Question

what is quantum theory and quantum efficiency

Answer 1

The "quantum efficiency" (Q.E.) is the ratio of the number of carriers collected by the solar cell to the number of photons of a given energy incident on the solar cell. ... The same mechanisms which affect the collection probability also affect the quantum efficiency.
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Answer 2

Here is your answer.

Quantum theory :- a theory of matter and energy based on the concept of quanta, especially quantum mechanics.

The "quantum efficiency" (Q.E.) is the ratio of the number of carriers collected by the solar cell to the number of photons of a given energy incident on the solar cell. ... The same mechanisms which affect the collection probability also affect the quantum efficiency.

Hope it helps you.