Metamaterials which are artificially structured subwavelength particles capable of manipulating light have enabled novel nanophotonic phenomena not possible with conventional materials. Metasurfaces which are 2D planar metamaterials consisting of thin layers of optically resonant structures arranged in a periodic pattern can capture and control lightwave to realize various nanophotonic phenomena. In contrast to plasmonic materials, dielectric metamaterials have high refractive index and most importantly support distinct electric and magnetic Mie-type resonances. This offers additional degree of freedom in tailoring light-matter interactions at the nanoscale. In addition, traditional dielectrics such as silicon are compatible with CMOS devices making it easy to integrate into practical devices.
Herein, I propose metaphotonic devices based on dielectric metasurfaces for nanoscale manipulation of light. First, I developed a fundamentally new route to achieve high Q-factor transparency window without resorting to positional displacement of resonators to excite the sub radiant dark modes of the system, which is a pre-requisite for traditional EIT metasurface. Instead, interference between bright and dark mode is enabled by a slot which also can be used to tune the amplitude and linewidth of the transparency window. Furthermore, I show the effect of lattice symmetry on the Q-factor of the transparency window.
Next, I demonstrate a route to achieve structural colors by exploiting anapole modes in a nanodisk made from the perovskite, methylammonium lead triiodide.
Furthermore, I show that by careful design and introduction of a split gap and exploitation of collective modes in a metasurface made from such nanodisk, anti-Hermitian coupling between the two halves of the disk can be achieved, leading spectrally sharp absorption spectra which is important for high performance compact structural color pixels with reduced optical crosstalk.
Lastly, I propose using a perovskite as base material for a tunable high efficiency metalens which is capable of focusing incident light to diffraction limited spots. Specifically, I designed a tunable polarization insensitive metalens made of nanopillars of cesium lead tribromide operating in the visible regime. Through ion exchange, the halide atom can be replaced by either an iodide or a chloride, achieving focusing efficiencies as high as 89%.

Two-terminal monolithic perovskite-silicon tandem solar cells have the potential to reduce the levelized cost of energy of today’s mainstream photovoltaic systems by 10%–18%. This can be enabled by adding a low-cost wide-bandgap perovskite cell on top of a commercial silicon cell to significantly increase its theoretical efficiency limit by utilizing a wider range of the solar spectrum.

While numerous lab-scale tandem cells with efficiencies ≥ 30% have been demonstrated, they still need to scale to full area, high throughput, excellent yield, and have stability on par with silicon cells.This dissertation focuses on scaling two-terminal tandems to full area (i.e., ≥ 220 cm2) by slot-die coating the perovskite layer on industry-relevant silicon bottom cell surfaces. Four key scaling strategies are implemented to achieve a uniform and high tandem efficiency across a commercial cell size. The first strategy is the addition of nanotexture to boost the tandem's short-circuit density; the second is the management of high-risk microscopic perovskite film defects; the third is fabricating semi-conformal perovskite films that can handle rough silicon bottom cell surfaces (i.e., before adding nanotexture); and the fourth is thickening the perovskite film by two to three folds to further improve film coverage.

The best 1 cm2 tandem achieved an efficiency of 26.3%, and across an M2-sized (i.e., 243 cm2) silicon wafers, the average efficiency was 22% with a standard deviation of 3.7%. This work demonstrates a pathway to scale tandems via slot-die coating and offers recommendations aimed at realizing high manufacturing yield.

Refractory high entropy alloys (RHEAs) have emerged as a promising class of structural materials, demonstrating exceptional mechanical performance in aggressive environments. However, the complex atomic environments, significant lattice distortion, and vast compositional space of RHEAs present challenges to understanding the mechanisms that govern structure-property relationships. In this work, two machine-learning potentials (MLPs) for MoNbTaW and MoNbTaWV RHEAs were developed. The MLPs were rigorously validated against lattice constants, elastic constants, generalized stacking fault energies, thermodynamic properties and screw dislocation core structures. Molecular dynamics simulations with the developed MLPs were applied to study the microstructural evolution and deformation mechanisms in MoNbTaW and MoNbTaWV RHEAs. Atomistic simulations revealed the influence of the chemical composition and local ordering on the mobility of edge and screw dislocations, as well as the effects of lattice distortion and diffuse anti-phase boundary energy (DAPBE) on dislocation behaviors during nanostructural evolution. Notably, with the increase in Nb concentration in the MoNbTaW RHEAs, DAPBE and lattice distortion are simultaneously enhanced as the chemical short-range order evolves into nanoscale B2 precipitates. This evolution results in high lattice distortion due to the lattice mismatch between B2 precipitates and random matrix. Consequently, B2 nanoprecipitates provide a stronger pinning effect, hindering edge dislocation motion while promoting cross-slip of screw dislocations, leading to a reduced screw-to-edge ratio in slip resistance and mobility discrepancy. Based on the mechanisms, a high-throughput exploration of the MoNbTaW RHEA system was conducted to identify candidates with reduced screw-to-edge discrepancy. To accelerate these explorations, a graph neural network model was developed to enhance Monte-Carlo simulations for ordered states, enabling more efficient identification of stable atomic configurations.
In the MoNbTaWV RHEAs, Monte-Carlo simulations reveal that Mo-Ta pairs are still the most favorable, with ordering limited to short-range interaction. Dislocation simulations indicate that adding V to MoNbTaW RHEAs reduces the mobility of both edge and screw dislocations. The increased lattice distortion accounts for the decreased edge dislocation mobilities. And the increased lattice distortion also promotes the diffusivity of alloys by decreasing the vacancy migration barriers. This increased diffusivity promotes kink-pair nucleation on multiple planes, leading to cross-kinking, which further slows screw dislocation mobility.

The rapid advancement of technological innovation has led to increasingly complex supply chains, making them more vulnerable to threats such as counterfeiting and tampering. This has heightened the demand for robust, unclonable identifiers. Dendritic Identifiers (DIs), formed through Laplacian instabilities such as the Saffman-Taylor effect, exhibit stochastic fractal structures with unpredictable branching and termination, influenced by fluid rheology, system geometry, and environmental conditions.These identifiers are highly adaptable, directly applicable to object surfaces, and inherently unique due to their random growth processes, qualifying them as Physical Unclonable Functions (PUFs). DIs also possess intrinsic data encoding capabilities, making them compatible with computer vision systems like Oriented Fast and Rotated Brief (ORB).
Coupling DIs with blockchain platforms further enhances supply chain transparency and security.
This study focuses on forming dendritic identifiers using a high-viscosity, shear-thinning fluid on transparent plastic substrates through a Dispense-Compress-Separate (DCS) system. Factors influencing the wavelength between dendritic fingers were systematically analysed. Two predictive models—the Lifted Hele-Shaw Cell (LHSC-Stamping) and Flexographic (RTR-Rolling) models—were compared and validated. The RTR model was refined to improve predictive accuracy by physically justifying adjustments to the gap widening coefficient (κ). The practical applicability of DIs was demonstrated by successfully printing on real-world items (heat spreader and silicon wafer), establishing their potential for secure, scalable authentication.

Cadmium Telluride (CdTe) is a direct bandgap semiconductor with a bandgap of 1.5 eV. According to the Shockley-Queisser limit, the theoretical efficiency of CdTe solar cells is 33%. Currently, the highest laboratory-recorded power conversion efficiency for CdTe solar cells reaches 23.1%. While the short-circuit current (JSC) is optimized, the open-circuit voltage (VOC) and fill factor (FF) have less utilization. Doping is an important strategy to enhance VOC. Additionally, due to the high electron affinity of CdTe, implementing a back contact between CdTe and the electrode is necessary to enhance the fill factor.Using an AsCl3 vapor annealing doping approach, arsenic-doped CdSeTe devices have achieved approximately 18% efficiency, much higher than CdSeTe devices fabricated without vapor annealing. Besides the significant enhancements of efficiency, this vapor annealing approach led to a longer carrier lifetime of over 72 ns and VOC of 850 mV.
The As2Te3 and As2Se3 solutions were synthesized using DI water and ammonium sulfide as solvents at room temperature. Subsequent experiments and characterizations show that these arsenic chalcogenides can serve as dopants and back contacts. In the case of the As2Te3 solution, the formation of tellurium promotes hole transport. Compared to the As2Ses doped CdSeTe device, the fill factor (FF) of the CdSeTe device doped with As2Te3 increased from 70.44% to 73.09%.
Antimony chalcogenides can potentially serve as dopants. Initially, Sb2S3 films were synthesized, and the impact of precursor processing ambient on crystal growth behavior was investigated. This project demonstrates the feasibility of synthesizing antimony chalcogenides, which can be used as dopants and back contacts in CdSeTe solar cells. In the next section of the chapter, Sb2Se3 and Sb2Te3 solutions, using en and edtH2 as solvents, will be synthesized and can be applied to the CdSeTe substrate. In addition to their role as dopants, Sb2Se3/Sb2Te3 could also work as back contacts. However, compared to Sb2Se3, the conduction band offset between CdTe and Sb2Te3 is larger, which leads to electron transport to the back contact and results in electron-hole recombination at the back contact. The FF increased from 67.68% to 70.70% when switching from Sb2Te3 to Sb2Se3 as the dopant sources.

Rising global energy demands and environmental challenges have driven the search for alternative renewable energy sources. As one of the abundant, economically, and eco-friendly sustainable energy sources, photovoltaic technology has garnered considerable attention in recent decades. Perovskite solar cells (PSCs) have emerged as a promising candidate for commercial solar cells, thanks to the excellent properties including the low-cost fabrication, high efficiency, and controllable band gap. The power conversion efficiency (PCE) has surged from 3.1% to 27.0% for single-junction devices since the introduction of the first PSC in 2009. Despite this impressive progress, poor long-term stability remains a major bottleneck for widespread commercialization.In this work, an extensive literature review was conducted and multiple strategies were presented to tackle the stability issues of PSCs. Firstly, double perovskite Cs2AgBiBr6 was synthesized and utilized as a passivation layer in PSCs. This interlayer effectively reduced non-radiative recombination, passivated surface defects, and enhanced exciton transport, leading to a notable increase in both device efficiency and longevity. In another approach, low-dimensional carbon nanomaterials—carbon quantum dots (CQDs), multi-walled carbon nanotubes (MWCNTs), and graphene—were integrated into the FAPbI3 photoactive layer via the two-step sequential deposition method. The effects on perovskite crystallinity, optical properties, and overall device performance were systematically analyzed. Notably, one-dimensional MWCNTs modified PSCs demonstrated improvements in both efficiency and Stability. Despite these advancements, further enhancement in thermal stability is needed. High-entropy materials (HEMs) present a promising opportunity due to their high configurational entropy, which overcomes the mixing-enthalpy barrier of compound formation, as well as exceptional mechanical strength and corrosion resistance. A synthesis strategy based on the CsMBr3 crystal structure was designed to fabricate six-element high-entropy perovskite bromides Cs(CaCdMgPbSnZn)Br3. The extreme conditions (~1,000°C) typical of conventional synthesis routes was avoided utilizing a low-temperature hydrothermal method (130°C). The resulting HEMs demonstrated exceptional thermal and ambient stability.
Overall, this work offers valuable insights into improving the long-term stability of perovskite solar cells through device engineering.