Photo Response Research Articles

Quasi-single-crystal Tin Halide Perovskite Films with High Structural Integrity for Near-infrared Imaging Array enabling Hidden Object Recognition.

Near-infrared (NIR) image sensors based on solution-processed thin film are gaining prominence in various applications, including security detection, remote sensing, medical imaging, and environmental monitoring, owing to superior penetration capabilities of NIR light. However, the reported perovskite image sensors suffer from limited resolution and performance due to poor structural integrity, bioincompatibility, and constrained response wavelength range from lead-based perovskite materials employed. In this study, we present non-toxic quasi-single-crystal (QSC) CH(NH2)2SnI3 (FASnI3) perovskite films, prepared via a simple spin-coating technique, that demonstrate high structural integrity and effective NIR response. Through a series of in situ characterizations, we reveal that the orderly growth mode of QSC-FASnI3 perovskite films enables a more oriented crystal growth with reduced trap and grain boundaries. Consequently, self-powered NIR photodetector based on QSC-FASnI3 films exhibited large detectivity over 1013 Jones in the NIR range (780-890 nm). Ultimately, due to the high structural integrity, the high-resolution 64 × 64 (4096) pixels NIR imaging array, exhibiting reduced photo and dark response non-uniformity value, was fabricated on the thin-film transistors (TFT) backplanes, enabling ultraweak NIR light (63 nW cm-2) real-time imaging, fingerprint imaging, and hidden object recognition. This work pioneers the application of lead-free perovskite for high-resolution NIR imaging arrays.

Ultrafast spectroscopy of coherent phonons across the pressure driven insulator to metal phase transition in V2O3

Nowadays, materials science is moving towards the understanding and control of materials in nonequilibrium states by making use of perturbative techniques to investigate their dynamical responses. From this perspective, the use of ultrashort light pulses seems to be a relevant approach as it can selectively address different degrees of freedom in solid-state systems and more particularly electrons. Such a method can help to decipher the physical phenomena arising from electronic correlations and complements a more conventional methodology where the phase diagrams of materials are investigated at thermodynamical equilibrium. Here, we combine femtosecond optical spectroscopy and a high-pressure setup to monitor the ultrafast out-of-equilibrium photo response of a V2O3 thin film across the pressure driven insulator-to-metal transition. The experimental results demonstrate the possibility to use the spectroscopy of coherent phonons as a thermodynamical phase marker in V2O3 thin films. In addition, the frequency behavior of the ultrafast coherent phonon mode (A1g character) seems to reflect the manifestation of a strong coupling between the lattice and electronic degrees of freedom near first-order transition lines with a pronounced drop in frequency around the critical pressure. Published by the American Physical Society 2024

Submicron-scale Au-decorated TiO2 mesoporous spheres for enhanced photon harvesting in DSSCs through near-field enhancement, light scattering, and dye loading

Light harvesting materials are crucial for capturing the sunlight in a device such as a solar cell for better efficiency. In this study, we developed high surface area, submicron-sized TiO2 spheres (MTS) incorporated with anisotropic Au nanoparticles (Au_MTS) to create highly light-absorbing photoanodes for enhanced dye-sensitized solar cell (DSSC) efficiency. The high surface area of MTS (∼125 m2/g) allows for increased dye-loading, while their submicron size (150–300 nm) provides superior light-scattering capabilities for significantly enhancing the photoanode’s light absorption. Furthermore, incorporating of anisotropic Au nanoparticles enables broadband surface plasmon resonance (SPR) coupling, synergistically boosting photon harvesting in the Au_MTS photoanodes. The interconnected tiny TiO2 nanoparticle network in MTS supports charge carrier generation and transport, providing ample sites for dye adsorption and efficient electron pathways. Au_MTS with varying amounts of Au nanoparticles synthesized by a greener microwave-assisted synthesis method and DSSC devices were fabricated and compared with devices made from pristine MTS and P25 nanoparticles. The optimal Au_MTS device, containing ∼1.3 wt% Au nanoparticles, achieved a maximum power conversion efficiency (PCE) of ∼7.7%, representing improvements of ∼40% and ∼60% over pristine MTS (PCE of ∼5.2%) and P25 nanoparticles (PCE of ∼4.71%), respectively. Overall, this work demonstrates the effectiveness of plasmonic mesoporous photoanodes in enhancing DSSC performance through improved photo response, light scattering, and dye loading.

