Recently, there has been substantial interest in the fluorination of nanomaterial thin films used in various optoelectronic devices for optimum charge transport across semiconducting layers. The discovery of electrophilic fluorinating agents such as Selectfluor® (F-TEDA) has led to the development of novel methods for fluorination of metal oxides such as tin oxide (SnO2) in this work. Herein, we elucidate the fluorination of SnO2 thin film using X-ray photoelectron spectroscopy (XPS) depth profiling. The interaction of F-TEDA molecule with SnO2 surface occurs via N-F bond. Fluorine is found to occupy interstices and substitutional sites in SnO2 lattice. The interstitial fluorine (1.21 at%) decays off by a depth of 61 nm in SnO2 film. The substitutional fluorine (1.28 at%) in SnO2 results in remarkable changes in its electronic structure due to the lowering of oxygen defects by ~80%. The electrical properties of F-SnO2 film is examined by impedance spectroscopy analysis. F-SnO2 exhibits an increase in electrical conductivity by ~1-2 order magnitude and a rise in electron density by ~65%, making it suitable as a charge transport layer in photoelectrochemical cells (PEC). The PEC in aqueous medium at neutral pH with F-SnO2 as the charge transport layer shows ~81% increase in the photocurrent density (at 1.6 V versus RHE) and decrease in charge transfer resistance by ~36%. Thus, the efficient transport of photogenerated charge carriers is observed in PEC with minimal recombination losses for fluorinated SnO2 films. This study helps in understanding the role of defect passivation via single-step fluorination of metal-oxide for charge transport layers that can be extended to perovskite solar cells in the future.

Chemical insights into electrophilic fluorination of SnO2 for photoelectrochemical applications

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.