Accurate molecular recognition from the lowest unoccupied molecular orbital

Abstract

The quantification of the lowest unoccupied molecular orbital level (LUMO) for molecular semiconductors is of great importance, because it determines the charge transport process and hence the performances of diverse electronic devices. Unfortunately, there is always lack of a convenient technique to determine the intrinsic LUMO. This work provides a reliable electrical spectroscopy by employing an easy-operating hot electron transistor, to make an accurate measurement. By taking advantage of a novel method, named the first derivative-assisted linear fitting method, the determination of the intrinsic LUMO becomes more scientific. Here, four kinds of molecular semiconductors are selected as the research objects and the values can be precisely decided even with a quite small difference in LUMO, which demonstrate the universality and the accuracy of our method. As expected, all the measured values are highly repeatable and it further confirms that we have provided a practical technique for the LUMO detection.

Introduction

In virtue of some special characteristics, such as the remarkable visible light absorption, the low light refraction and the small spin orbit coupling, molecular semiconductors have been widely researched in photovoltaic cell, light-emitting diode, spin valve and son on^1–4. It has greatly promoted the development of molecular electronics which is always a hot research field involving chemistry, physics, informatics and material sciences. For achieving an efficient device-performance, molecular semiconductors with suitable energy levels are typically chosen to match well with the Fermi level of the electrode to minimize the electrical losses in charge injection or extraction^5–7. In molecular heterojunction-based devices, just as organic photovoltaic cell, the donor and acceptor should be designed with appropriate energy levels to improve the efficiency of charge transfer and exciton separation, while suppress the energy loss from radiation and non-radiation recombination^8,9. In order to obtain the required energy levels, the molecular semiconductors are always provided with specific structures by molecule design and structure tailoring so that the species can be unlimited^10,11. Consequently, a feasible method to measure the energy levels is imminent which will contribute to an in-depth understand for the fundamental physics and hence engineering the molecule-based devices¹². Currently, HOMO has been confirmed to be accurately determined by ultraviolet photoemission spectroscopy (UPS), due to its ultra-high energy resolution (50meV)¹³. Unfortunately, no applicable method is present to accurately ensure the intrinsic LUMO, but instead by some inadequate substitutes.

As the most powerful approach, inverse photoemission electron spectroscopy has been always utilized to in-situ probe the LUMO directly. However, its low energy resolution and the irreversible damage to the molecular films restrict the application only to some well-established small molecules, just as C₆₀^14,15. Besides, as a rarely available instrument, it is always not popular in the field of molecular electronics. For convenience, cyclic voltammetry method (CV) is most widely employed in practice. Unexpectedly, the measurement depends strongly on the experimental conditions, including electrodes, solvent, electrolyte and even solubility of molecules, which normally lead to the poor reproducibility^16,17. In order to achieve a relatively precise measurement, UPS has been employed to detect the LUMO by virtue of the ultra-high energy resolution, although indirectly estimated by combining the obtained HOMO with the optical bandgap from UV–vis absorbance spectrum^18,19. However, the inherent exciton binding energy from optical bandgap makes the measured LUMO deviate from the intrinsic value¹⁵. Consequently, a feasible method, to in-situ detect the intrinsic LUMO of molecular semiconductors as convenient as cyclic voltammetry and as accurate as UPS, is eagerly expected presently.

In this study, we propose a novel three-terminal device, named hot electron transistor, to determine the LUMO of molecular semiconductors, which make the apparatus a handy tool in molecular electronics. By monitoring the charge flow in a real device, the energy level alignment between metal and the molecular semiconductors can be recorded in the measured electronic spectroscopy. From it, the intrinsic energy barriers built up between the Fermi level of metallic base and the LUMO level of molecular semiconductors can be scientifically determined by a novel method which is designated as the first derivative-assisted linear fitting method. This operation eliminates the interfacial interaction between metal and molecules, making the obtained LUMO approach to the intrinsic values. Here, four species of molecular semiconductors are introduced in this experiment and the accurate determinations of LUMO are sufficient to affirm the universality of our method. Even if the differences of LUMO for these molecular semiconductors are quite small, the values can be easily distinguished from each other which illustrate a considerable energy resolution of this hot electron technology. In short, this work provides a precise and scientific method to determine the LUMO of molecular semiconductors. It will contribute to an in-depth understanding of the device physics as well as the device-performance optimization.