Inspection and comparative analysis of light and thermal response dynamics of Cu/V₂O₅/n-Si and Cu/La-V₂O₅/n-Si MIS diodes

Schottky Barrier Diodes (SBDs) are pivotal in modern electronics for their quick switching and low forward voltage drop, enabled by metal-semiconductor junctions. SBDs are renowned for their performance, primarily due to their metal-semiconductor intersection. This study focuses on Cu/V2O5/n-Si and Cu/La-V2O5/n-Si SBDs, examining the impact of lanthanum doping on their performance. Transition Metal Oxides (TMOs) like Vanadium Pentoxide (V2O5) offer unique electronic, magnetic and optical properties making them suitable for various applications. The fabrication process involved sol-gel spin coating and DC magnetron sputtering to create a thin V2O5 layer on n-type silicon wafers, followed by copper contact deposition. Galvanizing temperatures ranged 300° C to 500° C to study the structural, optical, and morphological changes in V2O5 thin films. Key findings include the significant reduction in ideality factor (n) with increasing annealing temperatures for Cu/V2O5/n-Si SBDs, reaching as low n value of 5.26 at 500°C, indicating improved device performances. For Cu/La-V2O5/n-Si SBDs, the ideality factor consistently decreased with higher light intensities, showcasing enhanced performance due to La doping. Barrier height (ɸB) also varied, with higher values observed for La-doped V2O5, enhancing charge recombination and increasing oxygen vacancies. Photodiode parameters were significantly enhanced by doping of the La. The Cu/La-V2O5/n-Si SBDs demonstrated high photosensitivity (PS = 3327.5 %), photo responsivity (R = 33.39 mA/W) and detectivity (D* = 9.82 × 10¹⁰ Jones), making them highly efficient for optoelectronic applications. Overall, this study highlights the potential of Cu/La-V2O5/n-Si SBDs for high-efficiency, optoelectronic applications, with optimized doping concentrations and annealing conditions significantly improving their performance.

Defect induced persistence photoconductivity in spray pyrolyzed ZnO thin films: Impact of Sm3+ doping

The persistent photoconductivity of the rare earth ion doped ZnO is an emerging field. The present work focuses on the effect of samarium (Sm3+) ion doping on the persistence photo response behaviour ZnO host matrix. The Zn1-xSmxO (x = 0.0 to 0.10) thin films were deposited on chemically cleaned glass substrates using spray pyrolysis technique. The films showed polycrystalline nature and hexagonal wurtzite structure without any impurity peaks. The Zn0.93Sm0.07O films showed maximum crystallite size of 24.2 nm and minimum dislocation density. The gradual change in the thickness of the fibrous nature was observed with the addition of Sm3+ ions into ZnO lattice. Energy dispersive analysis of x-ray and X-ray photoelectron spectroscopy confirmed the presence of elements and its oxidation states in the deposited film respectively. The area under the curve of deconvoluted photoluminescence spectra of deposits confirmed the decrease in the various defect percentage with increase in the doping concentration of Sm3+ ions. The photoluminescence spectra of Zn0.93Sm0.07O films showed maximum near band edge emission and minimum defects. The Zn0.93Sm0.07O films showed higher carrier concentration of 1×1017 cm−3, mobility 32 cm2/Vs and lower resistivity of 1×102 Ω cm due to improved film quality. The Zn0.93Sm0.07O films exhibited the current value under dark and ultraviolet light illumination was in the range of 10−6 A and 10−4 A respectively. The maximum photocurrent was noticed at 375 nm which corresponds to the bandgap of the deposited films. The Zn0.93Sm0.07O films showed faster photo response (5 s and 131 s of response and recovery time) due to the presence of minimum trap states. Hence the Zn0.93Sm0.07O films can be used in the fabrication of light dependent resistors and ultraviolet sensors.

