Seth Shumate

Computational Model of Ductal Carcinoma In Situ : The Effects of Contact Inhibition on Pattern Formation

The computational model presented in this paper focuses on modeling ductal carcinoma in situ (DCIS), which is the most commonly detected preinvasive form of breast cancer. The model aims to understand the biological mechanisms and resultant growth dynamics of DCIS. The cellular automaton model based on observed phenotypic characteristics of DCIS emphasize the important role of contact inhibition on lesion pattern formation. Computer simulations resembled the cribriform, micropapillary, solid, and comedo patterns of DCIS. The model has led to insights about the progression of the preinvasive disease such as possible explanations for coexisting micropapillary and cribriform patterns commonly found through histological analyses.

Microstructural influence of hydrogenated amorphous silicon on polycrystalline emitter solar cells prepared by top-down aluminum induced crystallization

Top-down Aluminum Induced Crystallization (TAIC) is a variant of metal induced crystallization (MIC) in which aluminum and silicon layers do not exchange places. This study examines the influence of the quality of hydrogenated amorphous silicon, a-Si:H, on the resultant output of TAIC polycrystalline emitter solar cells by controlling the hydrogen content and bonding distribution during a-Si:H deposition. Surprisingly, it was found that device-quality a-Si:H was not the best precursor for TAIC as determined by solar cell output characteristics.

Field enhancement due to surface structuring during aluminum induced crystallization of amorphous silicon

Aluminum induced crystallization (AIC) of amorphous silicon (a-Si) may potentially be causing the formation of plasmonic nanostructures on the silicon surface. Field enhancement within the silicon layer will be quantified in order to develop an understanding of the observed enhancement. Computer simulations using HFSS are presented here. The electric fields absorbed inside the silicon are obtained as a function of the incident wavelength due to irregular nanostructures of aluminum patches to simulate the induced aluminum-silicon patches.

Modeling of the hydrogen selective emitter for n-type silicon solar cells

A simulation of the Hydrogen Selective Emitter (HSE) process is performed using readily available open source software from PV Lighthouse. An experimental boron (B) profile from Yingli solar is analyzed using EDNA 2 and this output is used with PC1D to create inputs for Griddler 2. Griddler allows for the simulation of cell parameters for a full size bifacial type device. We find that an efficiency boost of 0.2 to 0.4% absolute is possible by applying the HSE process to an experimental n-type silicon solar cell. We also show that the number of silver (Ag) gridlines at the front of the cell could be reduced by 33% while gaining at least 0.14% in efficiency over the baseline cell.

Progress on the hydrogen selective emitter for N-type solar cells

A novel, one-step and self-aligned selective emitter process has been tested on n-type solar cells. Results indicate that the electrical activity of acceptor impurities near the surface are responsible for increased surface recombination, not their physical presence. Lab-scale n-type solar cell efficiencies have been increased by up to 18.4%. Quantum efficiency measurements on these cells show dramatic increase in short wavelength response up to 750 nm.

Large-grain polysilicon seed layers on glass for epitaxial silicon solar cells

Thin-film silicon solar cells remain a promising technology to approach wafer-based efficiencies at thin-film costs. Epitaxial growth of silicon cells on seed layers has been a prominent approach with demonstrated efficiencies. However, cost-effective seed layers on glass or other low-cost substrates still remain one of the biggest road blocks to the success of this technology. Top-down aluminum induced crystallization (TAIC) has been developed to produce large-grain silicon seed layers on glass. Initial cells have been fabricated by Hot-Wire CVD at the National Renewable Energy Laboratory (NREL). The seed layers with grain-gaps show poor electrical characteristics comparable to reported cells grown on wafer templates with defect densities around 2 × 106 cm-3. New seed layers without grain gaps have been developed and are in queue for cell fabrication.

Self aligned hydrogenated selective emitter for n-type solar cells

Selective emitter cell architectures are one avenue for increasing industrial solar cell efficiency. N-type cell based technology is also gaining considerable attention for the same purpose. This paper describes a novel, single step selective emitter process using atomic hydrogen to passivate boron acceptor impurities. Grid lines act as a mask to hydrogenation, which lowers the surface concentration of electrically active boron between grid lines. Using EDNA to model this complex emitter, it was shown that Jsc can be increased in the emitter by 0.94mA/cm2 with a short, low temperature atomic hydrogen treatment. A hydrogenation system has been developed, and initial experimental results on aluminum doped polycrystalline thin films shows its effectiveness. Cell fabrication is being developed to test this process on fabricated solar cells to verify theoretical results. Special processing considerations are discussed.

Passivation studies with hydrogenated boron emitters

The Hydrogen Selective Emitter (HSE) is a self-aligned selective emitter for n-type silicon solar cells. In this study, Quinhydrone-methanol passivation is applied to hydrogenated boron emitters to extract emitter saturation current density (J0e) data using photoconductance lifetime measurements. Etch-back studies are performed to extract J0e vs. Rsh curves of counterpart boron emitters (hydrogenated and non-hydrogenated). It is shown that a hydrogenated boron emitter can suppress Auger recombination over a standard boron emitter and thus lead to efficiency enhancement for solar cells.

Top-down Aluminum Induced Crystallization for N-type solar cell emitters

Top-down Aluminum Induced Crystallization (TAIC) has been used to form the p+ emitters of n-type solar cells. TAIC is a low temperature process with the potential for very good junction passivation and avoidance of parasitic absorption of amorphous silicon experienced by HIT cells. During experimentation, several crystallization possibilities emerged. The structure of these emitters were determined by Raman spectroscopy, SEM, and TEM. Solar cells were fabricated and measured. Theoretical projections and loss analyses were done by modeling these cells using PC1D. The highest efficiency cell achieved was 7.26% out of a theoretical 8.73%. These cells had no ARC/surface passivation, texturing, or a back surface field.

Fabrication and characterization of c-si solar cells integrated with ordered metallic nanostructure arrays

In this study we present the fabrication process and characterization techniques to integrate metallic nanostructures on the surface of crystalline Si (c-Si) solar cells. These structures are designed to enhance light trapping at particular wavelengths [2]. Tuning the wavelength to maximize the efficiency can be achieved by changing the sizes and shapes of these structures. A special design of these structures atop c-Si solar cell is expected to affect the absorption near the band gap. These structures have been fabricated by electron beam lithography on c-Si substrates. The processing integration and preliminary characterization results of metallic nanostructures on c-Si solar cells are reported.