A self-powered HgTe quantum dots/PBDB-T:Y6 bipolar broadband photodetector for logic gates

Abstract

Optoelectronic logic gates (OELGs) have become one of the excellent candidates for logic devices in the post Moore era, with great potential for complex optical computing, secure optical communication, and image processing. As an important component of OELGs, bipolar photodetectors (BPDs) face problems such as limited logic functionality, narrow response range, slow response speed, and high-power consumption. Here, we propose a self-powered BPD with a back-to-back structure based on HgTe quantum dot (QD) and organic material PBDB-T:Y6 stacking. The results show that the BPD exhibits a broadband bipolar photoresponse (300–1800 nm) under a bias voltage of 0 V, with a rapid response speed in the microsecond range. By modulating the device with three light sources within the positive and negative photoresponse wavelength ranges, the HgTe QDs/PBDB-T:Y6 BPD successfully achieves five logic gate operations (“OR”, “AND”, “NAND”, “NOR”, and “NOT”). Based on excellent fast and broadband bipolar optoelectronic response, we further confirm the potential application of the HgTe QDs/PBDB-T:Y6 BPD in broadband optical communication encryption. This work provides a useful reference for the combination of QDs and organic materials in the development of high-performance BPDs.

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New concepts

Due to the limitations of the bandgap of optoelectronic materials and the working mechanism of bipolar photodetectors (BPDs), the BPDs that have received widespread attention in the field of optoelectronic logic gates (OELGs) face issues of limited logic functionality, narrow response range, slow response speed, and high-power consumption. This work proposes a novel strategy of coupling narrow and wide bandgap materials (i.e., inorganic short-wave infrared HgTe quantum dots (QDs) and organic visible-near infrared PBDB-T:Y6). The short-wave infrared HgTe QDs are synthesized through oriented crystallization growth. The back-to-back structure consisting of two photodiodes is constructed, achieving bidirectional carrier transport and self-powered bipolar response in the broadband range of 300–1800 nm. By controlling the optical switch, a dual channel optical communication encryption system is successfully simulated, which can achieve image encoding and encrypted transmission. These findings elucidate an effective method for coupling QDs with organic materials to promote the development of BPDs.

Introduction

Over the past two decades, data have exploded and the miniaturization of electronic devices has approached its inevitable physical limits due to quantum confinement effects.¹ As a result, the demand for electronic devices with diverse functions and low manufacturing costs in the information society is rapidly increasing.² In the post-Moore era, logic gate devices, as the most basic hardware for complex information processing through Boolean logic operations, have attracted widespread attention.³ Optoelectronic logic gates (OELGs) perform logic operations through the interplay of optical signals and electronic components, offering many advantages such as fast data processing and transmission capabilities, low power consumption, and reduced signal crosstalk.^4–7 OELGs are considered a good candidate for replacing traditional electronic logic gates and all-optical logic gates, and are expected to make up for their shortcomings in cost, optical loss, integration scale, and data processing capacity.⁸

