| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1990: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1989: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1988: ¥600,000 (Direct Cost: ¥600,000)
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| Research Abstract |
The increase of the photovoltaic efficiency in solar cells is realized by improving both the optical absorption efficiency and the extraction efficiency of electron-hole pairs. The former is related to the layer widths of an amorphous semiconductor superlattice, while the latter is governed by the width of the exponential tail in the absorption spectra. With this situation in mind, the purpose of the present research is to clarify theoretically the influence of the variation in the layer widths of an amorphous semiconductor superlattice on the width of the exponential tail in the absorption spectra. The results obtained from our study are summarized as follows.
(a) Even when the fluctuations of the diagonal terms are fixed independent of the widths of well layers, the effects from the fluctuations of the diagonal terms become more serious according as the widths of well layers decrease. As a result, the width of the exponential tail in the absorption spectra increases and the electrons
… More
in the tail region become more localized.
(b) Even when the fluctuations fo the diagonal terms as well as the variations in the widths of well layers are fixed independent of the widths themselves of well layers, the influence on the fluctuations of the tunneling probabilities between the adjacent well layers become more marked according as the widths of well layers are reduced. As a consequence, the width of the exponential tail in the absorption spectra increases.
(c) In realistic physical systems, the fluctuations of the diagonal terms cannot be independent of the widths of well layers. In fact, the variations in the widths of well layers becomes more distinguished according to the decrease of well-layer widths. This is because the decrease of well-layer widths causes the increase both the interlayer effects and in the levels. As a consequence, the diagonal terms are inevitably influenced.
hs causes the increase both the interlayer effects and in the levels. As a consequence, the diagonal terms are inevitablly influenced.
(d) From these results, the photovoltaic efficiency can be increased by improving both the optical absorption efficiency and the electron-hole extraction efficiency. This can be achieved by
i. reducing the variations in the widths of well layers, and
ii. minimizing the interlayer effects between a barrier and well layer, thus decreasing the topological disorder in well layers as much as possible. Less
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