摘要:

Amorphous silicon technology offers an avenue for low‐coast, thin‐film photovoltaic applications. The performance of amorphous silicon‐based solar cells is limited by light‐induced degradation. The inadequate existing understanding of the electronic phenomena in amorphous silicon materials and devices hampers resolution of this problem. We are posing questions that should stimulate researchers to develop better descriptions for device performance and better microscopic models for defect sites. The issue of Staebler‐Wronski degradation should not be addressed separately from initial performance, but research should focus on material and device properties in the stabilized state. The main focus of the a‐Si:H research sponsored by the United States Department of Energy will be on improving the stabilized performance, which we anticipate to accomplish through focused development of optimized multijunction device structures combined with an improved understanding of materials.

ISSN:0094-243X    

DOI:10.1063/1.41012

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Stable Materials Advisory Research Team (SMART) was established to develop a unified approach to address the stability problem in a‐Si:H based solar cells. The goal of the coordinated research effort by industrial laboratory and research institution members is to resolve whether a‐Si:H based materials are intrinsically unstable and if high efficiency cells can have a 20 year lifetime. This paper reviews ongoing research which addresses both material and device issues in the effort to improve the material properties and solar cell performance. Results are presented for materials and device structures obtained using several deposition techniques with hydrogen content varying from about 20% to 8%. Also several issues are discussed which arose from the wide range of measurements carried out on the same materials in different laboratories.

ISSN:0094-243X    

DOI:10.1063/1.41044

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Studies of metastability relate defect creation to the motion of hydrogen between different bonding sites. The mechanism is discussed in terms of a hydrogen density of states distribution, whose general features are obtained from simple chemical models of hydrogen bonding and weak Si‐Si bonds. The model relates metastability to the equilibrium defect density and to the hydrogen diffusion.

ISSN:0094-243X    

DOI:10.1063/1.41031

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Ten years after it was first proposed, the Adler model of the Staebler‐Wronski effect in hydrogenated amorphous silicon (a‐Si:H) remains plausible and elegant. Adler suggested that during illumination, charged threefold‐coordinated silicon dangling‐bond defects capture photogenerated electrons and holes and reconfigure into metastable neutral dangling bonds. We present recent refinements to this model and review the considerable experimental evidence that a‐Si:H has important metastable charge‐trapping defects. Problems with this and other models of the Staebler‐Wronski effect are discussed.

ISSN:0094-243X    

DOI:10.1063/1.41041

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this work, the local density total energy calculations of various bonding configurations for H in crystalline Si are used to develop a density of states for H trapping in amorphous silicon (a‐Si:H). This density of trapping states is compared with various experimental results and is used to interpret H transport measurements.

ISSN:0094-243X    

DOI:10.1063/1.41011

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We discuss a new molecular dynamics approach for investigating the light‐induced degradation in a‐Si:H. In this approach Si‐Si and newly developed Si‐H interatomic potential have been utilized to describe a 60‐atom a‐Si:H model containing 10% H, similar to device‐quality material. Molecular dynamics schemes for investigating hydrogen‐induced defects and bond‐breaking models of the Staebler‐Wronski effect are discussed.

ISSN:0094-243X    

DOI:10.1063/1.41013

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The steady‐state defect density in hydrogenated amorphous silicon (a‐Si:H) under illumination was investigated for a wide range of illumination intensities and temperatures. The saturation defect density under illumination is both temperature and light intensity dependent. A chemical equilibrium model for light‐induced defect generation is proposed. According to the model, defect generation is enhanced under illumination due to the reduction of the defect formation energy when the bands are populated by photogenerated carriers. Defect generation is a self limiting process and the defect density reaches a saturation value at long illumination time despite the existence of an extended distribution of defect formation sites.

ISSN:0094-243X    

DOI:10.1063/1.41014

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We investigate undoped amorphous hydrogenated silicon with spin‐dependent photoconductivity (SDPC). In addition to recombination via single carriers in tail states and dangling bonds, a broad resonance is observed, attributed to recombination of excitonic states. A study of the influence of light‐induced degradation on the different recombination processes in a‐Si:H is presented. The experiments are well described by existing theories, which assume exciton‐like states to be the electronic precursor for metastable defects.

ISSN:0094-243X    

DOI:10.1063/1.41015

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A comprehensive model for the metastable defects in a‐Si:H is developed by adapting a recent theory for several kinds of defects in crystalline semiconductors, particularly the DX center in AlGaAs. This new model accounts in a unified way for all of the major observations of defects induced by light, quenching, doping, or compensation; as well as for their anneal. The stretched‐exponential time dependence of defect densities with light or annealing, and saturation of the density are also explained. This model is based on foreign atoms rather than on Si‐Si bond breaking, and in undoped materials it is suggested that uncontrolled impurities are the source.

ISSN:0094-243X    

DOI:10.1063/1.41016

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Sufficient information has become available about the density and distribution of the dangling‐bond defects, the defect annealing behavior, the light‐induced defect generation rates (dNs/dt)LI, and the saturated light‐induced defect densities (Nsat) in amorphous silicon (a‐Si:H) to allow the development of a comprehensive defect model. The model which we have developed describes the density of defect states in function of growth conditions, of annealing and of lighg‐soaking. We apply this model to the defect distributions which are established by various combinations of light‐soaking and annealing.

ISSN:0094-243X    

DOI:10.1063/1.41017

出版商:AIP    

年代:1991

数据来源: AIP