“…TEY mode collects signal from the surface 5-10 nm of the film, giving a good representation of sub-surface composition. PEY mode probes the surface 2-3 nm of the film, the area of the film most prone to degradation effects due to air and light exposure, 49 and is hence of less relevance to the current study. FY mode probes to a depth of ∼250 nm, a thickness greater that the BHJ film thickness, hence collecting signal from the underlying hole transport layer (HTL) and substrate and thus of less relevance to the current study.…”