P3HT Heterojunction Photodetectors

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Functional Inorganic Materials and Devices

Structural engineering of Si/TiO2/P3HT heterojunction photodetector for tunable response range Liang Chen, Wei Tian, Chaoxiang Sun, Fengren Cao, and Liang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b20182 • Publication Date (Web): 27 Dec 2018 Downloaded from http://pubs.acs.org on January 2, 2019

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ACS Applied Materials & Interfaces

Structural engineering of Si/TiO2/P3HT heterojunction photodetector for tunable response range

Liang Chen, † Wei Tian,*,† Chaoxiang Sun†, Fengren Cao† and Liang Li*,†

†

School of Physical Science and Technology, Center for Energy Conversion Materials

& Physics, Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006, P. R. China Email: [email protected], [email protected]

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT To meet the demands of next-generation optoelectronic circuits, the design and construction of photodetectors with tunable photoresponse range and self-powered feature are urgently required. To achieve selective wavelength detection, a band-pass filter is usually required to dislodge interfere of certain wavelength light, which inevitably enhances the weight and increases the cost. Here, we demonstrate a self-powered photodetector with tunable response range by constructing a heterojunction structure consisting of P3HT, TiO2 interlayer and silicon nanowires. Through controlling the P3HT concentration, both core-shell and embedded configurations can be obtained, which exhibit different response range. This work provides a convenient route to construct self-powered wavelength-selective photodetector, which may finds application in light communication and biomedical engineering.

KEYWORDS: Si, P3HT, self-powered, tunable photoresponse range, photodetector


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INTRODUCTION Wavelength-selective photodetectors are crucial for wide applications, including light communication,

biomedical

sensing,

imaging

systems

and

environmental

monitoring.1-4 Generally, most of reported photodetectors are nonselective, and their photoresponse ranges are determined by the bandgap of the photoactive component.5-7 Silicon (Si) is the most important component in a variety of semiconductor devices, including photodetectors, solar cells and logic circuits, due to its versatile properties, controllable fabrication process and highly-developed integration techniques.8-10 Particularly, vertically-aligned Si nanowire (NW) array has been developed as building block for high performance photodetectors, owing to its strong light-trapping effect and effienct charge transport feature.11 A number of Si NWs based photodetectors have been designed and constructed.12-14 One typical feature of the Si based photodetectors is their wide response range from UV light to near-infrared light, which is determined by the narrow bandgap of Si. To achieve wavelength-selective detection, a variety of strategies have been utilized. The conventional method is to combine Si photodetectors with band-pass filters.15 Besides, it is demonstrated that by varying the radius of Si NW, its light absorption and photocurrent spectra alter accordingly. Based on this phenomenon, the researchers demonstrated that the spectral sensitivities of Si NW photodetectors can be governed by NW radius, which enabled the selective color imaging.16 The integration of Si with plasmonic nanoparticles is also an effective approach.17 The absorption band of surface plasmon resonance can be easily manipulated by the shape and size of nanoparticles,



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inter-particle distance and surrounding medium, which provide a platform to modulate the spectral range of Si based photodetectors. Nevertheless, the application of the above strategies has been severely limited by their inherent problems. Spectral filtering inevitably limits the quality of color sensing and increases the device size and weight. The controllable synthesis of Si NW with certain radius is difficult, which is time consuming and requires complicated process. The non-suppressed absorption hinders the plasmon-assisted strategy. Meanwhile, plasmonic nanoparticles usually bring about inferior visible/infrared response.18 Therefore, facile and effective methods are urgently needed to fabricate wavelength-selective Si based photodetector. Apart from wavelength-selective, the design of self-powered photodetector that can function independently without external power sources is also one of the pursing objects in optoelectronic field. The common approaches to realize self-powered photodetector are to construct p-i-n or Schottky junction as the photoactive layer by exploiting their photovoltaic effects.19,

20

The integration of Si with metal oxides,

metal sulfides and graphene have been constructed and respectful performances have been demonstrated.21-23 Enlightened by the above results, integrating Si NWs with suitable semiconductors provides a viable path to construct heterojunction photodetectors with self-powered capability, large responsivity and fast response speed. As a solution-processable polymer material, poly(3-hexylthiophene) (P3HT) has been explored as light absorber in organic solar cells.24 The hybrid solar cells of Si/P3HT have earned respectful power conversion efficiencies due to their appropriate band

alignment

and

interface

compatibility.

