One of the key issues in the field of photovoltaics (PVs) is how to achieve high optical to electrical power conversion efficiencies, not just for a few small (less than a cm-square) area laboratory devices, but in a manufacturing environment for production PV cells over very large areas, on the order of 100s of cm.  There are many factors that can affect the photovoltaic (PV) cell efficiency from theoretical maximums, including material defects that affect the lifetime of the photogenerated electron so they recombine before exiting the cell and areas of increased extraneous series resistance that prevent the voltage (electrical power) from being delivered to the load you wish to power. However, most current characterization techniques provide material information locally, on the order of 10s of nm, or conversely, the PV measurement represents a single average macroscopic number of the entire device. In fact, what you want is a 2D image of how various parameters that affect the PV cell efficiency are varying as a function of position across the entire device. One way of achieving this is by recording the luminescence given off by a PV cell under optical or electrical excitation (see Figure 1).