Investigating the efficacy of Palladium Doped Ceria for the Photodegradation of Azo Dyes

Ceria (CeO2) was prepared by microwave assisted precipitation method while sonothermal method was utilized for the synthesis of palladium doped ceria (Pd-CeO2) photocatalyst. HR-TEM analysis confirms the face centered cubic geometry (FCC) of CeO2. The particle size of Pd-CeO2 calculated from HR-TEM analysis (7.6±2.18 nm) is in close relation with XRD (8.25±0.25 nm). The SAED pattern of Pd-CeO2 shows the poly crystallinity where the d-spacing was 0.31 and 0.30 nm which corresponds to CeO2 and Pd crystal facets 111 and 100 respectively. The amount of dopant and existence of Pd, Ce and O was confirmed from EDX spectra and elemental mapping. BET surface area analysis of CeO2 (64.45 m2/g), Pd-CeO2 (60.20 m²/g) revealed that the decrease in the surface area of CeO2 due to Pd loading which is confirmed by pore volume (0.079 cm³/g) for CeO2 and pore volume for Pd-CeO2 (0.073 cm³/g). The photocatalytic activity of Pd-CeO2 was screened against a model azo dye Acid red-4 (AR-4). The fluctuation of the rate of photodegradation (PD) of AR-4 was observed under different reaction conditions. Therefore, the reaction parameters were optimized to achieve best catalytic activity up to PD; 98%. The kinetic study suggests that the PD of AR-4 follows 1st order kinetics with regression coefficient (R2=0.973) and rate constant (k=0.024/min). Recycling study revealed the prolong use of catalyst without significant loss of activity. DFT study and experiments revealed the synergism of Pd on the photo response of CeO2. Perhaps this synergistic effect due to metal support interaction, causes redistribution of charges and Fermi energy levels. The synthesized catalyst showed potential application for the treatment of textile industrial effluents.

Spectral Analysis on Color Detection Sharpness of Animal Vision toward Polychromatic Vision System

AbstractSpectral discrimination by animal visions such as human, bird, and butterfly is numerically compared by angular analysis of photo‐response (PR) which will be recorded at photo‐receptors. Hyperspectral imaging system is utilized to simulate various animal vision. Bird vision is acute to discriminate colors among different vegetables due to its evenly spaced and narrow spectral responsivity of photo‐receptors compared to that of human. Butterfly vision is excellent in discriminating red tomato ripening due to the exclusive photo‐receptors detecting only over 600 nm. Even real and fake fruits in the same perceived color for human is discriminated by bird vision. Artificial vision with finely resolved polychromatic artificial cone cells are demonstrated surpassing human vision using visible multispectral camera. This provides insights on designing novel bio‐inspired vision system.

Ag nanoparticles at p-Si/ MAPbI3 perovskite interface: improved photo responsivity and response speed in photodetection

Although enhanced performances of photovoltaic devices by embedding metal nanoparticals in charge transport layer, doping into active layer bulk, decorating the active layer surface, and inserting at the interface between semiconductor and the electrode were reported, the effect of incorporating metal NPs at the interface of single crystal semiconductor and perovskite is rarely tackled. Herein the effects of incorporating Ag nanoparticals (AgNPs) at p-Si/MAPbI3 perovskite interface on the photodiode performances were investigated. The results showed that compared with reference device (without AgNPs) the photoresponsivity of the device incorporating AgNPs is greatly improved with the exception for light with wavelengths fall in the spectral range where AgNPs have strong optical absorption. This effect is extremely significant for relatively shorter wavelengths in visible region, and a maximal improvement of around 10.6 times in photoresponsivity was achieved. The physical origin of the exception for spectral range that AgNPs have strong optical absorption is the cancelation of scatter resulted enhancement through AgNPs by band-to-band absorption resulted reduction of photocurrent, in which the generated electron has energy near the fermi level and the hole has large effective mass, which relax by nonradiative recombination, thus making not contribution to the photocurrent. More importantly, the AgNP decorated device showed much faster photo response speed than reference device, and a maximal improvement of around 7.9 times in rise and fall time was achieved. These findings provide a novel approach for high responsive and high speed detection for weak light.