Thus,


it

is

expected

that

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high-performance and self-powered photodetectors would be achieved by coupling Si NW and P3HT. In this work, we demonstrate a heterostructure based photodetector consisting of n-type Si NW arrays, a TiO2 interlayer and an p-type organic P3HT film. Due to the built-in electric filed at the p-P3HT/n-Si interface, photo-excited carriers can be efficiently separated without the assistance of external power supply, thus endowing the device with self-powered capability. Furthermore, by controlling the precursor concentration of P3HT, core-shell and embedded structures were obtained. As a result, the manipulation of charge transfer and recombination at the heterojunction interface is realized, leading to tunable photoresponse range. Specifically, when the P3HT concentration is low (10 mg/mL), the resulting device exhibits UV-Vis-NIR broadband detection (300-1100 nm). In contrast, the device fabricated with high P3HT concentration (30 mg/mL) operates as a filterless, visible-blind red and NIR photodetector with a response range from 640 to 1100 nm.

EXPERIMENTIONAL SECTION Materials.

Silver

nitrate

(AgNO3,

≥99.9%)

were

purchased

from

Shanghai Aladdin Chemistry Co., Ltd. Hydrofluoric acid (HF, ≥40%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Hydrogen peroxide (H2O2, 30%) and nitric acid (HNO3, 65-68%) were purchased from Shanghai Linfeng Chemical Reagent Co., Ltd. Chlorobenzene (C6H5Cl, 99.9%) purchased from Alfa Aesar. P3HT (Mw≈60,000) is purchased from Xi’an Polymer Light Technology Corp.



Fabrication of Si NWs-TiO2-P3HT photodetector. The vertically-aligned Si NW arrays were prepared by a chemical etching process according to previous report.25 Atomic layer deposition (ALD, Ensure NanoTech, Beijing, China) was employed to deposit 5 nm TiO2 interlayer on Si NWs. The detailed procedure was the same as that in our previous report.25 The TiO2 deposited Si NWs were annealed under argon atmosphere at 500 ℃ for 1 hour. The purchased P3HT powders were dissolved in chlorobenzene to obtain precursor solution (5, 10, 20, 30, and 40 mg/mL). After 20 min of UV-ozone cleaner treatment for TiO2-Si substrates, P3HT solution was spin coated on the substrates by 1000 rpm/min and 2000 rpm/min for 20 s, respectively. Finally, Ga-In alloy and silver paste were deposited on Si and P3HT film as conductive electrodes, respectively. Material characterization. X-ray diffractometer (XRD, D/Max-Ⅲ-B-40KV, Cu Κα radiation, λ = 0.15418 nm) was used to determine the phase. The morphology and composition were characterized by a field-emission scanning electron microscope (FE-SEM, Hitachi, SU8010) and energy dispersive X-ray spectroscopy (EDX), respectively. The reflection spectra of samples were collected by a UV-Vis spectrophotometer (Shimadzu, UV-3600). The photoluminescence (PL) spectra were characterized by fluorescence spectrometer (FP-6500) Photoelectric properties measurements. All of the photoelectric measurements, including current-voltage (I-V) curves, spectral responsivity, and time-dependent current (I-t) curves were collected by semiconductor characterization system (Keithley 4200) under 100 mW/cm2 simulated solar light (Newport ,94043A) and


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monochromatic light produced with a monochromator (Zolix, Omni-λ 3009) using order sorting filters. A power meter (Newport, 1936-R) was used to measure the light intensity. The response speed was recorded by an oscilloscope (Tektronix, 4045). The active area of 0.7 cm2 is defined by the electrodes (silver paste).

RESULTS AND DISCUSSION Figure 1a and 1b present the schematic structure of the devices. The core-shell architecture is consisted of Si NWs as core on planar Si substrate and organic P3HT as shell. The embedded architecture is made of Si NWs fully embedded in P3HT on planar Si substrate. Noted that ultrathin TiO2 layer was sandwiched between Si NWs and P3HT via ALD technique. On the basis of band structures of Si, TiO2 and P3HT, the band energy alignment of the Si/P3HT with and without TiO2 interlayer are plotted in Figure 1c. When P3HT and Si NWs are in direct contact, the energy band bending forms type II heterojunction, allowing photogenerated electrons to flow from P3HT to Si and holes from Si to P3HT. However, the hydrophobic feature of Si results in the uneven deposition of P3HT on its surface, greatly inhibiting the photoelectric performance. The TiO2 interlayer facilitates the deposition of P3HT, and improves the contact state between Si and P3HT. More importantly, the presence of TiO2 interlayer does not influence the migration of photogenerated carriers due to suitable band alignment. Under irradiation, the staggered alignment between P3HT and TiO2 will drive the electrons generated in P3HT to transport to TiO2, and then tunnel through the energy barrier at the Si/TiO2 interface to reach Si, though a small



