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Article

Highly Efficient Contact Doping for High-Performance Organic UV-Sensitive Phototransistors

by
Bin Li
1,†,
Yihan Zhang
1,†,
Yang Liu
1,
Yiwen Ren
1,
Xiaoting Zhu
2,
Lingjie Sun
1,2,*,
Xiaotao Zhang
3,
Fangxu Yang
1,*,
Rongjin Li
1,* and
Wenping Hu
1,2
1
Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China
2
Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Fuzhou 350207, China
3
Institute of Molecular Aggregation Science, Tianjin University, Tianjin 300072, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Crystals 2022, 12(5), 651; https://doi.org/10.3390/cryst12050651
Submission received: 22 March 2022 / Revised: 26 April 2022 / Accepted: 27 April 2022 / Published: 2 May 2022
(This article belongs to the Special Issue 2D Crystalline Nanomaterials)
Browse Figures
Versions Notes

Abstract

:
Organic ultraviolet (UV) phototransistors are promising for diverse applications. However, wide-bandgap organic semiconductors (OSCs) with intense UV absorption tend to exhibit large contact resistance (Rc) because of an energy-level mismatch with metal electrodes. Herein, we discovered that the molecular dopant of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was more efficient than the transition metal oxide dopant of MoO3 in doping a wide-bandgap OSC, although the former showed smaller electron affinity (EA). By efficient contact doping, a low Rc of 889 Ω·cm and a high mobility of 13.89 cm2V−1s−1 were achieved. As a result, UV-sensitive phototransistors showed high photosensitivity and responsivity.

1. Introduction

Organic ultraviolet (UV)-sensitive phototransistors are attracting intense attention because of their promising applications in sensing and optical communication [1,2]. Organic semiconductors (OSCs) are solution processable and may lead to low-cost, large-area and flexible phototransistors [3]. However, OSCs with intense UV absorption typically possess wide-bandgap and deep highest occupied molecular orbital (HOMO) [4], which leads to large contact resistance (Rc) because of the energy level mismatch with metal electrodes.
Several strategies have been proposed to tackle the problem of the large Rc of OSCs. The principle was to tune the work function (WF) of the electrodes to reduce the energy-level misalignment problem. The first method was inserting a contact oxide interlayer (COI) between the electrode and the semiconductor. For example, Darmawan et al. [5] studied a variety of oxide films, including oxides of Al, Hf, Zr, Ta, Ti and Si, and their effectiveness in improving pentacene transistors. They found that Al2O3 yielded the lowest Rc of 1.9 kΩ·cm. This method required strict control over the thickness of the COI. If the thickness was too large, tunneling would be blocked and Rc might be increased. On the contrary, if the thickness was too small, the effect would not be obvious [6]. The second method was using nondestructive electrodes. For example, Peng et al. [7] implemented mechanically transferred nondestructive Au contacts onto large-area monolayer crystals of 2,9-didecyldinaphtho [2,3-b:2′,3′-f]thieno [3,2-b]thiophene (C10-DNTT) and obtained a low Rc of 40 Ω·cm. However, the electrode prepared by this method was difficult to scale up for practical applications. The third method was the chemical modification of the metal electrodes. For example, Lamport et al. [8] demonstrated an Rc of about 200 Ω·cm using a self-assembled monolayer (SAM) of pentafluorobenzenethiol (PFBT) to modify the Au electrode. However, the materials that can be used as an SAM to tune the WF of the electrodes were scarce, which limited it application [9].
In recent years, doping has attracted more and more attention to reduce the Rc [10,11] because of its high effectiveness, the great diversity of dopants, and the possibility of up-scale production. The key for doping was to identify the suitable dopant, which can reduce the Rc to a large extent. For example, Minari et al. [12] chose FeCl3 as a contact dopant and obtained a low Rc of 8.8 kΩ·cm. However, as an ionic dopant, the high diffusivity of the small ions resulted in the instability of the devices [9,13]. Other types of popularly investigated dopants were MoO3 [14,15,16,17,18] and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) [19,20,21,22,23,24]. Although there has been intense investigation, it is still not clear which one was more efficient in reducing the Rc of wide-bandgap OSCs. In this study, we found that the molecular dopant of F4TCNQ was more efficient than the transition metal oxide dopant of MoO3 in reducing the Rc of a wide-bandgap OSC because of the more efficient doping of the OSC in the contact area. The conductivity of doped OSC was substantially increased after molecular doping by F4TCNQ, and the Rc was substantially reduced. Because of the reduced Rc, the organic phototransistors (OPTs) exhibited a high hole mobility of 13.89 cm2V−1s−1 and superior photosensitivity and responsivity.

