Intermediate Band Solar Cell with Extreme Broadband Spectrum Quantum Efficiency

We report, for the first time, about an intermediate band solar cell implemented with InAs/AlGaAs quantum dots whose photoresponse expands from 250 to $\sim 6000\mathrm{nm}$. To our knowledge, this is the broadest quantum efficiency reported to date for a solar cell and demonstrates that the intermediate band solar cell is capable of producing photocurrent when illuminated with photons whose energy equals the energy of the lowest band gap. We show experimental evidence indicating that this result is in agreement with the theory of the intermediate band solar cell, according to which the generation recombination between the intermediate band and the valence band makes this photocurrent detectable.

Figure 1

(a) Simplified band gap diagram of an IB material showing the three relevant optical transitions and (b) idealized band diagram of a QD IBSC in short-circuit conditions illuminated by white light and considering finite carrier mobility. ${\epsilon }_{Fe}$ and ${\epsilon }_{Fh}$ are the quasi-Fermi energies for electrons and holes in the CB and VB, respectively.

Figure 2

(a) Layer structure of the QD IBSC under study and (b) AFM image of the QDs.

Figure 3

Experimental setup.

Figure 4

Spectral photocurrent of the QD IBSC at 300 K and 20 K.

Figure 5

(a) Simplified IBSC equivalent circuit in short-circuit conditions. (b) Small-signal model for illumination causing IB to CB transitions.

Figure 6

IR small-signal photocurrent in the QD IBSC as a function of supra-band gap photocurrent.

Figure 7

Spectral photocurrent of the QD IBSC as a function of supra-band gap photocurrent.