portion of electrons recombine with the holes produced in Si. As a result, large photocurrent is attained for the heterojunction.26 The top-surface and cross-sectional SEM images of the as-obtained Si and Si/TiO2/P3HT heterojunction are shown in Figure 2. Figure 2a and b show the typical morphology of as-fabricated Si NW arrays, revealing that Si NW has the diameter of 200 nm and length of 3 μm. P3HT layer was deposited on the Si NW surface using spin-coating process. Precursor solutions with different concentrations were used to tune the loading of the P3HT. Different precursor concentrations (5, 10, 20, 30, and 40 mg/mL) were obtained by adding different amount of P3HT into a fixed volume of chlorobenzene. Here, the resultant devices were denoted as Si/TiO2/P3HT-x, where x denotes the precursor concentration of P3HT. After deposition of P3HT (10 mg/mL), n-p inorganic-organic core-shell architecture was observed (Figure 2c and 2d). If a denser P3HT solution (30 mg/mL) was deposited, Si NWs were completely embedded in P3HT film, forming an imbedded configuration (Figure 2e and 2f). To make a clear comparison, the top-view and cross-sectional SEM images of the Si/TiO2/P3HT with varying concentration of P3HT (from 5 to 40 mg/mL) are shown in Figure S1 and S2, respectively. As shown, with the increase of the P3HT concentration, the P3HT layer becomes denser. When the concentration is 10 mg/mL, Si NWs are coated by P3HT film but the independent wires can still be clearly observed without P3HT filling between wires. When the concentration reaches 40 mg/mL, Si NWs were completely embedded in organic P3HT, and the gaps among Si NWs were fully filled with P3HT. Because the 5 nm TiO2 is too thin to be directly observed by SEM, EDX is used to


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confirm the presence of TiO2 thin layer on Si surface. The EDX spectrum of Si/TiO2 shows obvious peaks of element Ti and O (Figure S3a). The mapping images in Figure S3b, c and d reveal that both Ti and O signals distribute on the Si surface uniformly. The photodetectors based on different P3HT concentrations were fabricated and their photoelectric properties were measured. Noted that to make a parallel comparison, the devices were fabricated under the same conditions except for the concentration of P3HT. As a key parameter for photodetector, responsivity (R) is denoted as the ratio of the photocurrent output in response to incident power, which is calculated by the following equation:27 R = (Ip-Id)/PS

(1)

where Ip is the photocurrent, Id is the dark current, P is the light power intensity, and S is the active area. Figure 3a shows the comparative responsivity of the as-fabricated devices with varying P3HT concentrations (5, 10, 20, 30, and 40 mg/mL) and the detailed parameters are summarized in Table 1. It is obvious that their responsivity in wavelength range of 300-640 nm decreases as the P3HT concentration increases. In comparison with Si/TiO2/P3HT-10, Si/TiO2/P3HT-5 exhibits lower responsivity, which is probably ascribed to the fact that the P3HT thickness is too thin to absorb sufficient photon energy. The same trend is observed in the 640-1100 nm wavelength range, the responsivity decreases with the concentration increases expect for 5 mg/mL. It is found that for Si/TiO2/P3HT-10, the peak responsivity value is 0.59 A/W at 920 nm and the lowest value is 0.05 A/W at 300 nm.



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As shown in Table 1, the maximum rejection ratio (NIR/UV rejection ratio) can reach 3080 for Si/TiO2/P3HT-30, while the maximum rejection ratio is less than 11 for Si/TiO2/P3HT-10. The result clearly demonstrates that the photoresponse range can be tuned by changing the P3HT concentration. Specifically, when the P3HT concentration is 10 mg/mL, the as-fabricated device functions as a broadband UV-Vis-NIR

device

with

response

range

between

300-1100

nm.

While

Si/TiO2/P3HT-30 is a UV-Vis blind red and NIR photodetector. Figure 3b shows the reflectivity spectra of Si NWs/TiO2/P3HT with different thicknesses. The pristine Si NWs exhibit ultralow reflection in the spectral region of 300-1100 nm due to its strong light trapping effect. Upon the deposition of 5-nm-thick TiO2, there is no apparent change in reflection, as shown in Figure S4. For Si/TiO2/P3HT samples, when the P3HT concentration is low (5, 10 and 20 mg/mL), the reflectivity nearly remains unchanged. As the concentration increases to 30 and 40 mg/mL, the reflection exhibits a tiny increase. It is found that the reflection in wavelength from 640 to 1100 nm increases, suggesting the thick P3HT layer will block the effective absorption of light with wavelength from 640-1100 nm of Si NW arrays. While the reflection values for all samples are almost the same in the spectra region from 300 to 640 nm, which is mainly attributed to the absorption of P3HT. Noted that no matter how much the P3HT concentration is, the reflection of as-fabricated Si/TiO2/P3HT samples are less than 10%, suggesting the strong light harvesting ability. The Si/TiO2/P3HT-40 sample exhibits a litter higher reflection as compared with other samples. This is because too thick P3HT film changes the


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surface morphology Si NW array, which poses a negative influence on the light trapping effect of Si NW, thus reducing the absorption and increasing the reflection. We also tested the absorption of P3HT layer on FTO substrate. As shown in Figure S5, the P3HT film mainly absorbs the light ranging from 300 to 650 nm. With the increase of the P3HT thickness, the absorption increases. The inset in Figure S5 shows that the calculated bandgap of P3HT is 1.92 eV. Based on the above results, excellent monochromatic light response is expected for the as-fabricated devices. In order to reveal the reason why the responsivity varies with the increase of P3HT film thickness, PL spectra were recorded from Si/TiO2/P3HT samples, as shown in Figure 3c. In the measurement process, the excitation wavelength is set as 450 nm. It can be seen the photoluminescence peaks locate within range from 625 to 650 nm and the peak intensity increases with the increase of P3HT concentration. Considering the fluorescence is caused by internal carrier recombination within the film, the higher fluorescence intensity represents the more serious recombination.28 It is concluded that the thick P3HT film not only reduces the absorption of Si, but also enables electron-hole pairs to recombine, thus reducing photoresponse between 300 and 640 nm. This is consistent with the results of responsivity and absorption spectra. It is worth noting that the PL peak shows a slight red-shift as the P3HT concentration increases. This is possibly due to the increased thickness of P3HT film. Previous report demonstrated that the PL spectrum of polymer film changes when the film thickness varies, because film morphology and polymer chain aggregation affect the optical and electrical properties.29 Higher concentration usually results in lower



solvent evaporation rate, which favors the entanglement of polymer chains and formation of stronger aggregates. Thus, PL spectrum changes when P3HT concentration varies. Figure S6 illustrates the I-t curves of Si NWs with and without 5 nm ALD-TiO2 interlayer curves under periodic white light illumination at 0 V. The black curve shows the photoresponse of Si NW without TiO2 interlayer, exhibiting poor on/off ratio (< 2), with photocurrent of 32 nA and dark current of more than 20 nA. Upon deposition of TiO2 interlayer, the device exhibits a remarkable enhancement in photocurrent and a dramatic decrease in dark current, delivering a high on/off ratio (105). The performance enhancement is mainly attributed to the presence of TiO2 interlayer, which is beneficial for the uniform deposition of P3HT interlayer. In addition, the energy level alignment among Si/TiO2/P3HT has no negative influence on the photoelectric performance (Figure 1). Therefore, 5-nm-thick TiO2 interlayer were employed in all of our devices. Figure 4a shows the I-V curves of the Si/TiO2/P3HT-10 device illuminated by different monochromatic lights and in dark condition. The I-V curves do not cross the zero point, indicating the photodetector is able to detect light signal without the assistance of external power source. The I-t curves of the photodetector irradiated by various wavelength light at zero bias are plotted in Figure 4b. This device exhibits distinct response to broad wavelength range from UV (380 nm) to NIR (1050 nm). Figure S7 shows the measured power intensity for different wavelength. The time-dependent photoresponse curves display stable and reproducible characteristics,


