Unexpected Equilibrium Ionic Distribution in Cyanine/C₆₀ Heterojunctions

Abstract

The equilibrium ionic distribution in cyanine donor–fullerene acceptor bilayer systems is investigated using Rutherford backscattering spectroscopy, elastic recoil detection analysis, and time‐of‐flight secondary ion mass spectroscopy. Simultaneously, the potential profile inside the C60 layer is followed by Kelvin probe force microscopy. Experimental verifications are obtained by using different device architectures, different mobile counter ions, and alternative acceptor layers. The unexpected constant iodide profile inside C60 and the potential shift close to the donor–acceptor interface can be explained by an exchange of electrons and ions from acceptor to donor and vice versa. The proposed model explaining all of the observed experimental findings is supported by a thermodynamic model.

Anions for Near-Infrared Selective Organic Salt Photovoltaics

“…Although there may be some intermixing between the salts and C 60 shown in the SEM images as evidenced by charging near the interface, this appears to occur over a distance of ~2 nm and is thus not likely to impact the V oc of devices. It is important to note that anion diffusion from other molecular salts into C 60 has been observed for small halide ions 14 and while this process could potentially affect the V oc through changes in the interface gap, it is reported to occur over several weeks and is thus unlikely to affect newly fabricated devices with much larger counterions. The more pronounced voltage trends exhibited by CyClPhB, CyFPhB, CyTFM, and Cy 2 FCB are instead caused by band bending of the salt donors and concomitant changes in the interface gap as illustrated in Fig.…”