Defining the buried electronic structures in solution-processed organic heterojunctions by ultraviolet photoelectron spectroscopy analysis assisted with argon gas cluster ion beam sputtering

초록

The accurate characterization of buried electronic structures in solution-processed bulk heterojunctions (BHJs) remains challenging due to surface phase separation and spectral overlap between donor and acceptor components. In this study, a depth-resolved analytical methodology is demonstrated by integrating ultraviolet photoelectron spectroscopy (UPS) with argon gas cluster ion beam (Ar-GCIB) sputtering. This approach enables evaluation of the depth-dependent electronic structure and relative energy-level alignment in spin-coated P3HT:PCBM71 BHJ films with varying compositions (3:1, 1:1, and 1:3 by weight). Surface-sensitive UPS and reflection electron energy loss spectroscopy (REELS) reveal that the as-prepared BHJ films exhibit a P3HT-enriched surface, resulting in electronic structures dominated by the donor component. Upon controlled Ar-GCIB sputtering, the contribution of PCBM71 increases, enabling separation of donor and acceptor electronic states. By applying a linear combination analysis to the valence band spectra, the HOMO levels of P3HT and PCBM71 are extracted as a function of sputtering time. Notwithstanding the potential for modifications in polymeric materials induced by sputtering, the extracted HOMO offsets remain consistent (1.13–1.20 eV) across varying compositions and sputtering conditions, thereby indicating the preservation of the relative donor–acceptor energy-level alignment. This work demonstrates a practical methodology for probing buried electronic structures in complex BHJ systems that are not accessible by conventional surface-sensitive techniques. © 2026 Elsevier B.V.

키워드