Direct visualization of the photovoltaic effect in a single-junction GaAs cell via in situ electron holography

The nanoscale electric potential distribution in a gallium arsenide single p–n junction cell under artificial illumination, or the photovoltaic (PV) effect, was investigated using in situ electron holography with a transmission electron microscope. A custom-made specimen holder with biasing and illumination capabilities was used for this purpose. To determine the practical potential of the specimen prepared by a focused ion beam (FIB), the thickness of active layers that directly contribute to the PV effect was accurately derived by analyzing the results of in situ biasing electron holography. In situ light-illumination electron holography directly visualized the PV effect in the cell, where the potential difference between the p and n regions decreased with the increase in the intensity of light illumination. Using PV simulations, in conjunction with some reasonable assumptions regarding the practical specimen parameters in the FIB-milled specimen, we can generate a credible explanation of the experimental result. These findings will help to fully understand the PV effect in various types of solar cells, including perovskite and quantum dot cells.