2. Materials and Methods

2.1. Materials

Chlorobenzene (anhydrous, 99.8%), polystyrene (PS) (analytical standard, average molecular weight (Mw): ≈ 2,000,000), 2-decyl-7-phenyl-[1]benzothieno [3,2-b][1]benzothiophene (Ph-BTBT-10) (purity ≥ 99%), F4TCNQ and MoO3 were bought from Sigma-Aldrich. All materials were used without purification.

2.2. Substrate Cleaning

The organic field-effect transistors (OFETs) were fabricated on Si/SiO2 substrates. The SiO2 (300 nm)/Si wafers were sonicated twice in deionized water for 10 min. The substrates were then cleaned consecutively with acetone, isobutanol and acetone by ultrasonic. Finally, the substrates were dried by nitrogen flow and treated using oxygen plasma at 80 W for 30 min.

2.3. Semiconductor Deposition

The Ph-BTBT-10 and PS were dissolved in chlorobenzene at a ratio of 1:1 w/w and a total concentration of 20 mg/mL. The solution was then stirred at 100 °C for 30 min. The mixed solution was coated on a clean Si/SiO2 substrate by blade-coating [25]. The as-prepared thin film was annealed at 120 °C for 20 min to remove any residual solvent.

2.4. Electrode Preparation

F4TCNQ and silver were deposited by continuous thermal evaporation through the same shadow mask. The pressure in the vacuum chamber was less than 1 × 10−6 mbar, and the evaporation rate of the silver (thickness of 40 nm), F4TCNQ (thickness of 4 nm) and MoO3 (thickness of 2 nm) was 0.2 Ås−1, 2 Ås−1 and 0.3 Ås−1, respectively.

2.5. Calculation of Device Parameters

The optical bandgap (Eg) was calculated using the following equation: Eg = 1240/λb, where λb is the wavelength of the absorption edge, which can be extracted from the UV-Vis spectrum [26].
The mobility of the OFETs was calculated using the following equation: IDS = (W/2L)µCi(VGS − Vth)2, where IDS is the current, μ is the field-effect mobility, Vth is the threshold voltage, VGS is the gate voltage, L is the channel length, W is the channel width and Ci is the unit-area capacitance of dielectric (SiO2, 10 nF cm−2) [27].
The photosensitivity (P) was calculated by P = (Ilight − Idark)/Idark (Ilight refers to the photocurrent, that is, the source–drain current under light irradiation; Idark refers to dark current, which is IDS under dark conditions). The responsivity (R) was calculated by R = (Ilight − Idark)/(Pi × S), where Pi is the illumination intensity and S is the area of the channel region exposed to illumination. The detectivity (D*) was calculated by D* = RS1/2/(2eIdark)1/2, assuming that shot noise from Idark is the dominant contribution to the noise current [27].

