Effects of Cu from ZnTe:Cu contacts in CdS/CdTe cells

Abstract

CdS/CdTe devices processed with ZnTe:Cu/Ti back contacts are studied as a function of contact deposition temperature between -200°C and -400°C. Both the open-circuit voltage ( V, , ) and fill factor (FF) increase with temperature.

Effect of CdCl2 Treatment on the Interior of CdTe Crystals

“…In particular, the annealing stabilizes cadmium vacancy centers and results in the formation of Curelated centers. The latter result is consistent with the recent SIMS work at NREL demonstrating the incorporation of Cu into the device during CdCl 2 treatment [8]. While SIMS cannot differentiate between Cu in grain boundaries and Cu within the grains, this experiment suggests at least some of the Cu is incorporated into the grains.…”

“…It is generally accepted that the CdCl 2 process promotes grain boundary growth and passivation, and facilitates interdiffusion of S and Te near the CdTe/CdS junction [1][2][3][4][5]. Recently, evidence has been presented suggesting that CdCl 2 treatment affects doping and carrier barrier height at the grain boundaries [6,7] and results in the incorporation of Cu into the CdTe layer [8]. The above effects are not fully understood, and it is not known how they work in tandem to improve solar cell performance.…”

Thickness Simulation and Analysis of CdS/CdTe Solar Cell to Increase the Efficiency and Decrease the Toxicant Material of Cadmium

“…ZnTe becomes easily-doped with elements such as phosphorus, arsenic, etc. Impure ZnTe produces with Rf distribution and MOCVD technology [11]. Silvaco simulating software has been utilized.…”

Formation Of ZnTe: Cu/Ti Contacts at High Temperature for CdS/CdTe Devices

“…Devices with fill factors of 77% have been demonstrated by incorporating a Cu-doped ZnTe contact interface layer between the CdTe absorber and a Ti outer metallization [1]. The interface formed between ion-beam milled CdTe (i.e., no Te layer) and ZnTe:Cu yields a valence band without discontinuity [2].…”

“…This diffusion can be used to increase NA-ND in the CdTe layer -transforming the junction from an n-i-p structure (i.e., CdTe is lightly p-type, the depletion layer [Wd] extends across entire CdTe layer, and device voltage depends on work function near back surface) into an n-p structure (i.e., CdTe is more p-type, Wd is engineered to enable maximum current collection, and device voltage is determined by CdTe NA-ND) [4]. Techniques to vary Cu diffusion have included controlling the contact deposition temperature while maintaining a "near optimum" ZnTe:Cu thickness of about 0.5 µm [1], or controlling the ZnTe:Cu thickness while maintaining a "near optimum" deposition temperature of about 320°C [5]. Combined compositional (secondary ion mass spectrometry, SIMS) and capacitance-voltage (C-V) analysis has shown that Cu diffusion from the ZnTe:Cu layer occurs at the same time that NA-ND increases in the CdTe, reducing Wd of the device.…”