Photovoltage Decay in CDTE/CDS Solar Cells

Photo-voltage decay (PVD) is a common technique used to characterize numerous semiconductor devices. However, the technique has not been widely applied to CdTe-based solar cells. We have applied PVD to CdTe solar cells made with various fabrication conditions using a red (620 nm) LED and digital oscilloscope. We find the decay to be described by the equation v(t)=V₀+A₁exp (-t/tau₁)+A₂exp (-t/tau₂)+A₃ exp (-t/tautau₁) where v is the voltage, t is time, tau₁, tau₂ and tau₃ are characteristic decay times, and A₁, A₂, A₃ and V₀ are constants. The three time constants have values of approximately 5-10 mus, 50-100 mus, and 800-1500 mus respectively. In general, cells with lower conversion efficiency have shorter decay times. The exponential nature of the decay indicates that in CdTe/CdS solar cells, the PVD is dominated by capacitance effects. The time constants decrease with increasing temperature