3. Results and Discussion

Ph-BTBT-10 was used as an example OSC because of its excellent solution processibility, high stability and high hole mobility [28]. Ph-BTBT-10 showed intense absorption in the UV region (wavelength < 400 nm), which was an essential property for the development of high-performance UV-sensitive photodetectors (Figure S1) (see supplementary materials). Its optical bandgap was 3.16 eV (Figure S1) with a deep ionization potential (IP) of −5.63 eV, determined by ultraviolet photoelectron spectroscopy (UPS, Figure S2 and Table S1).
Centimeter-scale crystalline thin films of Ph-BTBT-10 were prepared by blade-coating of a blend solution of Ph-BTBT-10 and polystyrene (Figure 1a and Figure S3). The polystyrene acted as a binder to help form uniform and crystalline thin films over a large area [29]. After blade-coating, a vertical phase separation of Ph-BTBT-10 and PS occurred, and the Ph-BTBT-10 crystalline thin film was located on top of the PS [30].
As can be seen by the optical microscopy (OM) image presented in Figure 1b–d, the as-prepared thin film was uniform, continuous and flat. Under a polarized optical microscope (POM), when the sample was rotated by 45°, a consistent color change was identified, which indicated the high crystallinity of the thin film (Figure 1e,f).
As shown in Figure 2a, a typical transmission electron microscope (TEM) image revealed a uniform film morphology. The sharp and regular selected area electron diffraction (SAED) pattern confirmed its high crystallinity (Figure 2b) [28]. X-ray diffraction (XRD) patterns exhibited sharp diffraction peaks with a smooth baseline, which is indicative of crystalline thin films (Figure 2c). All XRD peaks were assignable to (00l) reflections. A diffraction peak assignable to (002) was observed at 2θ = 3.4°, and the d-spacing was calculated as 26 Å according to the Bragg equation (d = nλ/2sinθ). This value equaled the c-axis length of the single crystal structure of Ph-BTBT-10 [28], indicating that the Ph-BTBT-10 molecules were stacked, with the long axis perpendicular to the substrate [28]. Such a packing mode was in favor of the in-plane change transport in OFETs. Atomic force microscope (AFM) imaging showed that the root-mean-square (RMS) roughness of the thin film was 0.51 nm. The thickness was 11.2 nm, corresponding to four to five molecular layers (Figure S4). In OPTs with a staggered device configuration, the thickness of the OSC should be thin to exclude the possibility of injection limitations due to the transport from the metal contacts to the accumulated channel. A molecular-scale thickness, large-area, flat and crystalline thin film is desirable for the construction of OPTs.
Efficient injection is a prerequisite for all high-performance optoelectronic devices. Because of the deep HOMO level of wide-bandgap OSCs, it is difficult to match the WF of an electrode to the HOMO levels. Engineering the effective WF by inserting charge injection layers (CILs) has been proven to be effective in achieving low Rc. In this study, two types of CILs, i.e., MoO3 and F4TCNQ, were investigated. Ag was selected as the metal electrode because of its lower melting point. Compared with Au, detrimental thermal irradiation during vacuum evaporation, which is fatal for molecularly thin organic films, could be reduced. The width-normalized contact resistance was obtained by the transmission line method (TLM) [31]. As for the metal electrode without CIL, an Rc as large as 6300 Ω·cm was identified (Figure S5). After inserting the CILs, the Rc was reduced. A lower Rc was anticipated in the metal electrode with a CIL of MoO3 compared to that of F4TCNQ, because of the lower electron affinity (EA) of MoO3 (−6.7 eV) [32] compared to that of F4TCNQ (−5.2 eV) [33] (Figure S6). However, a lower Rc was identified after inserting F4TCNQ: Rc was measured to be 2500 Ω·cm with MoO3 and 889 Ω·cm with F4TCNQ (Figure 3).
