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Addition of Refractory Metals to CdTe Contact Interface Layers

National Renewable Energy Laboratory

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Technology Marketing Summary

Thin film cadmium telluride (CdTe) solar cells rely on a back contact, usually including a zinc telluride (ZnTe) interface layer doped with copper (Cu), to establish a low-resistance pathway for electrons to enter the device during operation. When Cu is allowed to diffuse into the CdTe absorber layer it creates a more favorable electrical contact with the back contact, and has the additional benefit of increasing carrier lifetime within the CdTe layer. Unfortunately, Cu readily reacts with oxygen which can create copper oxide (CuO) and prevent copper diffusion into the absorber layer. A solution that prevents copper from reacting with ambient oxygen is needed to enable enhanced CdTe photovoltaic devices.

Description

Researchers at NREL have created a novel method and device that incorporates a Group 4 metal, such as titanium (Ti), as a getter to react with oxygen and allow greater diffusion of Cu into the absorber layer. A Ti compound, such as TiTe2, is created to prevent Cu from reacting with oxygen during the sputtering process in which it is deposited. During deposition the compound is fractionated into its elements, producing an interface layer with a small amount of Ti getter that is enriched in Te. Extra Te that diffuses across the interface layer reduces the likelihood of defects in the absorber due to Te deficiency, which manifest as mid-gap recombination sites. This process results in a device with consistently higher voltage of about 100 mV and higher when compared to substantially identical devices using Ni or another metal as the outer contact.

Benefits
  • Increased electrical contact favorability
  • Longer carrier lifetime in absorber
  • Lower carrier recombination
Applications and Industries
  • CdTe photovoltaic devices
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Application 20150270423
Application
20150270423
DEVICES AND METHODS FEATURING THE ADDITION OF REFRACTORY METALS TO CONTACT INTERFACE LAYERS
Disclosed embodiments include CdS/CdTe PV devices (100) having a back contact (110,112) with oxygen gettering capacity. Also disclosed are back contact structures (110, 112) and methods of forming a back contact in a CdS/CdTe PV device (100). The described contacts and methods feature a contact having a contact interface layer (100) comprising a contact interface material, a p-type dopant and a gettering metal.
National Renewable Energy Laboratory 05/30/2013
Filed
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI 12-44PrototypeAvailable09/07/201709/07/2017

Contact NREL About This Technology

To: Bill Hadley<bill.hadley@nrel.gov>