Performance improvement photodetectors with high speed and detectivity using terbium-doped ZIF-8 and MOF-5 films

Crystal engineering is critical for improving the crystal quality and tuning the optoelectronic properties of metal-organic frameworks (MOFs) materials. Doping MOFs is one of the practical approaches to improve the optoelectronic properties of MOFs. Here, a simple and effective method is used to grow MOF nanoparticles as films on the surface of the material. MOF-5 and ZIF-8 nanoparticles can be uniformly grown as films on the Si substrates. The crystalline quality of MOF films is improved after doping with Tb. Meanwhile, two-dimensional conducting photodetectors and photodetector arrays were prepared with perovskite films. Meanwhile, planar conducting photodetector arrays were prepared with MOF films. The photoluminescence (PL) intensity of the Tb-ZIF-8 and Tb-MOF-5 films shows an improvement compared to both ZIF-8 and MOF-5 layers, which leads to improved charge carriers transfer. The maximum photocurrents were about 4 × 10−8 A and 3 × 10−8 A of exposed light at 525 and 425 nm, respectively, at a fixed bias of 10 V for Tb-ZIF-8. The highest photo response of approximately 2.4 × 10−7 and 1.2 × 10−7 A was measured under 525 and 450 nm for the Tb-MOF-5-based device, respectively. The photocurrent behavior is optimized in the visible range due to the increased number of photo-generated carriers at 525 nm. The Tb-MOF-5 based device is a more powerful photodetector than the Tb-ZIF-8 based device under the same conditions. In addition, the stability of Tb-MOF-5 and Tb-ZIF-8 based photodetectors was obtained 77 % and 30 %, respectively. The photodetectors of Tb-MOF-5 have higher stability and better performance than Tb-ZIF-8.

Nonlinear optical studies of Bismuth-doped Titanium di-oxide colloids achieved by femtosecond Z-Scan technique

In this paper, we explored the nonlinear optical (NLO) properties of Bismuth (Bi) doped titanium dioxide (TiO2) nanoparticle (NP) colloids in ethanol, with laser pulses of duration ∼ 150 femtoseconds (fs). The Bi-doped TiO2 NPs were synthesized via the chemical route, sol-gel method. The increased photo response of TiO2 upon doping it with metals has become a burning issue to extend the applications of metal-doped TiO2 NPs as integral parts in solar cells, catalysts, phototherapy, etc. The bandgap of anatase TiO2 NPs was observed to be reduced to 2.89 eV upon doping Bi. The modified band structure of the Bi-doped TiO2 NPs demonstrates novel chemical, mechanical, and optical properties. NLO studies were conducted on Bismuth-doped TiO2 NPs submerged in ethanol employing femtosecond laser input pulses with incoming wavelengths 700, 750, 800, 850, 900, and 950 nm. It has been detected that open aperture (OA) studies performed at an input peak intensity of 100 MW/cm2 on Bi-doped TiO2 NPs in ethanol were exhibiting complex NLO behavior, i.e., reverse saturable absorption (RSA) in saturable absorption (SA) and SA in RSA with mostly effective two-photon absorption (1 + 1) coefficients. Particularly, at ∼800 nm, the behavior observed was so complex, i.e., RSA in SA in RSA in SA, with an effective 3 PA (2 + 1) co-efficient (γ) ∼6.5 × 10−24 m3/W2. The closed aperture (CA) studies at ∼37 MW/cm2 exhibited self-defocusing effects, i.e., an intensity-dependent refractive index (n2) with a negative signature.

Hydrothermally derived Cr-doped SnS2 layered nanoplates: investigation of their controlled structural, morphological, optical, magnetic, photo response and photocatalytic activities

A facile method has been employed to synthesize pristine and Cr-doped SnS2 (Cr: SnS2) nanoplates (Sn1-xCrxS2, here x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) and Cr: SnS2 nanoplates (NPs) were successfully synthesized via hydrothermal method. The nanoplates' structure was hexagonal, with a preference for orientation along the (001) plane; there was no evidence of additional undesirable phases. FTIR and EDX were used to observe the existence of functional groups in the samples where Sn-S bonds were present in each of the produced pristine and Cr: SnS2 nanoplates. XPS measurements demonstrated the existence of Sn, S, and Cr. FESEM revealed that the morphological properties of the nanoplates included several hexagonal grains. Magnetic characterizations showed that with increasing doping concentration of Cr, SnS2 nanoplates become superparamagnetic from ferromagnetic. The band gap values for the pristine and Cr: SnS2 nanoplates calculated from the absorbance spectra decreased from 2.53 to 2.08 eV with an increase in doping concentration. The photoluminescence spectra of the pristine SnS2 and Cr: SnS2 nanoplates exhibit two strong emission peaks at around 562 and 666 nm for an excitation wavelength of 420 nm. The Cr: SnS2 nanoplates have demonstrated the resistive behavior of the sample. The Cr: SnS2 nanoplates have shown good photocatalytic activity towards the decolorization of rhodamine B under visible irradiation.

