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Photoluminescence-based Quality Control for Thin Film Absorber Layers of Photovoltaic Devices

National Renewable Energy Laboratory

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Technology Marketing Summary

Thin film Cu(In, Ga)Se2 (CIGS) photovoltaics offer a promising source of renewable generation, with low material and energy use in manufacturing and high efficiency. Research to improve this technology is focused on achieving the lowest cost per watt generated, which in turn relies on inexpensive commercial production. One shortcoming of CIGS photovoltaic production is that it is difficult to monitor the quality of the absorber layer during fabrication due to the complicated nature of CIGS devices, namely the inclusion of four constituent elements (cadmium, indium, gallium, and selenium). As a result, the quality of CIGS absorber layers is often not known until after the entire device is manufactured and cannot be modified. Real time quality control is essential in order to optimize the production of CIGS devices and improve the quality and economics of this technology.  


Researchers at NREL have created a system that allows in-situ evaluation of absorber layers immediately after deposition, providing real time feedback to the fabrication process. The system uses a single fiber to deliver light from a low-power pulsed diode laser into the absorber layer and collect the fluoresced light. The resulting measurement, time-resolved photoluminescence (TRPL), can be correlated to charge carrier lifetime, one of the most important properties of an absorber layer. The fluoresced light is measured by a solid state photodetector the does not require liquid nitrogen cooling and a digital oscilloscope rather than single-photon counting, so that millions of measurements can be taken per second. The effect of these components is a compact, low power, no maintenance solution that is able to accurately measure the quality of a CIGS absorber layer immediately after deposition. 

  • Allows evaluation of CIGS absorber layer in-situ, providing real time feedback to fabrication process
  • Utilizes inexpensive and safe diode laser
  • Able to collect broad spectrum of light (1000-1300 nm)
  • Easily implemented into existing manufacturing processes with no maintenance required
Applications and Industries
  • CIGS photovoltaics
  • Thin film manufacturing
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 9,075,012
Photoluminescence-based quality control for thin film absorber layers of photovoltaic devices
A time-resolved photoluminescence-based system providing quality control during manufacture of thin film absorber layers for photovoltaic devices. The system includes a laser generating excitation beams and an optical fiber with an end used both for directing each excitation beam onto a thin film absorber layer and for collecting photoluminescence from the absorber layer. The system includes a processor determining a quality control parameter such as minority carrier lifetime of the thin film absorber layer based on the collected photoluminescence. In some implementations, the laser is a low power, pulsed diode laser having photon energy at least great enough to excite electron hole pairs in the thin film absorber layer. The scattered light may be filterable from the collected photoluminescence, and the system may include a dichroic beam splitter and a filter that transmit the photoluminescence and remove scattered laser light prior to delivery to a photodetector and a digital oscilloscope.
National Renewable Energy Laboratory 07/07/2015
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
REL ROI 10-04PrototypeAvailable09/07/201709/07/2017

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To: Bill Hadley<>