Applications of scanning Kelvin probe microscopy in the characterization of photovoltaic materials and devices

We have in recent years developed scanning Kelvin probe microscopy (SKPM), and applied this nanometer resolution technique to the characterization of III-V-, II-VI-, and thin film Si-based single- and multi-junction solar cell devices. In this presentation, we will report our improvements of the SKPM technique and show three examples of the potential measurements. We will first show a Bi-incorporation-induced junction movement in a MBE-grown single-junction GaInNAs cell. This junction movement caused significant device degradation, especially in the short wavelength range. We then present potential distributions among the top and bottom junctions in a GaInP$_{2}$/GaAs tandem-junction cell. A light-induced potential flattening in the top junction and a potential accumulation in the bottom junction was clearly measured. Lastly, we will show a non-uniform distribution of the electric field across an a-Si:H $n-i-p$ junction, and this electric field was significantly improved by depositing buffer layers at the $n/i$ and $i/p$ interfaces.