Result

Device design and working principle

As shown in Fig. 1a, our experiments are performed by a typical vertical triode which consists of an emitter (E), a base (B) and a collector (C). The emitter is a 13-nm thick Al film with the ultra-thin AlO_x tunneling barrier formed by in-situ plasma-oxidization process. Then, the base should be noble metal, which can apply to avoid electrical interactions with polymers at the interface. Therefore, a 10-nm thick Au film is defined as the base to weaken the interfacial interaction between the metal and the objective molecules, due to its noble property²⁰. The polymer solutions, including PCE10, PBDB-T, PBDB-T-2F and PBDB-T-2Cl, are spin coated on the surface of Al/AlO_x/Au tunnel junction to form series molecular films to act as the research objects. Here, the thickness of the polymer film is critical to the detection of hot electrons, and we always control it about 100nm. This is because the thin polymer film is always penetrated by the top electrode during the vapor deposition process, while the thick polymer film will result in no hot electron signals. Finally, the collector should be made of a metal with a low evaporation temperature. Otherwise, it is easy to cause penetration of the device, leading to the failure of the hot electron transistor. Hence, a 13-nm thick Al film is prepared as the collector to measure the hot electron current (I_C-hot) from the molecular films. Details of the fabrication have been shown in method section. In this device, the energy of original electrons can be regulated by the external bias V_EB, while the energy level alignment between base and collector is naturally given by the energy barrier at Au/molecule interface²¹. Figure 1b further introduces the working principle of hot electron transistor. When a negative voltage (V_EB) is swept on the Al/AlO_x/Au tunneling junction, the original electrons tunnel through AlO_x barrier and generate an emitter current I_E. A fraction of these electrons will ballistically transport across the Au film without any energy dissipation and then record as “hot electrons”¹⁴. The energy of these hot electrons can be regulated by the external V_EB. Once the energy is capable to overcome the energy barrier (− eV_EB > φ), a portion of hot electrons will enter into the LUMO and result in a collector current (I_C-hot). It is worth to mention that the I_C-hot in this manuscript can be detected without applying any collector–base voltage V_CB (Fig. 1c). Thus, the value is identified as a purely diffusive current which derives entirely from the hot electrons²². This is because the built-in voltage between the base (Au) and collector (Al) is always directed to accelerate the hot electrons across the polymer film and get rid of the interference of traps, without applying external voltage. This character will ensure the pure hot electron transport in the whole device, which ensure the accuracy of detection.

Fig. 1.

Sketch diagram of the hot electron transistor. (a), Framework structure of this device. The vertical structure is prepared from bottom to top, including Al, AlO_x, Au, molecular semiconductors and Al. (b-c), Working principle of the device. When a negative bias V_EB is swept on Al/AlO_x/Au junction, hot electrons will be generated in the Au film. Once the energy is not enough to overcome the the barrier height φ, they should bounce back at the interface and do not contribute to any I_C-hot (b); When the energy is higher than the barrier height φ, a part of hot electrons will enter into the LUMO and be measured as a collector current I_C-hot (c).

Electrical characterization

In order to acquire an undoubted hot electron signal, a credible Al/AlO_x/Au tunneling junction and Au/molecule/Al diode must be confirmed in advance. Firstly, the Al/AlO_x/Au stack should be ensured as a tunneling junction so that the emitter current (I_E) originates from electron tunneling transport. The typical I_E-V_EB characteristic indicates a weak temperature dependence of the I_E which makes the Al/AlO_x/Au stack a prospective non-leaky tunnel junction (Supplementary Fig. 1)²³. Here, the energy of hot electrons can be regulated by employing different V_EB. These Al/AlO_x/Au tunneling junctions are provided with the considerable I_E that guarantees a measurable hot electron signal, even with a large amount of energy loss in the transport process. Secondly, the integrity of molecular films should be ensured so that the current detected by collector electrode derives from electrons transporting though the molecular semiconductors. In Supplementary Fig. 2, all the I_diode-V_CB curves show some strong temperature dependences. The behaviors suggest that the electrons have been transported though the molecular films via a thermally active hopping process²⁴. Here, it is more important to concern with the generated electrons at positive voltage which represent the charge injection from Au to molecular semiconductors. However, the temperature dependences are quite unconspicuous. Therefore, the photo-response experiments of these molecular diodes are carried out at a fixed V_CB (1V) (Supplementary Fig. 3). The distinct temperature dependences further confirm the integrity of these molecular films. Furthermore, these photo-responsive characteristics illustrate some smooth curves which prove that the Au/molecule interfaces are very well²⁵. As a result, I_C-hot can be successfully detected with varying V_EB in the hot electron transistors. These I_C-hot-V_EB curves (named hot electron spectroscopies) present a distinct on–off switch state, while the magnitude of I_C-hot is only one thousandth of I_EB which demonstrates the tremendous electron loss in the transport process²⁶. In combination with the clear temperature-dependent I_C-hot in Supplementary Fig. 3, it unambiguously demonstrates that the measured hot current is a purely diffusive current originating entirely from injected hot electrons (Supplementary Fig. 4)²⁷.

