What is the difference between indoor and outdoor photovoltaics?

An indoor photovoltaic (IPV) cell works according to the same fundamental physics as an outdoor solar cell. The key difference is the type of light and the intensity of light it is designed to capture.  

Indoor lighting contains only visible wavelengths, while sunlight also includes large amounts of infrared. Because of this difference in spectrum, indoor PV uses semiconductor materials with slightly higher bandgaps, which are better at converting visible light, whereas outdoor PV uses materials optimized for the full solar spectrum.   

The intensity of light is also different. Indoor light is about 1,000 times weaker than sunlight, meaning an indoor cell generates extremely small currents. Outdoors, large currents make resistive losses a major concern. Indoors, resistive losses matter far less; instead, the tiny photocurrents must compete with equally tiny leakage currents caused by microscopic defects in the PV device. Minimizing this leakage current is therefore one of the most important goals in indoor PV design.  

Since the light conditions are so different, the efficiency of indoor and outdoor solar cells cannot be directly compared. Indoor cells may show higher relative efficiency, but always under much lower light levels.