Charge-transfer dynamics in van der Waals heterojunctions formed by thiophene-based semiconductor polymers and exfoliated franckeite investigated from resonantly core-excited electrons.

Abstract

Organic/inorganic van der Waals heterojunctions formed by a combination of 2D materials with semiconductor polymer films enable the fabrication of new device architectures that are interesting for electronic and optoelectronic applications. Here, we investigated the charge-transfer dynamics at the interface between 2D layered franckeite (Fr) and two thiophene-based conjugated polymers (PFO-DBT and P3HT) from the resonantly core-excited electron. The unoccupied electronic states of PFO-DBT/Fr and P3HT/Fr heterojunctions were studied using near-edge X-ray absorption fine structure (NEXAFS) and resonant Auger (RAS) synchrotron-based spectroscopies. We found evidence of ultrafast (subfemtosecond charge-transfer times) interfacial electron delocalization pathways from specific electronic states. For the interface between the PFO-DBT polymer and exfoliated franckeite, the most efficient interfacial electron delocalization pathways were found through π*(S-N) and π*(S-C) electronic states corresponding to the benzothiadiazole and thiophene units. On the other hand, for the P3HT polymer, we found that electrons excited to π-π* and S1s-π*(C-C) electronic states of the P3HT polymer are the most affected by the presence of exfoliated franckeite and consequently are the main interfacial electron-transfer pathways in this heterojunction. Our results have important implications in understanding how ultrafast electron delocalization is taking place in organic/inorganic van der Waals heterojunctions, which is relevant information in designing new devices involving these systems.