能量转换与存储原理教学资料multijunctioncells

1、MultijunctionInorganic Solar Cells,Efficiency limits,Below band gap photons not absorbed,Thermalization of excess energy,Sources of energy loss,CB,VB,Increasing VOC and decreasing JSC,Triple-junction cells,Appl. Phys. Lett. 90, 183516(2007) Emcore Corporation, May (2006),World Record: 40.7% under 24

2、0 suns!,1.7-1.9 eV 1.3-1.4 eV 0.67 eV,The cells are in series; current is passed through device The current is limited by the layers that produces the least current. The voltages of the cells add The higher band gap must see the light first.,Current Matching,Individually Optimized Cells,Current-matc

3、hed cells for MJSC,Synopsys, Inc., February 2009,Current Matching,Current limited by lowest-current subcell Total VOC is equal to sum of subcell VOCs,Tunnel Junctions,Common 3-cell structure, 10-nm-thick layers of very highly doped semiconductor on each side allows carriers to tunnel from conduction

4、 band of n+ material to valence band of p + material,Efficiency for various top and middle cells when the substrate is germanium,Baur, C. et.al., Journal of Solar Energy Engineering, 2007,Lattice matching,One can tune the band gap of the III-V materials by varying the elemental composition To avoid

5、defects (dislocations), one must match the lattice constants of each layer. For this reason, it is not yet possible to make an efficient cell with the ideal band gaps shown on the previous slide.,C. Baur et.al, Trans. Of the ASME, 2007,Lattice Matching,Lattice Matched Prevent formation of dislocatio

6、ns,Metamorphic Buffer Layer Dislocations terminate in buffer,Substrate,LM Absorber,TJ,Absorber,TJ, etc.,Buffer Layer,Absorber,TJ,With metamorphic materials, lattice matching does not have to be perfect.,Structure of 40.7% world record cell,R.R.King et.al, Appl. Phys. Lett. 90, 2007,R.R.King et.al, A

7、ppl. Phys. Lett. 90, 2007,Lattice matched vs. Mismatched,These cells are highly optimized!,Lattice matched vs. mismatched,40.7% for MM and 40.1% for LM at 240, 135 suns (respectively) Lattice mismatched (metamorphic) cell structure Areal defect density is 8106cm-2 Higher voltage upper sub-cell uses

8、larger part of solar spectrum More freedom to choose upper and middle cell materials,R.R.King et.al, Appl. Phys. Lett. 90, 2007,Future - more junctions,GaInNAs introduced for 6-junction cell Bandgap 1.0eV, lattice matched with Ge.,G.Strobl, et al, IEEE 4th world conf. 2, 2006,A Very Different Approa

9、ch,Alan Barnett et al. PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS, Prog. Photovolt: Res. Appl. 2009; 17:7583,The two sets of sets do not have to be lattice matched to each other or current matched.,Summary,Highest efficiency Space & terrestrial concentrator Current and lattice matching Fut

10、ure research New semiconductors with ideal band gaps More junctions Improved tunnel junctions,King, R. Nature Photonics 2, 284 - 286 (2008) Karem, N. et. al., IEEE Transactions on Electron Devices, 46(10), 2116-2125, 1999 Spectrolab Photovoltaic Products Data sheets, Sherif, R.A. Photovoltaic Specialists Conference, 2005. Conference Record of the Thirty-first IEEE, 17-22, Jan.