16-01-2013, 12:08 PM
Nanostructure Devices
[attachment=47115]
Absorption
Only photons with sufficient energy can excite e-across the band gap Eg.
•Insufficiently energetic photons with
Ephot < Eg will not contribute to the photocurrent generation (1).
•Photons with Ephot > Eg will initially generate energetic excited charge carriers (2).
•Any energy in excess of Eg will be wasted heating up the solar cell through thermalization (3).
Energy loss in p-n junction
The fundamental loss mechanisms across the pn junction
1. Insufficient photon energies < Eg
2. Thermalization of energetic carriers
•If E > Eg, E →Eg
3. Energy loss across p-n junction
4. Energy loss at contacts
5. Recombination
Shockley Queisser Limit
The Shockley–Queisser limit or detailed balance limit refers to the maximum theoretical efficiency of a solar cell using a p-n junction to collect power from the cell.
The limit places maximum solar conversion efficiency around 33.7% assuming a single p-n junction with a band gap of 1.1 eV (typical for silicon).
Multijunction solar cells
Useful definition: ”Solar cell concepts that allow for a more efficient utilization of the sun light than solar cells based on only one electronic band gap.”
Main approaches:
Modification of the photonic energy distribution prior to absorption in a solar cell
Utilization of materials or cell structures incorporating several band gaps
Reducing losses due to thermalization
Control recombination process
[attachment=47115]
Absorption
Only photons with sufficient energy can excite e-across the band gap Eg.
•Insufficiently energetic photons with
Ephot < Eg will not contribute to the photocurrent generation (1).
•Photons with Ephot > Eg will initially generate energetic excited charge carriers (2).
•Any energy in excess of Eg will be wasted heating up the solar cell through thermalization (3).
Energy loss in p-n junction
The fundamental loss mechanisms across the pn junction
1. Insufficient photon energies < Eg
2. Thermalization of energetic carriers
•If E > Eg, E →Eg
3. Energy loss across p-n junction
4. Energy loss at contacts
5. Recombination
Shockley Queisser Limit
The Shockley–Queisser limit or detailed balance limit refers to the maximum theoretical efficiency of a solar cell using a p-n junction to collect power from the cell.
The limit places maximum solar conversion efficiency around 33.7% assuming a single p-n junction with a band gap of 1.1 eV (typical for silicon).
Multijunction solar cells
Useful definition: ”Solar cell concepts that allow for a more efficient utilization of the sun light than solar cells based on only one electronic band gap.”
Main approaches:
Modification of the photonic energy distribution prior to absorption in a solar cell
Utilization of materials or cell structures incorporating several band gaps
Reducing losses due to thermalization
Control recombination process