Photo of ultrathin on-chip solar cells (IMAGE) American Institute of Physics Caption Photo of ultrathin on-chip solar cells. The cells are the green squares and include an ultrathin layer of light-absorbing GaAs, which is key to their radiation tolerance. The surface of each green square is only 120 nanometers, about one-thousandth the thickness of a human hair, above the surrounding gray area. The gold-colored grids are electrically conducting metal contacts. Credit Armin Barthel Usage Restrictions Journalists may use this image only with appropriate credit. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.