Schottky Barrier Solar Cell Structures Research Articles

Analysis of Non-Uniform Creation of Light-Induced Defects in Schottky Barrier Solar Cell Structures

ABSTRACTHydrogenated amorphous silicon (a-Si:H) TCO/n+/i/Ni Schottky barrier solar cells were degraded with illuminations of white and red light through both sides of the structure. Because the forward dark I-V's are sensitive to the distribution and any spatial variation of defects in the i-layer, these measurements were used to characterize the degraded cell structures. These characteristics were analyzed using a charged defect distribution of gap states consisting of D+, D°, and D states derived from corresponding film analysis. It was found that the non-uniformities of light induced defects created in the i-layer can be represented by two regions of different defect densities. The relative densities depend on the direction of illumination and their ratio even with white light is about a factor of four. This non-uniformity is expected to be less for p-i-n cells which have higher built-in potential and hence electric fields.

Effect of the metal-semiconductor interface on carrier collection in a-Si: H Schottky barrier solar cell structures

Abstract The internal quantum efficiencies of intrinsic hydrogenated amorphous silicon (a-Si:H) Schottky barrier solar cell structures have been used to determine the effects of the metal/a-Si:H contact on the collection of photogenerated carriers. The results of different metal contacts, as well as controlled interfacial oxides, are analyzed using a detailed numerical model AMPS (analysis of microelectronic and photonic structures). Direct correlation is established between the nature of the interface and the short wavelength quantum efficiencies where electron back-diffusion to the metal contact is the primary loss mechanism of carriers photogenerated at these lower wavelengths. The results are also found to be consistent with electron surface recombination velocities at the metal/a-Si:H contact which depend not only on the metal work function and the presence of an interfacial oxide but also on the formation of metal silicides.

Reversible, Light Induced Changes in a-Si:H Films and Solar Cells

Continuous progress is being made in the conversion efficiencies of a- Si:H solar cells and efficiencies in excess of 11% have been achieved. Because of these advances and the development of a-Si:H cell technologies there is an increased interest in the long term performance of a-Si:H cells and the mechanisms responsible for their degradation. The reversible light-induced changes in a-Si:H solar cells are generally associated with the Staebler-Wronski effect (SWE) (1). This effect has been studied on a wide range of a-Si:H materials using a variety of different experimental techniques and this talk reviews the results that have been obtained on a- Si:H films and solar cells (2). It discusses in greater detail recent studies on a-Si:H solar cell structures in which simultanous measurements have been made on the changes in both the photovoltaic properties as well as their electronic properties and densities of gap states. In particular it focuses on several results obtained with semitransparent metal-undoped a-Si:H Schottky barrier solar cell structures (3).

Electron-hole recombination in reactively sputtered amorphous silicon solar cells

The electron-hole recombination has been investigated in reactively sputtered hydrogenated amorphous silicon (a-SiHx) metal Schottky barrier solar cell structures. We find that electron-hole recombination proceeds through states in the middle of the gap. These states, whose density depends on the degree of hydrogenation, have been associated with Si dangling bonds and their effective carrier capture cross section was estimated to be 6×10−15 cm2.