Nano-Optics-Enabled High-Efficiency Solar Cells

Glancing angle coupling of light into dielectric media is a desirable feature that can benefit the performance of solar cells. At a highly refractive dielectric interface, however, the transmission angle is limited small (e.g., ~15 deg for air/Si) by Snell’s law. In this thesis, we propose a new method of light coupling that overcomes the conventional limits of refractive transmission. A vertical dipole structure is designed to enable glancing propagation into high-index media, enhancing light absorption and carrier collection for a given thickness of active medium. A vertical-dipole nano-optic structure was introduced to a conventional finished silicon cell (~16% efficiency). The vertical dipoles reradiate incident light into oblique directions inside the active medium (Si). The glancing propagation along the junction interface results in a synergistic, uncompromised improvement of cell performance (i.e., enhancing photocarrier generation without sacrificing carrier transport) and demonstrates 20% cell efficiency. We have further studied low-voltage, broadband photocarrier multiplication in a graphene/SiO2/Si structure and demonstrate external quantum efficiency 146-200% (internal quantum efficiency 218-384%) as measured with photocurrent in UV-to-NIR (325-850nm). The self-induced electric field (~106 V/cm) in 2D electron gas enables impact ionization at low bias (< 2V), in a way promising and compatible with photovoltaic operation

Electrically-triggered micro-explosion in a graphene/SiO2/Si structure

Electrically-triggered micro-explosions in a metal-insulator-semiconductor (MIS) structure can fragment/atomize analytes placed on it, offering an interesting application potential for chip-scale implementation of atomic emission spectroscopy (AES). We have investigated the mechanisms of micro-explosions occurring in a graphene/SiO2/Si (GOS) structure under a high-field pulsed voltage drive. Micro-explosions are found to occur more readily in inversion bias than in accumulation bias. Explosion damages in inversion-biased GOS differ significantly between n-Si and p-Si substrate cases: a highly localized, circular, protruding cone-shape melt of Si for the n-Si GOS case, whereas shallow, irregular, laterally-propagating trenches in SiO2/Si for the p-Si GOS case. These differing damage morphologies are explained by different carrier-multiplication processes: in the n-Si case, impact ionization propagates from SiO2 to Si, causing highly-localized melt explosions of Si in the depletion region, whereas in the p-Si case, from SiO2 towards graphene electrode, resulting in laterally wide-spread micro-explosions. These findings are expected to help optimize the GOS-based atomizer structure for low voltage, small-volume analyte, high sensitivity chip-scale emission spectroscopy

Bring More Attention to Syntactic Symmetry for Automatic Postediting of High-Quality Machine Translations

Automatic postediting (APE) is an automated process to refine a given machine translation (MT). Recent findings present that existing APE systems are not good at handling high-quality MTs even for a language pair with abundant data resources, English-to-German: the better the given MT is, the harder it is to decide what parts to edit and how to fix these errors. One possible solution to this problem is to instill deeper knowledge about the target language into the model. Thus, we propose a linguistically motivated method of regularization that is expected to enhance APE models' understanding of the target language: a loss function that encourages symmetric self-attention on the given MT. Our analysis of experimental results demonstrates that the proposed method helps improving the state-of-the-art architecture's APE quality for high-quality MTs.Comment: This paper is presented at ACL 202

Bioprinting of Physiomimetic Human Islet-like Cellular Aggregates-Vascular Platform for Functional Maturation of Beta Cells

Pancreatic islets are point-shaped cellular aggregates surrounded by capillary network and extracellular matrix (ECM) and aligned with blood vessels. Recent advances in bioprinting technology have enabled the construction of engineered pancreatic tissue recapitulating unique structural features of the human islets. However, current human pluripotent stem cell-derived islets lack vasculatures and pancreatic tissue-relevant environments, which are key triggers of insulin producing-beta cell maturation. In this study, we fabricated human islet-like cellular aggregates (HICAs)-vascular platform using pancreatic tissue-derived ECM-based peri-islet niche-like (PINE) bioink reinforced with basement membrane proteins to attain functional maturation of beta cells. Stem cell-derived islets encapsulated in the PINE bioink showed increased insulin secretion capacity compared to islets encapsulated in the other ECM-derived bioink, confirming that 3D pancreatic-mimetic microenvironment could support beta cell functions with biochemical cues. We further investigated whether the bioprinted HICAs could assemble into co-printed blood vessel, contacting endothelial cells, via biostructural cues. Bioprinting of HICAs-vascular platform guided not only pancreatic tissue-specific architecture but the mature behavior of beta cells in vitro. Our platform will potentiate the application of the physiomimetic pancreatic tissue model for diabetes research, opening chances for precision therapeutic drug testing and mature tissue transplants.2

Construction of 3D hierarchical tissue platforms for modeling diabetes

Diabetes mellitus (DM) is one of the most serious systemic diseases worldwide, and the majority of DM patients face severe complications. However, many of underlying disease mechanisms related to these complications are difficult to understand with the use of currently available animal models. With the urgent need to fundamentally understand DM pathology, a variety of 3D biomimetic platforms have been generated by the convergence of biofabrication and tissue engineering strategies for the potent drug screening platform of pre-clinical research. Here, we suggest key requirements for the fabrication of physiomimetic tissue models in terms of recapitulating the cellular organization, creating native 3D microenvironmental niches for targeted tissue using biomaterials, and applying biofabrication technologies to implement tissue-specific geometries. We also provide an overview of various in vitro DM models, from a cellular level to complex living systems, which have been developed using various bioengineering approaches. Moreover, we aim to discuss the roadblocks facing in vitro tissue models and end with an outlook for future DM research.11Nsciescopu

3D Bioprinting of Human Islet-like Cellular Aggregates-Vascular Platform for Modeling Diabetes

Pancreatic islets have spheroidal microarchitecture, surrounded by vasculatures and extracellular matrix (ECM), and are located along with a large blood vessel. However, current stem cell-based islet models lack the pancreatic tissue-specific microenvironment and vascular features of islets. In this regard, we developed pancreatic tissue-derived ECM-based peri-islet niche-like (PINE) bioink supplemented with basement membrane proteins, which can promote the structural integrity of islets and the functional maturation of β cells by providing biochemical cues. We further investigated whether the co-culture of endothelial cells could enhance insulin secretion capacity of stem cell-derived islets via secreting paracrine factors. Finally, we fabricated human islet-like cellular aggregates-vascular platform using PINE bioink and 3D bioprinting technology to recapitulate each unique tissue architecture (e.g., spheroid and tubular structure) and validated the applicability of this platform for diabetes modeling. The developed platform reflected not only structural characteristics of pancreatic tissue and but also physiomimetic responses from diabetic islets and vessels. Our platform will facilitate developing improved pharmacotherapies for patients, opening chances for precision diabetic medicine.1

Construction of Physiomimetic Pancreatic Tissue Models Using Stem Cell-Derived Islets and Extracellular Matrix-Based Pancreatic Islet Niche-Like Bioink

2

Physiomimetic bioprinting of stem cell-derived human pancreatic islet-like cellular aggregates-vascular platform for studies of diabetic diseases

2

3D Bioprinting of Islet-like Aggregates Using Dual-crosslinked Hydrogel with Promoted Biofunctionality and Enhanced Shape Stability

1