Growth of CuIn 3Se 5 layer on CuInSe 2 films and its effect on the photovoltaic properties of In 2Se 3/CuInSe 2 solar cells

Abstract

The growth of CuIn 3Se 5 layer on bulk CuInSe 2 films has been studied for the fabrication of CuInSe 2 solar cells, using the three-stage process which involved the sequential evaporation of In–Se, Cu–Se, and In–Se elemental sources. After growing CuInSe 2 films, the film surface was converted to a defect chalcopyrite (CuIn 3Se 5) compound. The X-ray diffraction and AES depth analysis indicated the formation of the CuIn 3Se 5 phase on the CuInSe 2 surface. By the formation of the CuIn 3Se 5 phase, the absorption edge was shifted from 1200 to 1000 nm wavelength and the binding energies of Cu, In, and Se were shifted to higher energies. The current–voltage curves of In 2Se 3/CuInSe 2 cells fabricated with a thick CuIn 3Se 5 layer on a CuInSe 2 film displayed a kink effect which was possibly caused by the increase of series resistance and light absorption in the CuIn 3Se 5 layer instead of the junction region. The cells with a thin CuIn 3Se 5 layer at the In 2Se 3/CuInSe 2 interface yielded solar efficiency of 8.46% with an active area of 0.2 cm 2.