Bidirectional optical signal transmission between
two identical devices using perovskite diodes
Chunxiong Bao, Weidong Xu, Jie Yang, Sai Bai, Pengpeng Teng, Ying Yang, Jianpu Wang, Ni Zhao, Wenjing Zhang, Wei Huang and Feng Gao
The self-archived postprint version of this journal article is available at Linköping University Institutional Repository (DiVA):
http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-165094
N.B.: When citing this work, cite the original publication.
Bao, C., Xu, W., Yang, J., Bai, S., Teng, P., Yang, Y., Wang, J., Zhao, Ni, Zhang, W., Huang, W., Gao, F., (2020), Bidirectional optical signal transmission between two identical devices using perovskite diodes, NATURE ELECTRONICS, 3(3), 156-164. https://doi.org/10.1038/s41928-020-0382-3
Original publication available at:
https://doi.org/10.1038/s41928-020-0382-3 Copyright: Nature Research
1
Bidirectional optical signal transmission between two identical
1devices using perovskite diodes
2Chunxiong Bao1,2,§, Weidong Xu1,3,§, Jie Yang1,2,§, Sai Bai1, Pengpeng Teng1,4, Ying Yang4, Jianpu 3
Wang3, Ni Zhao5, Wenjing Zhang2*, Wei Huang3,6*, Feng Gao1* 4
1Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping 58183,
5
Sweden. 6
2International Collaborative Laboratory of 2D Materials for Optoelectronics Science and
7
Technology, Institute of Microscale Optoelectronics, Shenzhen University, Shenzhen 518060, 8
China. 9
3Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM),
10
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech 11
University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China. 12
4State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University
13
of Aeronautics and Astronautics, Nanjing 210016, China. 14
5Department of Electronic Engineering, The Chinese University of Hong Kong, New Territories,
15
Hong Kong SAR, China. 16
6Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical University (NPU),
17
127 West Youyi Road, Xi’an 710072, China. 18
§These authors contributed equally: C. Bao, W. Xu, J. Yang
19
*Correspondence to: wjzhang@szu.edu.cn (W. Zhang), iamwhuang@nwpu.edu.cn (W. Huang), 20
feng.gao@liu.se (F. Gao) 21
22
2
Abstract
1
The integration of optical signal generation and reception into one device – and thus allowing 2
bidirectional optical signal transmission between two identical devices – is of value in the 3
development of miniaturized and integrated optoelectronic devices. However, conventional 4
solution-processable semiconductors have intrinsic material and design limitations that prevent 5
them from being used to create such devices with high performance. Here, we report an efficient 6
solution-processed perovskite diode that is capable of working in both emission and detection 7
modes. The device can be switched between modes by changing the bias direction, and it exhibits 8
light emission with an external quantum efficiency of over 21% and a light detection limit on a 9
sub-picowatt scale. The operation speed for both functions can reach tens of megahertz. Benefiting 10
from the small Stokes shift of perovskites, our diodes exhibit high specific detectivity (more than 11
2×1012 Jones) at its peak emission (~804 nm), allowing optical signal exchange between two 12
identical diodes. To illustrate the potential of the dual-functional diode, we show that it can be 13
used to create a monolithic pulse sensor and a bidirectional optical communication system. 14
3
Bidirectional optical signal transmission typically requires two sets of optical transmitters 1
and receivers. However, integrating the functionalities of transmitter and receiver into one device, 2
and creating bidirectional optical signal transmission between two identical devices, is important 3
for miniaturized and monolithic optoelectronic systems1,2. Such dual-functional devices have 4
previously been fabricated with III—V semiconductors1,2, but their creation using solution-5
processed semiconductors is of particular interest due to their lightweight, mechanical flexibility, 6
and simple integration with complementary metal–oxide–semiconductor (CMOS) technology3–7. 7
Creating devices with satisfactory performance using solution-processable semiconductors 8
(such as organic semiconductors or colloidal quantum dots) is though challenging due to intrinsic 9
limitations in material properties and device structures. Specifically, the large Stokes shift of 10
organic semiconductors make it impossible for organic light-emitting diodes (LEDs) to effectively 11
absorb the light emitted by an identical device8,9; the bulk heterojunction (BHJ) structure of 12
organic photodetectors is also not suitable for light emission because of the luminescence 13
quenching in the BHJ layer10. For quantum dot LEDs, their thin recombination zone (1 to 2 14
monolayers) and poor charge transport limit the thickness of the emitting layer11,12, making it far 15
thinner than the optimal thickness required for photodetectors and limiting the detection 16
sensitivity13–15. 17
Metal halide perovskites are versatile and solution-processable semiconductors that have 18
shown strong performance for both light emission and detection16–31. For example, perovskite 19
LEDs have demonstrated external quantum efficiencies (EQEs) above 20% (ref. 25–29), and 20
perovskite photodetectors have achieved a low detection limit of sub-pW/cm2, as well as 21
nanosecond scale response times20–22. These advances, together with the small Stokes shift of 22
perovskite materials32, suggest that high performance solution-processable dual-functional
4
perovskite diodes, which can simultaneously function as an optical transmitter and receiver for 1
bidirectional optical communications, could be developed. But efforts to create such dual-2
functional perovskite devices has so far had limited success. 3
Most high-efficiency perovskite emitters are based on quasi-two-dimensional structures, 4
consisting of different thickness of PbI6 sheets sandwiched by bulky cations33. A cascade energy
5
transfer from the large-gap component to the small-gap component is observed and hence the 6
emission occurs at the band tail close to that of three-dimensional (3D) perovskites24,34. In addition 7
to enhancing the radiative recombination rate, this concept minimizes optical losses from 8
reabsorption due to reduced absorption–emission spectral overlap24,26,34,35. This is clearly 9
favourable for LED performance, but makes the device insensitive to detecting light emitted by 10
the identical devices. Furthermore, the response time for perovskite LEDs have rarely been 11
investigated, but such measurements are important for dual-functional devices and their 12
application in optical communications. In addition, the common device structure for perovskite 13
photodetectors is not applicable for efficient light emission due to the strong photoluminescence 14
(PL) quenching induced by the charge transport layers20–22. 15
In this Article, we report optical signal transmission between two identical dual-functional 16
diodes based on high-efficiency 3D perovskite emitters. The large absorption emission spectral 17
overlap of 3D perovskite emitters provides the opportunity for solution-processed semiconductors 18
to achieve high sensitivity to the light emitted from the identical device. The perovskite diodes 19
demonstrate efficient and intense light emission with an EQE over 21% under the positive bias, 20
and a high sensitivity reaching the sub-picowatt scale when operating as photodetectors under zero 21
or reverse bias. We also show that a fast response speed reaching tens of megahertz (MHz) can be 22
obtained as both light emission and detection devices, making them promising for optical 23
5
communication. With this approach, we build an efficient bidirectional optical communication 1
system based on two identical perovskite diodes (Fig. 1a) and a photoplethysmogram sensor for 2
arterial pulse wave tracking. 3
4
Figure 1 Schematic illustration of the dual-functional perovskite diode used as the
light-5
emitting and detecting devices. a, schematics of using perovskite diodes for inter- and intra-chip
6
data communications. b, Schematics of the energy diagram of the perovskite diode under forward
7
bias as an LED and reverse bias as a photodetector.Light emitted from the forward-biased diode
8
induces photocurrent in the reverse-biased diode. c, Absorption and photoluminescence (PL)
9
spectra of the perovskite film. The large spectral overlap enables efficient absorption of the light
10
emitted from the other identical device.
