A novel approach for designing efficient broadband photodetectors expanding from deep ultraviolet to near infrared

Extending the detection limit: innovations in infrared quantum dot photodetectors reaching up to 18 μm

A regrowth method was used to synthesize large-sized colloidal quantum dots (CQDs). With the assistance of doping engineering, the synthesized CQD detectors demonstrate exceptional long-wavelength infrared detection performance, reaching up to 18 μm, significantly extending the spectral response limit for CQD-based infrared detectors. These detectors also achieve a reasonably high detectivity of 6.6 × 108 Jones.

Highly Emissive Lanthanide-Based 0D Metal Halide Nanocrystals for Efficient Ultraviolet Photodetector

Recently, lanthanide-based 0D metal halides have attracted considerable attention for their applications in X-ray imaging, light-emitting diodes (LEDs), sensors, and photodetectors. Herein, lead-free 0D gadolinium-alloyed cesium cerium chloride (Gd3+-alloyed Cs3CeCl6) nanocrystals (NCs) are introduced as promising materials for optoelectronic application owing to their unique optical properties. The incorporation of Gd3+ in Cs3CeCl6 (CCC) NCs is proposed to increase the photoluminescence quantum yield (PLQY) from 57% to 96%, along with significantly enhanced phase and chemical stability. The structural analysis is performed by density functional theory (DFT) to confirm the effect of Gd3+ in Cs3Ce1- xGdxCl6 (CCGC) alloy system. Moreover, the CCGC NCs are applied as the active layer in UVPDs with different Gd3+ concentration. The excellent device performance is shown at 20% of Gd3+ in CCGC NCs with high detectivity (7.938 × 1011 Jones) and responsivity (0.195 A W-1) at -0.1 V at 310 nm. This study paves the way for the development of lanthanide-based metal halide NCs for next-generation UVPDs and other optoelectronic applications.

CVD-Grown Monolayer MoS2 and GaN Thin Film Heterostructure for a Self-Powered and Bidirectional Photodetector with an Extended Active Spectrum

Photodetector technology has evolved significantly over the years with the emergence of new active materials. However, there remain trade-offs between spectral sensitivity, operating energy, and, more recently, an ability to harbor additional features such as persistent photoconductivity and bidirectional photocurrents for new emerging application areas such as switchable light imaging and filter-less color discrimination. Here, we demonstrate a self-powered bidirectional photodetector based on molybdenum disulfide/gallium nitride (MoS2/GaN) epitaxial heterostructure. This fabricated detector exhibits self-powered functionality and achieves detection in two discrete wavelength bands: ultraviolet and visible. Notably, it attains a peak responsivity of 631 mAW-1 at a bias of 0V. The device's response to illumination at these two wavelengths is governed by distinct mechanisms, activated under applied bias conditions, thereby inducing a reversal in the polarity of the photocurrent. This work underscores the feasibility of self-powered and bidirectional photocurrent detection but also opens new vistas for technological advancements for future optoelectronic, neuromorphic, and sensing applications.

Synergetic enhancement of CsPbI3 nanorod-based high-performance photodetectors via PbSe quantum dot interface engineering

The advancement of optoelectronic applications relies heavily on the development of high-performance photodetectors that are self-driven and capable of detecting a wide range of wavelengths. CsPbI3 nanorods (NRs), known for their outstanding optical and electrical properties, offer direct bandgap characteristics, high absorption coefficients, and long carrier diffusion lengths. However, challenges such as stability and limited photoluminescence quantum yield have impeded their widespread application. By integrating PbSe colloidal quantum dots (CQDs) with CsPbI3 NRs, the hybrid nanomaterial harnesses the benefits of each component, resulting in enhanced optoelectronic properties and device performance. In this work, a self-powered and broadband photodetector, ITO/ZnO/CsPbI3:PbSe/CuSCN/Au, is fabricated, in which CsPbI3 NRs are decorated with PbSe QDs as the photoactive layer, ZnO as the electron-transporting layer and CuSCN as the hole-transporting layer. The device performance is further improved through the incorporation of Cs2CO3 into the ZnO layer, resulting in an enhancement of its overall operational characteristics. As a result, a notable responsivity of 9.29 A W-1 and a specific detectivity of 3.17 × 1014 Jones were achieved. Certainly, the TCAD simulations closely correlate with our experimental data, facilitating a comprehensive exploration of the fundamental physical mechanisms responsible for the improved performance of these surface-passivated heterojunction photodetectors. This opens up exciting possibilities for substantial advancements in the realm of next-generation optoelectronic devices.

