Implication of Surface Passivation on the In-Plane Charge Transport in the Oriented Thin Films of P3HT

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript “Implication of Surface Passivation on the In-plane Charge Transport in the Oriented Thin Films of P3HT” provides a systematic investigation of surface passivation using OTS to enhance charge transport in FTM-processed RR-P3HT films for OFET applications. The experimental design is rigorous, combining optical, structural, and electrical characterizations. The findings are significant for optimizing organic semiconductor interfaces. However, several critical questions and concerns must be addressed to strengthen the manuscript. The following are some suggestions that could enhance the quality of this work.

Major concerns

1. OTS-F exhibits the highest mobility (0.18 cm²V⁻¹s⁻¹) but a lower on/off ratio compared to OTS-A. Does the reduced on/off ratio indicate increased off-state leakage or interfacial traps? How does the SAM’s dielectric integrity vary between OTS-A and OTS-F?
2. The manuscript attributes the superior performance of OTS-F (octadecene) to enhanced molecular ordering. However, toluene and octadecene differ in polarity, boiling point, and OTS solubility. How do solvent properties (e.g., viscosity, surface tension) influence the kinetics of SAM formation? Is the improved performance due to prolonged reaction time at 100°C or intrinsic solvent-SiO₂ interactions?
3. While Scherer’s equation links crystallite size to mobility, the FWHM values for OTS-A and OTS-F are nearly identical. Could strain or anisotropic crystallite shapes affect the accuracy of crystallite size calculations? Is there any possibility to consider alternative models to decouple size and strain effects?
4. The dichroic ratio (DR) is used to infer molecular orientation, does DR alone can distinguish edge-on vs. face-on configurations? AFM measurements may help to validate the claimed edge-on orientation.
5. SAMs with long alkyl chains (e.g., OTS) are prone to degradation under ambient conditions. Were stability tests (e.g., humidity exposure, thermal cycling) conducted to assess device performance retention over time?
6. The manuscript emphasizes in-plane charge transport or mobility but does not quantify anisotropy. How does charge transport parallel vs. perpendicular to the FTM orientation direction compare? Are there any other measurements to confirm directional dominance? As reference, Doi: 10.1002/inf2.12400; 10.1016/j.synthmet.2020.116382

Minor concerns

1. Device metrics (e.g., mobility) are reported for single samples. Were multiple devices tested to ensure reproducibility?
2. The threshold voltage (V_th​) decreases with OTS-F. Does this correlate with reduced interfacial traps or altered dielectric capacitance?
3. Could residual octadecene (high boiling point) remain in the SAM after annealing, affecting semiconductor morphology?

Comments on the Quality of English Language

It can be improved.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

In this manuscript, thin films of RR-P3HT were fabricated using a solution-processable FTM method. Interface trap sites were studied via surface passivation with OTS, and the optical anisotropy of the films and film morphology were adjusted. Overall, the work lacks key experiments. The current material characterization and electrical testing data can't support the final conclusions, and major revisions are needed before acceptance.

1. Why choose Ag as the source/drain electrode? The work functions of P3HT and Ag don't seem to match.
2. There's no need to go into the principles of conventional characterization methods such as XRD and GIXD, as they are well-known.
3. Additional tests should be added. Use contact angle measurements with different polarity liquids to determine surface energy and polarity, better explaining the properties of different OTS interfaces (IEEE Electron Device Letters, 2025, 46, 3, 504-507).
4. XRD and GIXD cannot fully show the growth characteristics of P3HT crystalline cells at different interfaces. More detailed surface morphology data from AFM, SEM, etc., is needed.
5. Large crystalline cells often make the P3HT layer rough. Higher crystallinity doesn't necessarily mean higher carrier mobility (Adv. Intell. Syst. 2020, 1900176). Also, authors should provide the missing property research for OTS-B, OTS-C, and OTS-E.
6. The transfer characteristics curve in Fig.5 needs sweep in both directions to check hysteresis, crucial for interface trap study. The output characteristics curves should also be provided.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

Review report on the manuscript “Implication of Surface Passivation on the In-plane Charge

Transport in the Oriented Thin Films of P3HT” N. R. Purabiarao et al. and submitted to the journal Electronic Materials.

 

The authors showed that mobility of charge carriers in organic field-effect transistor based on regioregular poly[3-hexylthiophene] (RR-P3HT) can notably increase if the trap states near SiO2 dielectrics are suppressed by casting oriented thin films of RR-P3HT via the Floating Film Transfer Method on octadecyltrichlorosilane (OTS) passivated SiO2 surfaces. OTS treatment has improved the optical anisotropy of thin films and the surface wettability of SiO2. Notably, using octadecene as a solvent during OTS passivation, as opposed to toluene, resulted in a significant enhancement of charge carrier transport. Specifically, passivation with OTS-F (10 mM OTS in octadecene at 100°C for 48 hours) led to an increase of the mobility at least by ca two orders of magnitude.

 

Results are correct, justified and can contribute to further development of polymer based electronic devices. Before publication, I recommend to improve the manuscript by the following points.

