Improved Intrinsic Stability of CdTe Polycrystalline Thin Film Devices

A systems-driven approach linking upstream solar cell device fabrication history with downstream performance and stability has been applied to CdS/CdTe small-area device research. The best resulting initial performance (using thinner CdS, thicker CdTe, no oxygen during VCC, and the use of NP etch) was shown to simultaneously correlate with poor stability. Increasing the CdS layer thicknesssignificantly improved stability at only a slight decrease in overall performance. It was also determined that cell perimeter effects can accelerate degradation in these devices. A 'margined' contact significantly reduces the contribution of edge shunting to degradation, and thus yields a more accurate determination of the intrinsic stability. Pspice discrete element models demonstrate howspatially localized defects can effectively dominate degradation. Mitigation of extrinsic shunting improved stabilized efficiency degradation levels (SEDL) to near 20% in 100?C tests. Further process optimization to reduce intrinsic effects improved SEDL to better than 10% at the same stress temperatures and times.