The impact of different metallization layers on CdTe solar cells contacted with ZnTe:Cu buffer layers

It is difficult to form ohmic contact with CdTe because of its high work function (5.7 eV), so a buffer layer is oftenused to decrease the barrier height. Previously, we demonstrated high efficiency solar cells using rapid thermal processing (RTP) to activate back contacts comprised of a ZnTe:Cu buffer and gold metallization layer. However, since Au is not practical for commercialization in this work we explore chromium and titanium as more practical alternatives. It was found that comparable performance could be obtained with each metal, but that the optimal Cu loading scaled as one would expect based on solubility. Comparisons of current-voltage and quantum efficiency behavior among devices produced with insufficient, optimal, and excess Cu dosing are used to provide insight into the role(s) of this critical impurity for device performance. Reliability tests were carried out under different stressing conditions and the results show the relation of the degradation with both the metal and the presence of illumination.