 

1) I found a missing schematic figure, where the interaction between the rr-P3HT, passivation layer and oxide-based insulator is shown. Together with this scheme also a dominant orientation of rr-P3HT chains should be shown, particularly, with respect to the source, drain and gate contacts.

2)  Discussion on peaks in the Electronic Absorption Spectroscopy section (3.2) is kind of shaky. On one side, it is explicitly written that “The main absorption peak (λmax) is observed at 554 nm (A0-1), with significant vibronic shoulders at 524 nm (A0-2) and 604 nm (A0-0)”, while the following sentence says: ”The A0-0 peak indicates defects and intermolecular interactions, while the A0-1 peak is associated with π-π* transitions. The A0-2 peak suggests structural variations along the polymer backbone and is

linked to π-electron conjugation”. Do the authors realize that one sentence completely contradicts the other one? More specifically, once we speak about A0-n peak it always means the transition g,0 -> S,n, where g (S) is the ground (excited) state, while 0,n numerates the vibrational levels within respective electronic states. Hence, A0-n peaks are always vibronic peaks, dominantly formed by transitions inside repeat units, i.e., where the excitation transfer between repeat units along the polymer backbone is suppressed. In such case, energies E(n) of respective vibronic level satisfy E(n) = E(0) + n*h*omega , i.e., they linearly increase with n. Intensities of such peaks are proportional to the Franck-Condon terms <0/n>**2 ~  HR**n/n!, where HR is the Huang-Rhys factor. For HR = 1, the relative heights of respective peaks would be 1, 1, 0.5, while for HR = 2, they would be 1, 2, 2. Hence, comparing to experimental data, it would rather suggest HR =2. Conversely, we also see that the energies of respective peaks 1240/604 = 2.05, 1240/554 = 2.24 and 1240/524 = 2.37 (in eV) doesn’t follow the linear relation. This indicates that and ideal vibronic limit is perturbed, possibly by the exciton delocalization. For more realistic estimates of the excitonic bandwidth and HR relative heights of more peaks would have tro be analyzed. More, parameters, 0.24 and 0.073 in Eq. 2. are based on analyzing of a different rr-P3HT morphology. Therefore, parameters of the bandwidth in the Table 1. represents just only a qualitative estimate, which compares the effect of the passivation agent on the crystallization…..  I suggest to include these remarks into the text.

3) As a promoting argument for higher crystallinity of P3HT is one effect, what was not mentioned in your manuscript. Trap states in rr-P3HT have two effects. For the first, they decrease the value of the mobility. For the second, they bring dependence on charge concentrations, due to the trap filling. I highly recommend to introduce the following references: In the ref. [Phys. Chem. Chem. Phys., 2017, 19, 7760—7771, note the mechanism of the charge transfer in Fig. 7, it is exactly your case] it was shown that for high values of energy disorder the mobility increases with higher charge concentration, while for low energy disorder, the mobility is not only higher, but independent on the charge concentration (check figure 8.a of this reference with your data). The mobility dependence on the charge concentration is controlled in OFETs by the mobility dependence on the gate voltage [Phys. Chem. Chem. Phys., 2018, 20, 2308—2319, note that the mobility in Fig. 5 is not only generally lower than in your case, but also gate dependent]. Note also that in your data, OTS-E and OTS-F provide not only high mobilities, but the slope  scales perfectly linearly with the gate voltage, while, for the OTS-D case the mobility is not only the lowest one, but the slope v.s. gate voltage deviates partly off the linear profile. This means that the mobility becomes gate voltage-dependent. The mobility dependence on gate voltage can be also found in ref. [J. Appl. Phys., 2000, 87, 4456–4463] or trap-controlled mobility dependence on the charge concentration is found in ref. [Phys. Status Solidi, 2014, 251, 487–525.]

4) Technically, I recommend larger figures and also large figure captions.

 

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Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised manuscript can be accepted

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript can be considered for acceptance.

Reviewer 3 Report

Comments and Suggestions for Authors

Review report on the manuscript “Implication of Surface Passivation on the In-plane Charge

Transport in the Oriented Thin Films of P3HT” N. R. Purabiarao et al. and submitted to the journal Electronic Materials.

 

The authors showed that mobility of charge carriers in organic field-effect transistor based on regioregular poly[3-hexylthiophene] (RR-P3HT) can notably increase if the trap states near SiO2 dielectrics are suppressed by casting oriented thin films of RR-P3HT via the Floating Film Transfer Method on octadecyltrichlorosilane (OTS) passivated SiO2 surfaces. OTS treatment has improved the optical anisotropy of thin films and the surface wettability of SiO2. Notably, using octadecene as a solvent during OTS passivation, as opposed to toluene, resulted in a significant enhancement of charge carrier transport. Specifically, passivation with OTS-F (10 mM OTS in octadecene at 100°C for 48 hours) led to an increase of the mobility at least by ca two orders of magnitude.

 

I recommend to accept for the publication in Electronic Materials.

Comments for author File: Comments.docx