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Yu et al. Energy Mater. 2026, 6, 600044 Page 3 of 14

ITO surface through combined steric and electronic effects. Simultaneously, the phenyl substituent
suppresses pre-aggregation in solution via steric hindrance, enabling the formation of denser and more
homogeneous SAM films . As a result, P-4PACz creates smoother, lower-energy ITO surface, leading to
[35]
improved active layer wetting and interfacial contact. Using P-4PACz as the HTL, bulk-heterojunction OSCs
based on PM6:BTP-eC9 photoactive system exhibit enhanced hole extraction, suppressed bimolecular and
trap-assisted recombination, and prolonged carrier lifetimes compared to devices employing symmetric
4PACz or PEDOT:PSS. Consequently, the champion P-4PACz-based device shows a PCE of 19.03%,
outperforming symmetric 4PACz (champion 18.28%) and PEDOT:PSS (champion 18.22%) controls, and
delivers the longest T₈₀ lifetime of up to 782 h under controlled conditions (25 °C, 25% relative humidity,
AM 1.5G illumination 100 mW/cm ). These results demonstrate that asymmetric molecular engineering of
2
SAM-based HTLs enables synergistic optimization of interfacial energetics, film morphology, and
charge-transport dynamics. This strategy provides a practical pathway toward high-efficiency and stable
OSCs compatible with scalable fabrication.

EXPERIMENTAL
Material synthesis
PM6, BTP-eC9, Y6, PY-DT, L8-BO and PNDIT-F3N were from Solarmer Materials Inc (Beijing),
PEDOT:PSS (CLEVIOS™ P VP AI 4083) was purchased from Heraeus, 4PACz and P-4PACz (Beijing Green
Guardee Technology), 1-Naphthyl chloride (1-CN) and 1,8-Diiodooctane (DIM) were purchased from TCI
(Shanghai). The ITO-coated glass (≤ 15 Ω/square) was purchased from Advanced Election Technology. All
reagents were purchased from Sigma-Aldrich and were used without further purification.

Device fabrication
Devices with the conventional ITO/HTL/active layer/PNDIT-F3N/Ag architecture were fabricated on
commercial ITO glass. Substrates were sequentially ultrasonicated in DI water, IPA, acetone and IPA for
15 min each, dried under nitrogen and oxygen-plasma treated for 300 s to yield hydrophilic surfaces. Inside a
nitrogen glovebox, SAM films (0.3 mg mL in ethanol) were spin-coated at 3,000 rpm for 30 s, rested for 30 s
-1
and annealed at 85 °C for 10 min; when required, a PEDOT:PSS reference was deposited at 5000 rpm for 20 s
and annealed at 150 °C for 10 min in air. Active layers were then spin-coated at 3,000 rpm for 30 s under the
same inert atmosphere: PM6:BTP-eC9 and PM6:L8-BO were cast from 16 mg mL chloroform (D:A 1:1.2
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with 0.25 vol% DIM) and annealed at 95 and 90 °C for 5 min, respectively; PM6:Y6 was processed from
17 mg mL chloroform (D:A 1:1.2, 0.5 vol% 1-CN) and annealed at 85 °C for 10 min; PM6:PY-DT was
-1
deposited from 16 mg mL chloroform (D:A 1:1.25, 1.5 vol% 1-CN) and annealed at 100 °C for 10 min. The
-1
PNDIT-F3N was dissolved in methanol at a concentration of 0.5 mg mL with 0.5 vol% acetic acid and was
-1
spin-coated onto the active layer at a speed of 3,000 rpm for 30 s, and 100 nm Ag electrodes were thermally
evaporated through a shadow mask at 3 × 10 Pa to define an active area of 0.06 cm , completing the device.
2
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Measurements and instruments
The ultraviolet-visible (UV-Vis) absorption spectra of the films were recorded on an HP 8453
spectrophotometer (Hewlett-Packard, USA). Single crystals of 4PACz and P-4PACz were grown via the
vapor diffusion method. Sufficient powder of 4PACz or P-4PACz was dissolved in dichloromethane and
transferred into a small vial. The small vial was then placed into a larger vial containing methanol, and the
whole system was sealed and stored in a refrigerator. Suitable block-like single crystals for X-ray diffraction
analysis were obtained after several days. Atomic force microscopy (AFM) imaging was performed in
tapping mode using a Bruker Dimension Icon system (Bruker, USA). Conductive AFM (C-AFM)
measurements were conducted on an Asylum Research Cypher AFM system (Oxford Instruments, UK).
During these measurements, the sample was either illuminated or kept in the dark using a top-mounted
integrated LED, while a bias voltage of -8.7 mV was applied between the conductive tip and the sample.