Open Circuit Voltages for PERC Local Back Surface Fields Directly Resolved at the Nanoscale

The open circuit voltage is a critical indicator of solar cell performance and degradation. At the often-critical nanoscale, however, V
_OC
detection is much more challenging, due to practical limitations on spatial resolution, voltage resolution, and/or measurement times. Accordingly, a new Atomic Force Microscopy based approach is described for directly imaging the local V
_OC
. This is demonstrated with cross-sectioned monocrystalline PERC cells around the entire circumference of a poly-Si via. The V
_OC
maps reveal 1-3 μm of uniform Al in-diffusion throughout this local Back Surface Field. Such high spatial resolution methods for photovoltaic performance mapping are especially promising for identifying markers of degradation in silicon and other solar cell technologies.