The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then publish the changes below to finish undoing the edit.
Latest revision | Your text | ||
Line 36: | Line 36: | ||
In monolithic cells, the positive and negative contacts are situated on the top and bottom of the cells. As a result, photogenerated carriers produced in the middle semiconductor layers must travel through multiple layers without recombining to reach the contacts. This is one additionally difficulty associated with MJ cells. Tunnel junctions, heavily doped regions connecting the n and p terminals of adjacent layers, are used to aid this carrier transportation. These p-n junctions (typically double hetero junctions) are made with the aim of minimizing electrical losses (voltage drops) as well as optical losses (photon absorption). The latter is done by using wide band gap tunnel junction materials to allow the photons to pass into the lower layers. However, this makes obtaining high tunnelling peak current difficult so thinning the depletion layer by means of a highly doped (>10<sup>19</sup> cm <sup>-3</sup>) junction is necessary. This design promotes quantum tunneling and yet also serves as an effective potential barrier for minority carriers. However, the exact physics behind quantum tunneling are not yet fully understood. Figure 4 on the right shows the band diagram of a double hetero tunnel junction. | In monolithic cells, the positive and negative contacts are situated on the top and bottom of the cells. As a result, photogenerated carriers produced in the middle semiconductor layers must travel through multiple layers without recombining to reach the contacts. This is one additionally difficulty associated with MJ cells. Tunnel junctions, heavily doped regions connecting the n and p terminals of adjacent layers, are used to aid this carrier transportation. These p-n junctions (typically double hetero junctions) are made with the aim of minimizing electrical losses (voltage drops) as well as optical losses (photon absorption). The latter is done by using wide band gap tunnel junction materials to allow the photons to pass into the lower layers. However, this makes obtaining high tunnelling peak current difficult so thinning the depletion layer by means of a highly doped (>10<sup>19</sup> cm <sup>-3</sup>) junction is necessary. This design promotes quantum tunneling and yet also serves as an effective potential barrier for minority carriers. However, the exact physics behind quantum tunneling are not yet fully understood. Figure 4 on the right shows the band diagram of a double hetero tunnel junction. | ||
[[File:Tunneljunctionband.JPG|center|thumb|Figure 4: Band diagram of a double hetero tunnel junction | [[File:Tunneljunctionband.JPG|center|thumb|Figure 4: Band diagram of a double hetero tunnel junction]] | ||
== Design Considerations == | == Design Considerations == |