Browsing by Author "Mohite, Aditya D."
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Item Bacteria as Bio-Template for 3D Carbon Nanotube Architectures(Springer Nature, 2017) Ozden, Sehmus; Macwan, Isaac G.; Owuor, Peter S.; Kosolwattana, Suppanat; Autreto, Pedro A.S.; Silwal, Sushila; Vajtai, Robert; Tiwary, Chandra S.; Mohite, Aditya D.; Patra, Prabir K.; Ajayan, Pulickel M.It is one of the most important needs to develop renewable, scalable and multifunctional methods for the fabrication of 3D carbon architectures. Even though a lot of methods have been developed to create porous and mechanically stable 3D scaffolds, the fabrication and control over the synthesis of such architectures still remain a challenge. Here, we used Magnetospirillum magneticum (AMB-1) bacteria as a bio-template to fabricate light-weight 3D solid structure of carbon nanotubes (CNTs) with interconnected porosity. The resulting porous scaffold showed good mechanical stability and large surface area because of the excellent pore interconnection and high porosity. Steered molecular dynamics simulations were used to quantify the interactions between nanotubes and AMB-1 via the cell surface protein MSP-1 and flagellin. The 3D CNTs-AMB1 nanocomposite scaffold is further demonstrated as a potential substrate for electrodes in supercapacitor applications.Item Cavity-control of interlayer excitons in van der Waals heterostructures(Springer Nature, 2019) Förg, Michael; Colombier, Léo; Patel, Robin K.; Lindlau, Jessica; Mohite, Aditya D.; Yamaguchi, Hisato; Glazov, Mikhail M.; Hunger, David; Högele, AlexanderMonolayer transition metal dichalcogenides integrated in optical microcavities host exciton-polaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe2-WSe2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavity – van der Waals heterostructure systems.Item Design principles for electronic charge transport in solution-processed vertically stacked 2D perovskite quantum wells(Springer Nature, 2018) Tsai, Hsinhan; Asadpour, Reza; Blancon, Jean-Christophe; Stoumpos, Constantinos C.; Even, Jacky; Ajayan, Pulickel M.; Kanatzidis, Mercouri G.; Alam, Muhammad Ashraful; Mohite, Aditya D.; Nie, WanyiState-of-the-art quantum-well-based devices such as photovoltaics, photodetectors, and light-emission devices are enabled by understanding the nature and the exact mechanism of electronic charge transport. Ruddlesden-Popper phase halide perovskites are two-dimensional solution-processed quantum wells and have recently emerged as highly efficient semiconductors for solar cell approaching 14% in power conversion efficiency. However, further improvements will require an understanding of the charge transport mechanisms, which are currently unknown and further complicated by the presence of strongly bound excitons. Here, we unambiguously determine that dominant photocurrent collection is through electric field-assisted electron-hole pair separation and transport across the potential barriers. This is revealed by in-depth device characterization, coupled with comprehensive device modeling, which can self-consistently reproduce our experimental findings. These findings establish the fundamental guidelines for the molecular and device design for layered 2D perovskite-based photovoltaics and optoelectronic devices, and are relevant for other similar quantum-confined systems.Item Direct visualization of ultrafast lattice ordering via resonant electron-phonon coupling in 2D hybrid perovskites(2021-08-25) Zhang, Hao; Mohite, Aditya D.Understanding and tracing the dynamic interactions between charge carriers and crystal lattice has remained a challenge in photo-excited semiconductors. Specifically, a direct visualization of carrier-lattice interactions (electron-phonon coupling) provides crucial insights in such as hot-carrier lifetime and recombination rates, which are key factors for device fabrications. In this study, we’ve monitored the transient structural response of two-dimensional perovskites (2DPKs) by tracking the evolution of the wavevector-resolved electron diffraction patterns, through femtosecond ultrafast electron diffraction (UED). Analysis of the Bragg peak intensities reveals a unique positive response, suggesting an ultrafast lattice ordering resulting from a resonant transfer from hot-carriers to perovskite lattice. Simulated structural response and calculation of vibrational modes may reveal the presence of non-polar optical phonons, which induces in-plane octahedral tilts and a reduction of distortion toward symmetrized phase, consistent with the predicted electron-phonon interactions through optical deformation potential via non-polar modes. Finally, we show the strength and the dynamics of the reported electron-phonon coupling process can be further tailored via