A new data mining algorithm was developed to identify the strongest correlations between capacitance data (measured between -1.5 V and +0.49 V) and first- and second-level performance metrics (efficiency [η%], open-circuit voltage [V_OC], short-circuit current density [J_SC], and fill-factor [FF]) during the stress testing of voltage-stabilized CdS/CdTe devices. When considering only correlations between first- and second-level metrics, 96.5% of the observed variation in η% was attributed to FF. The overall decrease in V_OC after 1,000 hours of open-circuit, light-soak stress at 60°C was about -1.5%. As determined by our algorithm, the most consistent correlation existing between FF and third-level metric capacitance data at all stages during stress testing was between FF and the apparent CdTe acceptor density (N_a) calculated at a voltage of +0.49 V during forward voltage scans. Since the contribution of back-contact capacitance to total capacitance increases with increasing positive voltage, this result suggests that FF degradation is associated with decreases in N_a near the CdTe/back contact interface. Also of interest, it appears that capacitance data at these higher voltages appears to more accurately fit the one-sided abrupt junction model.

Date Published: 13 September 2011
PDF: 8 pages
Proc. SPIE 8112, Reliability of Photovoltaic Cells, Modules, Components, and Systems IV, 81120V (13 September 2011); doi: 10.1117/12.896648

Published in SPIE Proceedings Vol. 8112:
Reliability of Photovoltaic Cells, Modules, Components, and Systems IV
Neelkanth G. Dhere; John H. Wohlgemuth; Kevin W. Lynn, Editor(s)