Optimization of the p(+)-ZnTe layer for back contacts of ZnTe thin-film solar cells

Abstract

We have studied the performance of ZnTe-based heterojunction diodes grown on p-GaAs substrates by using pulsed laser deposition (PLD). In the X-ray diffraction measurements, ZnTe and CdS thin films grown on p-GaAs (100) substrates appeared to have a cubic crystalline structure while the ZnO film showed a hexagonal structure. The structure of n(+)-ZnO/i-ZnTe/p-GaAs with insertion of a CdS buffer layer between n(+)-ZnO and i-ZnTe showed strong rectifying diode characteristics, and its open-circuit voltage (V (oc) ) and short-circuit current density (J (sc) ) under 1,000 Wm(-2) air mass 1.5 global (AM 1.5G) illumination were measured about 0.32 V and 0.61 mAcm(-2), respectively. When an inserted another layer, a ZnTe:Cu layer, as a p(+)-layer for the contacts on p-GaAs substrate, the value of V (oc) and J (sc) of the n(+)-ZnO/CdS/i-ZnTe/ZnTe:Cu/p-GaAs structure increased to 0.39 V and 0.81 mA/cm2, respectively. As the thickness of i-ZnTe were increased from 210 to 420 nm, the photoelectric conversion efficiency of the n(+)-ZnO/CdS/i-ZnTe/ZnTe:Cu/p-GaAs structure increased to 0.24%.