Study of ZnTe:Cu Back Contacts on CdTe/CdS Thin Film Solar Cells

Abstract

Vacuum-evaporated Cu-doped ZnTe films have been studied as the intermediate layer between CdTe and metal contacts in CdTe/CdS thin-film solar cells for the formation of low resistance back contacts. Different metals (Au, Ni, Co) have been investigated as the contact material to the ZnTe layer. The effects of Cu concentration, ZnTe:Cu layer thickness, and ZnTe post-deposition annealing temperature on the cell performances have been investigated. We found that different metal contacts on the ZnTe layer lead to different doping densities in the CdTe layer and different open-circuit photovoltages of the solar cells. The possible formation of a back contact diode at the CdTe/ZnTe interface was explored, based on capacitance-voltage analysis. The series resistance of the CdTe/CdS cells was reduced significantly by the introduction of the ZnTe layer. Fill factors greater than 0.76 and an energy conversion efficiency of 12.9% have been achieved using ZnTe back contacts on electrodeposited CdTe.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

“…183 The materials used to obtain ohmic contact in superstrate CdTe devices are graphite paste, Te/Au, Sb/Au, Ni, PbTe, SnTe, HgTe, ZnTe, Cu/Au, Cu/graphite, Cu doped ZnTe with metallization and Cu/Mo. [184][185][186][187][188][189][190][191][192][193][194][195][196] The most commonly used metal to make a non-rectifying contact with CdTe is Cu. There are various methods to apply Cu at the CdTe back surface; evaporation of thin Cu lms onto the CdTe surface; application of graphite paste containing Cu powder/Cu salts or Cu doped alloys; and dipping or spraying the Te-rich surface with Cu salt solutions.…”

Polycrystalline thin film cadmium telluride solar cells fabricated by electrodeposition. Annual technical report, 20 March 1995--19 March 1996

“…This is consistent with our SEM and optical microscopy observations of CdS surfaces. There have been a lot of reports [5][6][7][8][9] on the structural properties of CdS films prepared by CBD . However, the results are scattered over a wid� range because of different depos i tion conditions used in various laboratories.…”