P-type absorber material, an n-type material is mandatory for creating a good p-n junction. The heterojunction Absorber/Buffer cell requires a transparent conducting oxide (TCO) layer at the front contact enables photons to access into the cell and the active interface as well as considered one of the electrodes for collecting current. Our problem is how can reduce the carrier recombination at the back side of the structure and improve the cell efficiency?.
in general theory, the best and reasonable thing that can be used is using different layers for the engineering of energy diagram so that electron and hole transmit to their collector electrode before recombination. Of course, using high mobility materials can also be beneficial as the active layers. on the other hand you need more stable excitons against breaking down which relates to the kind of materials you use.
Dear Idris,
the thickness of the absorbing layer must be adapted
a) to the absorbtion coefficient alfa for the corresponding light energy: d ~ alfa-1
b) to the extension of the space charge area w: d ~ w
if the thickness d is too small, the separation efficiency decreases.
The back contact must lay outside of the optimized inner electric field.
With regard
R. Mitdank
CdMgTe (CMT) films is one of the best solution. Epitaxially grown CMT films on CdTe reduces the recombination at the back surface and also helps in reflection of electrons towards the charged collection region.
To reduce the back contact recombination one of the most used techniques is creating a BSF(back surface field).
Further the inclusion of materials which form an efficient contact with the bulk materials is also a prominent technique such as the ones used in HIT solar cells.
Also in many cases the use of intrinsic layers reduces the overall recombinations.
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