| Date | May 2016 | Marks available | 2 | Reference code | 16M.3.hl.TZ0.21 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | 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:
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.
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”.
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