alternating the organic layers of 2D perovskites, resulting in difference in mechanical rigidity and intrinsic distortions. This study on the structural dynamics of 2D perovskites may provide fundamental information on tailoring specific electron-phonon coupling channels, paving a pathway for the design of efficient perovskite-based opto-electronic devices.Item Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction(Springer Nature, 2016) Cummins, Dustin R.; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K.; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K.; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D.; Sunkara, Mahendra K.; Gupta, GautamItem High-phase purity two-dimensional perovskites with 17.3% efficiency enabled by interface engineering of hole transport layer(Elsevier, 2021) Sidhik, Siraj; Wang, Yafei; Li, Wenbin; Zhang, Hao; Zhong, Xinjue; Agrawal, Ayush; Hadar, Ido; Spanopoulos, Ioannis; Mishra, Anamika; Traoré, Boubacar; Samani, Mohammad H. K.; Katan, Claudine; Marciel, Amanda B.; Blancon, Jean-Christophe; Even, Jacky; Kahn, Antoine; Kanatzidis, Mercouri G.; Mohite, Aditya D.State-of-the-art p-i-n-based 3D perovskite solar cells (PSCs) use nickel oxide (NiOX) as an efficient hole transport layer (HTL), achieving efficiencies >22%. However, translating this to phase-pure 2D perovskites has been unsuccessful. Here, we report 2D phase-pure Ruddlesden-Popper BA2MA3Pb4I13 perovskites with 17.3% efficiency enabled by doping the NiOX with Li. Our results show that progressively increasing the doping concentration transforms the photoresistor behavior to a typical diode curve, with an increase in the average efficiency from 2.53% to 16.03% with a high open-circuit voltage of 1.22 V. Analysis reveals that Li doping of NiOX significantly improves the morphology, crystallinity, and orientation of 2D perovskite films and also affords a superior band alignment, facilitating efficient charge extraction. Finally, we demonstrate that 2D PSCs with Li-doped NiOX exhibit excellent photostability, with T99 = 400 h at 1 sun and T90 of 100 h at 5 suns measured at relative humidity of 60% ± 5% without the need for external thermal management.Item Highly efficient photoelectric effect in halide perovskites for regenerative electron sources(Springer Nature, 2021) Liu, Fangze; Sidhik, Siraj; Hoffbauer, Mark A.; Lewis, Sina; Neukirch, Amanda J.; Pavlenko, Vitaly; Tsai, Hsinhan; Nie, Wanyi; Even, Jacky; Tretiak, Sergei; Ajayan, Pulickel M.; Kanatzidis, Mercouri G.; Crochet, Jared J.; Moody, Nathan A.; Blancon, Jean-Christophe; Mohite, Aditya D.Electron sources are a critical component in a wide range of applications such as electron-beam accelerator facilities, photomultipliers, and image intensifiers for night vision. We report efficient, regenerative and low-cost electron sources based on solution-processed halide perovskites thin films when they are excited with light with energy equal to or above their bandgap. We measure a quantum efficiency up to 2.2% and a lifetime of more than 25 h. Importantly, even after degradation, the electron emission can be completely regenerated to its maximum efficiency by deposition of a monolayer of Cs. The electron emission from halide perovskites can be tuned over the visible and ultraviolet spectrum, and operates at vacuum levels with pressures at least two-orders higher than in state-of-the-art semiconductor electron sources.Item Hybrid graphene metasurfaces for high-speed mid-infrared light modulation and single-pixel imaging(Springer Nature, 2018) Zeng, Beibei; Huang, Zhiqin; Singh, Akhilesh; Yao, Yu; Azad, Abul K.; Mohite, Aditya D.; Taylor, Antoinette J.; Smith, David R.; Chen, Hou-TongDuring the past decades, major advances have been made in both the generation and detection of infrared light; however, its efficient wavefront manipulation and information processing still encounter great challenges. Efficient and fast optoelectronic modulators and spatial light modulators are required for mid-infrared imaging, sensing, security screening, communication and navigation, to name a few. However, their development remains elusive, and prevailing methods reported so far have suffered from drawbacks that significantly limit their practical applications. In this study, by leveraging graphene and metasurfaces, we demonstrate a high-performance free-space mid-infrared modulator operating at gigahertz speeds, low gate voltage and room temperature. We further pixelate the hybrid graphene metasurface to form a prototype spatial light modulator for high frame rate single-pixel imaging, suggesting orders of magnitude improvement over conventional liquid crystal or micromirror-based spatial light modulators. This work opens up the possibility of exploring wavefront engineering for infrared technologies for which fast