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Materials for solar conversion, Question 2 - Coggle Diagram
Materials for solar conversion
Prof.questions
Question 1
Number of electron (in conduction band) = number of holes in valence band
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Instrinsic Fermi Level Range (E_F): Represented as a green shaded region => indictate that it varies within the bandgap
Conduction Band (E_C): The blue solid line
Valence Band (E_V): The red solid line.
Doped (n-type) Fermi Level: The purple dashed line, positioned closer to the conduction band
Question 3
Losses
• 01:
Thermalization Loss
:
High-energy photons lose excess energy as heat.
• 02:
Non-Absorption Loss
:
Low-energy photons pass through without being absorbed
Solutions
1. Multi-juntion solar cell
Use multiple bandgaps to absorb a wider spectrum.
2. Intermediate Band Cells
:
Introduce energy levels to capture low-energy photons.
3. Up/Down Conversion
:
Modify photon energy to better match the bandgap
4. Hot Carrier Cells
:
Capture high-energy carriers before energy loss as heat.
Question 4
1st Generation (Crystalline Silicon - c-Si)
✔ High efficiency (~26.7%)
✔ Long lifespan (>25 years)
✔ Broad spectral absorption range
✔High carrier mobility
❌ Expensive manufacturing
❌Photons energy is wasted (heat)
2nd Generation (Thin-Film - CdTe, CIGS)
✔ Low cost & Reduced mass (light weight)
✔ Fabrication on flexible substrate
❌Toxic material (Cd),
❌ Scarce material (Te, In)
3rd Generation (Perovskites, Quantum Dots, Multi-Junction)
✔ High potential efficiency (>47%)
✔ Uses abundant & non-toxic materials
✔ Durability
❌ Reducing cost/watt of delivred solar
electricity
Question 2
Question 2
The p-side: Full of positive holes (+)
The n-side: Full of negative electrons (-)
When they touch
electron (n-region) fill the hole (p-region)
the hole (p-region) move into n-region and combine with e-
This process is called
diffusion
How Does the
Space Charge Region
Form?
The p-region loses some holes, leaving behind negatively charged
acceptor ions (−)
The n-region loses some electrons, leaving behind positively charged
donor ions (+)
=> a region without any free charge carriers
space charge region (depletion region)
The fixed charges (positive in the n-side and negative in the p-side) create a built-in
electric field (E)
, pointing from
the n-side to the p-side
What Does the Electric Field Do?
prevents more electrons from moving into the p-region.
prevents more holes from moving into the n-region.
This means current cannot easily flow unless an external voltage is applied (like in a solar cell or diode)