To explore the reason why F4TCNQ is more efficient than MoO3 as CILs, we paid attention to the doping of OSCs in addition to the tunning of the WF of the metal electrode. The charge transfer degree between Ph-BTBT-10 and F4TCNQ was determined quantitatively by infrared (IR) spectroscopy. As for F4TCNQ, the C≡N stretching mode was commonly used to measure the degree of charge transfer [34]. The C≡N stretching mode was observed at 2227 cm−1 in pristine F4TCNQ, which was consistent with previous reports [34]. For F4TCNQ-doped Ph-BTBT-10, this peak was red shifted to 2200 cm−1 (Figure 4a,b); the shift was consistent with previous reports [34], indicative of electron transfer from Ph-BTBT-10 to F4TCNQ [34]. The degree of charge transfer was calculated to be as large as 0.824 (Table S2), indicative of efficient doping [34]. To further prove that effective doping occurred, two terminal devices were fabricated with the same pristine and doped Ph-BTBT-10 thin film as those used in the contacts of the devices. Notably, the current of F4TCNQ-doped Ph-BTBT-10 film increased over three orders of magnitude compared to that of pristine Ph-BTBT-10 thin film at a voltage bias of 2 V (Figure 4c), indicating that the conductivity of the doped thin film was remarkably improved. As a comparison, the MoO3-doped Ph-BTBT-10 thin film showed little change in conductivity, indicative of ineffective doping. The high doping efficiency of F4TCNQ might be explained by the recent investigations of Norbert Koch and coworkers, who show that the EA of the p-dopant does not have to exceed the IP of the OSC, and doping efficiency is determined by the overall density of the states of the entire sample and its Fermi–Dirac occupation [35]. It can be concluded that F4TCNQ doped the semiconductor in the contact region, thus increasing the conductivity of the contact region and reducing the Rc [6,9,36].
OFETs based on different contacts (F4TCNQ and MoO3 as CILs) were constructed. A schematic diagram of the device is shown in Figure 5a, and a cross-sectional scanning electron microscope (SEM) image of the device is shown in Figure 5b. OFETs with Ag–F4TCNQ electrodes exhibited a maximum mobility of 13.89 cm2V−1s−1 and an average mobility of 12.03 cm2V−1s−1, which were higher than those of the device based on Ag–MoO3 electrodes (a maximum mobility of 10.12 cm2V−1s−1, and an average of 8.43 cm2V−1s−1, Figure 5c,d and Figure S7). The mobility of OFETs with Ag–F4TCNQ electrodes prepared by us was high in the recently reported OFETs with Ph-BTBT-10 as a semiconductor (Table S3) [28,37,38,39,40,41,42,43]. Typical transfer curves showed negligible hysteresis, indicating a good interfacial quality (Figure 5e). The output I-V curves were linear in the low VDS region, in accordance with the observation of a low Rc (Figure 5f). The off-state current of OFETs with the Ag–F4TCNQ electrode was similar to that of undoped devices (Figure S8), because the F4TCNQ was doped in the contact region instead of the channel region [44]. The on-state current of OFETs with the Ag–F4TCNQ electrode was significantly improved (Figure S8) because of the reduced Rc and increased mobility after contact doping [45].
Encouraged by the low Rc and high mobility, OPTs were constructed with Ag–F4TCNQ electrodes. As the laser power intensity increased, the transfer curves at different wavelengths (λ = 310 nm, 365 nm, 405 nm) shifted upward, resulting in a higher source–drain current, and the threshold voltage also shifted to a more positive value (Figure 6a–c). The variation of the maximum threshold voltage (ΔVth) could be as high as 27.5 V under illumination. The significant shift in Vth is attributed to the photogating effect, in which photo-generated electrons were captured by the polystyrene and generated additional electric field-like negative VGS to increase the channel conductivity [46]. P, R and D* are important parameters for evaluating the performance of OPTs [27]. Under incident wavelengths of 310 nm, 365 nm and 405 nm, the maximum R values were calculated as 5.35 × 105 AW−1, 1.21 × 104 AW−1 and 9.12 × 103 AW−1, respectively; the maximum p values were 6.70 × 106, 1.35 × 108 and 3.65 × 108, respectively (Figure 6d–f). Under incident wavelengths of 310 nm, 365 nm and 405 nm, the maximum D* values were estimated to be 3.85 × 1017 Jones, 9.68× 1017 Jones and 1.79 × 1017 Jones, respectively (Figure S9).
The R at λ = 310 nm was higher than the vast majority of the values reported so far (Figure S10) [47,48,49,50,51,52,53,54,55,56,57,58,59]. The transfer curves of the devices did not shift under laser irradiation of wavelengths from 450 to 550 nm, indicating little response to other wavelengths of light (Figure S11). Moreover, under 365 nm UV light (31.70 μW cm−2) irradiation, the photocurrent remained without decay up to 3 × 103 s (Figure S12). In addition, the OPTs demonstrated photo-switching behavior (Figure S13).

