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Multilayer Carbon Nanotube Films

National Renewable Energy Laboratory

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Technology Marketing Summary

Perovskite photovoltaics are a new class of light absorbers with exceptional and unparalleled progress in solar power performance. A perovskite is any material with a specific ABX3 crystal structure. In photovoltaic applications, the A cation can be either organic, inorganic, or hybrid in composition. The B component is typically a metal cation such as lead, and X is a halide such as iodine or bromine. Work on solar cells using perovskite materials has advanced rapidly as a result of the material’s excellent light absorption, charge-carrier mobilities, and lifetimes – resulting in high device efficiencies with low-cost, industry-scalable technology. While the potential for perovskite photovoltaic devices is high, commercialization will require overcoming other challenges relating to material stability, efficiency, and environmental compatibility


Carbon nanotube films have been identified as a promising replacement for Spiro-OMeTAD as hole-selective transport layers in perovskite photovoltaic devices.  While Spiro works well as a hole-selective transport layer, there are serious concerns that it is also a significant source of perovskite cell performance degradation over time due to migration of Li atoms into the perovskite bulk.  As such, replacement transport layer materials are currently under investigation, including carbon nanotubes.

Researchers at NREL have created a novel invention in which a bilayer of carbon nanotubes is used as a hole transport layer, wherein a first carbon nanotube layer (wrapped in a P3HT polymer) provides an energetically favorable contact interface with the perovskite absorber layer, while the second carbon nanotube layer doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is optimized for transport of holes out of the perovskite device. This bilayer improves stability of the absorber layer and enables perovskite device architectures desiring a transparent hole-selective contact (e.g. for BIPV window applications). A prototype device can transition from a highly transparent bleached state (68% visible transmittance) to a highly absorbing colored photovoltaic state (<3% visible transmittance) in the presence of heat. This could allow for the production of windows that become tinted and photovoltaic in the presence of sunlight, producing clean electricity and reducing building cooling costs.

This technology is within the Hole and Electron Extraction Layer Engineering group of NREL’s perovskite portfolio. For further information regarding NREL's broader perovskite portfolio, please visit NREL's Perovskite Patent Portfolio website.

The Hole and Electron Extraction Layer Engineering group comprises improvements to material layers in a perovskite solar cell device beyond the perovskite absorber layer itself. These technologies overcome the limitations of metal-organic device interfaces and device interface layers such as spiro-OMeTAD.

  • Improved absorber stability
  • Can be used in transparent perovskite device architectures
Applications and Industries
  • Perovskites
  • Photovoltaics
  • Building integrated photovoltaics (BIPV) window applications
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI 17-54PrototypeAvailable05/11/201705/11/2017

Contact NREL About This Technology

To: Bill Hadley<>