Solar power is a clean and renewable source of energy, but it has struggled to compete with fossil fuels on cost. Most solar cells, which absorb sunlight and produce electrical energy, are built from silicon. SLAC’s Kevin Stone is exploring a new class of materials for solar cells. Like silicon, these materials are crystals; but unlike silicon, they are formed by gently heating and drying from solution at low temperatures. In essence, they can be painted on, either on light, flexible backing or on conventional silicon cells as a way to improve the silicon cell’s efficiency. These crystals have a complex structure that seems to organize itself spontaneously as the solution is converted to a solid. Using advanced tools at the Stanford Synchrotron Radiation Lightsource, Stone has been able to watch these crystals assemble at the atomic level and gain clues to the forces that guide this process. By understanding this fascinating chemical mystery, scientists will also gain insights needed to design more effective and economical solar cells.