4. Conclusions

The molecular dopant of F4TCNQ was more efficient than the transition metal oxide dopant of MoO3 in reducing the Rc of OPTs based on a wide-bandgap OSC because of the more efficient doping of the contact. Through efficient contact doping, a substantially reduced Rc of 889 Ω·cm and a high mobility of 13.89 cm2V−1s−1 were achieved in the OFETs. Benefiting from the reduced Rc and excellent charge transport properties, UV-sensitive OPTs exhibited high performance with R and P up to 1.21 × 104 AW−1 and 1.35 × 108, respectively, under 365 nm light. This study showed that doping by molecular dopant was a powerful method to reduce the Rc of wide-bandgap OSCs for high-performance optoelectronic devices.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst12050651/s1, Figure S1: UV-Vis spectra of the powders of Ph-BTBT-10; Figure S2: (a, b) UPS spectra of the crystalline film of Ph-BTBT-10. The cutoff tail and Fermi tail are marked in the figures; Figure S3: (a) Optimization of scraping speed. (b) Optimization of annealing temperature; Figure S4: AFM images of the crystalline thin film of Ph-BTBT-10; Figure S5: (a) Width-normalized contact resistances obtained by TLM as a function of the channel length of OFETs with metal electrode without CIL under a gate voltage of −50 V. (b) Width-normalized contact resistances of OFETs with metal electrode without CIL under different gate voltage; Figure S6: Energy level diagrams of Ph-BTBT-10, F4TCNQ and MoO3; Figure S7: (a) Transfer electrical property of the OFET with Ag–MoO3 electrodes. Inset shows the schematic of the device structure. (b) Output curves of the OFET with Ag–MoO3 electrodes. Inset is the enlarged output I-V curve in the low VDS region. The channel length is 100 μm and the channel width is 100 μm; Figure S8: Transfer curves of contact-doped (F4TCNQ) and undoped devices in the dark. The channel length was 100 μm and the channel width was 100 μm; Figure S9: Detectivity (D*) of OPTs as a function of the laser power density at wavelengths of (a) 310 nm, (b) 365 nm and (c) 405 nm. The channel length was 100 μm and the channel width was 100 μm.; Figure S10: Statistics of responsivity values of the UV OPTs based on different organic semiconductors; Figure S11: Transfer characteristics of the OPTs under different illumination intensities at the wavelengths of (a) 550 nm and (b) 450 nm, respectively. The channel length was 100 μm and the channel width was 100 μm; Figure S12: Photocurrent stability characterization of the OPTs as a function of time under VDS = −50 V, VGS = −20 V and λ = 365 nm at 31.70 μW cm−2. The channel length was 100 μm and the channel width was 100 μm; Figure S13: (a.b) The photo-switching properties of contact-doped (F4TCNQ) and undoped devices. The channel length was 100 μm and the channel width was 100 μm; Table S1: The HOMO level of Ph-BTBT-10 calculated by UPS Spectrum; Table S2: Calculated the degree of charge transfer of F4TCNQ-Ph-BTBT-10; Table S3: Comparison of partial electrical characteristics of recently reported OFETs based on Ph-BTBT-10.

Author Contributions

Conceptualization, supervision, validation, and project administration R.L., F.Y. and L.S.; investigation, data curation, B.L., Y.Z., Y.L., Y.R. and X.Z. (Xiaoting Zhu); resources, X.Z. (Xiaotao Zhang) and W.H.; writing—original draft preparation, B.L.; writing—review and editing, B.L.; funding acquisition, R.L. and F.Y. All authors have read and agreed to the published version of the manuscript.

