Improvement in the spectral response at long wavelength of a-SiGe:H solar cells by exponential band gap design of the i-layer

A new band gap profile (exponential profile) for the active layer of the a-SiGc:H single junction cell has been designed and experimentally demonstrated. In this paper we compare its optical and electrical characteristics with the two more common profiles: the U- and V-shapes. As predicted by the simulations, the new profile combines the advantages of both profiles. Like the V-shape, the exponential shape reduces the amount of Ge in the i-layer, decreasing both the space charge defect density inside the i-layer and the recombination losses. It also improves the electric field. At the same time. the exponential shape generates the same current density as the U-shape. (C) 2002 Elsevier Science B.V. All rights reserved.