| Date | May 2019 | Marks available | 1 | Reference code | 19M.3.hl.TZ1.18 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | 18 | Adapted from | N/A |
Question
This question is about solar cells.
Some solar cells use photovoltaic semi-conductors. Compare, giving reasons, the electrical conductivity of metals and semi-conductors as temperature increases.
Suggest one advantage of a dye-sensitized solar cell (DSSC) over a silicon based photovoltaic cell.
Markscheme
metal conductivity decreases AND semi-conductor conductivity increases [✔]
metal: collisions between «already free moving» electrons/vibrating lattice ions and electrons increase [✔]
semi-conductor:
provides sufficient energy for electrons to move to conduction band
OR
allows semiconductors to ionize forming freely moving electrons [✔]
Any one of:
cheaper [✔]
uses light of lower energy [✔]
plentiful resources [✔]
renewable resources [✔]
use of nanoparticles provides large surface area exposure to sunlight [✔]
can absorb better under cloudy conditions [✔]
better conductivity [✔]
more flexible [✔]
Examiners report
Candidates struggled to express themselves adequately in comparing the change in electrical conductivity of metals and semi-conductors as temperature increases. Many scored 1 mark for stating the effect of increasing temperature, but very few scored any marks for the explanation.
Generally answered well with most candidates able to suggest one advantage of a DSSC over a silicon based photovoltaic cell.
Syllabus sections
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18M.3.hl.TZ2.18b.ii:
Outline why complex B absorbs light of longer wavelength than complex A.
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18M.3.hl.TZ2.18b.i:
State the feature of the molecules responsible for the absorption of light.
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18M.3.hl.TZ1.15c:
The structure of two dyes used in DSSCs are shown.
Predict, giving a reason, which dye will absorb light of longer wavelength.
- 18N.3.hl.TZ0.15d.ii: Outline the effect of sunlight on the dye in the solar cell.
- 18N.3.hl.TZ0.15d.iii: State the purpose of TiO2.
- 18N.3.hl.TZ0.15d.i: Identify the structural feature of the dye that allows the conversion of solar energy into...
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18N.3.hl.TZ0.15d.iv:
Deduce the reduction half-equation at the cathode.
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17M.3.hl.TZ2.18a.ii:
The structures of 11-cis-retinal and β-carotene are given in section 35 of the data booklet. Suggest a possible wavelength of light absorbed by each molecule using section 3 of the data booklet.
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17M.3.hl.TZ1.19b:
Both photosynthesis and the Grätzel cell use energy from sunlight to bring about reduction. Deduce an equation for the reduction reaction in the electrolyte of a Grätzel cell.
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17M.3.hl.TZ2.19a:
Contrast how absorption of photons and charge separation occur in each device.
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17N.3.hl.TZ0.19b:
The natural absorption of light by chlorophyll has been copied by those developing dye-sensitized solar cells (DSSCs). Outline how a DSSC works.
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19M.3.hl.TZ1.18a:
Some solar cells use photovoltaic semi-conductors. Compare, giving reasons, the electrical conductivity of metals and semi-conductors as temperature increases.
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19M.3.hl.TZ2.20a:
Sketch graphs to show the general effect of increasing temperature on the electrical conductivity of semiconductors and metals on the axes below.
- 19N.3.hl.TZ0.20d(ii): Suggest an advantage of the DSSC over silicon-based photovoltaic cells.
- 19N.3.hl.TZ0.20d(i): Outline the functions of the dye, TiO2 and the electrolyte in the operation of the...
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18M.3.hl.TZ1.15a:
Early photovoltaic cells were based on silicon containing traces of other elements. State the type of semiconductor produced by doping silicon with indium, In, giving a reason that refers to its electronic structure.
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19M.3.hl.TZ2.20b:
Explain the function of dyes in a dye-sensitized solar cell (DSSC).
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16N.3.hl.TZ0.21c:
Dye-sensitized solar cells (DSSC) convert solar energy into electrical energy.
(i) Describe how a DSSC converts sunlight into electrical energy.
(ii) Explain the role of the electrolyte solution containing iodide ions, I−, and triiodide ions, I3−, in the DSSC.
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17M.3.hl.TZ2.19b:
Suggest one advantage a DSSC has over a silicon based photovoltaic cell.
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18M.3.hl.TZ1.15b:
Dye-sensitized solar cells, DSSCs, use a dye to absorb the sunlight. State two advantages that DSSCs have over traditional silicon based photovoltaic cells.
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17M.3.hl.TZ1.19a:
Identify two ways in which the structure of the dye shown resembles the chlorophyll molecule. Use section 35 of the data booklet.
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18M.3.hl.TZ2.18a:
Draw the Lewis (electron dot) structure for an appropriate doping element in the box in the centre identifying the type of semiconductor formed.
- 20N.3.hl.TZ0.14b: Doping of silicon increases the conductivity in semiconductors. Explain how doping improves...
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20N.3.hl.TZ0.14a:
Doping of silicon increases the conductivity in semiconductors.
Describe the doping in p-type and n-type semiconductors.
