Harnessing materials for a low-carbon future is a multifaceted grand challenge. Organic semiconductors continue to reveal exciting new physics and chemistry for boosting optical and electronic properties for energy applications from solar energy and lightweight electronics to high-efficiency lighting. A critical knowledge gap for these materials is understanding how disorder and defects in the atomic structure of organic molecular crystals and polymer semiconductors limits their ability to absorb or emit light and to move energy around in a device. This project will use cutting edge scanning transmission electron microscopy and electron beam spectroscopy and diffraction tools to probe the links between composition and bonding, molecular packing, and optical transitions in organic and hybrid semiconductors. These results will define opportunities for defect and interface engineering in organic optoelectronic devices (organic light emitting diodes, thin film transistors, and photovoltaics) and begin to unlock organic semiconductors for energy conversion and lighting technologies.