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Page 10 of 14 Yu et al. Energy Mater. 2026, 6, 600044

Figure 5. (A) J ph -V eff characteristics for the corresponding devices, (B and C) light-intensity dependence of J SC and V OC , (D) Nyquist plots,
(E) transient photovoltage, (F) transient photocurrent decays.

[Figure 5A]. The charge dissociation probability (P ) and charge collection probability (P ) are defined as
coll
diss
follows: P = J ph,SC /J and P = J ph,MPP /J , where J denotes the photocurrent density and J denotes the
coll
diss
ph
sat
sat
sat
saturation current density. P is typically evaluated under short-circuit conditions and quantifies the
diss
efficiency of exciton dissociation into free charge carriers, whereas P is evaluated at the maximum power
coll
point voltage and reflects the efficiency with which photogenerated free charges are collected by the
electrodes. Under short-circuit conditions, the P value for devices based on ITO/4PACz, ITO/P-4PACz,
diss
and ITO/PEDOT:PSS were 95.03%, 97.27%, and 96.19%, respectively. At the maximum power point, the P coll
values were 84.32%, 88.39%, and 86.84%. These results indicate that the device employing P-4PACz exhibits
the highest exciton dissociation efficiency.
The trap-assisted recombination behavior was further investigated by examining the semi-logarithmic
dependence of V on light intensity [Figure 5B]. The fitted slope, expressed in units of n·kT/q, approaches
OC
the ideal value of 1 kT/q when trap-assisted recombination is minimal. The device employing P-4PACz
exhibits the smallest slope (n = 1.17), which is notably lower than those of the 4PACz-based (n = 1.25) and
PEDOT:PSS-based (n = 1.21) devices, indicating more effective suppression of trap-assisted recombination
in the P-4PACz-based device. The bimolecular recombination behavior was assessed by analyzing the J -P light
SC
relationship, described by the power-law dependence J ∝ P [Figure 5C]. A value of α closer to unity
α
SC
signifies weaker trap-assisted recombination. As illustrated in Figure 5C, the P-4PACz-based device achieves
the highest α value (α = 0.987), surpassing the 4PACz-based (α = 0.967) and PEDOT:PSS-based (α = 0.975)
devices, demonstrating more pronounced suppression of bimolecular recombination in the P-4PACz-based
device [42,43] .

The recombination impedance spectra of different devices appear in Figure 5D. The P4PACzbased device
exhibits the highest recombination resistance (1.54 kΩ), significantly exceeding those of the 4PACzbased
(1.11 kΩ) and PEDOT:PSSbased devices (0.67 kΩ), indicating more effective suppression of carrier
recombination . The P4PACz interlayer can simultaneously optimize energylevel alignment and improve
[44]