Photovoltage Decay in CDTE/CDS Solar Cells

Abstract

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