general Flashcards
What does it mean to dope a semiconductor?
Doping the intentional introduction of impurities into an intrinsic semiconductor to modulate its electrical properties.
What do fourth generational solar cells combine?
The low cost and flexibility of conducting polymer films (organic) with the lifetime stability of novel nanostructures (inorganic).
What are fourth generational solar cells?
Solar cells based on organic-inorganics, offering improved power conversion efficiency over 3rd generational solar cells, whilst maintaining their low cost base.
Why are active inorganic nano-materials incorporated into 4th generational solar cells?
To improve the harvesting of solar energy and the manipulation of electrical charges, enhancing efficiency and lifetime stability.
How could the properties of hybrid organic-inorganic solar cells possibly be tailored?
By varying the sizes of the nano-particles (the quantum size effect).
How are hybrid organic-inorganic solar cells prepared?
By inexpensive, wet chemical synthesis.
What are the advantages of hybrid organic-inorganic solar cells?
- Cost effective.
- Efficient electron transportation.
- Strong optical absorption.
- Efficient exciton dissociation.
What does the photoeffective layer consist of in hybrid organic-inorganic solar cells?
Interconnected, semiconducting nanoparticles in a solid semiconducting polymer phase.
Why does a large bandgap result in larger open circuit voltage?
It causes a large potential barrier.
Why does a small bandgap result in a large short circuit current?
Because many photons will create electron hole pairs.
What is the dilemma when selecting a material based on bandgap?
P=VI
A small bandgap results in a large short circuit current, whilst a large bandgap results in a large open circuit voltage.
What is the ideal bandgap?
Usually around 1.5eV
What does the ideal bandgap size depend on?
The solar spectrum.
What are the five assumptions limiting solar efficiency?
- Single bandgap energy.
- One e- h+ pair per photon.
- Non-use of sub band gap photons.
- Single population of each charge carrier type.
- One-sun incident intensity.
What device principles are used to overcome the “non-use of sub-bandgap photons” efficiency limitation?
Up conversion.
What device principles are used to overcome the “one-sun incident intensity” efficiency limitation?
Concentrator solar cells.
What device principles are used to overcome the “single population of each charge carrier type” efficiency limitation?
- Hot carrier solar cells.
- Intermediate band solar cells.
- Quantum well/dot solar cells.
What device principles are used to overcome the “one e- h+ pair per photon” efficiency limitation?
- Down conversion.
- Multiple exciton generation.
- Avalanche generation.
What device principles are used to overcome the “single band gap energy” efficiency limitation?
- Multi-junction solar cells.
- Quantum dot/well solar cells.
What 5 solar cells are the paths to ultra-high conversion efficiencies?
- Multi-junction cells.
- Multiple absorption path cells.
- Multiple energy level cells.
- Multiple spectrum cells.
- Multiple temperature cells.
What is theoretical efficiency limit for multijunction solar cells utilising other high efficiency approaches?
> 80%
What happens when module temperature increases?
Efficiency decreases so the module must be cooled by natural ventilation.
What can be done to increase open circuit voltage?
- Increase bandgap.
- Increase doping.
- Increase minority carrier diffusion length.
- Decrease Sr.
What can be done to increase short circuit current?
- Reduce bandgap.
- Reduce reflection.
- Increase minority carrier diffusion length.
- xj at optimal level.
What can be done to increase fill factor?
- Decrease series resistance.
- Increase doping.
- Use a thick emitter.
