Amorphous Silicon‐Based Solar Cells

Abstract

Crystalline semiconductors are very well known, including silicon (the basis of the integrated circuits used in modern electronics), Ge (the material of the first transistor), GaAs and the other III-V compounds (the basis for many light emitters), and CdS (often used as a light sensor). In crystals, the atoms are arranged in near-perfect, regular arrays or lattices. Of course, the lattice must be consistent with the underlying chemical bonding properties of the atoms. For example, a silicon atom forms four covalent bonds to neighboring atoms arranged symmetrically about it. This "tetrahedral" configuration is perfectly maintained in the "diamond" lattice of crystal silicon. There are also many noncrystalline semiconductors. In these materials the chemical bonding of atoms is nearly unchanged from that of crystals. Nonetheless, a fairly small, disorderly variation in the angles between bonds eliminates the regular lattice structure. Such noncrystalline semiconductors can have fairly good electronic properties-sufficient for many applications. The first commercially important example was xerography [1, 2], which exploited the photoconductivity of noncrystalline selenium. As do all semiconductors , selenium absorbs those photons from an incident light beam that have photon energies exceeding some threshold energy. The photon that is absorbed generates a positively charged "hole" and a negatively charged electron that are separated and swept away by the large electric fields used in xerography. However, solar cells require that photogenerated electrons and holes be separated by relatively modest electric fields that are "built-in" to the device, and selenium and many other noncrystalline semiconductors proved unsuitable for making efficient cells.

Where Is the Electronic Oscillator Strength? Mapping Oscillator Strength across Molecular Absorption Spectra

“…1 Producing stronger absorbers would reduce the required thickness of light-absorbing materials, enhancing free charge carrier collection, optimizing voltage generation and fill factors, and lowering the cost of solar energy utilization. 2 Despite its obvious benefits to solar energy conversion, the development of better light absorbers in the UV–vis spectral region has been at most incremental. Ultrathin films of 10–20 nm can be used in specialized light-harvesting systems, assisted by plasmonic enhancement effects.…”

“…Effective use of solar energy requires matching the electronic transitions of light-harvesting structures to the solar irradiance at the earth’s surface . Producing stronger absorbers would reduce the required thickness of light-absorbing materials, enhancing free charge carrier collection, optimizing voltage generation and fill factors, and lowering the cost of solar energy utilization . Despite its obvious benefits to solar energy conversion, the development of better light absorbers in the UV–vis spectral region has been at most incremental.…”

Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices

“…It is essential to measure, monitor, and control the thickness, structure, phase, and composition of solar cell component layers in the same configuration used in manufacturing, especially for devices processed over large areas. Doped ( n -type and p -type) and undoped (intrinsic) hydrogenated silicon (Si:H) thin films are used in single, tandem, and multijunction solar cell applications in both n - i - p substrate and p - i - n superstrate configurations [ 5 , 6 , 7 , 8 , 9 , 10 ]. These Si:H films prepared by plasma enhanced chemical vapor deposition (PECVD) may exhibit several structural transitions during growth in the PV device configuration.…”

Analysis of initial stabilization of cell efficiency in amorphous silicon photovoltaic modules under real outdoor conditions

“…Studies on the behavior of PV plants has led to an increasing interest in understanding the factors affecting cell efficiency and PV plant performance [13][14][15] in greater detail. Field experience in a-Si:H PV modules is the most extensive of all the thin-film technologies [16,17]. Knowledge obtained over the last three decades with a-Si:H manufacturing and a-Si:H PV plants is now used in other emerging thin-film technologies: CIS, CISG, TeCd, etc.…”