Efficient and Stable Multicolor Emissions of the Coumarin-Modified Cs3LnCl6 Lead-Free Perovskite Nanocrystals and LED Application

Lanthanide-based lead-free perovskite materials hold great promise for the development of high-resolution full-color displays in the future. Here, various Cs3LnCl6 perovskite nanocrystals (NCs) emitting light across the visible to near-infrared spectrum with remarkably high photoluminescence quantum yield (PLQY) are systemically prepared. Especially, by introducing multifunctional coumarin small molecules into Cs3EuCl6 NCs as an intermediate state, Cs3EuCl6 NCs can achieve an impressive PLQY of 92.4% with pure red emission and an exceptional energy transfer efficiency of nearly 93.2%. Furthermore, the lanthanide-based electroluminescent devices in red, green, and blue are successfully fabricated. Among them, the Cs3EuCl6-NC-based red light-emitting diode (LED) demonstrates a FWHM of 18 nm at 617 nm, an external quantum efficiency up to 5.17%, and a maximum brightness of 2373 cd m-2, which is the most excellent reported for lead-free narrowband (within 20 nm) emission devices. Notably, these devices exhibit an operating half-life of 440 h at a brightness level of 100 cd m-2, surpassing the performance of most reported lead-free perovskite LEDs (PLEDs). This work opens up exciting possibilities for the future commercialization of lanthanide-based PLEDs in the display industry, paving the way for more vibrant, energy-efficient, and long-lasting display technologies.

Recent Advances in Broadband Photodetectors from Infrared to Terahertz

The growing need for the multiband photodetection of a single scene has promoted the development of both multispectral coupling and broadband detection technologies. Photodetectors operating across the infrared (IR) to terahertz (THz) regions have many applications such as in optical communications, sensing imaging, material identification, and biomedical detection. In this review, we present a comprehensive overview of the latest advances in broadband photodetectors operating in the infrared to terahertz range, highlighting their classification, operating principles, and performance characteristics. We discuss the challenges faced in achieving broadband detection and summarize various strategies employed to extend the spectral response of photodetectors. Lastly, we conclude by outlining future research directions in the field of broadband photodetection, including the utilization of novel materials, artificial microstructure, and integration schemes to overcome current limitations. These innovative methodologies have the potential to achieve high-performance, ultra-broadband photodetectors.

Water-stable perovskite CsPb2Br5/CdSe quantum dot-based photoelectrochemical sensors for the sensitive determination of dopamine

A heterojunction of CdSe quantum dots in situ grown on the perovskite CsPb2Br5 (CsPb2Br5/CdSe) for water-stable photoelectrochemical (PEC) sensing was simply synthesized using the hot-injection method. Due to the inherent built-in electric field and the matching band structure between CsPb2Br5 and CdSe, the CsPb2Br5/CdSe p-n heterojunction demonstrates enhanced photoelectrochemical properties. Accelerated interfacial charge transfer and increased electron-hole pair separation enable hydrolysis-resistant CsPb2Br5/CdSe sensors to exhibit heightened sensitivity with an ultra-low detection limit (0.0124 μM) and a wide linear range (0.4-303.9 μM) in subsequent dopamine detection. Moreover, the CsPb2Br5/CdSe sensors show excellent anti-interference ability, as well as remarkable stability and reproducibility in water solvent. It is noteworthy that this work is conducted in an aqueous environment, which provides an inspiring and convenient way for photoelectric and photoelectrocatalysis applications based on water-resistant perovskites.

Solution-Processed Sb2S3-Based Heterojunction for Self-Powered Broad Band Weak Light Detection

Antimony sulfide (Sb2S3) has recently regained the attention of photovoltaic researchers as a promising solar absorber; however, its application for the detection of white light remains relatively unexplored. Herein, we report on the self-powered heterojunction photodetector based on a device-grade Sb2S3 film made at low temperature with solution processing. The Sb2S3 absorber film was prepared by single-step spin coating of a novel precursor ink using antimony trichloride as the antimony source along with the low melting thioacetamide as the sulfur source in 2-methoxyethanol, a low boiling environmentally friendly solvent. A simple TiO2/Sb2S3 heterojunction device made by using the film shows a power conversion efficiency of 1.22% without any hole transporting layer. Interestingly, the self-powered photodetector performance of the device under white light exhibits a high on/off ratio of 2.2 × 104 under 1 sun illumination. Moreover, this optical filter-free ultraviolet-visible absorbing near-infrared blind photodetector is equally capable of detecting both strong and weak white light, with a response time of 98 ms. Further, an example of the real-life application of the device is successfully demonstrated by constructing a weak light-detecting sunlight tracking system.

