The Study of Deep Levels in CdS/CdTe Solar Cells Using Admittance Spectroscopy and its Modifications

Measurements of an admittance over a wide frequency range were used to detect the defect electronic states and evaluate their properties in CdTe based solar cells. Cells prepared in various ways, from various facilities all exhibited a high defect state density (>10 14 cm -3 , and often >10 15 cm -3 ). Two distinct energy levels or bands were observed at approximately 0.37eV and 0.61eV above the valence band. These were tentatively attributed to Cu Cd - and V Cd -- respectively. Various post-CdTe deposition treatments, as well as stress tests, were applied to alter the defect state densities. The high defect concentration measured was not observed to inhibit cell performance in any way.