Transient Ion Drift Measurements of Polycrystalline CdTe PV Devices

The well known transient ion drift (TID) method is used to quantify the density of mobile Cu interstitial ions in polycrystalline CdTe PV cells. Average Cu
_i

⁺
ion densities in optimally processed cells are 20% of the background ionized acceptor doping level. A preliminary estimate of the diffusion coefficient for Cu
_i

⁺
ions in the polycrystalline CdTe absorber is D(Cu
_i
)=1.3E-6 [cm
²
/sec] times exp[-0.29 eV/(KB*T)] in the temperature range of 25degC to 55degC from TID measurements. Aspects of the TID method as pertains to practical thin film polycrystalline devices are discussed