Changes in minority carrier lifetimes in a-Si:H, p-i-n photovoltaic cells due to light soaking have been investigated using the open circuit voltage decay (OCVD) method over the temperature range 223 K to 296 K.
Using light from a Xenon flash lamp for excitation produced unexpected results: in the light soaked material, band-to-band transitions were evident at a higher temperature than for the asdeposited samples and became increasingly pronounced as the temperature was reduced. Results obtained using red light at 670 nm from a pulsed diode laser to produce relatively uniform- illumination throughout the thickness of the film, however, produced results very similar to those obtained for as-deposited films.
Plots of the reciprocal of the trap activation time versus 1000/T for the results for both xenon lamp and laser excitation can be fitted by straight lines. Two distinct sets of lines with activation energies in the ranges 0.07 to 0.20 eV and 0.38 to 0.51 eV are obtained with the activation energy and the exponential prefactors exhibiting a Meyer-Neldel relationship.