Q1. Ideal diode and ideality factor Two solar cells have an open circuit voltage

Question

Q1. Ideal diode and ideality factor Two solar cells have an open circuit voltage of 0.85 V and the same short circuit current under a given spectrum. One has an ideality factor of 1 the other has an ideality factor of 2. Use the diode equation to work out. the dark saturation current in each case as a fraction of Jsc. (You may neglect parasitic resistances). By finding the maximum of the power-voltage characteristic in each case compare the fill factors. How much more efficient is the 'ideal diode as a photoc onverter?

Explanation / Answer

Diode equation, I = IS (eVD/nVT) - 1) , where I is diode current, Is is the reverse saturation current, VD is the diode voltage, n is the ideality factor, VT is the thermal voltage, in this equation, taking VT= 1 and I = 1, since considering both the quantities to be unity, therefore, for ideality factor 1,

1 = IS (e0.85/ 1 x 1 - 1)

1 = IS  (e0.85  - 1)

1 = IS (2.339 - 1)

1 = IS ( 1.339)

IS = 1/ 1.339 = 0.74682 amp

For ideality 2,

1 = IS (e0.85/2 - 1)

1 = IS (e0.425 - 1)

1 = IS (1.529 - 1)

1 = IS (0.529)

IS = 1/0.529 = 1.9011 amp.

  

  

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