Homojunction Device

Homojunction Device
Crystalline silicon is the primary example of this kind of cell:
A Single material-crystalline silicon is altered so that one side is p-type,dominated by positive holes,and the other side is n-type,dominated by nagative electrons.The p/n junction is located so that the maximuum amount of light is absorbed near it.The free electrons and holes generated by light deep in the silicon deffuse to the p/n junction,then separate to produce a current if the silicon is of sufficient high quality.
In this homojunction design,we may vary several aspects of the cell to increase conversion efficiency:
*Depth of the p/n junction below the cell's surface.
*Amount and distribution of dopant atoms on either side of the p/n junction.
*Crystallinity and purity of the silicon.

Some homojunctions cells have also been designed with the positive and negative electrical contacts on the back of the cells.This geometry eliminates the shadowing caused by the electrical grid on top of the cell.A disadvantage is that the carge carriers,which are mostly generated near the top surface of the cell,must travel farther all the way to the back of the cell to reach on electical contact.To be able to do this,the silicon must be of very high quality,without crystal defects that cause electrons and holes to recombine.



From: http://www1.eere.energy.gov/solar/silicon.html