11 12
Perovskite diode as a light-emitting device 13
6
The device structure of the perovskite diodes is indium tin oxide (ITO)-coated 1
glass/polyethylenimine ethoxylated (PEIE)-modified zinc oxide (ZnO)/formamidinium lead 2
iodide (FAPbI3) perovskite (~50
nm)/poly(9,9-dioctyl-fluorene-co-N-3
(4butylphenyl)diphenylamine) (TFB; ~40 nm)/molybdenum oxide (MoOx; ~7 nm)/gold (Au; ~80
4
nm) (Fig. 1a). An efficient passivation agent of 2,2′-[oxybis(ethylenoxy)]diethylamine (ODEA) 5
developed in our recent work29 is used to minimize the defects in the perovskite layer. As we show
6
in Fig. 1b, when the diode works under a positive bias larger than the turn-on voltage, the electrons 7
and holes are injected into the perovskite emitters and generate light emission via efficient radiative 8
recombination. Similarly, when the diode works under a zero or reverse bias, upon excitations by 9
photons with energy equal to or higher than the bandgap of the perovskite, the photo-generated 10
carriers are separated and collected as an electrical signal (Fig. 1b). The optimized perovskite 11
diode (with 30% ODEA passivation and precursor concentration of 0.13 M) simultaneously show 12
the best electroluminescence (EL) (Supplementary Fig.1) and photodetector performance (as 13
discussed later). The absorption and PL spectra of the optimized perovskite film in Fig. 1c show a 14
large overlap with only a small Stokes shift (~40 meV), indicating that the perovskite film would 15
be sensitive to the light emitted by the same film. 16
We first demonstrate the high performance and fast response speed of the perovskite diodes 17
as LEDs. The characterization results show a low turn-on voltage of ~1.3 V (Supplementary Fig. 18
1a) and a maximum radiance of ~314 W sr-1 m-2 (Fig. 2a). A peak EQE of 21.2% is obtained, 19
which is among the highest reported EQE values of perovskite LEDs25–29. The high EL 20
performance of our devices mainly benefits from the effective passivation of ODEA to the iodide 21
vacancy on the perovskite crystal surfaces, which have been investigated in details in our previous 22
work29. 23
7 1
Figure 2 Characterizations of the perovskite diodes when working as the light emitter. a,
2
External quantum efficiency (EQE) and radiance versus current density curves of the optimized
3
perovskite LEDs. The inset is the photograph of the LED driven by a 3.0 V bias. b, Transient EL
4
intensity and current characterization of the perovskite LEDs. c,Frequency response curves of the
5
perovskite LED under different drive pulse voltages. d, Frequency response of perovskite LEDs
6
with different device areas.
7 8
For the characterization of the response speed, we first monitor the evolution of the EL 9
intensity and current of the diodes driven by square-wave voltages (Fig. 2b). At a low frequency 10
of 100 Hz, both the EL intensity and the current well follow the change of the drive voltage. In the 11
case of higher frequency of 100 kHz, we observe a slight lag of the EL intensity to the voltage 12
change as well as obvious overshoots of the current, which may result from the charging and 13
discharging effects of the parasitic capacitance. In order to confirm it, we fit the transient current 14
8
curves with an exponential function and obtain time constants of ~120 ns and ~172 ns for the 1
charging and discharging processes, respectively (Supplementary Fig. 2a). Considering a serially 2
connected resistance (50 Ω) to the device, the device capacitance is determined to be 2.9±0.5 nF. 3
This calculated value agrees well with the measured value (Supplementary Fig. 2b), indicating 4
that the parasitic capacitance of the device limits the response speed when functioning as an LED. 5
We note that passivation of trap states can not only boost the EL efficiency but also reduce the 6
parasitic capacitance (Supplementary Fig. 2b) and consequently improve the response speed 7
(Supplementary Fig. 2c). We further measure the EL frequency response of the perovskite diode 8
driven by different voltages to determine the cutoff frequency of the device. As shown in Fig. 2c, 9
the cutoff frequency increases with increasing drive voltage and shows a maximum 3-dB cutoff 10
frequency of 1.90 MHz at 4.0 V. The increase of the cutoff frequency can be attributed to faster 11
injection of charges under higher drive voltage, similar to that observed in inorganic and organic 12
diodes36–38.
