Low Cost Thin Film Building-Integrated PV Systems: Cooperative Research and Development Final Report, CRADA Number CRD-07-239

In this CRADA, NREL's Silicon group members performed the following research activities: (1) investigation of the role of hydrogen in growth of a mixed-phase nc-Si:H/a-Si:H material; (2) role of hydrogen in light-induced degradation of a-Si:H and development of Staebler-Wronski effect resistive a-Si:H; and (3) performing characterizations of UniSolar's a-Si:H and nc-Si materials, with goal to help optimizing large-area uniformity and quality of the UniSolar's nanocrystalline Si:H

Flexibility-assisted heat removal in thin crystalline silicon solar cells

Thin crystalline silicon solar photovoltaics holds great potential for reducing the module price by material saving and increasing the efficiency by reduced bulk recombination loss. However, the module efficiency decreases rather sensitively as the module temperature rises under sunlight. Effective, inexpensive approach to cooling modules would accelerate large-scale market adoption of thin crystalline silicon photovoltaics. For effective cooling, we exploit high flexibility of single-crystalline thin silicon films to create wavy solar cells. These wavy cells possess larger surface area than conventional flat cells, while occupying the same projected area. We experimentally demonstrate that the temperature of thin wavy crystalline silicon solar cells under the sunlight can be significantly reduced by increased convective cooling due to their large surface area. The substantial efficiency gain, achieved by the effective heat removal, points to high-performance thin crystalline silicon photovoltaic systems that are radically different in configuration from conventional systems.Comment: 33 pages, 17 figure

Comparison of biomechanical and structural properties between human aortic and pulmonary valve

Funding Information: This study was supported by a grant from the Latvian Council of Science.Objective: Pulmonary valve autografts have been reported as clinically effective for replacement of diseased aortic valve (Ross procedure). Published data about pulmonary valve mechanical and structural suitability as a long-term substitute for aortic valve are limited. The aim of this study was to compare aortic and pulmonary valve properties. Methods: Experimental studies of biomechanical properties and structure of aortic and pulmonary valves were carried out on pathologically unchanged human heart valves, collected from 11 cadaveric hearts. Biomechanical properties of 84 specimens (all valve elements: cusps, fibrous ring, commissures, sinotubular junction, sinuses) were investigated using uniaxial tensile tests. Ultrastructure was studied using transmission and scanning electron microscopy. Results: Ultimate stress in circumferential direction for pulmonary valve cusps is higher than for aortic valve (2.78±1.05 and 1.74±0.29 MPa, respectively). Ultimate stress in radial direction for pulmonary and aortic cusps is practically the same (0.29±0.06 and 0.32±0.04 MPa, respectively). In ultrastructural study, different layout and density in each construction element are determined. The aortic and pulmonary valves have common ultrastructural properties. Conclusions: Mechanical differences between aortic and pulmonary valve are minimal. Ultrastructural studies show that the aortic and pulmonary valves have similar structural elements and architecture. This investigation suggests that the pulmonary valve can be considered mechanically and structurally suitable for use as an aortic valve replacement.Peer reviewe

Carrier Selective, Passivated Contacts for High Efficiency Silicon Solar Cells based on Transparent Conducting Oxides

AbstractWe describe the design, fabrication and results of passivated contacts to n-type silicon utilizing thin SiO2 and transparent conducting oxide layers. High temperature silicon dioxide is grown on both surfaces of an n-type wafer to a thickness <50Å, followed by deposition of tin-doped indium oxide (ITO) and a patterned metal contacting layer. As deposited, the thin-film stack has a very high J0,contact, and a non-ohmic, high contact resistance. However, after a forming gas anneal, the passivation quality and the contact resistivity improve significantly. The contacts are characterized by measuring the recombination parameter of the contact (J0,contact) and the specific contact resistivity (ρcontact) using a TLM pattern. The best ITO/SiO2 passivated contact in this study has J0,contact = 92.5 fA/cm2 and ρcontact = 11.5 mOhm-cm2. These values are placed in context with other passivating contacts using an analysis that determines the ultimate efficiency and the optimal area fraction for contacts for a given set of (J0,contact, ρcontact) values. The ITO/SiO2 contacts are found to have a higher J0,contact, but a similar ρcontact compared to the best reported passivated contacts

New Real-Time Quantum Efficiency Measurement System: Preprint

This paper describes a newly developed technique for measuring the quantum eficiiency in solar cells in real-time using a unique, electronically controlled, full-spectrum light source

Role of Heterogeneities in Staebler-Wronski Effect

The effect of light soaking (LS) on the properties of hydrogenated amorphous silicon presents many challenging puzzles. Some of them are discussed here, along with their present status. In particular the role of the heterogeneities in LS is examined. We find that for the majority of the solved as well unsolved puzzles the long range potential fluctuations arising from the heterogeneities in the films can provide answers which look quite plausible.Comment: 10 pages, 7 figure