temporal and spatial modulations are indispensable.Item Hybrid Perovskite Materials for Stable Optoelectronics Applications(2018-04-20) Tsai, Hsinhan; Ajayan, Pulickel M.; Lou, Jun; Mohite, Aditya D.Organic-inorganic hybrid perovskites materials have grab enormous attention in the material research community. This is because of their exceptional semiconducting properties such as direct band gap, free carrier generation, broad absorption range, long diffusion length and carrier lifetime, which enable highly efficient photovoltaic device over 22%, surpassing other classical semiconductors in few years. However, one fundamental bottleneck remains in this system that mitigates such material from wide use that are reproducibility, photo- and chemical instability. These are found to be closely related to the structure of the material, such as the hydroscopic nature of the organic cation, symmetry of the crystal structure and degree of thin film crystallinity. Therefore, the focus of this thesis is to understand the basic mechanism in structure that dominate the stability of perovskites materials properties and design robust hybrid perovskite structures through organic cation engineering. Through synthetic approach, we found that the bulky organic molecules can be inserted to the perovskite lattice, forming a layered structure with quantum and dielectric confinement, called Ruddlesden-Popper (RP) perovskites. Employing our previously developed hot-casting method, we were able to obtain near single crystalline thin film with preferred orientation. With the protection of the bulky molecules, the stability of the perovskite layers is much extended. Beyond the photovoltaics, the oriented, highly crystalline thin film can facilitate the current injection in light-emitting diodes (LEDs) which had high radiance with 1 % EQE in device performance. The devices also had low turn-on voltage which can decrease the energy consumption and benefit to lighting applications. This thesis demonstrates the detail solutions for fundamental problems and the research results can help to promote technologies and push the limits in hybrid perovskites optoelectronics society.Item Long periodic ripple in a 2D hybrid halide perovskite structure using branched organic spacers(Royal Society of Chemistry, 2020) Hoffman, Justin M.; Malliakas, Christos D.; Sidhik, Siraj; Hadar, Ido; McClain, Rebecca; Mohite, Aditya D.; Kanatzidis, Mercouri G.Two-dimensional (2D) halide perovskites have great promise in optoelectronic devices because of their stability and optical tunability, but the subtle effects on the inorganic layer when modifying the organic spacer remain unclear. Here, we introduce two homologous series of Ruddlesden–Popper (RP) structures using the branched isobutylammonium (IBA) and isoamylammonium (IAA) cations with the general formula (RA)2(MA)n−1PbnI3n+1 (RA = IBA, IAA; MA = methylammonium n = 1–4). Surprisingly, the IAA n = 2 member results in the first modulated 2D perovskite structure with a ripple with a periodicity of 50.6 Å occurring in the inorganic slab diagonally to the [101] direction of the basic unit cell. This leads to an increase of Pb–I–Pb angles along the direction of the wave. Generally, both series show larger in-plane bond angles resulting from the additional bulkiness of the spacers compensating for the MA's small size. Larger bond angles have been shown to decrease the bandgap which is seen here with the bulkier IBA leading to both larger in-plane angles and lower bandgaps except for n = 2, in which the modulated structure has a lower bandgap because of its larger Pb–I–Pb angles. Photo-response was tested for the n = 4 compounds and confirmed, signaling their potential use in solar cell devices. We made films using an MACl additive which showed good crystallinity and preferred orientation according to grazing-incidence wide-angle scattering (GIWAXS). As exemplar, the two n = 4 samples were employed in devices with champion efficiencies of 8.22% and 7.32% for IBA and IAA, respectively.Item Metallic 1T phase source/drain electrodes for field effect transistors from chemical vapor deposited MoS2(AIP, 2014) Kappera, Rajesh; Voiry, Damien; Yalcin, Sibel Ebru; Jen, Wesley; Acerce, Muharrem; Torrel, Sol; Branch, Brittany; Lei, Sidong; Chen, Weibing; Najmaei, Sina; Lou, Jun; Ajayan, Pulickel M.; Gupta, Gautam; Mohite, Aditya D.; Chhowalla, ManishTwo dimensional transitionmetal dichalcogenides (2D TMDs) offer promise as optoelectronic materials due to their direct band gap and reasonably good mobility values. However, most metals form high resistance contacts on semiconducting TMDs such as MoS2. The large contact resistance limits the performance of devices. Unlike bulk materials, low contact resistance cannot be stably achieved in 2D materials by doping. Here