13
Since the parasitic capacitance is affected by the device area, we further study the device-14
area-dependent speed of the perovskite LEDs. We show 3-dB cutoff frequencies of the LED with 15
different device areas in Fig. 2d, which demonstrates an increased 3-dB cutoff frequency with 16
decreasing device area, from 1.9 MHz for 7.25 mm2 device to 21.5 MHz for 0.1 mm2 device. 17
Considering its relatively large area, our device is among the fastest solution-processed LEDs38,39. 18
The nearly linear increase of the cutoff frequency with decreasing device area (Supplementary 19
Fig. 2d) origins from the smaller parasitic capacitance of the device with a smaller active area, 20
indicating that the response speed for these device areas (0.1 to 7.25 mm2) is dominated by the
21
resistance-capacitance (RC) constant. Therefore, a further improvement of the response speed can 22
be expected by reducing the device area. 23
9 Perovskite diode as a photodetector
1
Having demonstrated efficient and fast response of our devices when functioning as LEDs, 2
we proceed to investigate the device performance when working as photodetectors. We notice that 3
the ODEA passivation can significantly reduce the dark current (Supplementary Fig. 3a) and 4
measure a low dark current of 0.3 nA at -1 V with the optimized ODEA passivation, as shown in 5
the current density-voltage (J-V) curves in Fig. 3a. The photon-to-current EQE spectra of our 6
diodes (Supplementary Fig. 3b) exhibit a wide photoresponse range from ultraviolet (UV) to near 7
infrared (NIR) region (350 to 800 nm). The EQE peak at around 380 nm can be attributed to the 8
response of the hole transport layer TFB, which can be evidenced by the excitation spectrum of 9
TFB (Supplementary Fig. 3b). The EQE spectra of the devices fabricated from perovskite 10
precursors with different concentrations (Supplementary Fig. 3c) show that the EQE reaches a 11
maximum value when the precursor concentration is 0.13 M, which is also the optimized 12
concentration for light-emitting devices. The photocurrent (Fig. 3a) and EQE values 13
(Supplementary Fig. 3b) of the photodetector at visible to NIR region (400-800 nm) show only 14
a marginal decrease under 0 V bias as compared to the reverse bias, implying low energy barriers 15
at the interfaces between the perovskite layer and its neighboring charge transport layers. In order 16
to provide further evidence, we simultaneously monitor the relative photon-to-current EQE and 17
PL quantum efficiency (PLQE) of the device under different biases. As shown in Supplementary 18
Fig. 4a, under 1 µW excitation (450 nm), the PLQE shows nearly a constant ~80% quenching 19
under both 0 V and reverse bias compared with its peak value, and the EQE is nearly constant 20
during the same bias range. This result indicates efficient charge separation and collection at 0 V 21
bias, rationalizing the fact that the devices can work as efficient photodetectors. 22
10 1
Figure 3 Characterizations of the perovskite diode when working as a photodetector. a,
Current-2
voltage (I-V) curves of the perovskite photodetector under dark and illuminated light (with
3
different light powers). b, Specific detectivity of the perovskite photodetector under different
4
reverse biases, and the electroluminescence (EL) spectrum of the same perovskite diode under
5
forward bias. c, Transient photocurrent (TPC) characteristics at 0 V bias of perovskite
6
photodetectors with different device areas. d, Continuous track of the photo and dark current of
7
the perovskite photodetector under -0.5 V bias during a period of over 42 hours.
8 9
To evaluate the lowest detectable limit of our perovskite diodes as photodetectors, we 10
perform the dark current noise measurement and calculate the noise equivalent power (NEP). In 11
Supplementary Fig. 4b, we show the dark current noise of the diodes under different bias voltages. 12
We also calculate the shot noise and thermal noise based on the dark currents and the differential 13
resistances (see Methods section). The calculated shot noise and thermal noise are from 2.4 to 9.1 14
fA Hz-0.5 and 1.2 to 5.4 fA Hz-0.5 under -0.1 to -1.0 V bias, corresponding to a total noise from 2.7 15
to 10.7 fA Hz-0.5. This value agrees well with the measured values in Supplementary Fig. 4b,
16
indicating that the noise current is dominated by the shot noise and thermal noise. Based on the 17
11
EQE spectra and the measured noise, we evaluate the NEP to be 1.6×10-14 W Hz-0.5 (under 0 V
1
bias, at 670 nm where the EQE reaches the peak value). We also experimentally perform the weak 2
light response measurement and obtain a measured detectable light power of 0.8 pW for 630 nm 3
red light (Supplementary Fig. 4c). Our devices show linear response from the lowest detectable 4
limit (0.8 pW) to 20 µW, corresponding to a linear dynamic range of 148 dB (Supplementary Fig. 5
4d). We further calculate the specific detectivity (D*) spectra and show the results in Fig. 3b. We 6
achieve a peak D* of 5.3×1012 Jones in the visible region, which is among the highest reported 7
values for perovskite diodes20–23. Meanwhile, the photodetector shows high D* (2.0×1012 to
8
3.8×1012 Jones) at ~800 nm, indicating high sensitivity of the photodetector to the light emitted 9
from the identical diode. 10
We further perform transient photocurrent (TPC) to investigate the response time of our 11
diodes with different device areas (Fig. 3c). The device response time can be obtained by fitting 12
the TPC curves with an exponential function. We observe a faster response time for a device with 13
smaller active area, indicating that the parasitic capacitance also limits the response speed of the 14
photodetector. This conclusion is further backed up by the observed constant response time under 15
different reverse biases (Supplementary Fig. 5a), ruling out the possibility that the response time 16
is limited by the transit time of the carriers and indicating the importance of the parasitic 17
capacitance which affects the response time. The response time of the full-area (7.25 mm2) device 18
is fitted to be 237 ns (Fig. 3c), which is larger than the RC constant of the device measured under 19
dark, due to a larger capacitance under illumination (Supplementary Fig. 2b). When the active 20
area is decreased to 0.1 mm2, the pulse width (full width at half maximum, FWHM) of the TPC is 21
~6.8 ns and the falling time is ~3.9 ns (inset of Fig. 3c), which is among the fastest response times 22
of perovskite photodetectors20–23. The fast response time of our perovskite photodetector also 23
12
benefits from the effective passivation of the ODEA (Supplementary Fig. 5b, c). Based on the 1
pulse width (∆t) of the TPC we obtain a bandwidth (f-3dB) of the photodetector as ~65 MHz
2
according to the relation f-3dB=0.44/∆t. This bandwidth is close to that extracted from the frequency
3
response curve obtained from the fast Fourier transform of the TPC curve (Supplementary Fig. 4
5d). 5
We also investigate the stability of the perovskite photodetector working at reverse bias 6
