Nondestructive SEM measurement of minority-carrier transport parameters of CuxS/CdS solar cells as a function of heat treatment

Electron-beam-induced-current techniques of a scanning-electron microscope have been extended to allow nondestructive measurements to be performed on p-n heterojunction devices consisting of thin layers sensitively influenced by surface effects and under conditions where junction collection efficiency is less than perfect. When applied to CuxS/CdS solar cells formed on polycrystalline CdS with an epitaxial CuxS layer that was heat treated at 180°C in a hydrogen-argon ambient, the dominant change was found to be the greater than two increases in junction collection efficiencies to a maximum and then a decrease for treatment times up to 120 min. No significant variations were found in the minority-carrier diffusion lengths which remained in the 0.20- to 0.26-µm range for the CuxS and in the 0.41- to 0.46-µm range in the CdS. The Cuxsurface-recombination velocity retained a constant magnitude equal to its diffusion velocity. Optimization of the collection efficiency changes should lead to improved device performance.