LUMO determination by hot electron spectroscopy

Based on the above preparations, the emphasis of this research concentrates on how to precisely extract the intrinsic LUMO of molecular semiconductors from the measured hot electron spectroscopies. Just as mentioned above, once the energy barrier is overcome, hot electrons with high energy will be injected into the LUMO states directly. All the hot electron spectroscopies reveal some distinct threshold voltages and the corresponding interfacial energy barriers. It seems that the value of LUMO should be extracted by the difference of the Fermi level of Au and the interfacial energy barrier²⁸. However, this calculation is rather shoddy because it is short of consideration for the complicated interfacial interactions between Au and molecule semiconductors, such as the “pillow effect”, “image charge effect”, “charge transfer effect”, which lead to LUMO energy broadening at the interfaces^29–31. The broaden LUMO provides some available unoccupied molecular states for hot electrons entering into the molecules before reaching the intrinsic LUMO. Hence, the calculated LUMO by this “direct” operation is the polaronic level, such as the negative integer charge-transfer state^14,30,32.

To solve this problem, the linear-fitting method has been adopted to extract the barrier height between the Fermi level of Au base and the intrinsic LUMO of molecular semiconductors^14,21,22. This is because that there is no electrical interaction at the Au/molecule interfaces in an ideal case. Here, once the barrier height is surmounted, all the hot electrons will directly enter into the LUMO state so that the I_C-hot will illustrate a linear growth³³. The linear-fitting method has been widely employed in some techniques for energy level determination, such as CV³⁴, UPS³⁵ and inverse photoelectron spectroscopy³⁶. However, it is always an obstacle about how to choose the proper section to conduct the linear fitting. It is quite critical for guaranteeing the precision and credibility of the measured LUMO. To our knowledge, there is no relevant report in this aspect. Here, we propose a novel method, named first derivative-assisted linear fitting method, to solve the problem. According to the unchanged derivative of dI_C-hot/dV_EB-V_EB curve (first-order derivative spectroscopy), the reliable linear-fitting region of hot electron spectroscopy can be confirmed scientifically³³. The details will be described as below: (i) The I_C-hot-V_EB characteristic should be used for first-order derivative processing so as to acquire the derivative spectroscopy. According to the voltage of nonzero constant area in the derivative spectroscopy, the linear-fitting region of hot electron spectroscopy can be confirmed. (ii) A fitting line with specific function is adopted to simulate the data in the determinate region. (iii) Extending the fitting-line to I_C-hot = 0 by interpolating another line with the same function, the horizontal intercept can be used to extract the barrier height (φ). (iv) The LUMO of molecular semiconductor will be confirmed as follow:

$$\text{LUMO}=E_F-\phi$$ 1

E_F is the Fermi level of Au and its value is -5.3eV.

Based on the above method, the intrinsic LUMO can be determined accurately. Firstly, PCE10 is selected for the research. The hot electron spectroscopy and the corresponding first-order derivative spectroscopy have been shown in Fig. 2. According to it, a distinct “plateau region” from -2.38 V to -2.50 V, which corresponds to a linear increase in I_C-hot, can be ensured. The hot electron spectroscopy in the same voltage range is applied to linear fitting and then a straight line with given function can be acquired as below:

$$I_{C-hot}=-390.32\ast V_{\mathit{EB}}-739.25$$ 2

where, “ − 390.32” is the slope of the fitting line and “ − 739.25” is the vertical intercept. Surprisingly, the “Adjust R-Square” reaches up to 0.99999 (Supplementary Table 1). It means that the hot electron spectroscopy in the given region matches well with the fitting line. With the help of the extended line, the barrier height has been decided as -1.90eV, which is distinct from the energy of threshold voltage (-1.57 eV). According to the function (1), the LUMO of PCE10 can be calculated as -3.40eV, which is significantly different from the polarized unoccupied molecular state at the interface (-3.73eV). This value can be perfectly identical with the measurement from low-energy inverse photoemission electron spectroscopy in the previous literatures^37,38.

