p-n Heterojunction of Doped Graphene Films Obtained by Pyrolysis of Biomass Precursors

Abstract

Nitrogen-doped graphene [(N)G] obtained by pyrolysis at 900 degrees C of nanometric chitosan films exhibits a Hall effect characteristic of n-type semiconductors. In contrast, boron-doped graphene [(B)G] obtained by pyrolysis of borate ester of alginate behaves as a p-type semiconductor based also on the Hall effect. A p-n heterojunction of (B) G-(N) G films is built by stepwise coating of a quartz plate using a mask. The heterojunction is created by the partial overlapping of the (B) G-(N) G films. Upon irradiation with a xenon lamp of aqueous solutions of H2PtCl6 and MnCl2 in contact with the heterojunction, preferential electron migration from (B) G to (N) G with preferential location of positive holes on (B) G is established by observation in scanning electron microscopy of the formation of Pt nanoparticles (NP) on (N) G and MnO2 NP on (B) G. The benefits of the heterojunction with respect to the devices having one individual component as a consequence of the electron migration through the p-n heterojunction are illustrated by measuring the photocurrent in the (B) G-(N) G heterojunction (180% current enhancement with respect to the dark current) and compared it to the photocurrent of the individual (B) G (15% enhancement) and (N) G (55% enhancement) components.