under nitrogen atmosphere. The dark- and photo-current of the device under -0.5 V bias (Fig. 3d) 7
show negligible changes during the entire test period (~42 hours), indicating excellent reliability 8
and stability of the devices. It is worth mentioning that the stability of perovskite diodes under 9
reverse bias is usually very poor due to the accumulation of ionic defects in the perovskite film 10
under reverse bias40. We note that the efficient defect passivation of ODEA is critical for improving
11
the device stability. The devices without ODEA passivation exhibit increasing and fluctuant dark 12
currents under -0.5 V bias after several hours (Supplementary Fig. 6). Furthermore, our devices 13
show stable EL spectrum after working as light emission and detection devices. As shown in 14
Supplementary Fig. 7a, after working as the light emitting device at 25 mA cm-2 for a period of 15
20 hours, the peak position shows little change. Similarly, the EL peak position and intensity show 16
negligible changes after working as the photodetector at -0.5 V bias for 10 hours (Supplementary 17
Fig. 7b). It is worth noting that the stable device performance is obtained in a nitrogen environment 18
inside a glovebox. Upon exposure to air, the device performance will significantly degrade in 19
several minutes (Supplementary Fig. 8), suggesting the importance of developing encapsulation 20
technologies for the perovskite devices in order to enable practical applications in the future. 21
Signal exchange between two perovskite diodes and demonstrations 22
13
To demonstrate the response of the perovskite diode to the light emitted from an identical 1
diode, we study the opto-coupling performance between two identical perovskite diodes. Fig. 4a 2
shows the photocurrent of perovskite photodetectors (under -0.5 V bias) responding to the light 3
from an inter- or intra-chip perovskite LED driven by different current densities. The photographs 4
of the inter- and intra-chip configurations are shown in the insets of Fig. 4b; the distance between 5
the diodes for both intra- and inter-chip designs are ~1 mm (diode distance definitions are 6
schematically shown in Supplementary Fig. 12a and Fig. 13a). The response waveforms of the 7
perovskite photodetectors under 0 and -0.5 V bias to the emitted light from inter- and intra-chip 8
LEDs are exhibited in Supplementary Fig. 9a-d. Fig. 4b shows the ratio of the photodetector 9
(under -0.5 V bias) current to the LED drive current. For both inter-chip and intra-chip conditions, 10
the current ratio increases with increasing drive current densities, because the light emission EQE 11
increases with increasing drive current at low current region (Fig. 2a). Fig. 4c shows the frequency 12
response between the photodetector and LED, indicating a 3-dB cutoff frequency of ~1.2 MHz, 13
meaning that signals below 1.2 MHz can be well transmitted and received between our full-area 14
(7.25 mm2) perovskite dual-functional diodes. Supplementary Fig. 9e, f shows the measured 10 15
Hz and 1 MHz sinusoidal signals transmitted and received by our dual-functional diodes. 16
17
Figure 4 Photoresponse characteristics of the perovskite diode working as a photodetector to
18
light emitted from another identical diode which works as an LED. a, Photocurrent density of
14
the -0.5 V biased perovskite diode working as a photodetector (JPD), responding to light emitted
1
from an identical perovskite diode working as an LED driven with different current densities (JLED).
2
b, The current to current ratios of the -0.5 V biased perovskite photodetector and LED (JPD/JLED)
3
at different LED drive current densities. c, Frequency response of the perovskite photodetector to
4
the light emitted from the perovskite LED.
5
Dual-functional perovskite diodes as light emission and detection devices show great 6
potentials in minimization and integration of optoelectronic devices or systems because the devices 7
are based on the same structure and materials. To demonstrate their high sensitivity to the light 8
emitted from the identical device and the ease of integration, we use monolithic perovskite diodes 9
as the light source and sensor to build an optoelectronic heart pulse sensor. In this system, two 10
perovskite diodes are fabricated on one chip. The light emitted from one diode propagates into the 11
finger; part of the light is absorbed by the skin vascular bed, and the rest is transmitted though or 12
reflected by the tissue and partially detected by the other diode (Fig. 5a). As the hemoglobin 13
contained in blood can absorb a portion of the light, the volumetric changes of the blood flow due 14
to the pumping of the heart will induce the change of the light absorption by the vascular bed, 15
which can then be detected by the other diode. The photograph of the system is shown in Fig. 5b. 16
The cardiac cycles measured with our dual-functional perovskite diodes agree well with those 17
measured using a commercial pulse sensor, which includes an inorganic green LED and silicon 18
photodiode (Fig. 5c). The exact waveforms obtained by these two sensors are similar. The slight 19
difference is likely caused by the different penetration depth of the light as well as the difference 20
in the signal acquisition circuits. The enlarged waveforms measured by the perovskite and 21
commercial sensor shown in Fig. 5d can reflect the details of the pulse, including the systolic peak 22
and diastolic notch41,42. In addition, the waveform of our perovskite devices is robust with time 23
(Supplementary Fig. 10a) and reproducible in different devices (Supplementary Fig. 10b). The 24
ease integration of two functionalities in one device not only greatly simplifies the design and 25
15
process of devices, but also enables the miniaturization and even integration of different 1
functionalized devices. 2
16
Figure 5 Demonstration of the dual-functional perovskite diode for applications in biomedicine
1
and optical communications. a, b, Schematic illustration (a) and the photograph (b) of the
2
application of integrated perovskite light source and detector in one chip to be used in heart pulse
3
monitor. c, The waveforms of the heart pulse obtained using the commercial and perovskite
4
sensors. d, The enlarged waveform of the heart pulse monitored using the commercial and
5
perovskite sensors, which can clearly show the systolic peak and diastolic notch of the pulse signal.
6
e, Schematic illustration of using the dual-functional perovskite diode as the transmitter and
7
receiver in a bidirectional communication system for analog and digital signals. f, The photograph
8
of the user interface of the bidirectional optical communication system using dual-functional
9
perovskite diodes as the transmitter and receiver. The chat bubbles were later-added to guide the
10
eye. g, Waveforms of transmitted and received audio analog signals in the optical communication
11
demonstration system with two inter-chip dual-functional perovskite diodes as the transmitter and
12
receiver. h, Waveforms of transmitted and received digital signals between these two
dual-13
functional perovskite diodes at bit rates of 1 Mbit/s.
