Role of the graded band gap layer in increasing the short wavelength sensitivity of three cascade solar cells

In this paper two structures of three cascade solar cells are discussed and analyzed. The first one is a three cascade solar cell with upper wide gap "window", which exhibited an appreciable values of its main parameters (I_sc, V_oc). However, this structure has a limited short wavelength sensitivity because of the surface recombination. In order to improve the main parameters of the above mentioned structure - particularly the short wavelength sensitivity - a new structure of three cascade solar cells, with graded band gap upper layer is suggested. This structure has been elaborated by combining liquid phase epitaxy with gas-phase zinc diffusion technologies, and the graded band gap upper layer has been fabricated by utilization of a special cassette of penal-box type. This new structure has shown better parameters than the parameters of the three cascade solar cell with upper wide gap "window". It exhibits appreciable values of photo-current and output voltage. Furthermore, this structure provides high short wavelength sensitivity due to the utilization of the graded band gap layer.