MeV ion-induced changes in the density of states of amorphous silicon based alloys: The effect on the opto-electronic properties of thin films and solar cells

Amorphous silicon based alloy (a-Si:H) solar cells have been proposed as candidates for space solar cell arrays. However, before these devices are used for space applications, the effects of high-energy particle irradiation must be determined. The purpose of this dissertation is to investigate the effects of particle irradiation on the optoelectronic properties of a-Si:H thin films and solar cells. The irradiations were carried with 2.00 MeV helium-ion and 1.00 MeV proton fluences ranging from 10;No changes were observed in the band-to-band optical absorption coefficient of thin films. However, large increases in the sub-band-gap absorption were measured. The changes were modelled using a density-of-state function with a peak at about 1.35 eV below the conduction-band edge; the peak is sensitive to both fluence and annealing history.;Irradiation produced large decreases in the steady-state photoconductivity of thin films. Attempts to model the effect using the density-of-state function from the sub-band-gap optical absorption studies were not successful unless large changes were assumed in the quantum efficiency, and electron drift mobility and lifetime.;Simultaneous measurements of dual-beam photocurrent and photothermal deflection spectra suggest irradiation results in a decrease of the electron-drift mobility of thin-films. The change in mobility impedes the escape of photogenerated electrons from holes because of the coulombic potential well, resulting in geminate recombination.;The effect of irradiation on solar cells was investigated using current-voltage and quantum efficiency measurements. Cells recently fabricated were more radiation resistant than cells fabricated six years age. The difference in radiation resistance of cells is believed to be due to the fact that the newer cells have thinner and higher quality intrinsic layers. The annealing behavior of the cells was investigated. The cells anneal at room temperature and are restored to the preirradiated state with annealing at 200...