14
The fast response speed and high sensitivity to the light emission from the identical 15
perovskite diode makes these diodes promising for simplifying bidirectional optical 16
communication systems. To demonstrate the feasibility of using them in a realistic optical 17
communication system, we use two such perovskite diodes simultaneously as the transmitter and 18
receiver to build a bidirectional optical communication system instead of conventional double 19
transmitter/receiver systems (Fig. 5e). The data from a computer are modulated to the light 20
intensity of the perovskite diode which works as the transmitter. The modulated light is then 21
received by the other perovskite diode and transferred to the computer after amplification and 22
demodulation. Through this system, we successfully realize bidirectional communication using 23
two dual-functional perovskite diodes (Fig. 5f). The photograph and the video of the 24
communication system are shown in Supplementary Fig. 11 and the attached video. Both analog 25
(Fig. 5g) and digital (Fig. 5h) signals can be transmitted and received by the perovskite dual-26
functional diodes. As shown in Fig. 5h and Supplementary Fig. 12, the digital signal can be 27
exchanged between the full-area intra-chip dual-functional perovskite diodes (diode distance: 1 28
mm) at a bit rate of 1 Mbit/s. For inter-chip communication (diode distance: 13 mm), the bit rate 29
is below ~100 kbit/s (Supplementary Fig. 13), which is mainly limited by the amplifier we use. 30
17
Although the speed of the solution-processed perovskite device is promised to reach hundreds of 1
MHz or even GHz (Supplementary Note 1), the values are still lower than those obtained in 2
commercial devices made from inorganic semiconductor devices. For example, III-V compound 3
semiconductor laser diode43 and LED44 as transmitters have reached modulation speed of tens of 4
GHz and 800 MHz, respectively; InGaAs p-i-n photodiodes as receivers have reached response 5
speed faster than 100 GHz45. Although the bandwidth of our current system is behind what is
6
required for fiber-optic and visible light communication systems, our dual-functional perovskite 7
diodes show great potential in middle and low speed (below tens of Mbit/s) optical 8
communications, inter- and intra-chip data links for solution-processable optoelectronic integrated 9 circuits. 10 11 Conclusions 12
We have shown that optical signal transmitter and receiver functions can be integrated in 13
one device using metal halide perovskites. The two functions of the device can be reversibly 14
switched by changing the bias direction. The diode shows high performance comparable to state-15
of-the-art single-function perovskite devices when working as either a emitting or light-16
detecting device. The response speed of the perovskite light-emitting device is systematically 17
studied, and a high response speed of ~21 MHz demonstrated for a 0.1 mm2 device. The perovskite
18
diode shows high sensitivity to the light emitted by an identical diode, providing a unique 19
opportunity to simplify the integration of optoelectronic devices. We demonstrate this through 20
building a monolithic pulse sensor system and a bidirectional optical communication system based 21
on two identical perovskite diodes. Furthermore, we expect that the response speeds of our devices 22
could be further improved by decreasing the size of the pixel, since the devices are mainly limited 23
18
by the parasitic capacitance. This would allow the development of high-speed display-to-display 1
communication or data exchange. These features, coupled with the ease of integration on a wide 2
range of inorganic substrates and compatibility with CMOS, make the dual-functional perovskite 3
diodes promising for inter- or intra-chip data links in future solution-processed optoelectronic 4 integrated circuits. 5 6 Methods 7 Device fabrication 8
Patterned ITO glass substrates (sheet resistance: ~10 ohm/sq, transmittance: ~88%) were 9
firstly washed with detergent and then heated in ammonia and hydrogen peroxide mixed aqueous 10
solution at 80 °C for 30 minutes, followed by treating with UV-Ozone for 20 minutes. ZnO 11
nanoparticles dispersed in ethanol were spin-coated on the ITO substrates at 4000 rpm for 30 s in 12
air to form a ZnO layer. After that, the ZnO-coated substrates were transferred to a nitrogen filled 13
glovebox (H2O level<0.1 ppm; O2 level: 4.5-30 ppm). PEIE solution (0.05 wt% in isopropanol)
14
was spin-coated on the ZnO layer at 5000 rpm for 30 s and then annealed at 100 °C on a hot plate 15
for 10 minutes. Perovskite precursor solution in DMF (FAI:PbI2:ODEA=2:1:0.3 in molar ratio,
16
Pb2+ concentration: 0.13 M) was deposited on the ZnO/PEIE layer at 3000 rpm for 30 s and then 17
annealed at 100 °C for 10 minutes. After cooling to room temperature, TFB (12 mg mL-1 in 18
chlorobenzene) was spin coated on the perovskite film at 3000 rpm for 30 s, followed by the 19
thermal evaporation deposition of 7 nm MoOx (~0.5 Å/s) and 80 nm Au (~2 Å/s) at a pressure of
20
1×10-6 mbar.
