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High-efficiency, monolithic, multi-bandgap, tandem photovoltaic energy converters

National Renewable Energy Laboratory

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Technology Marketing Summary

Matching a semiconductor’s bandgap to incident photon energy is a well-known method to achieve the most efficient photovoltaic devices.  Since solar radiation consists of a wide range of wavelengths, having one semiconductor with a single bandgap to absorb all solar radiation is highly inefficient.  As such, the use of tandem or multi-bandgap converters having two or more discrete bandgaps to match different wavelengths of solar radiation has led to ultra-high efficiency photovoltaic devices. The semiconductor materials used in these multijunction devices, however, are prone to material defects which may significantly reduce device efficiency and are currently an area of intense study.

One strategy to growing multijunction semiconductor devices is to epitaxially deposit the device materials on lattice-matched substrates in order to minimize the internal strain on the material’s crystal lattice, which in turn minimizes the formation of material defects that degrade the electrical characteristics of the device. However, defect problems persist in multijunction cells because not all semiconductor materials with desirable bandgaps are able to be grown on adjacent lattice-matched materials.  While strategies have been developed to grow lattice-matched devices with absorber bandgaps in the lower range of the energy spectrum, the high-bandgap sub-cells in these devices are necessarily mismatched.  Because most of the power in a multijunction photovoltaic device is generated in the higher bandgap sub-cells, these defects are particularly concerning.  As such, methods of growing monolithic, multijunction photovoltaic devices with lattice-matched medium- and high-bandgap sub-cells are desirable.


Researchers at NREL have developed a way to create a high-efficiency, monolithic, multijunction, photovoltaic devices formed through the epitaxial lattice-matched growth of at least one high (> 1.7eV) sub-cell and at least one medium (1.1 -1.7eV) bandgap sub-cell, followed by the growth of a lattice-mismatched low (<1.1 eV) bandgap sub-cell on a compositionally graded layer. After growth of the sub-cells and removal of the substrate, an ultra-thin, monolithic, multijunction solar photovoltaic device is formed. Ultimately, these multijunction solar photovoltaic devices provide superior efficiency, lower cost, improved thermal management, device flexibility, and are adaptable and useful for monolithic integrated module applications.

  • Lower cost than traditional multijunction cells
  • Flexible materials
  • Lightweight devices
  • High-efficiency (33.1% conversion efficiency in an un-concentrated system, and 41.5% efficiency under 250 suns)
Applications and Industries
  • Concentrating Photovoltaic Devices
  • Extraterrestrial Photovoltaic Devices
  • Any application where high-efficiency and low weight is required (e.g. drones, portable devices)
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 8,067,687
High-efficiency, monolithic, multi-bandgap, tandem photovoltaic energy converters
A monolithic, multi-bandgap, tandem solar photovoltaic converter has at least one, and preferably at least two, subcells grown lattice-matched on a substrate with a bandgap in medium to high energy portions of the solar spectrum and at least one subcell grown lattice-mismatched to the substrate with a bandgap in the low energy portion of the solar spectrum, for example, about 1 eV.
National Renewable Energy Laboratory 11/29/2011
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI 05-05DevelopmentAvailable06/23/201606/23/2016

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To: Bill Hadley<>