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

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

Atomistic simulation of light-induced changes in hydrogenated amorphous silicon

We employ ab initio molecular dynamics to simulate the response of hydrogenated amorphous silicon to light exposure (Staebler-Wronski effect). We obtain improved microscopic understanding of PV operation, compute the motion of H atoms, and modes of light-induced degradation of photovoltaics. We clarify existing models of light-induced change in aSi:H and show that the Hydrogen collision model of Branz3 is correct in essentials.Comment: 10 pages, 3 figures, to be published in J. Phys. Cond matt. (Letter

Characterization of Epitaxial Film Silicon Solar Cells Grown on Seeded Display Glass: Preprint

We report characterizations of epitaxial film crystal silicon (c-Si) solar cells with open-circuit voltages (Voc) above 560 mV. The 2-um absorber cells are grown by low-temperature (<750 degrees C) hot-wire CVD (HWCVD) on Corning EAGLE XG display glass coated with a layer-transferred (LT) Si seed. The high Voc is a result of low-defect epitaxial Si (epi-Si) growth and effective hydrogen passivation of defects. The quality of HWCVD epitaxial growth on seeded glass substrates depends on the crystallographic quality of the seed and the morphology of the epitaxial growth surface. Heterojunction devices consist of glass/c-Si LT seed/ epi n+ Si:P/epi n- Si:P/intrinsic a-Si:H/p+ a-Si:H/ITO. Similar devices grown on electronically 'dead' n+ wafers have given Voc {approx}630 mV and {approx}8% efficiency with no light trapping features. Here we study the effects of the seed surface polish on epi-Si quality, how hydrogenation influences the device character, and the dominant junction transport physics

Proposed Route to Thin Film Crystal Si Using Biaxially Textured Foreign Template Layers

We have developed a new approach to growing photovoltaic-quality crystal silicon (c-Si) films on glass. Other approaches to film c-Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we have developed an approach to align the silicon grains biaxially (both in and out of plane) so that 1) grain boundaries are "low-angle" and have less effect on the electronic properties of the material and 2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass

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