Tungsten oxide nanocrystals doped with interstitial methylammonium cations

Doping of semiconductor nanocrystals is a well-established process to impart new or enhanced functionalities to the host material. In this work we present the synthesis of colloidal WO₃ nanocrystals doped with interstitial methylammonium cations. The organic cations are located within the voids of the WO₃ cage and increase the charge carrier concentration. As a result, the nanocrystals exhibit intense surface plasmon resonances in the near infrared, comparable to those obtained for WO₃ "bronzes" doped with alkali metals. We confirm the successful incorporation of these novel organic dopants through a combined experimental and theoretical study. Furthermore, we demonstrate the ability to dope the nanocrystals with even larger cations including formamidinium, providing a pathway to obtaining WO₃ doped with bespoke organic cations that offer additional functionalities for use in optics, electronics and catalysis.