A single surface-potential number averages away everything that makes a material interesting: grain boundaries, junction zones, patches of different doping or phase. The distribution across a surface tells the real story of the space-charge region, and mapping it is the measurement that reveals inhomogeneity.
Photogenerated carriers move according to local fields. A surface with strong potential variation separates charge unevenly: some regions drive carriers to the surface, others drive them away, and the net photoresponse is the area-weighted sum. Two samples with identical average potential but different distributions can behave very differently.
Grain size and boundary density, phase purity, dopant uniformity, junction sharpness in composite materials, and surface adsorbates. Processing artifacts, non-uniform deposition, incomplete annealing, leave their signatures in the map long before microscopy finds them.
Probe with a defined geometry and spacing appropriate to the feature size expected, sampling coarser than the features measures nothing. Keep probe pressure, illumination and atmosphere constant across the map. Record the scan parameters with the data: a map without its acquisition conditions is an image, not a measurement.
Look for: contrast scale (how strong is the variation), feature size distribution, and correlation with known structure. Compare maps across sample batches to separate material physics from preparation noise. Where photoresponse and potential maps are both available, their correlation is direct mechanistic evidence.
For photovoltage and potential characterization platforms, see Perfectlight's physical characterization systems and mechanism research solutions.
