AlxGa1-xAs/Si (x= 0–0.22) Tandem Solar Cells Grown by Metalorganic Chemical Vapor Deposition

Abstract

Studies of Alx Ga1-x As/Si (x=0–0.22) tandem solar cells have been carried out by using metal organic chemical vapor deposition (MOCVD). The GaAs/Si tandem solar cell consists of a GaAs top cell with the Al0.3Ga0.7As buffer layer and a Si bottom cell with the n+-p-p+ structure. The theoretical analyses of the Si bottom cell are carried out for tandem solar cell application. The suitable resistivity of the p-Si substrate for the Si bottom cell has been found to be 10 Ω· cm, which corresponds to the experimental results. The active-area conversion efficiency of 19.5% (1sun, AM0) for the GaAs/Si tandem solar cell has been achieved in the three-terminal configuration. In the case of the Alx Ga1-x As/Si tandem solar cell, x varies from 0.1 to 0.22. The crystalline quality of the Alx Ga1-x As heteroepitaxial layer grown on Si is improved, using a high-temperature growth process ( 800°C) and thermal cycle annealings ( 300–900°C). The active-area conversion efficiencies of 20.0% and 19.0% (1sun, AM0) for the Al0.15Ga0.85As/Si tandem solar cell are obtained with four-terminal and two-terminal configurations, respectively.