Consider two solar cells: Solar cell \'\'A\'\' has a bandgap energy of 1 eV and

Question

Consider two solar cells: Solar cell ''A'' has a bandgap energy of 1 eV and solar cell ''B'' has a bandgap energy of 1.7 eV. From all kind of possible losses, assume only the optical losses. Which of the following statements is TRUE? Non-absorption losses are higher in solar cell A than in solar cell B. Heating losses are higher in solar cell A than in solar cell B. According to the Shockley-Queisser analysis, radiative recombination is more important in solar cell B than in solar cell A. According to the Shockley-Queisser analysis, solar cell A can have an efficiency up to 50%.

Explanation / Answer

When the energy of a photon is equal to or greater than the band gap of the material, the photon is absorbed by the material and excites an electron into the conduction band. However, for photovoltaic applications, the photon energy greater than the band gap is wasted as electrons quickly thermalize back down to the conduction band edges.

Hence : A - FALSE (B has higher Non absorption loss). B - TRUE

Absorption of a photon creates an electron-hole pair, which could potentially contribute to the current. However, the reverse process must also be possible, according to the principle of detailed balance: an electron and a hole can meet and recombine, emitting a photon. This process reduces the efficiency of the cell. So max opern circuit voltage is always below the bandgap

Hence : C - FALSE ( A has less open circuit voltage)

The Shockley Queisser Limit calculation is a maximum efficiency around 33.7% assuming a single p-n junction with a band gap of 1.34 eV. The original calculation by Shockley and Queisser was 30% for a silicon solar cell.

Hence: D - FALSE

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