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regardless of the incident wavelength. To further quantify the detecting capability of the device, specific detectivity (D*) is measured at zero bias, and the corresponding curve is plotted in Figure 4c. Specific detectivity suggests the capability of a photodetector to detect weak photo signal, which is obtained from the following equation:30 D* = S1/2R/(2qId)1/2

(2)

where q is the electron charge, and Id is the dark current. As expected, specific detectivity shows the similar trend with the responsivity spectra. It is relatively low in the spectral range from 300 to 640 nm, then quickly rises up to the peak and decreases gradually. It is calculated that the maximum detectivity is 1.38×1014 Jones at 920 nm and the lowest value is 1.14×1013 Jones at 300 nm. Figure 4d shows the long-term photoresponse of the device under 920 nm light irradiation in air without encapsulation. After 900 s continued light irradiation, although the photocurrent has a tiny decay, the device still demonstrates reproducible and quick on/off response, indicating the photodetector possesses superior environmental stability. Figure 5a, c, and e show I-V curves of the device under illumination of different lasers (365, 532, and 980 nm) with varied light intensities at zero bias. The rectifying characters are observed for those I-V curves. The device exhibits significant increase in photocurrent and an ultralow dark current. It’s obvious that the photocurrent rises with increasing light power intensity, representing the strong light intensity correlation feature. It may be attributed to the superior sensitivity of the photodetector



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from UV to NIR light. The corresponding fitting curves of the photocurrent as a function light intensity is shown in Figure 5b, d, and f. The fitting curves equation can be described by the power law:31 I ∝ Pθ

(4)

where θ is an exponent. The curves show that θ = 0.57, 0.66, and 0.86, corresponding to the wavelength of 365, 532, and 980 nm, respectively. All of the factor θ are in the range between 0.5 to 1, indicating the charge generation, trapping and recombination govern the photoresponse within the heterojunction. Fast-response speed is crucial for photodetectors in many applications, such as fire alarm and space exploration.32 We use an oscilloscope and a modulated laser to evaluate the response time of the as-fabricated device (Figure 6a). Figure 6b show the voltage-time (V-t) characteristics of the device under varying frequency. As the frequency increases, the maximum value gets lower. When the frequency rises from 200 to 1700 Hz, the saturated value decreases by about 40%. However, the device exhibits fast and reproducible response during laser on-off cycles, regardless of the frequency. These results demonstrate the as-prepared photodetector can operate in a wide frequency range. The response speed contains two parts. The time required for voltage to go from 10% to 90% of final output or vice versa are defined as response time (tr) and decay time (td), resepectively.33-35 Derived from the single rise and decay processes at 1700 Hz (Figure 6c and 6d), tr is determind to be 84 µs and td is 153 µs, respectively. As a reference, the performance and photoresponse range of Si/TiO2/P3HT-30 were


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also measured. Figure 7a shows the I-V curves of the device under different monochromatic light illumination. Similarly, the device exhibits self-powered functionality. When monochromatic light with varying wavelengths, including 380, 550, 730, 830, 900, 980, and 1050 nm, were illuminated on the device, most of them were rewarded with high and fast photoresponse except for the light of 380 nm and 550 nm. The maximum photocurrent is up to 0.91 µA at zero bias under 980 nm light illumination, and the on/off ratio is as high as 18000, indicating the high sensitivity of the device. The response curve under on/off light cycles is shown in Figure 7b. The device possesses excellent reproducibility and stability. Figure 7c shows the detectivity spectrum of the device. As shown, the detectivity is quite low in the wavelength between 300 to 640 nm. It quickly increases from 600 nm and reaches the peak value of 5.25×1013 Jones at 920 nm, then gradually declines. Figure 7d illustrates the V-t curves of the device under varying frequency. Based on the enlarged curves in Figure 7e and 7f, tr is calculated to be 115 µs, and td is 155 µs. In comparison with previously-reported Si or P3HT based heterojunction devices (Table 2),12,

36-50

our devices exhibit comparable or even better performance, especially in

specific detectivity.

