Chemistry 3160 Final Assessment Page 5 of 8 Solar Radiation Spectrum 4. (15 poin

Question

Chemistry 3160 Final Assessment Page 5 of 8 Solar Radiation Spectrum 4. (15 points) Figure 3: Left: Schematic of Quantum Dot enhanced solar cells. Right: Solar spectrum The strong and tunable resonant absorption and emission of quantum dots makes them promising candidates for enhancing the performance of solar panels Imagine you want to build a solar panel using a coating of monodisperse cadmiun sulfide (CdS) quantum dots; what radius should your quantum dots be to maximize the absorption of solar photons? Explain any assumptions you make in answering this question. (Data for CdS can be found on the last page, though you need only set up an appropriate expression for the radius symbolically).

Explanation / Answer

Quantum dots are only 1 nm to 12 nm in diameter. Due to their small size, quantum effects arise due to the confinement of electrons and holes; as a result, material properties are very different than the normal material. band gap is dependent on the size of the dots. When excited from an external source,quantum dot formed from semiconductors as CdS emit light in the visible range as well as infrared and ultraviolet, depending on its size. The higher-frequency blue light is emitted by smaller dots suspended in solution (larger band gap); red light is emitted from solutions with larger dots (smaller band gap). So, smaller band gap is good for solar cell.

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