An ink for printed electronics

As demand rises for flexible and lightweight electronics, so does the need to develop industrial-scale, low-cost processes to fabricate them. One possible method to create printable electronics is to disperse a highly conductive, organic coating material on a flexible substrate. To date, a conducting polymer known as PEDOT:PSS has been at the heart of several prototype solar cells, LEDs, and other applications. The p-type organic thermoelectric material uses positively charged holes to conduct electricity. But various opto- and bioelectronic devices rely on complementary mixtures of p-type and n-type materials, the latter of which relies on negatively charged electrons for conductivity.

This picture shows an n-type conducting polymer ink in an ethanol solvent being sprayed on a surface. To make the ink, postdoc Chi-Yuan Yang and Simone Fabiano of Linköping University in Sweden and their colleagues started with BBL, a polymer known for its conductivity. They doped it with PEI, an insulating polymer that lowers the minimum thermodynamic work required to move an electron from a solid surface. The PEI dopant increased not only the conductivity but also the stability of the ink at ambient conditions. The researchers spray coated BBL:PEI and PEDOT:PSS onto the active layer of a solid-state thermoelectric generator. Its power output exceeded that of generators made with only p-type materials. (C.-Y. Yang et al., Nat. Commun. 12, 2354, 2021, doi:10.1038/s41467-021-22528-y ; photo courtesy of Thor Balkhed.)