Gain enhancement of perovskite nanosheets by a patterned waveguide: excitation and temperature dependence of gain saturation

Optical gain enhancement of two-dimensional CsPbBr3 nanosheets was studied when the amplified spontaneous emission is guided by a patterned structure of polyurethane-acrylate. Given the uncertainties and pitfalls in retrieving a gain coefficient from the variable stripe length method, a gain contour [Formula: see text] was obtained in the plane of spectrum energy (ℏω) and stripe length (x), whereby an average gain was obtained, and gain saturation was analysed. Excitation and temperature dependence of the gain contour show that the waveguide enhances both gain and thermal stability due to the increased optical confinement and heat dissipation, and the gain origins were attributed to the two-dimensional excitons and the localized states.

High-sensitivity self-powered photodetector based on an in-situ prepared CsPbBr3 microwire/InGaN heterojunction

Low-dimensional CsPbBr3 perovskite materials have gained widespread attention, derived from their remarkable properties and potential for numerous optoelectronic applications. Herein, the sample of CsPbBr3 microwires were prepared horizontally onto n-type InGaN film substrate using an in-plane solution growth method. The resulting CsPbBr3 microwire/InGaN heterojunction allows for the achievement of a highly sensitive and broadband photodetector. Particularly for the implementation in a self-supplying manner, the best-performing photodetector can achieve a superior On/Off ratio of 4.6×105, the largest responsivity ∼ 800.0 mA/W, a maximum detectivity surpassing 4.6× 1012 Jones, and a high external quantum efficiency approaching 86.5% upon 405 nm light illumination. A rapid response time (∼ 4.48 ms/7.68 ms) was also achieved. The as-designed CsPbBr3 microwire/InGaN heterojunction device without any encapsulation exhibits superior comprehensive stability. Besides, the device featuring as a single pixel imaging unit can readily detect simple images under broadband light illumination with a high spatial resolution, acknowledging its outstanding imaging capability. The robust photodetection properties could be derived from the intense absorption of CsPbBr3 MWs and high-efficiency charge carriers transporting toward the in-situ formed CsPbBr3/InGaN heterointerface. The results may offer an available strategy for the in-situ construction of best-performing low-dimensional perovskite heterojunction optoelectronic devices.

Dual-Interface Engineering in Perovskite Solar Cells with 2D Carbides

Passivating the interfaces between the perovskite and charge transport layers is crucial for enhancing the power conversion efficiency (PCE) and stability in perovskite solar cells (PSCs). Here we report a dual-interface engineering approach to improving the performance of FA0.85 MA0.15 Pb(I0.95 Br0.05 )3 -based PSCs by incorporating Ti3 C2 Clx Nano-MXene and o-TB-GDY nanographdiyne (NanoGDY) into the electron transport layer (ETL)/perovskite and perovskite/ hole transport layer (HTL) interfaces, respectively. The dual-interface passivation simultaneously suppresses non-radiative recombination and promotes carrier extraction by forming the Pb-Cl chemical bond and strong coordination of π-electron conjugation with undercoordinated Pb defects. The resulting perovskite film has an ultralong carrier lifetime exceeding 10 μs and an enlarged crystal size exceeding 2.5 μm. A maximum PCE of 24.86 % is realized, with an open-circuit voltage of 1.20 V. Unencapsulated cells retain 92 % of their initial efficiency after 1464 hours in ambient air and 80 % after 1002 hours of thermal stability test at 85 °C.

Polarization-Sensitive, Self-Powered, and Broadband Semimetal MoTe2/MoS2 van der Waals Heterojunction for Photodetection and Imaging

The emerging type II Weyl semimetal 1T' MoTe2 as a promising material in polarization-sensitive photodetectors has aroused much attention due to its narrow bandgap and intrinsic in-plane anisotropic crystal structure. However, the semimetal properties lead to a large dark current and a low response. Herein, we demonstrate for the first time an all-2D semimetal MoTe2/MoS2 van der Waals (vdWs) heterojunction to improve the performance of the photodetectors and realize polarization-sensitive, self-powered, and broadband photodetection and imaging. Owing to the built-in electric field of the heterojunction, the device achieves a self-powered photoresponse ranging from 520 to 1550 nm. Under 915 nm light illumination, the device demonstrates outstanding performance, including a high responsivity of 79 mA/W, a specific detectivity of 1.2 × 1010 Jones, a fast rise/decay time of 180/202 μs, and a high on/off ratio of 1.3 × 10.3 Wavelength-dependent photocurrent anisotropic ratio is revealed to vary from 1.10 at 638 nm to 2.24 at 1550 nm. Furthermore, we demonstrate the polarization imaging capabilities of the device in scattering surroundings, and the DoLP and AoLP images achieve 78% and 112% contrast enhancement, respectively, compared to the S0. This work opens up new avenues to develop anisotropic semimetals heterojunction photodetectors for high-performance polarization-sensitive photodetection and next-generation polarized imaging.

