Zirconium nitride contacts for cadmium telluride solar cells

cadmium telluride (CdTe);back contact;Schottky barrier;transition metal nitrides

Yang, Zhengfeng ; Rockett ; Angus A.

关键词: cadmium telluride (CdTe);    back contact;    Schottky barrier;    transition metal nitrides;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/50676/Zhengfeng_Yang.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

CdTe/CdS solar cells were produced with ZrN as a back contact by magnetronsputtering. ZrN films have been produced with crystalline quality and uniformity on CdTe.With good crystalline quality and uniformity on substrate materials, ZrN films have a lowresistivity of 12.3 to 22.0 μΩ-cm, comparable to that of good conductive metals, whichwould permit thin back contacts. Annealing at temperature up to 270°C for 30 minutes didnot affect the structure or properties of the ZrN.The effect of the thickness of the ZrN films on their back contact performance wasstudied. As the thickness of the ZrN films becomes larger, the improved microstructure ofZrN films contributes to the better cell performance. However, thicker ZrN leads to peelingoff of films. Thicknesses beyond 300 nm do not result in better contacts.Cu is known to improve the performance of CdTe/CdS solar cells. However, a dualeffect of Cu on the performance of CdTe/CdS solar cells indicates that the ones with more Cudoping perform worse and even drop to zero. SIMS depth profiles exhibit that Cu is a fastdiffuser and higher temperatures stimulate more Cu to diffuse into ZrN films and bulk ofCdTe.Compared to the conventional back contact material Au, ZrN films have lower opticalreflectance and higher transmission. This advantage would permit thinner absorber layers forthe resulting solar cells.The work function of ZrN was measured to be 4.1 eV by ultraviolet photoelectronspectroscopy (UPS). Transmission electron microscopy (TEM) indicated that the ZrN grewas columnar crystals perpendicular to the surface of CdTe with a rock-salt structure and (111)texture. A 2-3 nm thick amorphous layer of ZrN was observed at the CdTe/ZrN interface.Energy dispersive spectroscopy (EDS) showed that Cd and Te were present in the amorphouslayer and the Zr:N ratio was not 1, off stoichiometric ZrN. The low work function combinedwith the amorphous layer at the interface contributed to the resulting observed Schottkybarrier contact to the CdTe.