The intermediate band solar cells based on quantum dots, get points by implementing these techniques epitaxial within a cell of GaAs. The aim is to harness the photons of less than one gap, which otherwise would not be absorbed, improving the efficiency of the cell.
In the right figure, we see how the InAs (Indium-Arsenide) is housed in the center of the GaAs matrix. A photon of less than one GAP (width of the band gap) can generate an electron hole pair from the BV to the BI, so that later you do another photon jump of the BI to the BC. thus increasing the current photogenic.
I would think a little about the Fermi seudoniveles that relate to the gas of free electrons moving in their respective energy bands (BV, BI and BC) and radiatively coupled (electron pair generation gaps between bands by absorbing light photons E> Eg, and recombination, of a predominantly radiative (as in the GaAs)). In the left figure, we show the structure of a cell of BI in balance. The inserted material in the middle of the band gap or area where initially the charge density is zero, would be what we call base (this in GaAs cell could be done with (InAs) by epitaxy, forming what are called quantum dots), and is the Banda Intermediate or BI. Above it is the area with doping, "n", and below the zone "p". The energy jumps to overcome are: E G (between BV and BC), E H (between BV and BI) and E L (among BI and BC). When photons of light hit in the face "n" of the cell, we see on the right side of the figure, we can find high-energy photons (type 3), capable of generating electron hole pairs (eh) between BV and BC, and less energy (type 1 and 2), can generate eh pairs between BV and BI y entre BI y BC (estos electrones que saltarían de BI a BC, lo harían en un doble salto, que como sabemos es lo que se busca para aumentar la corriente fotogeneradora que se extraería por el terminal n de la célula (la corriente convencional es opuesta al movimiento real de los electrones).
En la figura de la derecha, E FV , E FI y E FC , representan los tres seudoniveles de Fermi correspondientes a los gases de los electrones de las distintas bandas acoplados radiativamente. La radiación luminiscente que origina los posibles pares de e-h citados, tendrán un potencial químico µ bo-bf electroluminiscente resultante de la diferencia de energías between the original bands (bo) and end (bf) of which has generated the jump. If we divide the potential between the electron charge e, we obtain the voltage V the current is injected.
Curiously, this is the success of this theory, we can see that the higher voltage is produced between BV and BC, but can also play with the double jump. This is achieved by increasing the photogenic power without loss of tension (it is important that the BI is isolated from the outside or serial connection). Here's why:
V = (μ-μ BV BC) / e = (E-E FC FV) / e = (E-E FC FV) + (E-E FC FV)
A. Data from Luque and A Martin (Development of intermediate band solar cells. Summary extensive).
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