Universal Strategy To Reduce Noise Current for Sensitive Organic

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A universal strategy to reduce noise current for sensitive organic photodetectors Sixing Xiong, Lingliang Li, Fei Qin, Lin Mao, Bangwu Luo, Youyu Jiang, Zaifang Li, Jinsong Huang, and Yinhua Zhou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b16788 • Publication Date (Web): 22 Feb 2017 Downloaded from http://pubs.acs.org on February 23, 2017

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ACS Applied Materials & Interfaces

A Universal Strategy to Reduce Noise Current for Sensitive Organic Photodetectors

Sixing Xiong, † Lingliang Li, ‡ Fei Qin, † Lin Mao,†Bangwu Luo, †Youyu Jiang, † Zaifang Li,† Jinsong Huang*,‡ and Yinhua Zhou*,†

†

Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China

‡

Department of Mechanical and Materials Engineering, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588-0656, USA

1

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ABSTRACT Low noise current is critical for achieving high-detectivity organic photodetectors. Inserting charge blocking layers is an effective approach to suppress the reverse-biased dark current. However, in solution-processed organic photodetectors, the charge transport material needs to be dissolved in solvents that don’t dissolve the underneath light-absorbing layer, which is not always possible for all kinds of light absorbing materials developed. Here, we introduce a universal strategy of transfer-printing a conjugated polymer poly(3-hexylthiophene) (P3HT) as the electron-blocking layer to realize highly sensitive photodetectors. The transfer-printed P3HT layers substantially and universally reduced the reverse-biased dark-current by about three orders of magnitude for various photodetectors with different active layers. These photodetectors can detect the light signal as weak as several picowatt per square centimeter, and the device detectivity is over 1012 Jones. The results suggest that the strategy of transfer-printing P3HT films as the electron-blocking layer is universal and effective for the fabrication of sensitive organic photodetectors.

KEYWORDS:

Organic

photodetectors,

solution-processing,

electron-blocking layer, suppressing dark current

2


transfer

printing,

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INTRODUCTION Solution-processed organic photodetectors (OPDs) have received tremendous attentions due to the advantages of low cost, light weight and easy fabrication.1-18 Donor-acceptor bulk-heterojunction (BHJ) active layers can be easily processed and exhibit efficient charge transfer, which are widely adopted in organic photodetectors.12, 14, 19-23 In the BHJ-type active layer, it is challenging to control the vertical phase separation of the donor and the acceptor. In that sense, the donor has the chance to contact the cathode and the accepter has the chance to contact the anode. This leads to the possible injection of electrons from the anode to the lower-lying lowest unoccupied molecular orbital (LUMO) level of the acceptor and holes from the cathode into the higher-lying highest occupied molecular orbital (HOMO) level of the donor under reverse bias. These charge-carrier injections result in high reverse-biased dark current and thus high noise, which reduces the sensitivity of photodetectors.24 Thus, the problem of charge-carrier injections should be addressed for highly sensitive photodetector. Inserting appropriate blocking layers between the active layer and the electrodes is an effective approach to suppress reverse-biased dark current.2, 25-26. Typically, an electron blocking layer (EBL) needs to fulfill the following requirements to effectively suppress the dark current: (i) The EBL should have appropriate energy levels to block the electron injection from anode; (ii) The EBL needs to have high hole mobility for efficient and quick hole collection; (iii) The film must be compact to prevent the direct contact between the active layer and the anode; (iv) From the point of view of solution-processing, the solvent for the EBL cannot dissolve or damage the pre-deposited active

layer.

