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Optical Method for Automated Real-Time Control of Elemental Composition, Distribution, and Film Thickness in CIGS Solar Cell Production



Laboratory: National Renewable Energy Laboratory (NREL)

Overview: The solar industry has shown significant growth over the past decade. From 2002 to 2007, the market for copper indium gallium selenide (CIGS) grew 60% annually, and it is estimated that the global CIGS market will grow to $7.6 billion by 2016.

CIGS solar cells are one of the most promising material systems for thin-film photovoltaic (PV) because of their proven efficiency advantages over other thin film materials such as cadmium telluride and amorphous silicon. Because of extreme competition and pricing pressures in the PV market, it is imperative to develop inline metrology tools for CIGS manufacturing that will increase efficiency, decrease costs, and increase throughput.

Three of the major challenges in CIGS PV manufacturing are control of CIGS composition, gallium gradient, and film thickness. NREL scientists have recently developed and demonstrated a new, all-optical method for real-time control of all three of these critical parameters. This new technology has great promise for reducing CIGS manufacturing costs by reducing plant-commissioning time, increasing module efficiency, reducing efficiency variations, and enhancing overall quality control.

Description: High efficiency Cu(In1-xGax)Se2 solar cells are fabricated using the three-stage method, with the Cu/(In+Ga) ratio in the range of 0.84 < x < 0.92, outside of which the cell performance will drop significantly. In addition, the distribution of In+Ga between the 1st and 3rd stages and the total film thickness are also important parameters. However, during the growth process, the deposition rates vary from stage to stage and from run to run, either as needed for optimization or due to system instability. As a result, it is challenging to control: 1) the Cu/(In+Ga) ratio; 2) the distribution of In+Ga between the 1st and 3rd stages ; and 3) the film thickness.

NREL scientists developed a novel method based on real-time optical metrology to control these three critical properties. This methodology is based on optical reflection measurements that can be easily incorporated into the deposition system for real-time inline measurement and control. For specific targeted Cu/(In+Ga) ratio, Ga distribution and film thickness, control signals can be sent in real time to properly: 1) terminate each of the stages in case of stationary substrates; or 2) adjust the moving speed of the substrates, the deposition rates, and/or the starting/ending positions of each or some of the stages in case of moving substrates. This invention provides a 10x improvement in the control of these critical properties and expands the parameter space that can be systematically explored.

This invention enables a new process for production of CIGS modules using the 3-stage method and utilizing optical monitoring for generation of control signals for precise control of I/III ratio, distribution of column I and III elements in the film, and film thickness. It has the potential to be developed into a new product built by an equipment manufacturer and sold to PV manufacturers, or it could be developed within a CIGS manufacturing company.


  • Reduced manufacturing costs
  • Reduced plant commissioning time
  • Reduced downtime
  • Enhanced quality control

Potential Applications:

  • Photovoltaics
  • Thin films
  • CIGS
  • Photovoltaic manufacturing

Opportunity: Available for licensing

Contact: Ty Ferretti

View the original listing at the Energy Innovation Portal.

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