21
Characterizations of materials and LEDs 22
19
Our perovskite films and devices were stored in nitrogen filled glovebox without being 1
deliberately kept away from light. The thicknesses of the films were determined using a Bruker 2
Dektak profilometer and the SEM cross-sectional images. The perovskite film deposited on 3
ZnO/PEIE coated ITO substrate was used to perform the ultraviolet–visible (UV-vis) absorption 4
spectra and PL spectra measurements. The vis absorption spectrum was measured using a UV-5
vis spectrophotometer (Lambda 900, PerkinElmer) with a ZnO/PEIE coated ITO substrate as 6
reference. The PL spectrum was measured using a spectrometer (Shamrock sr-303i-B, Andor 7
Technology) and the exciting light was from a continuous wave laser (450 nm). 8
The performance of the LED was measured in a nitrogen filled glovebox. A Keithley 2400 9
source meter was used to power the device. The drive voltage was swept from 0 to 5 V with an 10
interval of 0.02 V. At each voltage point, the EL spectra and intensities were monitored using a 11
spectrometer (QE Pro, Ocean Optics) coupled with a fiber connected integrating sphere (FOIS-12
1). During the measurement, the devices were placed over the entrance aperture on the surface 13
of the integrating sphere and only the forward emission light can be detected. To measure the 14
transient current and EL characteristics of the LEDs, a square wave voltage with pulse voltage 15
of 3.5 V was used to drive the LEDs. The current waveform was directly monitored by an 16
oscilloscope with an input impedance of 50 Ω. The EL intensities were detected using a silicon 17
photodiode (S1133, Hamamatsu) which was reversely biased (-9 V) with a 9 V lithium ion 18
battery. The current signal of the silicon photodiode was monitored by the oscilloscope with an 19
input impedance of 50 Ω. The transient current and EL measurements were carried out in air on 20
an encapsulated LED. The frequency response and bandwidth of the LED were determined 21
using unencapsulated devices in the nitrogen filled glovebox. The devices were driven by 22
sinusoidal voltage and the average EL intensities were measured using the QE Pro spectrometer 23
20
coupled with a fiber integration sphere. The frequency of the drive voltage was scanned from 1
1k to 50M Hz. 2
Photodetector characterizations 3
The characterizations of the photodetector were carried out in air at room temperature on 4
encapsulated devices, unless otherwise specified. To encapsulate the devices, a drop of UV 5
adhesive (~5 µL, Norland Products, NOA 73) is put on the metal electrode side of the device, then 6
covered with a glass slide. After the adhesive fully permeates the space between the device and 7
cover glass, it is solidified upon illumination with a UV lamp through the cover glass side for about 8
30 s. The J-V curves of the devices were measured using a Keithley 2400 source meter. The device 9
was fixed in a grounded metal box. An aperture with a diameter of ~3 mm on the box allows the 10
light to vertically shine on the device. For dark J-V curve measurements, the aperture was covered 11
with a black tape. For photo J-V curve measurements, a 630 nm laser beam was used to illuminate 12
the device. The diameter of the laser spot was about 1 mm and the power of the laser beam was 13
adjusted by changing its drive current using a Keithley 2400 source meter and calibrated using a 14
light power detector (Newport, 818-UV/DB). 15
The photo-to-current EQE of the device was measured using a solar cell spectral response 16
measurement system (QE-R3011, Enli Technology) which was calibrated with a standard Si 17
crystalline solar cell. The dark current noise spectra of the devices were measured using a lock-in 18
amplifier (SR830, Stanford Research System) coupled with a low noise preamplifier (SR570, 19
Stanford Research System). The sensitivity of the preamplifier was chosen to be 0.1 nA/V. The 20
instrument noise was first measured without connecting the device to the input. The shot noise 𝑖𝑛,𝑠, 21
thermal noise 𝑖𝑛,𝑡 and total white noise 𝑖𝑛were calculated based on the following equations:
21 𝑖𝑛,𝑠 = √2𝑒𝐼𝐷∆𝑓 (1) 1 𝑖𝑛,𝑡 = √4𝑘𝐵𝑇∆𝑓 𝑅 (2) 2 𝑖𝑛 = √𝑖𝑛,𝑠2 + 𝑖𝑛,𝑡2 (3) 3
where e the elementary charge, 𝐼𝐷 the dark current, ∆𝑓 the bandwidth, 𝑘𝐵the Boltzmann constant, 4
T the temperature, R the resistance of the devices. With the EQE and dark current noise (in), the
5
NEP and D* of the device can be calculated based on the following equations:
6 𝑁𝐸𝑃 = 𝑖𝑛 ℛ𝜆 (4) 7 𝐷∗ =ℛ𝜆√𝐴 𝑖𝑛 (5) 8 ℛ𝜆 = 𝐼𝑝ℎ 𝑃𝑖𝑛= 𝑒∙𝜆∙𝐸𝑄𝐸 ℎ𝑐 (6) 9
where ℛ𝜆 is the responsivity of the device at wavelength λ, A the device area, Iph the photocurrent
10
of the devices when incident light power is Pin, h the Plank constant, and c the light speed.
11
To study the weak light response and LDR of the photodetector, a laser beam driven by a 12
square wave voltage at a frequency of 8 Hz was used to illuminate the device. The output of the 13
drive voltage kept alternating on/off at a period of 20 s. The light power was adjusted using neutral 14
density filters and calibrated with the Si photodiode. The current signals of the devices were 15
recorded by the lock-in amplifier. The LDR was calculated using the following equation: 16
LDR = 20lg𝑃ℎ𝑖𝑔ℎ
𝑃𝑙𝑜𝑤 (7)
22
where Phigh and Plow are the highest and lowest light power among which the measured
1
photocurrent of the devices shows linear relation with the incident light power. 2
The TPC of the photodetector was measured using the oscilloscope with an input 3
impedance of 50 Ω when the device was excited by a pulse laser (wavelength: 337 nm, pulse width: 4
~4 ns) from a nitrogen laser (NL100, Stanford Research System) after attenuation with a neutral 5
density filter. To measure the TPC of the device under reverse biases, a Keithley 2400 source meter 6
was used to apply biases. 7
The stability of the photodetectors was investigated in the nitrogen filled glovebox on an 8
unencapsulated device. The incident light was from a red LED (650 nm) which was driven by an 9
alternating on/off voltage with a period of 20 s. The current of the photodetector was recorded by 10
a Keithley 2400 source meter. 11
To study the current response of the perovskite photodetector to the light emitted from a 12
perovskite LED with an identical structure, we used a Keithley 2400 source meter to drive the 13
perovskite LED at various currents and the photocurrent of the photodetector was monitored using 14
another source meter. To study the frequency response of the perovskite photodetector to light 15
emitted from a perovskite LED with an identical structure, we used sinusoidal voltage with 16
different frequency to drive the LED and used an oscilloscope to measure the current waveform 17
of the photodetector. 18
