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.