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EE 235 Presentation 1 Brian Lambson

This presentation discusses the groundbreaking approach to solar cell efficiency enhancement using intermediate band solar cells (IBSC) as proposed by Luque and Marti. The limiting efficiency for traditional single-bandgap solar cells is 40.7%, while the IBSC achieves an impressive 63.1% efficiency through photon-induced transitions. Key assumptions in the IBSC model include infinite carrier mobility and the prohibition of nonradiative transitions, with a focus on the role of different quasi-Fermi levels. Research into quantum dot and metallic IBSC structures is highlighted, showcasing the ongoing quest for optimal efficiency in photovoltaic technology.

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EE 235 Presentation 1 Brian Lambson

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  1. "Increasing the Efficiency of Ideal Solar Cells by Photon Induced Transitions at Intermediate Levels“ by A. Luque and A. Marti (1997) EE 235 Presentation 1 Brian Lambson

  2. Intermediate Band Solar Cell Single bandgap SC Limiting efficiency 40.7% (Shockley-Queisser model) Intermediate band SC Limiting Efficiency 63.1% (Luque and Marti) Image: G.F. Brown, J. W. Laser and Photonics Rev. (2009)

  3. IBSC Model Assumptions Infinite carrier mobility Ideal ohmic contacts No current extracted from IB Three separate quasi-Fermi levels for VB, CB, and IB Nonradiative transitions prohibited Radiative transitions occur through ACI, ACV, and AIV For a given photon energy, only ONE of the three transitions contributes Radiation escapes only through front of cell (perfect mirrors in back) Cell thickness ensures all photons with E greater than any gap energy absorbed Cell illumination is isotropic

  4. 63.1% - Calculations 1. ν = number of photons in particular mode ζ = distance along direction of ν from front (ζ=0) to back (ζ=1) of device 2. 3.

  5. Ideal Performance From the calculation for current and using qV= µCV, Luque and Marti found the power and efficiency for different values of εi

  6. Quantum Dot IBSC Band diagram QD-IBSC structure QD-IBSC has demonstrated the IB to CB transition: Source: Marti, A., E. Antolin, et al. Phys. Rev. Lett. (2006)

  7. Metallic IBSC • Incorporates transition metal into wide-bandgap material to induce intermediate band formation • CuGaS2 has been identified as material with strong potential for improvement. Now being actively researched Source: Marti, A., D. F. Marron, et al. J. Appl. Phys. (2008)

  8. Outlook • QD-IBSC – Engineering a large enough gap between the CB and IB is very challenging • Metallic IBSC – Concept has not yet been demonstrated experimentally • How to induce IB formation without degrading transport and other material properties • Theoretical model is an ongoing research topic • Major claim – best performance of any ideal non-complex PV devices– still holds today

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