Demonstration of the application 19
To demonstrate their application as the light source and detector in the biomedicine field, 20
we used two identical diodes on one chip as the LED and photodetector for a heart pulse sensor. 21
The LED was driven by a DC current of 2 mA from a source meter. One of the fingertips of C.X.B. 22
23
was gently pressed on the device and simultaneously cover the LED and photodetector pixels. The 1
current of the photodetector was monitored by an oscilloscope after amplification by a low noise 2
current preamplifier with a 10-Hz lowpass filter (Fig. 5a, b). For comparation, a commercial pulse 3
sensor integrated with a green inorganic LED, a silicon photodiode and filter/amplifier circuit were 4
fixed on another finger and monitored by the oscilloscope simultaneously. 5
In the demonstration system of bidirectional optical communication, two identical diodes 6
in the same or different chip was used as transmitter and receiver simultaneously. Two open-source 7
electronics platforms (Arduino UNO) were used to convert digital data to high/low voltage level 8
or vice versa. The user interfaces of the platforms allow the users to input and receive information 9
on the computers. The information input by User1 was transferred to ASCII codes and then 10
transmitted to the Arduino UNO board where the ASCII codes can be transferred to high/low 11
voltage level on the specified pin. The voltage drove the perovskite LED and made it blink. The 12
blinking light was then detected by the other perovskite diode, whose photocurrent was transferred 13
to voltage through a current preamplifier and then input to the specified pin of the other Arduino 14
UNO board, where the voltage signal was transferred to ASCII codes and transmitted to the 15
computer. The computer then transferred the ASCII codes into words and displayed on the user 16
interface for User 2. The information transmitted from User 2 to User 1 followed the same process. 17
The audio signal was transmitted as analog signal. The signal was firstly amplified and used to 18
drive one of the perovskite diodes through which the signal was modulated in the change of the 19
light intensity. The light signal was received by the other perovskite diode and then amplified by 20
a preamplifier before driving the loudspeaker. 21
24 Data availability
1
The data that support the plots within this paper and other findings of this study are available from 2
the corresponding author upon reasonable request. 3
4
Acknowledgements 5
We thank M. Kovalenko for helpful discussions. This work is supported by the ERC Starting Grant 6
(Grant No. 717026), the Major Research Plan of the National Natural Science Foundation of China 7
(Grant No. 91733302), the National Natural Science Foundation of China (Grant No. 51472164, 8
61704077), the National Science Fund for Distinguished Young Scholars (Grant No. 61725502), 9
the 1000 Talents Program for Young Scientists of China, Shenzhen Peacock Plan (Grant No. 10
KQTD2016053112042971), the Educational Commission of Guangdong Province (Grant No. 11
2015KGJHZ006), the Natural Science Foundation of Jiangsu Province (BK20171007), the 12
European Commission Marie Skłodowska-Curie Actions (691210), the Swedish Government 13
Strategic Research Area in Materials Science on Functional Materials at Linköping University 14
(Faculty Grant SFO-Mat-LiU no. 2009-00971), the Nanjing University of Aeronautics and 15
Astronautics PhD short-term visiting scholar project (Grant No. 180608DF06) and the China 16
Postdoctoral Science Foundation (2017M622744, 2018T110886); F.G. is a Wallenberg Academy 17 Fellow. 18 19 Author contributions 20
25
F.G. and C.B. conceived the idea; W.X. and P.T. fabricated the perovskite devices and performed 1
the electroluminescence (EL) efficiency characterizations; C. B. and J.Y. performed the EL speed 2
and photodetection measurements and the application demonstrations; S.B. synthesized and 3
tailored the ZnO nano-crystal and contributed to improve the device performance; F.G., W.H. and 4
W.Z. guided the experiments and discussed the data; F.G., C.B., W.X., J.Y. and S.B. wrote and 5
revised the manuscript, J.W., N.Z. and Y.Y. contributed to the result analysis and the revision of 6
the manuscript; F.G. supervised the project; All authors discussed the results and commented on 7
the manuscript. 8
Competing interests
9
The authors declare no competing interests.
10
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Supplementary information
6 732 1
Supplementary Figure 1 Electroluminescence performance of the perovskite LED. a, Current 2
density and radiance versus voltage curves of perovskite LEDs based on perovskite films with 3
different amount of ODEA additives. b, External quantum efficiency (EQE) versus drive current 4
density of perovskite LEDs based on perovskite films with different amount of ODEA additives. 5
c, Electroluminescence spectra of perovskite LEDs based on perovskite films with different 6
amount of ODEA additives. d, External quantum efficiency (EQE) versus drive current density of 7
perovskite LEDs based on perovskite films made from precursors with different concentrations. 8
9 10 11 12
33 1
Supplementary Figure 2 Response speed characterizations of perovskite diodes when 2
working as LEDs. a, Fitting curves of the LED transient current with exponential function. b, The 3
measured capacitance spectra of the perovskite LEDs under dark and illumination of 450 nm 4
monochrome light with power of ~1 µW. c. Frequency response curves of perovskite LEDs based 5
on perovskite films with different amount of OEDA additives. d, Cut-off frequencies of perovskite 6
LEDs with different device areas. 7
8
Supplementary Figure 3 Performance characterizations of perovskite photodetectors. a, 9
Dark current vs voltage curves of perovskite photodetectors based on perovskite film with different 10
amount of ODEA additives. b, External quantum efficiency (EQE) spectra of the perovskite 11
photodetector under different biases as well as the excitation spectrum of TFB. c, EQE spectra of 12
the perovskite photodetectors fabricated from perovskite precursors with different concentrations. 13
34 1
Supplementary Figure 4. Performance characterizations of perovskite photodetectors. a, 2
Simultaneously measured photoluminescence quantum efficiency (PLQE) and photo-to-current 3
conversion EQE of the perovskite diode. b, Noise current characteristics of the perovskite 4
photodetector under different reverse biases as well as the noise current flow of the instrument. c, 5
The current characteristics of the perovskite photodetector under illumination from an alternating 6
on/off laser with different incident light power, indicating that the photodetector is sensitive to 7