we build on our previous work in which we demonstrated that it is possible to achieve low contact resistance electrodes by phase transformation. We show that similar to the previously demonstrated mechanically exfoliated samples, it is possible to decrease the contact resistance and enhance the FET performance by locally inducing and patterning the metallic 1T phase of MoS2 on chemically vapor deposited material. The device properties are substantially improved with 1T phase source/drain electrodes.Item Revealing the impact of ammonium ions from different low-dimensional perovskite structures on the film formation and degradation mechanism of FAPbI3 via sequential deposition(AIP Publishing LLC, 2024) Wang, Yafei; Yuan, Shihao; Feng, Rongsen; Diao, Zecheng; Huang, Jie; Liao, Jiacai; Sidhik, Siraj; Shuai, Xinting; Wang, Meicong; Zou, Tao; Liang, Zhongwei; Zhang, Ting; Mohite, Aditya D.; Li, ShibinIn recent years, the organic–inorganic hybrid perovskite community has been widely employed as the photo-active layer in optical-electronic devices. The black α-phase formamidinium lead iodide (FAPbI3) is the most popular perovskite for realizing high-efficiency solar cells due to its suitable bandgap. However, the issue of stability is also a concern in the research on FAPbI3 solar cells. In this study, different ammonium ions, such as butylamine (BA), guanidine (GA), and butylene diamine (BDA), which are commonly used to construct two-dimensional perovskites, including Ruddlesden–Popper, Dion–Jacobson, and alternating cations in the interlayer space, respectively, were introduced in the fabrication of FAPbI3 using a sequential deposition method. Several structures of PbI2 precursor films were formed by introducing the aforementioned ions, which exhibited different arrangements and connection modes in lead iodides. BA-PbI2 precursor films exhibited higher specific surface areas, which were beneficial to the diffusion, ion exchange, and sequential reaction of FA+. The BDA-PbI2 precursor film slowed down the sequential reaction of FAPbI3 because of reduced van der Waals bonds. The nucleation dynamics and degradation processes of perovskites were deeply investigated in this study. Solar cells based on BA-PbI2, GA-PbI2, and BDA-PbI2 were also fabricated.Item Supramolecular block copolymer photovoltaics through ureido-pyrimidinone hydrogen bonding interactions(Royal Society of Chemistry, 2016) Lin, Yen-Hao; Nie, Wanyi; Tsai, Hsinhan; Li, Xiaoyi; Gupta, Gautam; Mohite, Aditya D.; Verduzco, RafaelA challenge in the development of bulk heterojunction organic photovoltaics (BHJ OPVs) is achieving a desirable nanoscale morphology. This is particularly true for polymer blend OPVs in which large-scale phase separation occurs during processing. Here, we present a versatile approach to control the morphology in polymer blend OPVs through incorporation of self-associating 4 2-ureido-4[1H]-pyrimidinone (UPy) endgroups onto donor and acceptor conjugated polymers. These UPy functionalized polymers associate to form supramolecular block copolymers during solution blending and film casting. Atomic force microscopy measurements show that supramolecular associations can improve film uniformity. We find that the performance of supramolecular block copolymer OPVs improves from 0.45% to 0.77% relative to the non-associating conjugated polymer blends at the same 155 °C annealing conditions. Impedance measurements reveal that UPy endgroups both increase the resistance for charge recombination and for bulk charge transport. This work represents a versatile approach to reducing large-scale phase separation in polymer–polymer blends and directing the morphology through supramolecular interactions.Item Embargo Synthesis of Halide 2D perovskite via kinetics and thermodynamics control(2024-04-15) Hou, Jin; Mohite, Aditya D.; Tang, MingTwo-dimensional halide perovskites have emerged as a “trending topic” low-dimensional semiconductors material in the past decade, for they exhibit a combination of properties – high structure tunability, flexible composition engineering, quantum wells, 2D materials, organic semiconductors, high stability, etc. Its unique structure and property have offered enormous research potential in fundamental physics, material science, chemistry, and photovoltaic device engineering. This thesis aims to explore and develop the synthesis of 2D perovskites, including improving the phase purity of 2D perovskites crystals, realizing the synthesis of 2D perovskite with high perovskite layer-thickness, and inventing novel 2D perovskites with various strategies. Firstly, this thesis addressed a major challenge in the 2D perovskite synthesis which is producing 2D perovskite crystals with desired perovskite-layer thicknesses (quantum well thickness, also known as n