For

example,

Peng

and

co-workers

3


used

methanol-soluble


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poly(9,9-bis(30-(N,N-dimethylamino) propyl)-2,7-uorene)-alt-2,7-(9,9-dioctyluorene) (PFN) as the EBL and achieved 3.44 nA cm-2.27 Gong et al. introduced

water-soluble cadmium

telluride quantum dots as EBL in solution-processed near-infrared polymer photodetectors, which reduced the dark current by ten-folds compared to the control device without the blocking layer, and therefore enhanced the detectivity to 5 × 1011 Jones at the bias of -0.5 V.28 Sampietro

et

al.

employed

poly[3-(3,5-di-tert-butyl-4-methoxyphenyl)-thiophene]

(poly-PT)

alcohol-soluble as

the

EBL,

and

successfully reduced the dark current to below 100 nA cm-2 at -1 V bias.29 However, the requirement of the orthogonality of the processing solvents for the EBL limits the selection of the solution-processed EBL for OPDs. Therefore, it is highly desirable to develop an effective method to alleviate or avoid the request of the solvent orthogonality for processing the active layer and EBL. Transfer-printing is a film fabrication method that the film is first prepared on a substrate, then transferred onto a medium substrate, and finally transfer printed onto the target substrate. It is a dry process that could avoid film damage due to the use of non-orthogonal solvents. The method has been previously used to prepare films for optoelectronics devices.30-39 In this work, we demonstrate a universal strategy to reduce dark current by transfer-printing a poly(3-hexylthiophene) (P3HT) film as the EBL in high-performance OPDs with three different light-absorbing active layers. The P3HT film is selected as the EBL because it has high-lying lowest unoccupied molecular orbital (LUMO) for electron-blocking, high hole mobility for hole transport and collection, and can be transfer-printed to form compact films. The transfer-printing of the P3HT EBL uses poly(dimethylsiloxane) (PDMS) 4


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as the transfer medium (Figure 1). The approach tactfully circumvents the requirement of the solvent orthogonality between the active layer and the EBL. Consequently, the insertion of the P3HT EBL substantially reduces dark current by about three orders of magnitude comparing with the photodetectors without the EBL in a series of OPDs based on different active layers. The OPDs with the P3HT EBL have a low noise current of about 10 fA Hz-1/2 and can detect light signal as weak as several picowatt per square centimeter.

RESULTS AND DISCUSSIONS Figure 1a shows the fabrication procedure and device structure of organic photodetectors where a transfer-printed P3HT layer is used as an EBL. The device structure of the OPDs is glass/ITO/PEIE/active layer/P3HT/MoO3/silver where PEIE is polyethylenimine ethoxylated. The details of transfer-printing P3HT EBL are included in the Experimental section. Three different donor polymers (Figure 1b) combined with acceptor fullerene derivatives were used as

the

active

layer.

The

donor

polymers

are

P3HT,

poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2 -ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] (PBDTTT-EFT) and poly(diketopyrrolopyrrole-terthiophene) (PDPP3T), respectively. The three polymers are representatives of recently widely developed conjugated polymers that contain different conjugated “star units”: thiophene, BDT, DPP.40-45 The absorbance of the three donor materials are shown in Figure 1c. They absorb light in different spectral region (maximum absorption peak are at 525 nm, 680 nm, 850 nm, respectively).

5



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Figure 2a shows the energy levels of the devices. The LUMO level of the P3HT Layer (about -3.0 eV) is higher-lying than the LUMO of the acceptor (-4.0 eV for PCBM and -3.7 eV for ICBA).46-48 The P3HT film on top of the active layer could efficiently block the electron injection from anode when the reverse bias is applied because of larger energy difference to overcome, as depicted in Figure 2b. Meanwhile, P3HT film has high hole mobility that has been widely used as hole transport layer.49-51 The P3HT EBL is soluble in the similar class of solvents used to process the three different active layers. Direct spin coating the P3HT layer on top of the active layer will lead to the damage of the beneath active layer. Transfer-printing is the appropriate method to deposit the P3HT EBL on top of these active layers (Figure 1). Therefore, the P3HT is an appropriate candidate as the EBL to suppress reverse-biased dark current for highly sensitive OPDs. To

optimize

the

thickness

of

the

P3HT

EBL,

we

fabricated

devices

(glass/ITO/PEIE/P3HT:ICBA/P3HT EBL/MoO3/Ag) with different thicknesses of the P3HT EBL as well as a control device without the EBL (glass/ITO/PEIE/P3HT:ICBA/MoO3/Ag). The thicknesses of the P3HT EBL varied from 50 to 130 nm by changing the spin speed (Table S1). Their current density-voltage (J-V) characteristics in the dark were shown in Figure 3. Comparing to the control device, all of the devices with the P3HT EBL were significantly reduced by three orders of magnitude under a bias of -0.1 V. When the thickness of P3HT EBL becomes thicker, the reverse dark current gets slightly smaller. When the layer is 130 nm, the device shows the dark current 9 × 10-10 A cm-2 under -0.1 V. Therefore, we choose the P3HT EBL thickness of 130 nm for the OPD devices.