Performance Improvement of Lead-Based Halide Perovskites through B-Site Ion-Doping Strategies

Owing to their excellent properties, lead halide perovskites have attracted extensive attention in the photoelectric field. Presently, the certified power conversion efficiency of perovskite solar cells has reached 25.7%, the specific detectivity of perovskite photodetectors has exceeded 1014 Jones, and the external quantum efficiency of perovskite-based light-emitting diode has exceeded 26%. However, their practical applications are limited by the inherent instability induced by the perovskite structure due to moisture, heat, and light. Therefore, one of the widely used strategies to address the issue is to replace partial ions of the perovskites with ions of smaller radii to shorten the bond length between halides and metal cations, improving the bond energy and enhancing the perovskite stability. Particularly, the B-site cation in the perovskite structure can affect the size of eight cubic octahedrons and their gap. However, the X-site can only affect four such voids. This review comprehensively summarizes the recent progress in B-site ion-doping strategies for lead halide perovskites and provides some perspectives for further performance improvements.

Phase Behavior and Role of Organic Additives for Self-Doped CsPbI3 Perovskite Semiconductor Thin Films

The phase change of all-inorganic cesium lead halide (CsPbI3) thin film from yellow δ-phase to black γ-/α-phase has been a topic of interest in the perovskite optoelectronics field. Here, the main focus is how to secure a black perovskite phase by avoiding a yellow one. In this work, we fabricated a self-doped CsPbI3 thin film by incorporating an excess cesium iodide (CsI) into the perovskite precursor solution. Then, we studied the effect of organic additive such as 1,8-diiodooctane (DIO), 1-chloronaphthalene (CN), and 1,8-octanedithiol (ODT) on the optical, structural, and morphological properties. Specifically, for elucidating the binary additive-solvent solution thermodynamics, we employed the Flory-Huggins theory based on the oligomer level of additives' molar mass. Resultantly, we found that the miscibility of additive-solvent displaying an upper critical solution temperature (UCST) behavior is in the sequence CN:DMF > ODT:DMF > DIO:DMF, the trends of which could be similarly applied to DMSO. Finally, the self-doping strategy with additive engineering should help fabricate a black γ-phase perovskite although the mixed phases of δ-CsPbI3, γ-CsPbI3, and Cs4PbI6 were observed under ambient conditions. However, the results may provide insight for the stability of metastable γ-phase CsPbI3 at room temperature.

Emission properties of Pd-doped CsPbBr3 perovskite nanocrystal: Infrared emission due to the Pd-doping

Perovskite-type materials have attracted great attention in recent times due to their interesting characteristics, such as their luminescent properties. The good photoluminescence quantum yields as well as the possibility of tuning the emission wavelength has allowed the study of these materials in several applications, such as sensors or LEDs. As sensors, making nanocrystals of these perovskites emitting in the near infrared (NIR) would open the possibility of using these materials in biomedical applications. In the present work, Pd-doped CsPbBr₃ perovskite nanocrystals (NCs) were synthesized and characterized. We show here Pd-doped NCs synthesized emit in NIR, at about 875 nm, using a laser emitting at 785 nm as the excitation source. This result is really new and promising, because it opens the possibility of using these nanocrystals in many applications as sensor in the field of nanobiomedicine in the future.

Piezo-phototronic effect regulated broadband photoresponse of a-Ga2O3/ZnO heterojunction

Amorphous Ga₂O₃ (a-Ga₂O₃) films have attracted considerable attention in the field of photodetectors due to their excellent optical absorption response and photoelectric properties. However, there are few studies that have utilized the piezo-phototronic effect to regulate the broadband photoresponse of Ga₂O₃-based photodetectors. Here, a flexible a-Ga₂O₃/ZnO heterojunction was constructed, which demonstrated a broadband response range from deep ultraviolet (265 nm) to the near-infrared (1060 nm) and realized a bidirectional adjustable photocurrent response via the piezo-phototronic effect. Under 265 nm illumination and 0.5 V bias, the responsivity and detectivity of the a-Ga₂O₃/ZnO heterojunction reached up to 12.19 A W^-1 and 4.71 × 10¹¹ Jones under 0.164% compressive strain, corresponding to enhancements of 67.7% and 66.8% compared to those under a strain-free state, respectively. Moreover, the broadband photoresponse of the a-Ga₂O₃/ZnO heterojunction beyond the bandgap limit was tunable under bidirectional strain. The working mechanism of photoresponse performance for the a-Ga₂O₃/ZnO heterojunction at different wavelengths was elucidated in detail. Oxygen vacancy-assisted carrier generation was found to be influenced by the wavelength of incident light, which mainly determined the broadband photoresponse of the heterojunction. The modulation of the a-Ga₂O₃/ZnO heterojunction photodetector was interpreted in light of the strain-induced regulation of the barrier height. This work represents an important step toward the development of adjustable broadband photodetectors based on a-Ga₂O₃ films.

