-time, nondestructive imaging. It’s difficult to improve processes you can’t see.Now, scientists from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a way to use optical microscopy to map thin-film solar cells in 3-D as they absorb photons.