Funding

The authors thank the National Natural Science Foundation of China (No. 51873148, 51903186, 52073206 and 51633006).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Schematic of blade-coating. (b–d) Optical microscopy (OM) and (e,f) polarized optical microscope (POM) images of the crystalline films of 2-decyl-7-phenyl-[1]benzothieno [3,2-b][1]benzothiophene (Ph-BTBT-10) on SiO2/Si substrates.
Figure 1. (a) Schematic of blade-coating. (b–d) Optical microscopy (OM) and (e,f) polarized optical microscope (POM) images of the crystalline films of 2-decyl-7-phenyl-[1]benzothieno [3,2-b][1]benzothiophene (Ph-BTBT-10) on SiO2/Si substrates.
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Figure 2. (a) Typical transmission electron microscope (TEM) image and (b) corresponding selected area electron diffraction (SAED) patterns of the crystalline film. (c) Measurement and simulation [28] of out-of-plane X-ray diffraction (XRD) patterns of the crystalline film.
Figure 2. (a) Typical transmission electron microscope (TEM) image and (b) corresponding selected area electron diffraction (SAED) patterns of the crystalline film. (c) Measurement and simulation [28] of out-of-plane X-ray diffraction (XRD) patterns of the crystalline film.
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Figure 3. (a) Width-normalized contact resistances obtained by transmission line method (TLM) as a function of the channel length of organic field-effect transistors (OFETs) with Ag-2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (Ag–F4TCNQ) and Ag–MoO3 electrodes under a gate voltage of −50 V. (b) Width-normalized contact resistances of OFETs with Ag–F4TCNQ and Ag–MoO3 electrodes under different gate voltages.
Figure 3. (a) Width-normalized contact resistances obtained by transmission line method (TLM) as a function of the channel length of organic field-effect transistors (OFETs) with Ag-2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (Ag–F4TCNQ) and Ag–MoO3 electrodes under a gate voltage of −50 V. (b) Width-normalized contact resistances of OFETs with Ag–F4TCNQ and Ag–MoO3 electrodes under different gate voltages.
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Figure 4. (a,b) Infrared (IR) spectra of pristine Ph-BTBT-10, pristine F4TCNQ and F4TCNQ-doped Ph-BTBT-10 film. (c) I-V curves of pristine Ph-BTBT-10, F4TCNQ-doped Ph-BTBT-10 and MoO3-doped Ph-BTBT-10 film. Curves of pristine and MoO3-doped Ph-BTBT-10 superposed. The channel length was 45 μm and the channel width was 200 μm. The thickness of Ph-BTBT-10 thin film was kept constant at 11.2 nm.
Figure 4. (a,b) Infrared (IR) spectra of pristine Ph-BTBT-10, pristine F4TCNQ and F4TCNQ-doped Ph-BTBT-10 film. (c) I-V curves of pristine Ph-BTBT-10, F4TCNQ-doped Ph-BTBT-10 and MoO3-doped Ph-BTBT-10 film. Curves of pristine and MoO3-doped Ph-BTBT-10 superposed. The channel length was 45 μm and the channel width was 200 μm. The thickness of Ph-BTBT-10 thin film was kept constant at 11.2 nm.
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Figure 5. (a) Schematic of the devices. (b) Cross-sectional scanning electron microscope (SEM) image of the device. (c) Histogram of the saturation mobility of OFETs with Ag–F4TCNQ electrodes. (d) Histogram of the saturation mobility of OFETs with Ag–MoO3 electrodes. (e) Typical transfer curves of the device using Ag–F4TCNQ electrodes. (f) Typical output curves of the device using Ag–F4TCNQ electrodes. Inset shows the enlarged output I-V curves in the low VDS region. The channel length was 100 μm and the channel width was 100 μm.
Figure 5. (a) Schematic of the devices. (b) Cross-sectional scanning electron microscope (SEM) image of the device. (c) Histogram of the saturation mobility of OFETs with Ag–F4TCNQ electrodes. (d) Histogram of the saturation mobility of OFETs with Ag–MoO3 electrodes. (e) Typical transfer curves of the device using Ag–F4TCNQ electrodes. (f) Typical output curves of the device using Ag–F4TCNQ electrodes. Inset shows the enlarged output I-V curves in the low VDS region. The channel length was 100 μm and the channel width was 100 μm.
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Figure 6. Transfer characteristics of organic phototransistors (OPTs) measured under different illumination intensities at wavelengths of (a) 310 nm, (b) 365 nm and (c) 405 nm. Responsivity (R) and photosensitivity (P) of OPTs as a function of the laser power density at wavelengths of (d) 310 nm, (e) 365 nm and (f) 405 nm. The channel length was 100 μm and the channel width was 100 μm.
Figure 6. Transfer characteristics of organic phototransistors (OPTs) measured under different illumination intensities at wavelengths of (a) 310 nm, (b) 365 nm and (c) 405 nm. Responsivity (R) and photosensitivity (P) of OPTs as a function of the laser power density at wavelengths of (d) 310 nm, (e) 365 nm and (f) 405 nm. The channel length was 100 μm and the channel width was 100 μm.
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Li, B.; Zhang, Y.; Liu, Y.; Ren, Y.; Zhu, X.; Sun, L.; Zhang, X.; Yang, F.; Li, R.; Hu, W. Highly Efficient Contact Doping for High-Performance Organic UV-Sensitive Phototransistors. Crystals 2022, 12, 651. https://doi.org/10.3390/cryst12050651

AMA Style

Li B, Zhang Y, Liu Y, Ren Y, Zhu X, Sun L, Zhang X, Yang F, Li R, Hu W. Highly Efficient Contact Doping for High-Performance Organic UV-Sensitive Phototransistors. Crystals. 2022; 12(5):651. https://doi.org/10.3390/cryst12050651

Chicago/Turabian Style

Li, Bin, Yihan Zhang, Yang Liu, Yiwen Ren, Xiaoting Zhu, Lingjie Sun, Xiaotao Zhang, Fangxu Yang, Rongjin Li, and Wenping Hu. 2022. "Highly Efficient Contact Doping for High-Performance Organic UV-Sensitive Phototransistors" Crystals 12, no. 5: 651. https://doi.org/10.3390/cryst12050651

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