Fig. 2.

LUMO determination of PCE10. (a) I_C-hot-V_EB characteristic of PCE10. The black line with specific function is the fitting line, while the cyan line with the same function is interpolated to extend the fitting line to I_C-hot = 0 and then extracted the barrier height φ. (b), The dI_C-hot/dV_EB-V_EB characteristic of PCE10. The plateau region is used to confirm the available data for linear fitting. (c), Energy level alignment between Au and PCE10. (d), Comparison of the LUMO between the measurement in this work and the values in previous literatures^37,38.

In order to illustrate the universality of this method, the other molecular semiconductors, including PBDB-T, PBDB-T-2F and PBDB-T-2Cl, are utilized for the study. Given the large difference of the barrier height between Au and molecules, different voltages are used to obtain the corresponding hot electron spectroscopies. As illustrated in Fig. 3, the first-order derivative spectroscopies of the three materials show the “plateau region” at -2.81 V ~ -3.00 V, -2.12 V ~ -2.32 V and -1.92 V ~ -2.00 V respectively. The barrier height of PBDB-T, PBDB-T-2F and PBDB-T-2Cl can be decided as -2.17eV, -1.81 eV and -1.67 eV by the following functions. It is obviously that the differences between the threshold voltage and the barrier height for the three structurally similar polymers are quite pronounced. It is because that some complicated electrical interaction s will be occurred at base/polymer interface. This interfacial interaction include “charge transfer effect’’, ‘‘pillow effect’’, ‘‘image charge effect’’, and et al.³⁹. Even if the structure is similar, the electrical interaction is sufficiently different at the base/polymer interface.

$$I_{C-hot}=-12.05\ast V_{\mathit{EB}}-26.13$$ 3

$$I_{C-hot}=-25.58\ast V_{\mathit{EB}}-46.17$$ 4

$$I_{C-hot}=-413.47\ast V_{\mathit{EB}}-693.28$$ 5

Fig. 3.

LUMO extraction of PBDB-T, PBDB-T-2F and PBDB-T-2Cl. (a-c-e), I_C-hot-V_EB characteristics of PBDB-T, PBDB-T-2F and PBDB-T-2Cl. The black line with specific function is the fitting line, while the cyan line with the same function is interpolated to extend the fitting line to I_C-hot = 0 and then extracted the barrier height φ. (b-d-f), The dI_C-hot/dV_EB-V_EB characteristics of PBDB-T, PBDB-T-2F and PBDB-T-2Cl. The plateau region is used to confirm the available data for linear fitting.

The “Adjust R-Square” reaches up to 0.99849, 1 and 1 respectively (Supplementary Table 1). Therefore, the hot electron spectroscopy in the simulated region can be highly coincided with the fitting line. By calculation, the LUMO of PBDB-T, PBDB-T-2F, PBDB-T-2Cl has been determined to be -3.13eV, -3.49eV, -3.63eV. Obviously, the different LUMO of these derivatives, which are formed by the little change of the structures, can be accurately detected. Even with a simple replacement from fluorine atoms to chlorine atoms in the side chain, a slight difference of 0.14 eV in LUMO can be distinguished by this method. When we compare the measured LUMO of PBDB-T-2F and PCE10, the difference of them is only 0.09 eV. Consequently, we can sure that hot electron spectroscopy should be provided with ultra-high resolution.

As a feasible method for energy level characterization, the repeatability of detection is a very critical technical index^40–42. In this study, 17 values of LUMO are summarized for the four molecular semiconductors and then shown by the column chart. From the Supplementary Fig. 5, the measured LUMO of each material fluctuates in a very small range. For example, the maximum and minimum LUMO of PBDB-T-2Cl is -3.60eV and -3.68eV, which declares a tiny range of 0.08eV. In order to get an intuitive image, we calculate the average value of LUMO and the corresponding standard deviation, and give a representation in Fig. 4. From the graph, the standard deviation is as low as 0.02eV which illustrate a quiet small fluctuation of LUMO from chip to chip. As a reference, CV, the most widely used approach, is utilized to probe the LUMO. We prepare 30 samples for every material and summarize the detected LUMO in Supplementary Fig. 6. It indicates a wide energy distribution for the measured values, where the LUMO from hot electron transistor can be included. For example, the maximum and minimum LUMO of PBDB-T is -3.10eV and -3.45eV, which declares a big range of 0.35eV^43–45. This may be that the CV measurement could be easily affected by the experimental environment. For a clearer comparison, all the measured LUMO, including error bar, have been listed in Supplementary Table 2. In this table, the reported LUMO by LEIPS detection, have added. It is not difficult to find that the LUMO obtained by our method is quite close to the value from LEIPS. However, the LEIPS is a rare instrument and its measurement is extremely inconvenient. Here, it is reasonable to believe that this study provides a convenient and accurate method for LUMO detection.

