https://phys.org/news/2019-01-efficiency-electronics.html

For organic—that is, carbon-based—semiconductors, this doping process is also highly important. Since the discovery of electrically conducting plastics and polymers, a field for which the Nobel Prize was awarded in 2000, research and development of organic electronics has accelerated quickly. OLED-displays are one example already on the market, for example, in the latest generation of smartphones. Other applications have not yet been fully realised, due in part to the fact that organic semiconductors are not yet efficient enough.

Doping in organic semiconductors operates through what is known as a redox reaction. This means that a dopant molecule receives an electron from the semiconductor, increasing the electrical conductivity of the semiconductor. The more dopant molecules that the semiconductor can react with, the higher the conductivity—at least up to a certain limit, after which the conductivity decreases. Currently, the efficiency limit of doped organic semiconductors has been determined by the fact that the dopant molecules could only exchange one electron each.