Photodetectors are the most crucial components in OELGs, converting optical signals into electrical signals. However, due to their inherent unidirectional carrier transport behavior, the traditional photodetectors often exhibit non-tunability, making it difficult to achieve multiple logic functions through a single device.^9,10 These limitations have sparked significant research interest in BPDs with tunable photoresponse. By combining new materials with various bipolar photoresponse induction strategies, the BPDs achieve special ternary outputs (“1”, “0”, and “−1”) depending on optical wavelength, light intensity, or bias voltage, thereby promoting the development of integrated multi-logic devices. Currently, the BPDs used in OELGs are mainly divided into two categories. Firstly, the gate-controlled BPDs require dual inputs of gate voltage and light. For example, Chen et al. realized the OELGs including “AND”, “OR”, and “XOR” by integrating the carbon-based graphdiyne/graphene heterojunction photodetector.¹¹ Complex logical operations typically require multiple BPDs, so the bias voltage as an additional input and power consumption still has limitations.¹² Secondly, the direct photo-controlled BPDs induced by defects use the coupled light response mechanism or a back-to-back structure.^13–28 Jiang et al. used a doped PdSe₂ BPD via a wavelength-dependent oxygen molecule desorption process in the Se vacancy to perform optoelectronic logic operations (“XOR”, “OR”, and “AND”).²⁹ Li et al. fabricated an indium tin oxide (ITO)/Ce-doping into BaTiO₃ (Ce-BTO)/Ag BPD with millisecond level response speed to demonstrate four representative logic gates (“OR”, “AND”, “NOR”, and “NAND”) via the coupled photoresponse mechanisms of plasmonic and photovoltaic effects.³⁰ The instability of defects and the limitations of material selection and response speed caused by the coupling effects also hinder the performance optimization of integrated devices with complex logic functions.³¹ A back-to-back structure is a promising approach that utilizes two asymmetric diodes to control the bidirectional transport of carriers.³² It is expected to achieve excellent bipolar photoresponse characteristics, such as high responsivity, fast response speed, broadband, and low dark current, through complementary selection of wide and narrow bandgap materials. Currently, the back-to-back structure BPDs mainly use perovskites,^{21,22,25–27} metal oxides,²³ and organic materials^24,26 as photoactive layer materials. Due to the material bandgap limitations, the working wavelength range of these bipolar OELGs is mainly concentrated in the visible (Vis)-near infrared (NIR) spectrum. If OELGs can be extended to the short-wave infrared (SWIR) range, they can utilize the wide bandwidth and anti-interference capabilities of SWIR light to develop more complex optical communication encoding and modulation schemes, achieving higher communication capacity, security, and stability to meet the demands for high-security communication in military, financial, and other fields.³³ Therefore, developing OELGs with high response speed and broadband response is of great significance.

Quantum dots (QDs) have become one of the most promising materials for photodetectors due to their tunable bandgap and excellent NIR response, and simple solution processing. QD-based photodetectors, such as PbS and HgTe QDs, can achieve an excellent detection rate exceeding 10¹² Jones in the NIR spectrum, maintaining high response speed even at wavelengths exceeding 1400 nm.³⁴ However, the QD-based photodetectors typically exhibit a high dark current exceeding 10⁻⁹ A cm⁻² and low Vis light response. Organic optoelectronic materials are easy to process in solution and exhibit a high response in the Vis spectrum.³⁵ Due to their low carrier mobility and high exciton binding energy, the organic semiconductor photodetectors exhibit slow response speed.³⁶ In summary, the QDs and organic materials exhibit significant complementarity in terms of optoelectronic performances. The integration of the two materials is expected to further expand the photoresponse range, enhance response speed, and reduce dark current of BPDs. Additionally, the solution processability of the QDs and organic materials resolves the issue of lattice mismatch incompatibility. Therefore, the QDs/organic based BPD is expected to lead to the development of OELGs with fast broadband photoresponse.

Based on the above discussion, we propose a stacked self-powered HgTe QDs/PBDB-T:Y6 BPD using QDs and organic materials for the first time. The device relies on back-to-back structures and active layer materials with wide and narrow bandgaps to achieve a broadband wavelength-dependent bipolar photoresponse from 300 to 1800 nm, exhibiting a microsecond level fast response speed. Specifically, the spin-coated heterojunction PBDB-T:Y6 mixed organic bulk heterojunction film is prepared as the top absorber for Vis light. The HgTe QDs are synthesized as the bottom infrared light absorber of the device. When illuminated with different wavelengths of light, the photo-generated carriers are excited at the top/bottom absorbers, where the carriers are transported and separated by the PBDB-T:Y6 or ZnO/HgTe QD interface, resulting in significant positive/negative photocurrents. Based on the optical control of three light sources in the positive and negative photoresponse wavelength ranges, the HgTe QDs/PBDB-T:Y6 BPD can realize all-in-one integration of five basic logic gate operations: “OR”, “AND”, “NAND”, “NOT”, and “NOR”. With the help of this superior broadband bipolar photoresponse, a dual channel encrypted communication system is simulated to demonstrate dual channel data transmission with encryption capability and improved efficiency.

