The scientists had built a solar cell by placing graphene on top of the high-performance semiconductor copper indium gallium diselenide (CIGS), which in turn was stacked on top of soda-lime glass (SLG), the same industrial-grade glass used for windows and bottles. When the researchers measured the baseline performance of the cell before proceeding to dope the graphene, they found to their surprise that the graphene had already been doped to the ideal level.

As they later discovered, this was because the sodium ions in the glass spontaneously transferred to the CIGS semiconductor by surface contact, and from there to the graphene, creating a concentration of impurities that happened to dope the graphene in just the right concentration.

Crucially, this method doesn't require high-temperature, chemical or vacuum processes, and the doping remained strong even when the cell was exposed to air for several weeks. What's more, the same method could also be applied to combinations of semiconductors and substrates other than CIGS and glass, where the concentration of doping impurities that reach graphene can be fine-tuned by inserting an insulating layer of the right thickness.

Eoin Treacy's view

Graphene has been a long time coming and it has not quite reached commercialisation yet. but the number of discoveries relating to it continues to increase and its potential is undiminished. We don’t know when the key mass production breakthrough will be made but it will be particularly transformative for the battery sector which remains in need of a major breakthrough to revolutionise energy storage.