Is there a frequency of choice for conventional photovoltaic cells?

 

How much of the incident energy is lost in conversion? (What is the typical efficiency of such a device?)

The frequency of choice is your choice depending how much efficient you want it to be; photovoltaic cells operate in a spectrum of frequencies, being more or less efficiency here or there :

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People are happy to convert 20% of the incoming energy from a monocrystalline silicon cell.

 

One reason is that some IR photons have too little energy to make carriers, other photons have more than necessary and the excess is waisted. With silicon, most have too much energy, and a wider bandgap would improve, but materials are expensive.

 

The other reason is that 1.12eV (with silicon) is necessary to make a carrier pair, but this charge is exploited under approximately 0.45V in the load. Other semiconductors lose about as much, but from a wider bandgap, the proportion is less.

 

One improvement is to stack several materials or varied bandgaps, each one converting the light it's best for.

 

An other is to concentrate light, as this results in a higher load voltage - but the main reason for concentrating is rather to save photocell area.

 

Efficiency is just one desire in photocells, very important on satellites for instance, where users afford indium phosphide and more; on Earth, the area cost determines very much the technology, leading to use amorphous silicon for instance. The next big things may well be organic Solar cells, as they look cheaper.