Results and discussion

Device structure design and composition of the HgTe QDs/PBDB-T:Y6 BPD

Materials synthesis, device fabrication, characterization studies, and measurements can be found in the Experimental section (ESI†). As depicted in Fig. 1a the HgTe QDs/PBDB-T:Y6 BPD is mainly composed of a Vis-NIR photodetection subunit (VPS) and a SWIR photodetection subunit (SPS), which are connected through an interlayer. Correspondingly, the energy band alignment of each material in HgTe QDs/PBDB-T:Y6 BPD is shown in Fig. 1b. The optical absorption spectra of narrow and wide bandgap active layers (HgTe QDs and PBDB-T:Y6) are shown in Fig. 1c. The organic PBDB-T:Y6 absorbs the entire Vis light to part of the NIR region (300–1000 nm), and the HgTe QD film achieves a wide-spectrum Vis-SWIR absorption from 300 to 1800 nm.

Fig. 1 Device structure diagram and characterization studies. (a) Device structure diagram of the HgTe QDs/PBDB-T:Y6 BPD. (b) Energy level diagram of the HgTe QDs/PBDB-T:Y6 BPD. (c) Normalized Vis-SWIR absorption curves of the HgTe QDs and PBDB-T:Y6 films. (d) Molecular structures for the donor and acceptor of the PBDB-T:Y6 active layer. (e) XRD patterns of the HgTe QDs. (f) TEM images of the HgTe QDs.

For the VPS, the organic polymer PBDB-T is selected as the donor material, which is a classic π-electron conjugated polymer with a high hole transport capability and a broad absorption spectrum in the Vis region.³⁷ Common fullerene materials are not the most ideal acceptors due to their relatively high cost and inherently low extinction coefficients in the Vis and NIR regions.³⁸ Therefore, a non-fullerene acceptor (NFA) Y6 is used to complement the absorption spectrum of PBDB-T, which is an emerging narrow-bandgap (1.5 eV) NFA with a high absorption coefficient in the NIR region.³⁹ The expansion of the absorption spectrum range plays a pivotal role in enhancing the sensitivity of the photodetector. The chemical structures of the PBDB-T and Y6 are shown in Fig. 1d. Due to the temperature dependent characteristics of the PBDB-T and Y6, they tend to aggregate at room temperature, affecting the formation of the donor/acceptor (D/A) interface and easily introducing defects in thin film, thereby affecting the formation of free charges.⁴⁰ Hence, the PBDB-T and Y6 were mixed and dissolved in 1,2-dichlorobenzene (o-DCB) to form a heterojunction film with a smaller-scale D/A phase separation structure and a bicontinuous interpenetrating network through a high temperature spin-coating method. The film morphology facilitates the diffusion and separation of excitons within the organic hybrid layer, promoting the generation of free charges and subsequent interlayer transport of photo-generated charge carriers. The scanning electron microscope (SEM) and atomic force microscopy (AFM) images of the BHJ film are presented in Fig. S1 and S2 (ESI†). As the organic materials disaggregate gradually at high temperature, the SEM and AFM images demonstrate uniform distribution, indicating good mixing of the donor and acceptor, and good contact in the formed composite film. Additionally, a root-mean-square roughness (RMS) of 1.88 nm is obtained and the low RMS value indicates good contact between the solution-processed organic hybrid film and the interlayer.

For the SPS, the dendritic HgTe QDs were prepared by using an oriented crystallization growth strategy with an exciton absorption peak at 1540 nm (as shown in Fig. S3, ESI†). As depicted in X-ray diffraction (XRD) patterns of Fig. 1e, all the diffraction peaks are precisely matched with the HgTe (JCPDS card no: 32-0665).⁴¹ The transmission electron microscopy (TEM) image of the dendritic HgTe QDs is depicted in Fig. 1f. The lattice spacing of the HgTe QDs is 0.37 nm, corresponding to the (111) planes of the HgTe. The Hg 4f and Te 3d spectra further confirm the successful synthesis of the HgTe QDs (Fig. S4, ESI†). By utilizing multi-layer spin coating and traditional solid-phase ligand exchange methods, a dense HgTe QDs film is formed with 1,2-ethanedithiol (EDT) serving as the ligand (Fig. S5 and S6, ESI†). Fig. S7 (ESI†) shows the bandgap of the HgTe QD film calculated by using the Tauc method, indicating that the bandgap of the HgTe QD film is 0.78 eV. Besides, referring to previous research by Prof. Lan's group, the valence band maximum (E_V) and Fermi energy (E_F) values of the HgTe QDs are approximately 4.88 eV and 4.54 eV, respectively.^42,43 The two subunits of Vis-NIR VPS and SWIR SPS are connected through an n-type ZnO electron transport layer (ETL), which exhibits a wide bandgap of 3.25 eV and excellent electron transport capabilities.⁴⁴ Since organic materials of PBDB-T and Y6 and long-chain oleylamine ligand passivated HgTe QDs have good solubility in non-polar solvents, the ZnO intermediate layer also plays a role in preventing solvent penetration and avoiding chemical damage to the organic active layer. Finally, the thermally evaporated p-type MoO₃ is used as the hole transport layer (HTL) connecting the HgTe QD layer and the Ag electrode.

Bipolar optoelectronic properties and working principle of the HgTe QDs/PBDB-T:Y6 BPD

Fig. 2a shows the cross-sectional TEM image of the device. Each layer is vertically stacked, with clear layering and no obvious wrinkles or defects at each interface. The element distribution is investigated using a scanning TEM equipped with an energy dispersive X-ray spectroscope (EDS), as shown in Fig. 2b, which further clearly illustrates each layer. The clear interfaces of different layers without the obvious element diffusion phenomenon prove that the ZnO layer effectively prevents solvent penetration, avoids chemical damage to the organic active layer, and ensures the normal operation of the organic photovoltaic element. During the measurement process, the ITO electrode layer was connected to the negative terminal of the source meter, while the Ag electrode layer was the positive electrode. Fig. 2c presents the I–V curves of the device under dark conditions, and 400 nm, and 1550 nm wavelength illumination, and the enlarged curves around zero bias voltage are shown in Fig. 2d. The HgTe QDs/PBDB-T:Y6 BPD exhibits obvious bipolar photoresponse characteristics under zero bias (Fig. 2d), suggesting that the device can serve as a self-powered BPD. Fig. 2e further demonstrates the bipolar photoresponse behavior of the HgTe QDs/PBDB-T:Y6 BPD under 400 and 1550 nm through five on/off cycles at a zero bias, exhibiting stable bipolar photocurrent outputs. The response and recovery times of the HgTe QDs/PBDB-T:Y6 BPD with an effective area of 0.024 mm² are determined as 23.0 μs and 39.4 μs, respectively (Fig. S8, ESI†). In addition, Fig. 2f shows that the polarity of the photocurrent at zero voltage exhibits a strong wavelength dependence, resulting in a broadband bipolar photoresponse (300–1800 nm). The photocurrent is in a positive state within the range of 300–900 nm, reaches its maximum value at 800 nm, gradually decreases with further wavelength increase, and reaches zero at ∼1000 nm. When the wavelength of light exceeds 1000 nm, the photocurrent increases significantly with opposite polarity, reaching a negative maximum at 1500 nm, and also decreases as the wavelength continues to increase. Based on the spectral photocurrent results, the responsivity (R) and detectivity (D*) are calculated and shown in Fig. S9 (ESI†). Although the R and D* performances of the HgTe QDs/PBDB-T:Y6 BPD still lag behind the state-of-the-art level of some other photodiode-type BPD (Table S1, ESI†), it has advantages of broadband photoresponse range and fast response speed.

Fig. 2 Characterization studies and optoelectronic performances of the HgTe QDs/PBDB-T:Y6 BPD. (a) Cross-sectional TEM image of the device. (b) Corresponding elemental mapping image of the device for Ag, Mo, Te, Zn, In and C. (c) I–V curves under dark conditions, 400 nm and 1550 nm and (d) enlarged curves around zero voltage of the BPD. (e) Repetitive photoresponse curves of the BPD under 400 nm and 1550 nm. (f) Bipolar spectral photoresponse of the BPD from 300 to 1800 nm at a 100 nm interval. (g) Illustrated band diagrams of the back-to-back structure in the dark equilibrium state. (h) Working principle diagrams of positive photocurrent mode with 300–900 nm and (i) negative photocurrent mode with 1000–1800 nm.

Fig. 2g–i illustrates the energy band diagrams of the HgTe QDs/PBDB-T:Y6 BPD to qualitatively clarify the physical mechanisms of the bipolar spectral response. The proposed HgTe QDs/PBDB-T:Y6 BPD can be regarded as being composed of two independent photodiodes connected in series back-to-back. There is a significant Fermi level difference between the ZnO ETL, MoO₃ HTL and PBDB-T, which produces a built-in potential and can effectively extract photo-generated carriers. Without external bias voltage or light, the diffusion current driven by the carrier concentration gradient and the drift current driven by the potential gradient reach equilibrium (Fig. 2g). These two are equivalent and cancel each other out, resulting in the device exhibiting a very small dark current (i.e., 10⁻¹⁰ A), namely a “net zero current” state.^21,25,26 However, as shown in Fig. 2h and i, the balance is broken under illumination. When 300–900 nm light illuminated, almost all the electrons generated in PBDB-T:Y6 BHJ diffuse and are trapped at the HgTe QDs/MoO₃ interface due to the blocking of MoO₃ layer, while the photogenerated holes are collected by ITO. As the accumulated charges increase, a potential is established, accompanied by interface band bending, which offsets the inherent built-in potential and ultimately generates a forward current without any external bias (Fig. 2h). Likewise, under 1000–1800 nm light irradiation, the carriers generated at HgTe QD layer diffuse and accumulate at the interface between ZnO and the PBDB-T:Y6 organic hybrid layer, as well as between HgTe QDs and MoO₃, thereby inducing a potential at the interface along with band bending and outputting a reverse current (Fig. 2i). The back-to-back structure composed of two photodiodes made of different materials provides a key working principle for bidirectional carrier transport, allowing controlled charges to be transferred in both directions in response to different irradiation conditions (e.g., wavelength and power density).

Demonstration of five basic OELGs via a single HgTe QDs/PBDB-T:Y6 BPD

Based on the bipolar photoresponse characteristics of the HgTe QDs/PBDB-T:Y6 BPD, we utilized three types of light source modulation (one modulation light source and two input light sources, with different wavelengths and adjustable illumination power) to achieve five basic photoelectric logic gates in a single device (“AND”, “OR”, “NAND”, “NOT”, and “NOR”). Taking the 400 nm Vis light and 1550 nm SWIR light as examples, they can induce photocurrent in opposite directions and be used to demonstrate five logic gates. The top panel of Fig. 3a shows the corresponding electrical logic outputs of the HgTe QDs/PBDB-T:Y6 BPD in response to optical inputs (“00”, “01”, “10”, and “11”), in which “0/1” denote “off/on” states of the input signals. The bottom panel of Fig. 3a illustrates schematic diagrams of these five light regulated logic gates. In the “AND” logic gate, the output signal is “1” only when both optical input signals are “1”; otherwise, the output state is “0”. Therefore, we need to select a SWIR light with a stronger irradiance as the modulation light source, so that only when the input states of the two Vis light input sources are “11”, the output photocurrent is positive and exceeds the reference current (I_output = 0 A). When the input states are “00”, “01”, and “10”, the photocurrent shifts negatively to below 0 A under the modulation of SWIR light. Fig. 3b shows the photocurrent output curve corresponding to the “AND” logic gate. The characteristic of the “OR” logic gate is that it outputs “1” when there is a “1” in the input state and outputs “0” when there is no “1”. Therefore, we choose a SWIR light with a weaker irradiance as the modulation light. At this time, if the input states are “01”, “10”, or “11”, the output photocurrent always exceeds the reference current I_output in a positive direction. The negative photocurrent below the reference current is only obtained for the “00” input, performing the “OR” logic gate, as shown in Fig. 3c. In addition, the HgTe QDs/PBDB-T:Y6 BPD can also perform inverting logic gate operations, such as “NAND”, “NOT”, and “NOR”. As shown in Fig. 3d, under strong Vis light modulation, if two SWIR light sources are used to achieve input states of “10”, “01”, or “00”, the output photocurrent will always exceed the reference current (0 A). However, in the case of an input state of “11”, a negative photocurrent will be generated. For the “NOT” logic gate, when the Vis light modulation source has a weaker irradiance, Fig. 3e illustrates the photocurrent of the HgTe QDs/PBDB-T:Y6 BPD under a single SWIR light input, where an input of “0” corresponds to an output of “1”, and an input of “1” corresponds to an output of “0”. When two SWIR input light sources are used, as long as one of them has an input state of “1”, the output photocurrent will be negative, corresponding to the operation of the “NAND” logic gate (Fig. 3f).

Fig. 3 Demonstration of five OELGs via a single HgTe QDs/PBDB-T:Y6 BPD. (a) Schematic diagrams of five basic logic gates and corresponding truth tables for inputs and outputs. (b) and (c) transient photocurrent curves of “AND” and “OR” logic gates in response to two Vis inputs under IR modulation. (d)–(f) Transient photocurrent curves corresponding to “NAND”, “NOT” and “NOR” logic gates in response to IR inputs under Vis modulation.

Potential optical communication encryption application of the HgTe QDs/PBDB-T:Y6 BPD

Based on the bipolar response characteristics, we simulated a dual-band encrypted optical communication system using the HgTe QDs/PBDB-T:Y6 BPD, referring to the previous application demonstration of the photoelectrochemical BPDs.^45,46 This system consists of two parts: optical signal transmitting end and the receiving end. Fig. 4a shows the transmitting signal composed of 400 and 1550 nm (“00”, “10”, “11”, “01”, where “0” and “1” correspond to the off and on states of the emitted light, respectively) and the corresponding output photocurrent of the HgTe QDs/PBDB-T:Y6 BPD (after normalizing the output photocurrent, it corresponds to the four different encoding states of “0”, “2”, “1”, and “−1” of the recognition signal). We simulated the encrypted transmission of an 18 × 17 matrix image (306 pixels) displaying the “UESTC” character to illustrate the encryption method of the system. The schematic diagram of the image with “UESTC” characters is Fig. 4b. The pixels with patterns are encoded as “1”, and the blank pixels are encoded as “0”. So, an 18 × 17 encoding matrix with “0/1” can be obtained (Fig. 4c). Then, each combination of 1 × 2 pixel blocks (“00”, “10”, “11”, “01”) corresponds to the use of two light sources (400 nm and 1550 nm) to form a synchronized transmission signal. Subsequently, the emitted optical signal is received and converted into photocurrent output by the HgTe QDs/PBDB-T:Y6 BPD and the traditional unipolar photodetector, respectively (Fig. 4d and e). After normalization, a 9 × 17 digital encoding matrix of “0/2/1” and “0/1” is obtained. Then, by comparing using Ciphertext, the 9 × 17 digital encoding matrix is decoded back to the 18 × 17 “0/1” digital encoding matrix. Finally, the pixels are filled according to the digital encoding matrix to obtain the image (“1” indicates pixel filling with blue, “0” indicates unfilled), thus obtaining the corresponding “UESTC” image. Since the traditional unipolar photodetectors cannot distinguish between 400 nm and 1550 nm through the polarity of the photocurrent, the output results corresponding to the four different optical signal input states only differ in intensity. At this time, the output results for the four input states “00”, “10”, “01”, “11” are “0”, “1”, “1”, and “2”, respectively. The output result “1” corresponds to both input states “10” and “01”, which cannot be distinguished during decoding (the pixels that cannot be distinguished are filled with gray), thus failing to accurately obtain the true image. Therefore, the dual-band encrypted optical communication system utilizing HgTe QDs/PBDB-T:Y6 BPD possesses secure optical communication encryption capabilities. Additionally, due to its broadband response, it can utilize infrared light for signal transmission, offering superior anti-interference properties compared to Vis light communication. Therefore, the HgTe QDs/PBDB-T:Y6 BPD holds a significant potential application in future advanced optical communication systems.

Fig. 4 Demonstration of dual-channel encrypted optical communication using HgTe QDs/PBDB-T:Y6 BPD. (a) Encoded photoresponses of the device under 400, 400 + 1550, and 1550 nm. (b) Input image displaying the characters of “UESTC”. (c) Encoded “0/1” digital matrix corresponding to the input image with two encoded light sources. The code in the left grid corresponds to the “on/off” status of the 400 nm Vis encoded light source, while the code in the right grid corresponds to the “on/off” status of the 1550 nm SWIR encoded light source in each 1 × 2 matrix. (d) Normalized photocurrent values received by the BDP and the corresponding decrypted image (identical to the input image). (e) Intercepted photocurrent values received by a traditional photodetector with unipolar photoresponse and the corresponding intercepted image (distinct from the input image). Four colored boxes and circles between (c)–(e) correspond to four input states, in which green corresponding to state “01”, yellow corresponding to state “10”, red corresponding to state “00”, blue corresponding to state “11” (i.e., the relations of the four kinds of input codes, LED on/off states, and the detecting photoresponses).

Conclusions

In summary, a back-to-back structure BPD using wide-narrow bandgap materials of PBDB-T:Y6/HgTe QDs heterojunctions was successfully designed and fabricated. The photocurrent polarity of the HgTe QDs/PBDB-T:Y6 BPD can be reversed by changing incident light wavelength with a fast response rate of 23 μs. Simultaneously, five fundamental OELGs of “AND”, “OR”, “NAND”, “NOT”, and “NOR” are successfully performed on a single device. Benefitting from unique bipolar photoresponse characteristics of the HgTe QDs/PBDB-T:Y6 BPD, a dual-channel optical communication system has been simulated to demonstrate its application in broadband optical communication security encryption. These results demonstrate a feasible method for combining inorganic QDs with organic materials. The analysis of the working principle contributes to enhancing the understanding of transport characteristics of BPDs with back-to-back configurations and provides effective theoretical and technical support for developing high-performance BPDs. However, considering that HgTe QDs and organic materials are susceptible to the influence of water molecules and oxygen, as well as the aggregation phenomenon of QDs after long-term operation, there is still significant room for optimization of the proposed HgTe QDs/PBDB-T:Y6 BPD to achieve applications, such as optimizing material synthesis and device packaging technology.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work is supported by the National Science Fund for Distinguished Young Scholars (Grant No. 62225106), the Natural Science Foundation of China (Grant No. U24A20229 and 62301114), the Sichuan Science and Technology Program (No. 2024NSFSC1428), and the Fundamental Research Funds for the Central Universities (Grant No. ZYGX2024XJ021). The authors appreciate Yue Fang, Xuan Wei, Youzuo Hu, Kai Wang, Yulu Tian, and Qin Cheng from Analysis and Testing Center, University of Electronic Science and Technology of China, for technical support.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4mh01925c

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