Tracking the Photoactivity At The Interface of SiC/Poly 2(2-Thienyl) Furan Thin Solid Film in Polymer Gel Electrolytes

Assemblies made by immobilizing nanoparticles SiC into poly 2(2-thienyl) furane (PTF) were subjected to optical and electrochemical investigation. The studies show that SiC, a molecular inorganic compound, and PTF produce reproducible photo responses. Optical studies show that the optical band gap of SiC is around 2.5 eV while PTF's is around 2.2 eV. The band gap values suggest these assemblies absorb the visible solar radiation spectra. Electrochemical studies in gel electrolytes indicate that PTF and PTF/SiC under illumination show p-p behavior, where hole accumulation dominates. SiC thin films lack such character. Electrochemical Impedance Spectroscopy (EIS) studies revealed that the PTF and PTF/SiC possess kinetic and diffusional charge transfer properties. The studied assemblies and the gel electrolyte showed stability and resistance to photodegradation as evidenced by the regeneration of the same photo response after a longer period of experimentation.

Creating electron traps in BiOBr nanosheet arrays by bulk-phase F doping to restrain carrier recombination for efficient photoelectrochemical water splitting system

Bismuth oxide semiconductors in the field of photoelectrochemical (PEC) water splitting face the problems of narrow photo response range and fast carrier compounding. On the basis of the above problems, we used a solvothermal method to prepare BiOBr nanosheet arrays (NSAs), which have a special structure that facilitates carrier transport. Subsequently, the F element was introduced into the bulk phase of BiOBr using a simple hydrothermal method. The results show that the BiOBr-F photoelectrode exhibits excellent photoelectrocatalysis performance under light and bias voltage. The photocurrent density of the BiOBr-F photoelectrode reached 28.35 μA cm−2 at 1.23 V vs. RHE, which is 2.01 times higher than that of the pure BiOBr, while a negative shift of the onset potential of 119 mV was obtained. The optical absorption tests show that the introduction of the F element forms an impurity energy level thereby extending the optical absorption range of BiOBr. Photoluminescence tests reveal that the introduction of F element effectively restricts the electron-hole pair recombination. This is due tothe fact that the F atoms replace some of the O atoms in BiOBr to create electron traps, thus forming a large number of electron-rich regions in the structure, which in turn reduces the electron-hole pair recombination. This work provides an effective solution to reduce the recombination between carriers by creating electron traps in semiconductor materials through bulk phase doping.

Oxygen desorption enabled visible light sensing in embossed TiO2 nanogratings fabricated via thermal nanoimprinting

In this work, the fabrication of the nanoimprinted titanium dioxide (TiO2) gratings via thermal nanoimprinting lithography method (T-NIL) and its visible light response are studied. A polydimethylsiloxane (PDMS) primary mould, which in turn made via pattern transfer of micro/nano tracks present in the optical discs is used in T-NIL process. A transparent TiO2 film on a FTO substrate was subjected to pattern transfer from the PDMS mould. The imprinted TiO2 was post annealed to obtain anatase phase. The optical properties and photo response behaviour of plain and nanoimprinted TiO2 films were measured and compared. Raman spectroscopy measurements indicated the surface enhanced Raman scattering in imprinted samples. The imprinted TiO2 showed reduced reflectance compared to plain TiO2 films due to the increased light path length because of multiple reflections leading to in coupling of light. Photo response was observed under visible light illumination conditions, wherein imprinted TiO2 films showed appreciable photocurrent, which is otherwise very minimal in plain TiO2. The visible light photosensing in imprinted TiO2 occur due to the oxygen adsorption-desorption during the post deposition annealing and under illumination respectively. This work makes use of low-cost PDMS primary mould and T-NIL at favourable temperature and pressure conditions with a promising outlook for fabricating imprinted TiO2 with photo sensing ability and adaptability for large area upscaling.

