8.1.3 Summary to: 8.1 Solar Cells - General Concerns

A solar cell converts light power into electrical power. It's overriding parameter is the over-all conversion efficiency h
Important "raw" numbers.
  • Maximum h Si solar cell » 25 %
  • Maximum sun power » 1 kW / m2.
  • Maximum commercial solar cell power » 200 W / m2.
  • Yearly average commercial solar cell power »25 W / m2.

Solar cell science and technology centers exclusively on moneyand saving the earth!

Solar cell I-U essentials

Equivalent circuit of solar cell and equations
h  =  const · UOC · ISC· FF
Any solar cell is essentially a large -area junction, usually of the pn-type.
It's essential parameter are the short-circuit current ISc, the open-circuit voltage UOC and the fill factor FF  
For optimal efficiency the bandgap Eg should be matched to the solar spectrum; we need around 1.5 eV.  
Maximum efficiency from the semiconductor physics point of view is achieved if all light with energy >=Eg produces minority carriers and all of these carrier are swept out as diode reverse current and  
Maximum efficiency from the module systems point of view is achieved if the semiconductor part is OK, only very little light is reflected by the solar cell module, series resistances and shunt resistances can be neglected, and everything is uniform and homogeneous  
The equivalent circuit diagram with the basic equation has is all!
Series and shunt resistances, unavoidable for large areas, are of overwhelming importance for solar cells with h <» 10 %  
       
Solar cell characterisitcs with series resistors
Effect of series resistance
 
       
Solar cell characterisitcs with shunt resistors
Effect of shunt resistance
 
     
Switching solar cells with individual characteristics in series and / or in parallel causes all kinds of problems.  
Cost scenario of solar cells
Courtesy Deutsche Bank
Worse: Any inhomogeneous solar cell (e.g. mc-Si solar cells) consists of locally different solar cells "somehow" connected internally  
Optimizing solar cells with respect to "money" thus provides exciting science and engineering!


 
There are many competing solar cell technologies and materials.
  • Bulk single-crystal and mc Si vs. thin film Si (a-Si:H, µc-Si:H. ..
  • Other thin-film semiconductors:CIGS, CdTe, ...
  • Exotica: TiO2- electrolyte ("Grätzel cell"), organic semiconductors, "Nano" materials, ...
 
Solar cells have a bright future!    
   
Exercise 8.1-4
All Quick Questions to 8.1

With frame Back Forward as PDF

© H. Föll (Semiconductor Technology - Script)