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Date May 2016 Marks available 2 Reference code 16M.3.hl.TZ0.21
Level HL Paper 3 Time zone TZ0
Command term State Question number 21 Adapted from N/A

Question

Traditional photovoltaic cells are made from n-type and p-type semiconductors.

State how n-type and p-type doping of silicon is achieved and the nature of electric charge carriers in each case.

n-type:

p-type:

[2]
a.

In dye-sensitized solar cells (DSSCs), nanoparticles coated with a black dye are trapped between electrodes in a liquid electrolyte. Explain the high efficiency of the DSSC structure.

[2]
b.

Markscheme

n-type:
«small amount of» As/Sb/P/group 15 element added AND «extra» electrons

p-type:
«small amount of» Ga/In/B/group 13 element added AND «extra electron» holes

Award [1 max] if only doping elements or only charge carriers are given.
Accept “group 5/group 5A/group V” for “group 15”.

Accept “group 3/group 3A/group III” for “group 13”.

a.

large surface area «increases chance photon will be absorbed»

«dye allows» absorption of a wide range of wavelengths
OR
dye converts most/all absorbed photons into electrons

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Options » C: Energy » C.8 Photovoltaic and dye-sensitized solar cells (HL only)

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