Band Diagram of Heterojunction Solar Cells through Scanning Tunneling Spectroscopy

The band diagram in heterojunction solar cells is of utmost importance when visualizing the possibility of charge separation and carrier transport. The diagram should in principle be drawn from the viewpoint of the charge carriers in the devices. While considering solar cells based on conjugated organics and/or inorganic compound semiconductors, we have shown in this Perspective that scanning tunneling spectroscopy (STS) can draw appropriate band diagrams, which the carriers would encounter during the separation and transport processes. Moreover, differential conductance (dI/dV) images in scanning tunneling microscopy are capable of energy mapping; one can therefore map domains of the materials in a bulk heterojunction (BHJ). Correlation between morphology of the components in BHJs and device performance can therefore be envisaged through STS.