Fig. 4.

LUMO energy distribution. (a), LUMO distribution of PBDB-T, PCE10, PBDB-T-2F, PBDB-T-2Cl from hot electron spectroscopy. (b), LUMO distribution of PBDB-T, PCE10, PBDB-T-2F, PBDB-T-2Cl from cyclic voltammetry.

Electronic transport energy gap calculation

Thanks to the precise determination of LUMO, we can obtain the accurate value of electronic transport energy gap by combing with the HOMO. However, this is always a great challenge in molecular electronics, owing to a big deviation of the detected LUMO existed in the previous techniques⁴⁶. The UPS is employed to probe the relevant energies of HOMO by producing a photo-generated electron at a given excitation source (21.22 eV). As shown in Supplementary Fig. 7, the E_cutoff is 16.38 eV, 16.26 eV, 16.20 eV and 16.60 eV, while the corresponding Δ is 0.15 eV, 0.16 eV, 0.14 eV and 0.53 eV respectively. Hence, the HOMO can be calculated as -4.99 eV, -5.12 eV, -5.16 eV and -5.15 eV for PBDB-T, PCE10, PBDB-T-2F and PBDB-T-2Cl. By calculating the difference of the HOMO and the LUMO from our method, the electronic transport energy gap can be decided as 1.86 eV, 1.72 eV, 1.67 eV and 1.52 eV for PBDB-T, PCE10, PBDB-T-2F and PBDB-T-2Cl.

Discussion

In this study, hot electron spectroscopy has been verified as a powerful method to determine the intrinsic LUMO of molecular semiconductors, while accurately identify the tiny change of LUMO caused by a subtle difference in structure. According to the investigation, these achievements should originate from an ultra-high electronic energy resolution of hot electron transistor. Here, the Al/AlO_x/Au tunneling junction is regarded as the probe. The energy of hot electrons can be regulated by the external bias V_EB. Owing to the quantum tunneling effect, these electrons are provided with exponential energy dependence, which illustrate a narrow energy distribution⁴⁷. It can experimentally be proved by the oscillatory emitter current in the magnified I_E-V_EB curve (Fig. 5a)⁴⁸. However, the energy distribution of hot electrons would not be obtained by the ordinary I-V characteristic, due to the unobvious oscillation. In general, the first derivative characteristic is always used to make a reasonable analysis^49,50. Here, the unobvious oscillations of I_E-V_EB curve can be transferred into some obvious waves. According to the full wave at half maximum (FWHM), we can decide the electronic energy resolution⁵¹. As shown in Fig. 5b, the first derivative characteristic is illustrated as a rough curve which is composed with countless waves. Therefore, all the hot electrons must be provided with high energy resolution. Since the emitter current derives from the measurement process of hot electron spectroscopy of PCE10, we are more concerned about the energy resolution in the linear fitting region. Figure 5c exhibits the first derivative characteristic from -2.38V to -2.50V which consists of 9 waves. According to the FWHM, the electronic energy resolution of a enlarge wave has been extracted as 6.3meV (Fig. 5d). Based on it, we can calculate the average value of the FWHM for the 9 waves as 5.9meV which represents the average electronic energy resolution in the linear fitting region. This result is in good agreement with that reported in the literatures⁴⁷. There is no doubt that the electronic energy resolution of hot electron spectroscopy is high enough, even in comparison with the most accurate UPS. Thanks to it, hot electron spectroscopy can be developed to be a precise method to determine the intrinsic LUMO and accomplish the researches in this work.

Fig. 5.

Electronic energy resolution of hot electron spectroscopy. (a), I_E-V_EB curve at a negative voltage. (b), The first derivative of I_E-V_EB curve. (c), The enlarged first-derivative curve from -2.38V to -2.50V. (d), The enlarged first-derivative curve with an individual wave.

