Questions on photovoltaic and dye-sensitized solar cells

1. (a) Explain why metals are good conductors of electricity whereas non-metals (other than graphite) are poor conductors of electricity.

(b) Explain how adding small amounts of gallium and arsenic to silicon improves the efficiency of the photoelectric effect.

2. The table below shows the wavelength of maximum absorbance for three named compounds together with their molecular formulas.

*The full structural formula of β-carotene can be found in Section 35 of the data booklet.

(a) Deduce the index of hydrogen deficiency for each compound.

(b) Explain the trend in the wavelength of maximum absorbance.

(c) 1,3-pentadiene and 1,4-pentadiene are structural isomers with the same index of hydrogen deficiency. Deduce, with an explanation, which of the two compounds will absorb light with the longer wavelength.

3. In a Grätzel DSSC a dye is covalently bonded to nanoparticles of titanium dioxide. One side of this plate is attached to a transparent plate made of tin(IV) oxide doped with fluoride ions and the other side is sealed to a separate plate containing an electrolyte of iodide ions on a thin sheet of platinum.

(a) Explain the function of:
(i) the dye.
(ii) the tin(IV) oxide.
(iii) the titanium dioxide.
(iv) the platinum.

(b) Explain with equations how the electrolyte of iodide ions functions.

(c) List two advantages that DSSCs have over silicon-based photoelectric cells.

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