Enhancing UV photodetection performance of an individual ZnO microwire p-n homojunction via interfacial engineering

As a typical broad bandgap semiconductor, ZnO has received considerable attention for developing optoelectronic devices in ultraviolet wavelengths, but suffers from a lack of high-quality single-crystalline p-type ZnO. Herein, we report the realization of a homojunction ultraviolet photodetector, which involves a p-type Sb-doped ZnO microwire (ZnO:Sb MW) and n-type ZnO layer. The p-type conductivity of the as-synthesized ZnO:Sb MWs was evidenced using an individual wire field-effect transistor. Due to its good rectifying ability and excellent photovoltaic effect, the constructed p-ZnO:Sb MW/n-ZnO homojunction is able to work as an ultraviolet photodetector in self-biased and reversely biased manners. By appropriately engineering the band alignment of the p-ZnO:Sb/n-ZnO homojunction via a MgO interface modification layer, the optimized photodetector exhibits performance-enhanced ultraviolet detection capabilities, such as the light on/off ratio reaching up to 1.6 × 10⁸, responsivity of over 267 mA W^-1 and specific detectivity of approximately 1.2 × 10¹⁴ Jones upon 365 nm light illumination at 0 V. The detector also produces faster response with rise/recovery times of 102 μs/3.6 ms. This study not only employed a novel method to synthesize genuine p-type ZnO with excellent stability and reproducibility, but also opened up substantial opportunities for developing high-performance ZnO homojunction optoelectronic devices.

In Situ Encapsulated Moiré Perovskite for Stable Photodetectors with Ultrahigh Polarization Sensitivity

Nanostructures provide a simple, effective, and low-cost route to enhance the light-trapping capability of optoelectronic devices. In recent years, nano-optical structures have been widely used in perovskite optoelectronic devices to greatly enhance the device performance. However, the inherent instability of perovskite materials hinders the practical application of these nanostructured optoelectronic devices. Here, in situ encapsulated moiré lattice perovskite photodetectors (PDs) by two nanograting-structured soft templates with relative rotation angles is fabricated. The confinement growth of the two nanograting templates leads to crystal growth with moiré lattice structure, which improves the light-harvesting ability of the perovskite crystal, thereby improving the device performance. The PD exhibits responsivity to 1026.5 A W^-1 . The Moiré lattice-perovskite-based PD maintained 95% of the initial performance after 223 days. After being continuously sprayed with water moist for 180 min, the performance is maintained at 95.7% of its initial level. The nanograting structure endows the device with high polarization sensitivity of I_max /I_min as high as 9.1.

Organic photodiodes: device engineering and applications

Organic photodiodes (OPDs) have shown great promise for potential applications in optical imaging, sensing, and communication due to their wide-range tunable photoelectrical properties, low-temperature facile processes, and excellent mechanical flexibility. Extensive research work has been carried out on exploring materials, device structures, physical mechanisms, and processing approaches to improve the performance of OPDs to the level of their inorganic counterparts. In addition, various system prototypes have been built based on the exhibited and attractive features of OPDs. It is vital to link the device optimal design and engineering to the system requirements and examine the existing deficiencies of OPDs towards practical applications, so this review starts from discussions on the required key performance metrics for different envisioned applications. Then the fundamentals of the OPD device structures and operation mechanisms are briefly introduced, and the latest development of OPDs for improving the key performance merits is reviewed. Finally, the trials of OPDs for various applications including wearable medical diagnostics, optical imagers, spectrometers, and light communications are reviewed, and both the promises and challenges are revealed.

Luminescent concentrators enable highly efficient and broadband photodetection

With luminescent concentrators, the high quantum yield luminescence emitted by embedded chromophores, featuring a broad absorption spectrum, can be well-tuned to match the peak response of integrated photodetectors. This integration can substantially enhance the device photoresponse all the way from deep UV to near-IR.