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Yu et al. Energy Mater. 2026, 6, 600044 Page 11 of 14

physical contact at the interface. This synergistic effect not only promotes efficient hole extraction but also
substantially reduces carrier recombination losses, thereby contributing to higher FF and PCE. To directly
visualize interfacial hole transfer, steady-state PL spectroscopy was performed. The PL intensity of the
PM6:BTP-eC9 blend was more effectively quenched on the ITO/P-4PACz substrate compared to
ITO/4PACz [Supplementary Figure 18].

Transient photovoltage (TPV) decay measurements show that the carrier lifetime of the device based on
P-4PACz (5.03 μs) is longer than that of the device based on 4PACz (3.23 μs), which is consistent with the
suppression of trap-assisted non-radiative recombination [Figure 5E]. Transient photocurrent (TPC)
analysis further indicates that the charge extraction speed of the device based on P-4PACz is accelerated, as
reflected in the reduction of the extraction time from 0.28 to 0.19 μs [Figure 5F]. Holes accumulated rapidly
at the 4PACz interface, but the charge extraction efficiency was limited. The asymmetric substitution at the
P-4PACz interface improved the alignment mode and the change in work function, forming a more efficient
charge extraction channel between the electrode and the active layer. This is also reflected in J , ultimately
SC
leading to the improvement of the higher PCE of the OSCs.

CONCLUSIONS
In summary, we report an easily accessible asymmetric carbazole-based self-assembled monolayer, P-4PACz,
featuring a unilateral phenyl substituent that rationally moderates π-π stacking and enhances dispersion and
solubility in solution. The resulting SAM exhibits improved molecular packing, higher conductivity, and
lower surface energy, which collectively facilitate better active-layer film formation. Furthermore, the
asymmetric design deepens the work function and optimizes energy-level alignment with the donor material,
thereby promoting efficient hole extraction and charge transport. These benefits synergistically enhance the
open-circuit voltage, short-circuit current density, and particularly the fill factor. This simple yet effective
strategy of tailoring intermolecular interactions to optimize film formation offers new insights into the
design of SAM materials for organic solar cells.

DECLARATIONS
Authors’ contributions
Device fabrication and testing: Yu, Y.; Wang, Z.
Density functional theory calculations: Hong, X.
Material characterization, data validation, methodology design, and critical data curation: Yu, Y.; Hong, X.;
Li, Y.
Manuscript drafting and overall coordination: Yu, Y.
Manuscript review, revision, and finalization: Yu, Y.; Hong, X.; Li, Y.; Wang, Z.; Kang, F.; Jiao, Z.; Wei, G.

Availability of data and materials
The data that supports the findings of this study are available from the corresponding author upon
reasonable request.

AI and AI-assisted tools Statement
Not applicable.

Financial support and sponsorship
This work was supported by the National Natural Science Foundation of China (Grants No. 52027817 and
No. 52471020), and the Tsinghua Shenzhen International Graduate School Overseas Research Cooperation
Fund (Grant No. HW2024008).

Conflicts of interest
All authors declared that there are no conflicts of interest.