An extensive XPS analysis on sensitized PBDB-T-SF thin films for photovoltaic applications

Abstract

A new investigation on the elemental composition and optical properties stability of PBDB-T-SF thin films was performed before and after chemical sensitization by immersion in nitromethane ferric chloride (FeCl 3 ) solution, in order to extend its photovoltaic potential. The paper presents the effect of ferric chloride on PBDB-T-SF thin films (90 ± 5 nm thickness) deposited on glass by spin coating. The optical properties changes were identified by spectrophotometry, simulated and modeled by spectroscopic ellipsometry, remarking a decrease in absorption coefficient, refractive index and extinction coefficient of the individual polymer thin film. The X-ray photoelectron spectroscopy (XPS) analysis shows the changes in terms of elemental composition. Additionally, related to the electrical properties, the study brings clarifications on the unusual increase of resistivity once the film is exposed to light, due to the attachment of iron ions to polymeric chains and to the existence of an iron oxide thin film on the top of polymer layer. These findings contribute to the understanding of the behavior of emerging fluorinated polymers, before and after chemical treatments and exposure to light. • Elemental composition and optical properties stability of PBDB-T-SF thin films • Complementarities between optical analysis and electrical measurements • Different photoconduction behavior of sensitized polymer thin films