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. Berkeley Lab scientists have developed a way to use optical microscopy to map thin-film solar cells in 3D as they absorb photons. It images optoelectronic dynamics in materials at the micron scale. This is small enough to see individual grain boundaries, substrate interfaces, and other internal obstacles that can trap excited electrons and prevent them from reaching an electrode, which saps a solar cell’s efficiency. So far, scientists have used the technique to better understand why adding a specific chemical to solar cells made of cadmium telluride (CdTe) - the most common thin-film material - improves the solar cells’ performance.