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Thin Film Photovoltaic Devices with a Minimally Conductive Buffer Layer

National Renewable Energy Laboratory

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Technology Marketing Summary

Thin film photovoltaic devices generate electrons which are collected on the surface of the device by a front contact layer. In order to minimize the impact of small manufacturing defects, it has become common to use a buffer layer between the front contact layer and the underneath window layer. Due to their location in the thin film stack, buffer layers must be minimally optically absorbent so that light can pass through and also have a low surface roughness so sufficient contact is made with the front contact. Buffer layers can also improve device performance if they have a more intermediate resistivity, but this has been difficult to accomplish with traditional manufacturing techniques.

Description

Researchers at NREL have developed a method to create a buffer layer that is minimally conductive as well as sufficiently optically transparent and smooth. The process incorporates a high permittivity host oxide precursor and an additive oxide precursor to create a buffer layer on the front contact with sufficient bandgap that minimal conductivity can be maintained. As a result the process can be integrated into existing manufacturing methods with the additional benefit that buffer layer properties such as resistivity, transmission, and chemical resistance may be tuned by injecting an additive during deposition. This tunability allows the creation of a high performance buffer layer with thickness that can be optimized to match the requirements of a particular thin film PV device.

Benefits
  • Minimal conductivity with sufficient transparency and smoothness
  • Tunable resistivity and thickness
Applications and Industries
  • Thin film CdTe
  • Thin film CIGS
  • Utility scale photovoltaics
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 9,496,426
Patent
9,496,426
Thin film photovoltaic devices with a minimally conductive buffer layer
A thin film photovoltaic device (100) with a tunable, minimally conductive buffer (128) layer is provided. The photovoltaic device (100) may include a back contact (150), a transparent front contact stack (120), and an absorber (140) positioned between the front contact stack (120) and the back contact (150). The front contact stack (120) may include a low resistivity transparent conductive oxide (TCO) layer (124) and a buffer layer (128) that is proximate to the absorber layer (140). The photovoltaic device (100) may also include a window layer (130) between the buffer layer (128) and the absorber (140). In some cases, the buffer layer (128) is minimally conductive, with its resistivity being tunable, and the buffer layer (128) may be formed as an alloy from a host oxide and a high-permittivity oxide. The high-permittivity oxide may further be chosen to have a bandgap greater than the host oxide.
National Renewable Energy Laboratory 11/15/2016
Issued
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI 11-75PrototypeAvailable09/07/201709/07/2017

Contact NREL About This Technology

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