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) = v(0) + A(1)exp (-t/tau(1)) + A(2)exp (-t/tau(2)) + A(3)exp (-t/tau(3)) where v is the voltage, t is time, tau(1), tau(2) and tau(3) are characteristic decay times, and A(1), A(2), A(3) and v(0) are constants. The three time constants have values of approximately 5 - 10 mu s, 50-100 mu s, and 800 - 1500 mu s 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.