values) greater than two. A novel method termed kinetically controlled space confinement (KCSC) for the growth of phase pure 2D perovskites of desired n values for both RP and DJ is introduced. Through this method a transformation from lower n to higher n in 2D perovskites is also demonstrated. Those finding will enable reproducible synthesis of 2D perovskites, specifically for n>4, which is very significant as the higher n 2D perovskites have narrower band gap and higher electrical conductivity, and those parameters are the most crucial factors for application in electronic devices. In the second part, a novel 2D perovskite series with formamidinium (FA) as cage cation is demonstrated. This series of 2D perovskite has the smallest bandgap among all the reported 2D perovskite. Its structure is perfectly linear with no distortion, taking a space group of p4/mmm (tetragonal) which is the maximum symmetry that can be achieved theoretically in 2D perovskite. This novel 2D behaves like a 3D one from all the perspectives, including structure, lattice softness, charge transport. The combination of low band gap with high stability makes it an outstanding candidate for solar cells, both single junction and tandems. Finally, this thesis presents a unique “n=1.5” 2D perovskites, which exhibit an intrinsic multi-layer thickness structure, consisting of alternating n=1 and n=2 layers. This unique structure provides an exciting platform to study the excitons, energy funneling and has huge potential for lasering applications. A new horizon for perovskites research is opened up with a lot of exploration and development on the way.Item Ternary CuIn7Se11: Towards Ultra-Thin Layered Photodetectors and Photovoltaic Devices(Wiley, 2014) Lei, Sidong; Sobhani, Ali; Wen, Fangfang; George, Antony; Wang, Qizhong; Huang, Yihan; Dong, Pei; Li, Bo; Najmaei, Sina; Bellah, James; Gupta, Gautam; Mohite, Aditya D.; Ge, Liehui; Lou, Jun; Halas, Naomi J.; Vajtai, Robert; Ajayan, Pulickel2D materials have been widely studied over the past decade for their potential applications in electronics and optoelectronics. In these materials, elemental composition plays a critical role in defining their physical properties. Here we report the first successful synthesis of individual high quality CuIn7Se11 (CIS) ternary 2D layers and demonstrate their potential use in photodetection applications. Photoconductivity measurements show an indirect bandgap of 1.1 eV for few-layered CIS, an external quantum efficiency of 88.0 % with 2 V bias across 2 μm channel with and a signal-to-noise ratio larger than 95 dB. By judicious choice of electrode materials, we demonstrate the possibility of layered CIS-based 2D photovoltaic devices. This study examines this ternary 2D layered system for the first time, demonstrating the clear potential for layered CIS in 2D material-based optoelectronic device applications.Item Titanium oxide improves boron nitride photocatalytic degradation of perfluorooctanoic acid(Elsevier, 2022) Duan, Lijie; Wang, Bo; Heck, Kimberly N.; Clark, Chelsea A.; Wei, Jinshan; Wang, Minghao; Metz, Jordin; Wu, Gang; Tsai, Ah-Lim; Guo, Sujin; Arredondo, Jacob; Mohite, Aditya D.; Senftle, Thomas P.; Westerhoff, Paul; Alvarez, Pedro; Wen, Xianghua; Song, Yonghui; Wong, Michael S.; Center for Nanotechnology Enabled Water TreatmentBoron nitride (BN) has the newly-found property of degrading recalcitrant polyfluoroalkyl substances (PFAS) under ultraviolet C (UV-C, 254 nm) irradiation. It is ineffective at longer wavelengths, though. In this study, we report the simple calcination of BN and UV-A active titanium oxide (TiO2) creates a BN/TiO2 composite that is more photocatalytically active than BN or TiO2 under UV-A for perfluorooctanoic acid (PFOA). Under UV-A, BN/TiO2 degraded PFOA ∼ 15 × faster than TiO2, while BN was inactive. Band diagram analysis and photocurrent response measurements indicated that BN/TiO2 is a type-II heterojunction semiconductor, facilitating charge carrier separation. Additional experiments confirmed the importance of photogenerated holes for degrading PFOA. Outdoor experimentation under natural sunlight found BN/TiO2 to degrade PFOA in deionized water and salt-containing water with a half-life of 1.7 h and 4.5 h, respectively. These identified photocatalytic properties of BN/TiO2 highlight the potential for the light-driven destruction of other PFAS.Item Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes(Macmillan Publishers Limited, 2016) Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D.; Boubanga-Tombet, Stephane; Blancon, Jean-Christophe; Najmaei, Sina; Ajayan, Pulickel M.; Lou, Jun; Taylor, Antoinette J.; Prasankumar, Rohit P.We have performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. The ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems.