The Impact of Oxide Transport Layers and Active Layer Composition on the Energy Band Alignment of the Frontier Orbitals in Non-Fullerene Acceptor Organic Solar Cells.

Authors

Noemi Vannucchi, Kun Wang, Fredrik O L Johansson, Chun Yuen Ho, Mariam Ahmad, Tanya Kumari, Hervé Cruguel, Zheshen Li, Roberto Félix, Morten Madsen, Andreas Lindblad, Nadine Witkowski

Published in

ACS applied materials & interfaces. Oct 20, 2026. Epub Oct 20, 2026.

Abstract

The PM6:Y7 blend is a leading system for non-fullerene acceptor organic photovoltaics (OPV), achieving power conversion efficiencies (PCEs) above 16%. In bulk heterojunction architectures, it is typically combined with transition-metal-oxide transport/extraction layers to enable efficient energy-level alignment and charge transport toward the electrodes. However, accurate determination of the frontier orbital band alignment across the device interfaces remains challenging and is the subject of ongoing debate. This work aims to map the energetic landscape within an inverted OPV device architecture by investigating how variations in the PM6:Y7 donor-to-acceptor mass ratio (1:1, 1:2, and 2:1) affect device performance and assessing the role of the oxide transport/extraction layers (MoO3 and ZnO). By combining valence band photoemission and X-ray absorption spectra relative to the Fermi level, we map the frontier orbital alignment between the blend active layer and the charge transport/extraction layers. Moreover, by exploiting the element selectivity of X-ray absorption spectroscopy, we are able to follow the evolution of the Y7 acceptor LUMO level in the blends with different compositions. We observe a nonlinear behavior in the acceptor LUMO level with the blend composition and find that the 1:1 blend exhibits a relative maximum, reflecting a maximized effective donor-acceptor dipole interaction. Combining this trend with the optimal 1:1-1:2 composition window, identified from band alignment analysis, suggests that stronger molecular dipole interactions in the PM6:Y7 1:1 blend can promote a favorable electronic structure for efficient charge extraction and reduced recombination effects. These findings are consistent with the PCE trend resulting from our device measurements, providing a general framework for correlating frontier-orbital alignment with device performance and guiding the design and optimization of OPV architectures beyond the specific system investigated here.

PMID:
42900525
Bibliographic data and abstract were imported from PubMed on 21 Oct 2026.

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