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An Al/ p -Si/poly[2-methoxy-5-(2-ethylhexoxy)- p -phenylenevinylene] (MEH-PPV)/Ag organic heterojunction has been prepared using homemade ultrasonic spray pyrolysis (USP) equipment for deposition of the organic thin film and physical vapor deposition (PVD) for the metallic contacts. The organic layer produced on glass was analyzed by optical and morphological methods. The bandgap of the organic thin film was found to be ~ 2.03 eV with a thickness of around 140 nm, using ultraviolet–visible (UV–Vis) and scanning electron microscopy (SEM) characterization, respectively. The amorphous nature of the MEH-PPV polymer was confirmed by its x-ray diffraction pattern. To determine the electrical parameters, the heterojunction based on MEH-PPV was characterized by current–voltage ( I – V ) and capacitance–voltage ( C – V ) measurements in the dark at room temperature. The ideality factor and barrier height of the organic heterojunction were found to be 3.6 eV and 0.56 eV to 0.59 eV, respectively, with an average series resistance of 94.39 Ω, based on the I – V characteristics. The barrier height was also calculated based on the capacitance–voltage measurements, yielding slightly different results due to the applied frequencies of 10 kHz ( ϕ B = 0.50 ) and 1 MHz ( ϕ B = 0.74 ) , respectively.

The research of ultraviolet photodetectors (UV PDs) have been attracting extensive attention, due to their important applications in many areas. In this study, PtSe 2 /GaN heterojunction is in-situ fabricated by synthesis of large-area vertically standing two-dimensional (2D) PtSe 2 film on n-GaN substrate. The PtSe 2 /GaN heterojunction device demonstrates excellent photoresponse properties under illumination by deep UV light of 265 nm at zero bias voltage. Further analysis reveals that a high responsivity of 193 mA·W –1 , an ultrahigh specific detectivity of 3.8 × 10 14 Jones, linear dynamic range of 155 dB and current on/off ratio of ~ 108, as well as fast response speeds of 45/102 μs were obtained at zero bias voltage. Moreover, this device response quickly to the pulse laser of 266 nm with a rise time of 172 ns. Such high-performance PtSe 2 /GaN heterojunction UV PD demonstrated in this work is far superior to previously reported results, suggesting that it has great potential for deep UV detection.

Van der Waals integration with abundant two-dimensional materials provides a broad basis for assembling functional devices. In a specific van der Waals heterojunction, the band alignment engineering is crucial and feasible to realize high performance and multifunctionality. Here, we design a ferroelectric-tuned van der Waals heterojunction device structure by integrating a GeSe/MoS 2 VHJ and poly (vinylidene fluoride-trifluoroethylene)-based ferroelectric polymer. An ultrahigh electric field derived from the ferroelectric polarization can effectively modulate the band alignment of the GeSe/MoS 2 heterojunction. Band alignment transition of the heterojunction from type II to type I is demonstrated. The combination of anisotropic GeSe with MoS 2 realizes a high-performance polarization-sensitive photodetector exhibiting low dark current of approximately 1.5 pA, quick response of 14 μs, and high detectivity of 4.7 × 10 12 Jones. Dichroism ratios are also enhanced by ferroelectric polarization in a broad spectrum from visible to near-infrared. The ferroelectric-tuned GeSe/MoS 2 van der Waals heterojunction has great potential for multifunctional detection applications in sophisticated light information sensing. More profoundly, the ferroelectric-tuned van der Waals heterojunction structure provides a valid band-engineering approach to creating versatile devices. Band alignment engineering is important to realize high performance and multifunctionality in a specific van der Waals heterojunction. Here, the authors observe band alignment transition of the heterojunction in a ferroelectric-tuned van der Waals heterojunction device with high performance.

The performance of solar cells based on molecular electronic materials is limited by relatively high nonradiative voltage losses. The primary pathway for nonradiative recombination in organic donor-acceptor heterojunction devices is believed to be the decay of a charge-transfer (CT) excited state to the ground state via energy transfer to vibrational modes. Recently, nonradiative voltage losses have been related to properties of the charge-transfer state such as the Franck-Condon factor describing the overlap of the CT and ground-state vibrational states and, therefore, to the energy of the CT state. However, experimental data do not always follow the trends suggested by the simple model. Here, we extend this recombination model to include other factors that influence the nonradiative decay-rate constant, and therefore the open-circuit voltage, but have not yet been explored in detail. We use the extended model to understand the observed behavior of series of small molecules:fullerene blend devices, where open-circuit voltage appears insensitive to nonradiative loss. The trend could be explained only in terms of a microstructure-dependent CT-state oscillator strength, showing that parameters other than CT-state energy can control nonradiative recombination. We present design rules for improving open-circuit voltage via the control of material parameters and propose a realistic limit to the power-conversion efficiency of organic solar cells.

As one of the most promising materials for two-dimensional transition metal chalcogenides (2D TMDs), molybdenum diselenide (MoSe 2 ) has great potential in photodetectors due to its excellent properties like tunable bandgap, high carrier mobility, and excellent air stability. Although 2D MoSe 2 -based photodetectors have been reported to exhibit admired performance, the large-area 2D MoSe 2 layers are difficult to be achieved via conventional synthesis methods, which severely impedes its future applications. Here, we present the controllable growth of large-area 2D MoSe 2 layers over 3.5-inch with excellent homogeneity by a simple post-selenization route. Further, a high-quality n-MoSe 2 /p-Si van der Waals (vdW) heterojunction device is in-situ fabricated by directly growing 2D n-MoSe 2 layers on the patterned p-Si substrate, which shows a self-driven broadband photoresponse ranging from ultraviolet to mid-wave infrared with an impressive responsivity of 720.5 mA·W −1 , a high specific detectivity of 10 13 Jones, and a fast response time to follow nanosecond pulsed optical signal. In addition, thanks to the inch-level 2D MoSe 2 layers, a 4 × 4 integrated heterojunction device array is achieved, which has demonstrated good uniformity and satisfying imaging capability. The large-area 2D MoSe 2 layer and its heterojunction device array have great promise for high-performance photodetection and imaging applications in integrated optoelectronic systems.

Green production of nanomaterials and their materials properties studies are majorly important for the futuristic development of nanodevices. We had green synthesized the ZnO and CuO nanoparticles using the extract of “Eucalyptus globulus ” leaves. The obtained ZnO and CuO nanoparticles were studied for their structural, morphological and optical properties. The green synthesized CuO and ZnO nanoparticles have showed the crystalline size of about 12.29 and 10.16 nm. The transmission electron microscopic images of green synthesized ZnO and CuO nanoparticles revealed the morphological information and their respective average sizes of 46 and 32 nm. Optical absorbance spectrum revealed the existence of morphology based quantum confinement in the green ZnO and CuO nanoparticles. Further we have fabricated the p-CuO/n-ZnO heterojunction device using the green synthesized nanoparticles and also evaluated the electrical properties of the p–n junction diode. Under the light illumination the photodiode characteristic were studied for the obtained p–n junction diode. Finally, the energy band diagram of the photodiode responsible for the electronic transport had also discussed. Graphical Abstract

High-performance lead-free K 0.5 Na 0.5 NbO 3 piezoelectric ceramics present a practical alternative to lead-containing counterparts by effectively reducing potential environmental hazards. This advancement is particularly relevant to the development of ferroelectric heterojunction devices for biomedical applications. Here, we design and fabricate a frequency-adjustable ferroelectric heterojunction based on the developed K 0.5 Na 0.5 NbO 3 piezoelectric ceramics with a high piezoelectric coefficient ( d 33  = 680 pC/N). By leveraging flexible encapsulation, the heterojunction achieves miniaturization ( φ  = 13.3 mm, h  = 2.28 mm) and suitability for implantation. After penetrating the rat skull, the ultrasound generated by the heterojunction at a frequency of 3 MHz reaches a focal depth of about 7.9 mm, a focal width of approximately 480 μm at −6 dB, and millimeter-scale continuous focal tuning (1.5 mm) within a narrow frequency range (2.7–3.3 MHz). Additionally, the implanted heterojunction enables long-term and high-precision transcranial neuromodulation, and consequently yields therapeutic effects in a myocardial infarction animal model. Collectively, this study highlights a viable strategy for developing and applying lead-free ferroelectric heterojunctions, expanding their potential in brain modulation, and providing new insights into clinical treatments of myocardial infarction. The authors present a frequency-adjustable ferroelectric heterojunction based on K 0.5 Na 0.5 NbO 3 piezoelectric ceramic, which enabling therapeutic effects in a myocardial infarction animal model by long-term and high-precision transcranial neuromodulation.

Broadband photodetectors based on narrow bandgap 2D materials have garnered considerable interest for application in the field of optoelectronic devices. However, their large dark current hinders device performance. In this work, a PtSe 2 /MoS 2 heterojunction was fabricated for a broadband photodetector operating within the range of visible to near-infrared. The device exhibited suppressed dark currents with a high rectification ratio of 10 4 . The built-in electric field of the heterojunction promoted carrier separation effectively, and the device achieved excellent photoelectric performance with responsivities of 1.7 × 10 3 , 27.52, and 21 mA/W at 635, 785, and 1550 nm wavelengths, respectively. Moreover, the specific detectivities ( D *) were 2.2 × 10 13 Jones (635 nm), 3.55 × 10 11 Jones (785 nm), and 2.72 × 10 8 Jones (1550 nm). The device demonstrated a rise/fall time of 131/241 µs under 1550 nm laser illumination. Visible and near-infrared imaging detection was also demonstrated based on the heterojunction device at room temperature. This work sheds light on the remarkable potential of PtSe 2 /MoS 2 heterojunctions in the domain of high-performance broadband photodetectors.

HighlightsA self-powered α-In2Se3/3R MoS2 heterojunction is successfully developed and shows strong photo response to the visible and near infrared light.The heterojunction photodetector delivers an ultrahigh photoresponsivity of 2.9 × 103 A W−1 and a substantial specific detectivity of 6.2 × 1010 Jones under a compressive strain of − 0.26%.This work demonstrates that the transport of photo generated carriers is clearly modulated by mechanical stimuli through the piezo-phototronic effect at the heterojunction interface.Semiconducting piezoelectric α-In2Se3 and 3R MoS2 have attracted tremendous attention due to their unique electronic properties. Artificial van der Waals (vdWs) heterostructures constructed with α-In2Se3 and 3R MoS2 flakes have shown promising applications in optoelectronics and photocatalysis. Here, we present the first flexible α-In2Se3/3R MoS2 vdWs p-n heterojunction devices for photodetection from the visible to near infrared region. These heterojunction devices exhibit an ultrahigh photoresponsivity of 2.9 × 103 A W−1 and a substantial specific detectivity of 6.2 × 1010 Jones under a compressive strain of − 0.26%. The photocurrent can be increased by 64% under a tensile strain of + 0.35%, due to the heterojunction energy band modulation by piezoelectric polarization charges at the heterojunction interface. This work demonstrates a feasible approach to enhancement of α-In2Se3/3R MoS2 photoelectric response through an appropriate mechanical stimulus.

In the current work, ZnO film (~ 143 nm) is deposited on the CMOS compatible Si substrate by using RF sputtering technique to form a p-n type heterojunction device and further, thin buffer layer of TiO 2 (~ 52 nm) is inserted in between ZnO and Si to reduce the interfacial defects remarkably in ZnO/TiO 2 /Si bilayer heterojunction for UV/Visible sensing applications. Smooth interface, and highly crystallite qualities of TiO 2 -brookite and ZnO-hexagonal wurtzite phases are observed from atomic force microscopy (AFM) and Field-emission gun scanning electron microscopy (FEG-SEM) and X-ray diffraction (XRD), respectively. X-ray photoelectron spectroscopy (XPS) clarifies the chemical states of elements, which indicate a significant amount of the reduction in oxygen vacancies after insertion of the TiO 2 thin layer. An enhanced absorption in UV region and slight red shift in emission are observed in UV-Visible spectroscopy and Photoluminescence (PL) plots for TiO 2 /ZnO bilayer heterojunction, and oxygen related complex defects are reduced due to TiO 2 insertion. Finally, Current-voltage (I-V) measurements demonstrate the dark current reduction in ZnO/Si heterojunction with TiO 2 incorporation and such heterojunction exhibits photovoltaic behavior under specific wavelengths (380 nm and 420 nm). A superior responsivity (0.17 A/W), detectivity (7.80 × 10¹³ Jones) with rapid response speed (< 1 s) at zero bias are achieved in the UV-A/Visible wavelength range for ZnO/TiO 2 /Si heterojunctions. The corresponding photo-carrier generation and transport mechanism are analyzed in detail by using corresponding energy band diagram. Therefore, all the results indicate that such TiO 2 thin layer inserted ZnO/Si heterojunction may provide a cost-effective feasible design strategy for the development of interfacial defect less, self-powered wavelength selective UV/Visible detectors in recent future.