6


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Figure 4 shows the J-V characteristics of the OPDs based on the three different active layers with and without the P3HT EBL. The OPDs are named in the form: OPD-X-y/n where X refers the name of polymer contained in the active layer, and y/n refers the OPDs with or without the EBL. Figure 4a displays the current density-voltage (J-V) curves in the dark and under illumination (100 mW cm-2) of P3HT:ICBA-based photodetectors (OPD-P3HT-y and OPD-P3HT-n). In the dark, the current density of the OPD-P3HT-y was 1.5 × 10-9 A cm-2 under -0.1 V, which was three orders of magnitude lower than that of OPD-P3HT-n (1.1 × 10-6 A cm-2 under -0.1 V). Similar results were also observed in PBDTTT-EFT:PCBM-based and PDPP3T:PCBM-based OPDs. The dark current was 3.9 × 10-9 A cm-2 for OPD-PBDTTT-EFT-y while 8.3 × 10-6 A cm-2 for OPD-PBDTTT-EFT-n under -0.1 V (Figure 4b). It was 4.9 × 10-9 A cm-2 under -0.1 V for OPD-PDPP3T-y, while 1.5 × 10-5 A cm-2 for OPD-PDPP3T-n under -0.1 V (Figure 4c). As for the on-current (under 100 mWcm-2 illumination), it is also reduced when the P3HT EBL (130 nm) is inserted between the active layer and the top electrode. The on-current drops from 9.5 to 8.4 mA/cm2 for P3HT:ICBA-based device, 13.8 to 6.8 mA/cm2 for PBDTTT-EFT-based device and 6.6 to 3.7 mA/cm2 for PDPP3T:PCBM-based device. The drop of on-current could possibly be attributed to the reasons: (1) Some of the charge carriers can be quenched in the thick P3HT EBL before collected by the electrode; (2) The interface between the P3HT EBL and the non-P3HT active layers (PBDTTT-EFT:PCBM and PDPP3T:PCBM ) could increases the difficulty of charge transport since the on-current drop for P3HT:ICBA device is less than the devices with the other two active layers. It should be noted the on-current is reduced less than half, while the dark current drops by three orders of magnitude when the P3HT EBL is 7



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inserted. Based on the equation 5, inserting the P3HT EBL layer will effectively enhance the detectivity and also improve the ability of detecting weak signals. In order to confirm the low dark current, 15 devices were fabricated based on each active layer. Their J-V characteristics indicate the highly reproduced low dark current with the P3HT EBL (Figure S1). Stabilized current in the dark under -0.1 V of OPD-PBDTTT-EFT-y and OPD-PDPP3T-y were also measured as shown in Figure 4d and 4e. The confirmed low reverse-biased dark current demonstrates that the transfer-printed P3HT EBL can effectively and universally suppress the dark current of various OPDs. To further evaluate the performance of OPDs, the noise current were characterized and analyzed. Noise current can be expressed as: 52

= + + ⁄ + =2 +

+ (", ) ⁄ + (", )

(1)

where e is the elementary charge, Id is the dark current, B is the bandwidth, K is the Boltzmann constant, T is the temperature, and RΩ is the shunt resistance of device. The is shot noise,

is thermal noise, ⁄ is 1/f noise and

is

generation-recombination (g-r) noise, respectively. The total of shot noise and thermal noise are also called “white noise” that is independent of frequency, while, the 1/f noise and g-r noise are dependent on the frequency. Figure 5a and 5c showed that the noise current in the frequency range from 5 Hz to 50 Hz. The noise current was independent of the frequency, indicating the 1/f and g-r noise are negligible in our OPDs. Previous work reported that the 1/f noise current was due to charge 8


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traps.53-54 Thus, it implies that the OPDs with the transfer-printed P3HT EBL had low trap densities. The noise current of our OPDs is dominated by white noise, including shot noise and thermal noise. The shot noise is calculated as: = &2 B

(2)

The shot noise of OPD-P3HT-y is calculated as 7.13 fA Hz-1/2 and the value of OPD-PBDTTT-EFT-y is 11.5 fA Hz-1/2. The thermal noise is calculated as: =

(3)

The thermal noise value of OPD-P3HT-y is 3.51 fA Hz-1/2 and the value of OPD-PBDTTT-EFT-y is 3.17 fA Hz-1/2. The white noise can be calculated as the following equation: ( = & +

(4)

Therefore, the total white noise of OPD-P3HT-y is calculated to be 8.04 fA Hz-1/2 and that of OPD-PBDTTT-EFT-y is 11.9 fA Hz-1/2 (Table 1). As shown in Figure 5, the noise spectral density (Snoise) of OPD-P3HT-y and OPD-PBDTTT-EFT-y measured by FFT under -0.1 V is 14.9 fA Hz-1/2 and 21.4 fA Hz-1/2, respectively (Table 1). There is small discrepancy between the measured noise current and the calculated total white noise current, which may be caused by the noise of the measurement instruments and/or noise from environment. In addition, it should be noted that the samples were fabricated in Wuhan and shipped to Lincoln, Nebraska for the noise measurement. The noise could slightly increase during the shipping (Figure S2).

9



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Such small total noise current indicated that the P3HT blocking layer is effective in suppressing the noise current. The important figure of merit to evaluate the performance of photodetector is detectivity (D*) and can be calculated as follows: √,

√,

) ∗ = -./ = 0

(5)

12345

η

6 = υ NEP =

(6) 1

(7)

where A is the device working area，NEP is the noise equivalent power, the R the responsivity, h is the Planck constant, υ is the frequency of light, η is the quantum efficiency and in is the root mean square noise current. Based on the equation, R of the OPD-P3HT-y is 0.19 A W-1 at 525 nm and the OPD-PBDTTT-EFT-y is 0.15 A W-1 at 680 nm. Considering the device area of 10.58 mm2, OPD-P3HT-y photodetector showed D*= 4.15×1012 cm Hz-1/2W-1 (Jones) at 525 nm and OPD-PBDTTT-EFT-y showed D*= 2.28×1012 Jones at 680 nm (Table 1). For the measurement of NEP, we applied 35 Hz modulated light onto the devices and gradually increased light intensity until we could not distinguish 35 Hz responsive signal from noise, as shown in Figure 5a and 5c. The device OPD-P3HT-y could detect the light intensity as weak as 7.6 pW cm-2 and the OPD-PBDTTT-EFT-y could detect as weak as 15.0 pW cm-2, which are the NEPs of these devices. Figure 5b and 5d shows the current density as a function of light intensity. The lowest detectable light intensity in this measurement agrees with the NEPs mentioned above. The linear dynamic range (LDR) demonstrates the range between the

10


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maximum and the minimum light intensity where the OPDs keep linear response. LDR is defined as: LDR = 20log /

/4

A31

(8)

where Ps is saturation input light power and the Pmin is the minimum detectable light power. The linear response range of OPD-P3HT-y is from 7.6 × 10-12 to 1.5 × 10-5 W cm-2 and the LDR is calculated about 130 dB. For the OPD-PBDTTT-EFT-y, the linear response range is from 1.5 × 10-11 to 4 × 10-5 W cm-2 and the LDR is also about 130 dB. It is noteworthy that the measurement of LDR is limited by the strongest light of our LED can provide, which is about 10-5 W cm-2 level. As shown in the figure, the device was not saturated under this light intensity, indicating the LDR value of these photodetector is more than 130 dB.

CONCLUSIONS In summary, we have demonstrated a strategy of transfer-printing a P3HT film between the active layer and top electrode to suppress reverse-biased dark current for high-performance organic photodetectors. The use of the transfer-printing technique circumvents the requirement of the orthogonality of processing solvents for the active layer and the electron-blocking layer. The particular selection of P3HT as the electron-blocking layer is because of the high-lying LUMO level and more importantly because it is suitable for transfer-printing to form compact films. The transfer-printed P3HT blocking layer is found able to substantially and universally reduce the reverse dark current by about three orders of magnitude for various photodetectors with different active layers. These photodetectors can detect the light signal as weak as to several picowatt per square centimeter and the detectivity is over 1012 Jones. The universality and excellent detectability of photodetectors indicates the 11



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strategy of transfer-printing blocking layers is promising for fabricating highly sensitive organic photodetector. In this work, we only demonstrate P3HT as the EBL. For other polymers, if it has high-lying LUMO, high hole mobility and good mechanical property to enable the easy film transfer-printing, it would likely be another effective EBL for photodetector applications. The transfer-printed blocking layers might also be feasible to be universally and widely used in other photodetectors with different types of active layers.

ASSOCIATED CONTENT Supporting Information The supporting Information is available free of charge on the ACS Publication website. Experimental Section, J-V characteristics of multiple devices to show the reproducibility, the thickness information of the P3HT EBL processed at different spin-coating speeds (Table S1).

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected] Author Contributions S.X.X. and Y.H.Z. conceived the idea. S.X.X., F.Q., L.M., B.W.L., Y.Y.J., and Z.F.L., performed the photodetector fabrication, measurement and optimization. L.L.L performed the noise measurement. Y.H.Z. and J.S.H. directed this work. S.X.X. wrote the first draft of the manuscript. All the authors revised and approved the manuscript. 12


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Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS The work is supported by the National Natural Science Foundation of China (Grant No. 51403071), the Recruitment Program of Global Youth Experts, the Fundamental Research Funds for the Central Universities, HUST (Grant No. 2016JCTD111). Huang wants to thank Department of Homeland Security (Award No. 2014-DN-077-ARI069-02) and National Science Foundation (Award ECCS-1348272) for financial support.

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Figure 1. (a) Fabrication procedure and device structure of organic photodetectors where a transfer-printed P3HT layer is used as an electron-blocking layer; (1) P3HT film was transferred from the silicon wafer onto the PDMS; (2) PDMS/P3HT was put onto a glass/ITO/PEIE/Active layer sample; (3) PDMS was peeled off from the P3HT film; (4) Top electrode was deposited to finish the device fabrication. (b) Chemical structures of polymers used in the active layers; (c) Absorbance spectra of the polymers, covering from the visible to infrared region.

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Figure 2. (a) Energy diagram of the electron-donors and acceptors. (b) A schematic demonstrates the P3HT layer blocks the electron injection under reverse bias.

19



Figure 3. Comparison of dark current density-voltage characteristics of devices (glass/ITO/PEIE/P3HT:ICBA/P3HT EBL/MoO3/Ag) with different thickness of the P3HT EBL and the device without the P3HT EBL.

-2

10

-3

10

The thickness of blocking layer 0 nm 55 nm 100 nm

53 nm 70 nm 130 nm

-4

10 2

Current Density (A/cm )

-5

10

-6

10

-7

10

Decrease

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

-8

10

-9

10

-10

10

-11

10

-1.0

-0.5

0.0

0.5

1.0

Voltage (V)

20


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Figure 4. Current density-voltage curves of organic photodetectors (glass/ITO/PEIE/active layer/(with or without EBL)/top electrode) in the dark and under illumination with different active layers. The active layers are: (a) P3HT:ICBA; (b) PBDTTT-EFT:PCBM; (c) PDPP3T:PCBM, respectively. Stabilized dark current density as a function of time at reverse bias: (d) P3HT:ICBA photodetector without or with EBL at -0.1 V; (e) PBDTTT-EFT:PCBM photodetector without or with EBL at reverse bias of -0.1 V.