MoS2-CdS composite for photocatalytic reduction of hexavalent chromium and thin film optoelectronic device applications

We introduce an enhanced light-harvesting MoS2-based nanocomposite exhibiting improved solar light induced photocurrent generation, both in solution and solid phases. The MoS2-CdS composite was synthesized via easy to achieve, cost effective, two-step solution process for the photocatalytic potassium dichromate [Cr(VI)] reduction and photocurrent generation in thin-film optoelectronic devices. Incorporating 10 wt% MoS2 into the composite increased the degradation efficiency of CdS from 43.9 to 91.9%. Furthermore, the MoS2-CdS composite demonstrated a 2.88-fold increase in the degradation rate constant and a 2.15% enhancement in the apparent quantum yield compared to controlled CdS. Additionally, the electrical power consumption per order decrease in Cr(VI) reduced from 25.74 kWh m−3 for controlled CdS to 9 kWh m−3 aimed at 10 wt% MoS2-CdS composite, indicating optimal synergy between the counterparts of MoS2-CdS in its composite. The resulting thin-film device with 10 wt% MoS2-CdS exhibited robust photocurrent generation and nonlinear I–V characteristics under solar illumination, attributed to the unique electronic properties of the MoS2-CdS heterojunction, influencing carrier transport via band alignment and interface carrier trapping effects. Moreover, photocurrent generation increased linearly with illumination intensity, and dynamic photo response studies revealed rapid photocurrent generation under illumination. Furthermore, the optoelectronic key parameters of CdS, including photosensitivity, photoresponsivity, and detectivity, were enhanced by factors of 5.09, 3.33, and 12.3, respectively, upon composite formation with MoS2. This study offers novel insights into developing high-performance and cost-effective bimetallic sulfide photocatalysts for efficient solar light-induced photocurrent generation in both solution and solid phases.

MBE-grown ZnTe epitaxial layer based broadband photodetector with high response and excellent switching characteristics

Zinc telluride (ZnTe) epitaxial layers were grown on gallium arsenide (GaAs) (211) substrate at different growth temperatures by molecular beam epitaxy. The fabricated interdigitated metal semiconductor metal configuration-based photodetector (PD) on ZnTe epitaxial layers exhibited a stable and excellent photo response in a broad spectral range (250–550 nm) up to 125 °C. The room temperature and higher temperature (125 °C) values of maximum current, spectral responsivity and detectivity at an applied bias of 5 V and 550 nm wavelength were 3.5 × 10−8 A, 0.1 A W−1 and 1 × 1011 Jones and 1.7 × 10−6 A, 2.5 A W−1 and 1.5 × 1011 Jones, respectively. The maximum photo-to-dark-current ratio (PDCR) value at zero bias and 100 °C was obtained for the ZnTe layer grown at an optimum growth temperature of 380 °C. The high PDCR value exhibits the self-powered capability of the detector. Furthermore, the detector exhibits good on–off switching to the illuminating light with rise and decay times less than 0.29 s and 0.4 s, respectively, at room temperature. The dependence of the photo response on material quality was analysed by varying the substrate growth temperature. The broadband responsivity of the ZnTe-based PD shows its capability as a multicolour detector in the UV and visible region with the use of suitable blocking filters.

Lead-Free Nanocrystal Inks for Flexible Optoelectronic Devices

The exploration of AgBiS2 quantum dots (QDs) as an environmentally friendly alternative to previously-explored infrared-absorbing QDs has continued to gain interest in the past few years. Applications in optoelectronic devices are facilitated by colloidally stable inks that can be used to deposit films with favorable material properties on diverse substrates, including flexible substrates applicable to lightweight and wearable sensors. Here, we demonstrate that a rapid biphasic ligand exchange process can be used to make a AgBiS2 QD ink. The properties of deposited films are explored in lateral photoconductive devices and in heterojunction photovoltaic devices. In addition to this, we also demonstrated the use of this environmentally benign QD ink in flexible devices: the photo response was unchanged when the device was flat or bent. These results demonstrate the versatility of solution-phase ligand exchange approaches to QD-based optoelectronic devices.

