What are the material properties of copper indium selenide/sulfide?

Question

Why it is sometimes prefered than cadmium telluride silicon,micro-crystalline silicon,polycrystalline silicon or Amorphous silicon?

and what makes it suitable for it to combine with these materials to produce a thin film solar cell?

note:the material properties,not the technology. thanks

Answer 1

The material is not separable from the technology.

We could say the efficiencies of these cells are higher, but the costs are higher too. That is what Wiki says, and you're not happy with that explaination. Wiki also indicates the band gap energies, and hole-electron reabsorbtion among other factors are different. You're not likely to understand why these are significant. So, here let's go over the physics. I am simplifying things, partly so you'll understand, and partly because I don't understand it very well myself - I'm a mechanical engineer, not a solid state physicist. So, some of the statements are not precisely true, but close enough. For example, electrons do not inhabit nice clean orbits like satellites around the Earth. They are believed to exist as an "electron cloud" distinquished by their quantuum states. The second statement is itself a simplifiation, but is almost true but incomprehensible, the first is really simplified and conveys the idea, but its way more complicated than that.

1. Particle Theory of Electromagnetic Radiation

Sunlight can be considered to consist of a bunch of particals called photons. The visible spectrum ranges from red, orange, yellow, green, blue, violet, and I think 1 or two others. The photons for each color have different energy and momentum, ranging from 1.8 eV (electron volts) for red to 3.1eV for blue.

2. Band Gap

Electrons on semiconductors are pretty much fixed in orbits with a certain amount of energy. The quantuum principle is that for each atomic/crystaline structure, electrons can have only certain discrete values or energies. The lowest value is the normal state. The next highest orbit requires 1.1 eV for silicon. There are other, higher values, but only certain ones. Now, when a photon of say 1.8eV is absorbed, the electron going into the next highest state gets 1.1eV, leaving 0.7eV to come out as a low energy photon, or some other way. Higher energy ones waste even more. These electrons can move throughout the material, and are electricity coming out of the solar cell.

This is the photoelectric effect (for which Albert Einstein was awarded the Nobel Prize). He did not get one for the special theory of relativativity.

Almost there, last part. When the electron goes up, it leaves behind a space with a missing electron, called a hole. Now, the hole can "steal" an electron from a nearby silicon atom, and the hole moves over there. So, holes (effectively a positive charge) move, as do electrons.

Also, if the electron drops back down and rejoins a hole, it emits the energy it absorbed (this is what an LED does). If this happens in a solar cell, the energy is lost. This is a big loss mechanism.

So, materials with higher band gap produce electrons of higher energy because they have higher voltage. This recovers more of the energy from the light.

Also, materials/solar cell designs with lower recombination rates yield more electrons, and thus more power.

Another approach is to have two materials, one to get the low energy photons, another to get higher energy photons. This raises efficiencies.

BTW, here's good references:

http://www.oilgae.com/energy/sou/ae/re/s...

http://www.windows.ucar.edu/tour/link=/p...

Hope all this stuff helps.... Good luck!

Answer 2

The chalcogenide semiconductors (e.g., CuGaSe2, AgInTe2, etc.) have lower melting points relative to their band gaps than the binary compound semiconductors (e.g., CdTe) or, even more so, the elementary semiconductors (e.g., Si.)

This can be a great convenience. It's only recently that the technology has developed to make these compounds with precise stoichiometry and thus make possible precise doping.

I published a paper way back in 1965 on two of these compounds in J. Phys. Chem. Solids. It was a piece of work before its time and was not appreciated.