One aspect of solar cell efficiency: Multiple wavelengths photon absorption in nano-silicon structures

Document Type

Conference Proceeding

Publication Date

10-19-2009

Abstract

Among several factors, like photon capture, photon reflection, carrier generation by photons, carrier transport and collection, the efficiency also depends on the absorption of photons. The absorption coefficient, α, and its dependence on the wavelength, λ, is of major concern to improve the efficiency. Nano-silicon structures (quantum wells and quantum dots) have a unique advantage that multiple direct and indirect band gaps can be realized by appropriate size control of the quantum wells. This enables multiple wavelength photons of the solar spectrum to be absorbed efficiently. We present a theoretical approach to calculate the absorption coefficient using quantum mechanical calculations on the interaction of photons with the electrons of the valence band. In our model, the oscillator strength of the direct optical transitions is enhanced by the quantum confinement effect in Si nanocrystallites. These kinds of quantum wells can be realized in practice in porous silicon. Our theoretical estimations show the absorption coefficient of silicon quantum dots to be comparable to that of bulk silicon, and is also nearly constant over the visible spectrum. © 2009 SPIE.

Publication Title

Proceedings of SPIE - The International Society for Optical Engineering

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