Facile SILAR deposited SnS/NiS vertical heterojunction for high performance flexible broadband photodetector

Low-cost, flexible broadband photodetectors fabricated from two-dimensional transition metal chalcogenides have garnered attention because of their excellent absorption coefficient and photoconductivity. Likewise, vertical heterojunctions fabricated from two two-dimensional (2D) transition metal chalcogenides (TMCs) also have drawn major curiosity lately owing to their superior optical performance. This work reports a p-p type II vertical Van der Waal's heterojunction structure by depositing thin film of NiS over SnS on a flexible paper substrate. Morphological and structural characterization confirms presence of a rhombohedral β-NiS crystal structure along with traces of Ni(OH)2 on orthorhombic SnS nanoparticles. The device fabrication method made use of the inexpensive, clean room free SILAR (Successive Ionic Layer Adsorption and Reaction) technique. A purposeful modification of narrow bandgap property of NiS is done by depositing it in an alkaline environment. The fabricated device records optical responsivity of 0.92 mA/W under UV illumination, 5.32 mA/W under Visible illumination, and 0.8 mA/W under NIR illumination. A maximum EQE of 1.3 % is observed along with superior response times of 0.114 s (UV),0.103 s (Visible) and 1.34 s (NIR). The acquired photo response is due to superior absorption property of NiS in UV region and SnS in the visible and NIR region. The difference in fermi level between two materials causes efficient separation of the charge carriers that results in junctional electric field upon light illumination. The device underwent flexibility testing and shown exceptional resistance to bending force making it suitable for numerous applications like wearable healthcare monitoring, security purposes and flexible image sensors.

(Invited) Nanohybrid Carbon Nanotube and P3HT Composite Semiconductor Materials for Solution Processed Optoelectronics

Carbon nanotube networks have demonstrated promise for enabling printable transistors which can be utilized as switching elements within active matrices. Such active matrices have been utilized for controlling pixels and interrogating sensor elements. A new promising technology for imaging, called an active pixel matrix, aims to integrate both the underlying transistor and sensor element within a single device, namely a phototransistor. Carbon nanotubes are poised to enable printable active pixel matrices for sensing applications, however, due to minimal absorption a secondary material needs to be added as a photo synthesizer. Additionally, the material must be sufficiently electrically coupled with the carbon nanotube network to allow for efficient carrier extraction. Our lab has previously developed techniques for crystallizing P3HT directly onto carbon nanotubes using solution-phase soft epitaxy. In this work, the solution phased technique has been adapted to functional carbon nanotube networks already deposited onto a surface.I will present the performance of a device that consists of a solution-processed carbon nanotube network, which acts as the carrier extraction layer, and a surface crystalized P3HT, which acts as the absorption element. First, I will detail the fabrication scheme and soft-epitaxial method of polymer crystallization. Next, I will overview how the P3HT crystallization affects the electronic performance of the devices, including the photo response. The device exhibits high responsivity, with a maximum responsivity value of 3 x 105. Additionally, the device exhibits a wide spectral response within the visible range, due to the exciton generation at the P3HT/CNT interface. I will also present the transient response of the device, which provides insight into the role of carrier injection/trapped states within the material.Lastly, I will discuss the potential applications for an active matrix of phototransistors, including neuromorphic computing. In these specific applications, the semiconductor can be utilized as the functional material within an Organic Electrochemical Transistor (OECT), where it exhibits behavior associated with mixed ionic/electronic conduction (MEIC). I will benchmark the performance, and discuss various methods to fabricated charge trapped switches, a key memory/computational element for future neuromorphic architectures.

Liquid phase exfoliation of few-layer borophene with high hole mobility for low-power electronic devices

Borophene, the two-dimensional allotrope of boron, has garnered significant interest in recent years due to its exceptional electronic, mechanical, and optical properties. In this work, an environment-friendly green approach has been utilized to synthesize p-type borophene, which consists of few layers as evidenced by electron and atomic force microscopic images. The Raman analysis indicated that these borophene layers possess β12 and χ3 phases. The photoemission spectra of these samples exhibit single exponential decay with a long lifetime of 7.2 µsec, showcasing its potential as a phosphorescent material in optoelectronics and quantum technologies. The photo-sensing capability of borophene was investigated by fabricating a Si/SiO2/Borophene/Ti/Pt photo-detector, which achieved an external quantum efficiency of 31 %, maximum photo responsivity of 200 mAW−1 and detectivity of 8.7x1011 Jones. Hall effect van der Pauw measurements revealed the p-type conductivity of the borophene film, along with a high hole mobility of 931.44 cm2V-1s−1 and a charge carrier density of 2 x 1012 cm−3, rendering these layers suitable for high-speed and low power electronic devices. This work emphasizes the importance of novel 2D materials like borophene with exceptional optoelectronic characteristics for developing future low-power electronic devices with remarkable performance.