weak light of 0.8 pW. d, Linear dynamic range characteristic of the perovskite photodetector. 8
35 1
Supplementary Figure 5 Response speed of perovskite photodetectors. a, Transient 2
photocurrent (TPC) of perovskite photodetector under different bias voltages. b, TPC of perovskite 3
photodetectors based on perovskite films with different amount of ODEA additives. c, Statistic 4
box chart of the response time of perovskite photodetectors based on perovskite films with 5
different amount of ODEA additives. The statistics is based on 6 different devices. d. Frequency 6
response of the perovskite photodetector with the device area of 0.1 mm2 obtained from the TPC 7
curve by fast Fourier transform (FFT). 8
36 1
Supplementary Figure 6 Photo- and dark- current of the perovskite photodetector based on 2
perovskite films without additives. 3
4
Supplementary Figure 7 EL spectrum stability of the diode after working as a light emitting (a) 5
and detecting (b) device for a period of time. 6
7
Supplementary Figure 8 The performance development of our devices measured under 8
ambient conditions. a, Work as an LED at a current density of 25 mA cm-2. b, Work as a 9
photodetector at -0.1 V bias. c, Work as a photodetector at 0 bias. During the measurement, the 10
relative humidity and room temperature are ~37% and ~18 °C. 11
37 1
Supplementary Figure 9 Current transfer characterizations of dual-functional perovskite 2
diodes. a, b, Current density of a perovskite photodetector under 0 V (a) and -0.5 V (b) bias 3
voltages responding to the light emitted from an inter-chip perovskite LED under different drive 4
current densities. c, d, Current density of a perovskite photodetector under 0 V (c) and -0.5 V (d) 5
bias voltages responding to the light emitted from an intra-chip perovskite LED under different 6
drive current densities. e, f, Response of the perovskite photodetector to the perovskite LED under 7
modulation frequencies of 10 Hz (e) and 1 MHz (f). 8
38 1
Supplementary Figure 10 Heart pulse waveforms collected using perovskite dual functional 2
devices as the light source and detector. a, Waveforms collected during a period of 200 s. b, 3
Waveforms monitored by three different perovskite devices. 4
5 6
7
Supplementary Figure 11 The photograph of the bidirectional optical communication system 8
using dual-functional perovskite diodes simultaneously as the transmitter and receiver. 9
39 1
Supplementary Figure 12 Optical communication between two intra-chip dual-functional 2
perovskite diodes. a, Dimension of the intra-chip dual-functional perovskite diodes. The distance 3
d=1 mm in the intra-chip communication demonstration system. b, c, d, Waveforms of transmitted 4
and received digital signals between these two dual-functional perovskite diodes at different bit 5
rates. 6
7
Supplementary Figure 13 Optical communication between two inter-chip dual-functional 8
perovskite diodes. a, Dimension of the inter-chip dual-functional perovskite diodes. The distance 9
d=13 mm in the inter-chip communication demonstration system. b, c, d, Waveforms of 10
transmitted and received digital signals between these two dual-functional perovskite diodes at 11
different bit rates. 12
40 Supplementary Note 1
1
For a photodiode, the response speed is mainly limited by two factors: the resistance-capacitance 2
(RC) time constant induced by the resistance and parasitic capacitance, and the transit time (ttr).1,2 3 𝑓−3𝑑𝐵−2 = ( 3.5 2𝜋𝑡𝑡𝑟) −2 + ( 1 2𝜋𝑅𝐶) −2 (S1) 4
where f-3dB is the 3-dB cutoff frequency. The RC constant can be effectively reduced by reducing 5
the device area. Based on the capacitance measurement of our devices, the capacitance of the 6
device with a small area of 0.01 mm2 can be estimated to be ~ 4 pF. For a resistance of 50 Ω, we 7
can obtain a RC constant of 0.2 ns, corresponding to a RC constant limited cutoff frequency of 8
~796 MHz. 9
The transit time for a diode can be expressed as3 10
𝑡𝑡𝑟 = 𝑊𝐷
𝜇𝐸 (S2) 11
where WD is the thickness of the depletion region, μ is the carrier mobility of the semiconductor, 12
E is the electrical field intensity in the depletion region. In our device, the semiconductor layers
13
can be considered as completely depleted layer due to the very small thickness and low free carrier 14
concentration. So, we can use the thickness of the semiconductor to replace the thickness of the 15
depletion region in function S2. 16
𝑡𝑡𝑟 = 𝑑2
𝜇𝑉 (S3) 17
where d is the thickness of the semiconductor, V is the sum of the applied reverse bias and the 18
build-in voltage. For our device, considering the thickness and mobility difference, the transit time 19
should be mainly determined by the transit time of the TFB layer. With the mobility (0.01 cm-2 V -20
1 s-1, Ref 4) and the thickness (~40 nm) of TFB and the build-in voltage (~1.5 V), we can estimate 21
the transit time of our device under 0 and -0.5 V bias as 1.1 and 0.8 ns, corresponding to transit 22
time limited cutoff frequency of 525 and 697 MHz. When consider both RC constant and transit 23
time, we can obtain the cutoff frequency of 438 and 524 MHz for 0 and -0.5 V biased device 24
(device area: 0.01 mm2), respectively. 25
From Functions S1 and S2 we can see that the response speed can be further improved by further 26
decreasing the device area and increasing the reverse bias, but too small device area will lead to 27
low signal-to-noise ratio and high reverse bias is significantly harmful to the stability of perovskite 28
devices. Another way to improve the response speed is to increase the junction thickness to 29
decrease the capacitance and use high mobility materials to decrease the transit time. For example, 30
if the carrier mobility of the charge transport materials is 0.1 cm-2 V-1 s-1 and the thickness is 80 31
nm, then the capacitance will be reduced to ~2 pF for a device with area of 0.01 mm2 (we assumed 32
a similar dielectric constant). This is corresponding to a RC time constant of 0.1 ns and a RC-33
constant-limited cutoff frequency of 1.6 GHz. According to Function S3, we can obtain a transit 34
time of 0.32 ns, corresponding to a transit-time-limited cutoff frequency of 1.7 GHz. 35
For a light-emitting diode, in addition to the above electric-transport limited factors, the 36
emission decay time should be considered. If the device speed is limited by the emission decay 37
time, in order to obtain faster speed, a shorter emission decay time is necessary. For perovskite 38
41
device with emission decay time of about 7 ns, if only consider the emission decay time, the cutoff 1
frequency has been experimentally demonstrated to be 491 MHz, and the device is capable in data 2
transmission in a rate of ~2 Gbit/s.5 3
4
Supplementary Reference 5
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