10

-3

10

-4

10

-5

10

-6

10

-7

10

-8

10

-9

10

-10

10

-11

P3HT:ICBA-based -0.5

0.0

0.5

1.0

10

-2

10

-3

10

-4

10

-5

10

-6

10

-7

10

-8

10

-9

-10

10

-11

Dark

PBDTTT-EFT:PCBM-based

-1.0

-0.5

0.0

0.5

-6

10

P3HT:ICBA-based -7

Without EBL With EBL

-8

10

-9

10

10

15

20

25

30

0

10

-1

10

-2

10

-3

10

-4

10

-5

10

-6

10

-7

10

-8

10

-9

10

-10

10

-11

Light

-1.0

Dark

W ithout EBL W ith EBL

PDPP3T:PCBM-based -0.5 0.0 0.5 1.0 Voltage (V)

(e)

-5

5

1.0

Voltage (V)

10

10

10


2

(d)

10

10

Voltage (V)

2

-1.0

Light

2

-2

(c)

0

-1

Current density (A/cm )

10


2

10

Dark

Dark current density (mA/cm )

Light

Dark current density (mA/cm )

2

(b) 10

0

-1

Current density (A/cm )

(a) 10 Current density (A/cm )

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


10

-5

10

-6

10

-7

10

-8

10

-9

PBDTTT-EFT:PCBM-based Without EBL With EBL

5

10

15

20

Time (s)

Time (s)

21


25

30


Figure 5: Noise current of Devices at different light intensities: (a) OPD-P3HT-y under 525 nm light illumination. (c) OPD-PBDTTT-EFT-y under 680 nm light illumination; The light was modulated by a function generator at 35 Hz. LDR measurement: (b) OPD-P3HT-y; (d) OPD-PBDTTT-EFT-y (a)

(b)

1E-6

1E-13

dark 7.60 16.3 18.7 52.6

noise -2 pW cm (NEP) -2 pW cm -2 pW cm -2 pW cm

1E-7

white noise shot noise

1E-14

P3HT:ICBA photodetector with EBL

-2

1E-12

Current density (A cm )

Signal current spectral density (A Hz

-1/2

)

1E-5

P3HT:ICBA photodetector with EBL

1E-8 1E-9 1E-10

NEP

1E-11

Noise current limit

1E-12

thermal noise 1E-15

10

20

30

40

1E-13 1E-12 1E-11 1E-10 1E-9

50

(d)

1E-6

1E-5

1E-4

1E-4

)

-1/2

1E-5 -2

Current density (A cm )

1E-13

1E-7

-2

PBDTTT-EFT:PCBM photodetector with EBL

1E-12

1E-8

Light intensity (W cm )

Frequency (Hz)

(c) Signal current spectral density (A Hz

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

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dark noise -2 15.0 pW cm (NEP) -2 25.7 pW cm -2 109 pW cm -2 745 pW cm white noise

PBDTTT-EFT:PCBM photodetector with EBL

1E-6 1E-7 1E-8 1E-9

NEP

1E-10

1E-14

1E-11

shot noisel

1E-12

thermal noise 1E-15

Noise current limit

1E-13 1E-12 1E-11 1E-10 1E-9

10

20

30

40

50

1E-8

1E-7

1E-6

-2

Light intensity (W cm )

Frequency (Hz)

22


1E-5

1E-4

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Table 1 The properties of P3HT:ICBA-based and PBDTTT-EFT:PCBM-based organic photodetectors with the EBL. P3HT:ICBA-based OPD

PBDTTT-EFT:PCBM-based OPD

0.19

0.15

(fA Hz-1/2)

14.9

21.4

(fA Hz-1/2)

8.04

11.9

NEP (pW cm2)

7.6

15

D* (Jones)

4.15 × 1012

2.28 × 1012

LDR (dB)

130

130

R (A/W) S

i

noise

white

23



Table of Contents

)

MoO3/Ag

-1/2

Signal current spectral density (A Hz

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

P3HT (transfer-printed)

1E-12

1E-13

Active layer PEIE

dark noise -2 7.60 pW cm (NEP) -2 16.3 pW cm -2 18.7 pW cm -2 52.6 pW cm

1E-14

Glass/ITO

white noise shot noise thermal noise

1E-15

10

20

30

40

50

Frequency (Hz)

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Universal Strategy To Reduce Noise Current for Sensitive Organic

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