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July 31, 2014

Homework Help: Solar Energy Please Help

Posted by Anonymous on Saturday, October 26, 2013 at 2:50pm.

Figure 1 shows a simplication of the AM1.5 solar spectrum at 1000W/m2. The spectrum is divided in three spectral ranges:

A for 0nm<λ<620nm

B for 620nm<λ<1240nm

C for 1240nm<λ<1860nm

The photon flux in each spectral range is also shown in the figure.

a) The hydrogenated silicon carbide material (a-SiC:H) is a new type of amorphous semiconductor material which has been recently studied for PV applications. This material has a relative large band gap of 2.0 eV. Imagine we integrate this material in a single-junction p-i-n solar cell as shown in Figure 2a below. In which spectral ranges does this solar cell convert light into charge carriers?

1)A
2)B
3)C


b) What is the Jsc (in mA/cm2) of the solar cell if only 65% of the absorbed photons result in a current?


c) The Voc in V of the a-SiC:H solar cell can be roughly estimated by the equation:

Voc=Egap(J)2q=Egap(eV)2
where q is the elementary charge, Egap(J) is the bandgap energy expressed in Joules, and Egap(eV) is the bandgap energy expressed in eV. The fill factor of the solar cell is FF=0.80. What is the efficiency of the solar cell (in %) ?

An up-convertor is a material which can convert two low-energy photons into a higher energy photon. Placing an up-convertor in our solar cell can help to reduce the spectral mismatch, since it can convert some photons with energy lower than 2 eV, which are not absorbed by the a-SiC:H cell, into a photon with an energy higher than 2 eV. Figure 2b depicts this possibility.

d) In the up-convertor 1, two photons are converted into one photon with 100% conversion efficiency. If all photons with energy above that of the band gap of a-SiC:H are absorbed in the a-SiC:H layer, in which spectral range can the photons be up-converted so that they contribute to the current in the cell as well?

1)A
2)B
3)C


e) In that case what would be the short-circuit current density and the efficiency of the solar cell illustrated in Figure 2b? Assume again that 65% of the absorbed photons result in a current.

Short-circuit current density in mA/cm2

Efficiency in %

f) In up-convertor 2 (see Figure 2c), three photons are converted into one photon with 100% conversion efficiency. if all photons with energy above that of the band gap of a-SiC:H are absorbed in the p-i-n cell, and convertor 1 absorbs only the photons in the spectral range as considered in parts e) and f), in which spectral part can the photons be up-converted by convertor 2 so that they contribute to the current in the cell as well?

1)A
2)B
3)C

g) In that case what would be the short-circuit current density and the efficiency of the solar cell illustrated in Figure 2c? Assume that 65% of the absorbed photons result in a current.

Short-circuit current density in mA/cm2

Efficiency in %

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