Conclusion

In conclusion, we have designed an easy-operating hot electron transistor to in-situ probe the LUMO of molecular semiconductors. By making use of the first derivative-assisted linear fitting method, the intrinsic LUMO can be scientifically determined from the hot electron spectroscopy for the first time. These values are provided with a high reproducibility and some have been verified by the LEIPS in literatures, which demonstrate our method to be an accurate measurement. It originates from the ultra-high electronic energy resolution of hot electron spectroscopy. In combination with the HOMO from UPS, electronic transport energy gaps have been confirmed precisely. By monitoring the flow of electrons in an authentic device, it not only offers a promising platform for the LUMO detection, but also provides a fire-new insight for the deep understanding of the device physics, which is crucial for the performance optimization.

Methods

Device fabrication

A special shadow mask is designed to prepare all the metallic electrodes, including emitter, base and collector, in a high vacuum evaporator chamber (base pressure ~ 10^–6 mbar). Firstly, a 13-nm thick Al film (purchase from Lesker with 99.95% purity)is evaporated by e-beam with a rate of 0.2 ~ 0.6 Å s^-1. Secondly, the film is used to plasma oxidized at 12W for 1 min and creates a AlO_x tunnel junction. Thirdly, a 10-nm thick Au film is fabricated by thermal evaporation with a rate of 1 Å s^-1. Fourthly, the molecular films are formed by spin coating. In order to guarantee the integrity of these films, the concentration of PCE10, PBDB-T, PBDB-T-2F and PBDB-T-2F is set as 12.5 mg ml^-1, 17.5 mg ml^-1, 17.5 mg ml^-1 and 17.5 mg ml^-1 respectively. Finally, Al is selected to be the top electrode which is prepared by thermal evaporation. For fear of the penetration of hot Al atoms in these molecular films, the evaporated process is divided into two steps (3 nm at 0.1 ~ 0.2 Å s^-1 and 9 nm at 0.8 ~ 1 Å s⁻¹).

Electrical characterization

Before the test, all the hot electron devices are introduced in the Lakeshore probe-station with high vacuum (chamber pressure about 1 × 10^–5 mbar) and adjustable temperature. A Keithley 4200 semiconductor analyzer system is employed to record the I–V curves.

Cyclic voltammetry

The CV is performed by the CHI760E electrochemical workstation with the standard three-electrode configuration, including working electrode (platinum rod), counter electrode (platinum rod), and reference electrode (saturated calomel electrode). Under the protection of nitrogen, the whole measurement is accomplished in 39 mg ml^-1 Bu₄NPF₆^- acetonitrile solution with a scan rate of 20 mV s⁻¹. Finally, the LUMO can be calculated by the following equation:

$$\text{LUMO}=-4.71\text{eV}-\text{e}\ast E_{\mathit{red}}$$ 6

where, E_red is the reduction potential.

Ultraviolet photoelectron spectroscopy

The prepared solutions are spin-coated on the surface of Au(30 nm)/SiO₂(298 nm)/Si substrates and then make the 5-nm thick films. Then, these samples will be placed into a high vacuum surface analysis system with the pressure of 3 × 10⁻⁸ Torr. The UPS measurements are performed by using He-discharge lamp (21.22 eV) as the excitation source and the operated voltage is ranged from 0 to -9 V. According to the secondary electron cut-off (E_cutoff) and the injected barrier (Δ) relative to the substrate, the HOMO can be calculated by the following equation:

$$\text{HOMO}=-\text{IP}$$ 7

$$\text{IP}=\text{WF}+\mathrm{\Delta }$$ 8

$$\text{WF}=21.22-E_{\mathit{cutoff}}$$ 9

where, IP and WF correspond to the ionization potential and work function of the molecular semiconductor respectively.

Author contributions

Xuehua Zhou: discuss and modify the whole framework. Shixing Yang: literature collection. Chao Han: construct the whole logic of this manuscript.

Funding

Key project of Anqing Normal University, ZK202403ZD, Open Fund of Ultra High Molecular Weight Polyethylene Fiber Engineering Research Center of Anhui Province,GCZX-2023-B003,Natural Science Foundation of Anhui Education Department,2022AH051045,'Jing Fu Yu Ying’ Innovation and Entrepreneurship Leading Plan Project of Anqing Normal University,2022JFYY010,Provincial innovation and Entrepreneurship Training Program for College Students,S202310372061,Zhejiang Medical Health Science and Technology Project,2023RC044,Zhejiang Province Traditional Chinese medicine science and technology project,2024ZL487

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request. If someone wants to request the data, please contact Xuehua Zhou, E-mail: zhouxuehua_246420@163.com.

Declarations

Competing interests

The authors declare no competing interests.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-024-77605-1.