Amorphous Silicon Research

This report describes the Solarex RD effort as part of the Thin Film Partnership with NREL under Subcontract No. ZAN-4-13318-01. The major goal of this program has been to develop the device and processing technology necessary to commercialize large-area amorphous silicon tandem PV modules. There were three major areas of investigation in this program 1 research on mid-gap amorphous silicon alloys 2 research on low-bandgap amorphous silicon alloys and 3 research on multijunction devices and modules. The effort on mid-gap alloys has been largely focused on understanding and reducing the light-induced degradation that occurs in all amorphous silicon alloys. This investigation showed that many of the metastable centers are charged both under illumination and in the dark and that the annealing recovery of the degradation could be accelerated significantly by the application of a strong reverse bias. The experimental observations have been modeled assuming that the accelerated recovery is associated with the local motion of protons near dangling bonds. According to this model, the metastable defects can be created when an electron is trapped at a weak Si-Si bond and a hole localizes on a nearby Si-H bond the hydrogen atom can then move as a proton to the negatively charged weak bond creating a new Si-H bond and two separated dangling bonds.