Figure 1. Basic device characteristics.

Scanning electron microscopy (SEM) image of the device cross-section along with the assignment of the respective layers (a). In some devices, the SnO_x or the AZO layer has been omitted. Note that the contrast between the AZO and the SnO_x layers in SEM is relatively poor. External quantum efficiency (EQE) of a representative device based on AZO/SnO_x (b). J/V characteristics measured in forward and reverse direction (c), and current density versus time under 0 V (black) and 0.75 V (red) bias (d).