CONCLUSION Self-powered photodetectors with tunable response range were demonstrated by a heterojunction structure consisting of P3HT, TiO2 interlayer and Si NWs, which were fabricated by combing spin-coating, ALD and wet chemical etching method. Through



controlling the P3HT concentration, both core-shell and embedded configurations can be obtained, which result in different response range. Si/TiO2/P3HT-10 exhibits broadband photodetection response ranging from 300 to 1100 nm, with large on/off ratio, fast response speed and outstanding light responsivity and detectivity values. While, for Si/TiO2/P3HT-30, it is not only maintained excellent light response at red light region to NIR, but also shows a high NIR/UV rejection ratio. Meanwhile, these devices can function without external power supply. This work inspires the development of high-performance, low cost, self-powered and wavelength-selective photodetectors.

ACKNOWLEDGMENTS We acknowledge the support from the National Natural Science Foundation of China (51422206, 51372159, 51872191, 51502184), 333 High-level Talents Cultivation Project of Jiangsu Province, 1000 Youth Talents Plan, Key University Science Research Project of Jiangsu Province, Six Talents Peak Project of Jiangsu Province, and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

SUPPORTING INFORMATION SEM images of Si NWs coated with P3HT (5, 10, 20, 30, and 40 mg/mL); EDX spectrum and elemental mapping of Si NWs/TiO2; UV-vis absorbance spectra and reflection spectrum; I-t curves under white light irradiation; The power density of 380,


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Figure Captions Figure 1. Schematic illustration of as-fabricated photodetectors based on (a) core-shell structure and (b) embedded structure. (c) Energy band diagrams of the device before and after contact.

Figure 2. Top-view and cross-sectional SEM images of (a), (b) pristine Si NWs. (c), (d) Si/P3HT-10. (e), (f) Si NWs and P3HT-30, respectively.

Figure 3. (a) Responsivity curves of the photodetector with different P3HT concentrations. (b) Reflection curves from 300 to 1100 nm. (c) PL spectra from 550 to 725 nm.

Figure 4. (a) I-V curves of the Si/TiO2/P3HT-10 under different wavelength light illumination. (b) I-t curves. (c) Detectivity curves. (d) Long-term photoresponse curve of Si/TiO2/P3HT-10 under 920 nm illumination at zero bias.

Figure 5. Photoelectric properties of the device under dark and illumination with different light intensities at various wavelength: (a) 365 nm, (c) 532 nm, (e) 980 nm. Relationship between the photocurrent and the light intensity at various wavelength



and the corresponding fitted curve using a power law: (b) 365 nm, (d) 532 nm, (f) 980 nm. Figure 6. (a) The system for measuring response speed. (b) Voltage response dependent on time curves at different frequencies (200-1700 Hz). (c) Enlarged rise time and (d) decay time measured at 1700 Hz.

Figure 7. Performance characterization of the Si/TiO2/P3HT-30: (a) I-V. (b) I-t curves. (c) Detectivity curves. (d) Voltage response dependent on time curves at different frequencies. (e) Rise time and (f) Decay time measured at 1700 Hz.

Table 1. Summary of the responsivity and rejection ratio of device with different P3HT concentration.

Table 2. Comparison of the critical parameters of our devices and other previously reported photodetectors.


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Figure 1



Figure 2


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Figure 3



Figure 4


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Figure 5



Figure 6


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Figure 7



Page 34 of 37

Table 1

Structures

Wavelength

Rmaximum

R400

Rejection

R600

Rejection ratio

Maximum

(nm)

(mA/W)

(mA/W)

Ratio

(mA/W)

(Rmaximum/R600)

Rejection

(Rmaximum/R400) Si/TiO2 /P3HT-5 Si/TiO2 /P3HT-10 Si/TiO2 /P3HT-20 Si/TiO2 /P3HT-30 Si/TiO2 /P3HT-40

ratio

920

377

30

12.6

57

6.6

23.6

920

595

99

6.0

98

6.1

10.8

920

335

16

20.9

16

20.9

41.9

920

308

8

38.5

11

28.0

3080.0

920

177

2

88.5

3

59.0

590.0


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Table 2

Wavelength

Voltage

On/off

R

D*

(nm)

(V)

ratio

(A/W)

(Jones)

920

0

8×103

0.31

5.2×1013

115/155 μs

This work

920

0

1.8×104

0.59

1.3×1014

84/153 μs

This work

625

-

550

-

2.1×1012

0.16/0.12 s

36

500

0

8.4×104

0.16

1.4×1012

-

37

MoS2/rubrene

532

4

-

0.5

-

P3HT Heterojunction Photodetectors

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