Transient or hysteresis effects in polycrystalline thin film CdS/CdTe cells are a function of pre-measurement
voltage bias and whether Cu is introduced as an intentional dopant during back contact fabrication. When Cu is added,
the current-density (J) vs. voltage (V) measurements performed in a reverse-to-forward voltage direction will yield
higher open-circuit voltage (Voc), up to 10 mV, and smaller short-circuit current density (Jsc), by up to 2 mA/cm2,
relative to scanning voltage in a forward-to-reverse direction. The variation at the maximum power point, Pmax, is
however small. The resulting variation in FF can be as large as 3%. When Cu is not added, hysteresis in both Voc and
Jsc is negligible however Pmax hysteresis is considerably greater. This behavior corroborates observed changes in
depletion width, Wd, derived from capacitance (C) vs voltage (V) scans. Measured values of Wd are always smaller in
reverse-to-forward voltage scans, and conversely, larger in the forward-to-reverse voltage direction. Transient ion drift
(TID) measurements performed on Cu-containing cells do not show ionic behavior suggesting that capacitance transients
are more likely due to electronic capture-emission processes. J-V curve simulation using Pspice shows that increased
transient capacitance during light-soak stress at 100 °C correlates with increased space-charge recombination. Voltagedependent
collection however was not observed to increase with stress in these cells.
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