Two-step photon absorption in InP/InGaP quantum dot solar cells

Abstract

Intermediate band solar cells promise improved efficiencies beyond the Shockley-Queisser limit by utilizing an intermediate band formed within the bandgap of a single junction solar cell. InP quantum dots (QDs) in an In0.49Ga0.51P host are a promising material system for this application, but two-step photon absorption has not yet been demonstrated. InP QDs were grown via metalorganic chemical vapor deposition, and a density, a diameter, and a height of 0.7 × 1010 cm−2, 56 ± 10 nm, and 18 ± 2.8 nm, respectively, were achieved. Time-resolved photoluminescence measurements show a long carrier lifetime of 240 ns, indicating a type-II band alignment of these InP quantum dots. Several n-i-p In0.49Ga0.51P solar cells were grown with both 3 and 5 layers of InP QDs in the i-region. While the solar cells showed an overall loss in short circuit current compared to reference cells due to emitter degradation, a sub-bandgap enhancement of 0.11 mA/cm2 was clearly observed, due to absorption and collection from the InP QDs. Finally, two-step photon absorption experiments have shown unambiguous photocurrent generation involving an intermediate band within the bandgap at temperatures up to 250 K.

Dual Junction GaInP/GaAs Solar Cell with Enhanced Efficiency Using Type‐A InP Quantum Wells

“…[21][22][23] The photon absorption in type-A QW structure is described by thermionic field emission boundary. [31] We have earlier reported GaInP SJ solar cell with type-A InP QWs with enhanced efficiency of 22.41%. [30] The schematic diagram and simulated structure is shown in Figure 1 and 2.…”

Iii-v Solar Cells

“…In order to approach the ideal matrix material bandgap of 1.95 eV, larger bandgap materials have more recently been both experimentally and theoretically investigated, but with limited success. Some examples with encouraging results are InP/In-GaP [53][54][55], InAs/InGaP [56,57], InAs/AlGaAs [58] and In(As)P/InGaP [59]. A more detailed discussion of the progress reached with such 0D structures can be found in the review chapter [16], cited earlier.…”

Effects of front InGaP layer thickness on solar cell characteristics in InP/InGaP quantum dot solar cells

“…25) Two-step two-photon absorption has been so far demonstrated in type-II InP/InGaP QD solar cells. 26) However, in InP QD solar cells, the quantum efficiency is decreased in the visible and ultraviolet region compared to the reference InGaP solar cell with no InP QDs, indicating that the short-wavelength light is not absorbed by the host InGaP layer without QDs but by the QD layers. 25) To clarify this issue we have demonstrated enhanced short-circuit current density (J sc ) in a device with thick front i-InGaP layer.…”