Correlations of single-crystal CuInSe2 surface processing with defect levels and cell performance

The surface treatments include polishing, etching, and annealing, In particular, high-resolution photoluminescence (PL) and deep-level transient spectroscopy (DLTS) are used to identify the dominant defect states in cleaved and processed solar (cell structures (including heterostructure formation with (Cd,Zn)S and Schottky barriers with Al on p-CuInSe₂ single crystals). These results are correlated with the junction electrical characteristics. Atomic-level images using spectroscopic scanning tunneling microscopy (SSTM) confirm the physical nature of the defect levels. Radiative recombination levels originating from the processing are identified near the surface region of the CuInSe ₂ crystals. The energy and depth locations of these states that evolve from the formation of a defect nonstoichiometric interfacial layer can limit the performance of the (Cd,Zn)S₂ single crystal CuInSe2 cells. The four major trapping levels have been confirmed by DLTS measurements. Two of these are shallow levels in the energy regions 100-114 and 150-185 meV, and two are deep levels in the range 340-385 and 475-496 meV, respectively