Growth, fabrication, and characterization of InGaN solar cells

The InGaN alloy system offers a unique opportunity to develop high efficiency multi-junction solar cells. In this study, single junction solar cells made of InxGa1-xN are successfully developed, with x = 0, 0.2, and 0.3. The materials are grown on sapphire substrates by MBE, consisting of a Si-doped InGaN layer, an intrinsic layer and an Mg-doped InGaN layer on the top. The I-V curves indicate that the cell made of all-GaN has low series resistance (0.12 Omega cm(2)) and insignificant parasitic leakage. Contact resistances of p and n contacts are 2.9 x 10(-2) Omega cm(2) and 2.0 x 10(-3) Omega cm(2), respectively. Upon illumination by a 200 mW/cm(2), 325 nm laser, V-oc is measured at 2.5 V with a fill factor of 61%. Clear photo-responses are, also observed in both InGaN cells with 0.2 and 0.3 Indium content when illuminated by outdoor sunlight. But it is difficult to determine the solar performance due to the large leakage current, which may be caused by the material defects. A thicker buffer layer or GaN template can be applied to the future growth process to reduce the defect density of InGaN films.