Band Alignment and Internal Field Mapping in Solar Cells

The internal fields and band offsets developing at individual interfaces, a critical aspect of device performance, are generally inaccessible by standard electrical tools. To address this problem, we propose chemically resolved electrical measurements (CREM) capable of resolving the internal details layer-by-layer. Applied to nanoporous photovoltaic cells, we thus extract a realistic band diagram for the multi-interfacial structure and, in particular, resolve the two p-n-like junction fields built spontaneously in the device. The lack of homogeneity common to many of these nanoporous cells is exploited here to "see" deep into the cell structure, beyond the typical depth limitations of the surface-sensitive technique. Further information on the cell operation under "real" working conditions is achieved by studying the charge trapping at each specific layer under optical and electrical stimuli. Our methodology overcomes a missing link in device characterization and in fundamental studies of nanoscale solid-state devices.