1. EE 235 Presentation 1 Brian Lambson

2. 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. 1.Infinite carrier mobility 2.Ideal ohmic contacts 3.No current extracted from IB 4.Three separate quasi-Fermi levels for VB, CB, and IB 5.Nonradiative transitions prohibited 6.Radiative transitions occur through A CI, A CV, and A IV 7.For a given photon energy, only ONE of the three transitions contributes 8.Radiation escapes only through front of cell (perfect mirrors in back) 9.Cell thickness ensures all photons with E greater than any gap energy absorbed 10.Cell illumination is isotropic

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

5. From the calculation for current and using qV = µ CV, Luque and Marti found the power and efficiency for different values of ε i

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

7. Source: Marti, A., D. F. Marron, et al. J. Appl. Phys. (2008) - 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

8.  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