Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fundamentals of PV Efficiency Interpreted by a Two-Level Model   Elementary physics of photovoltaic energy conversion in a two-level atomic PV
is considered. We explain the conditions for which the Carnot efficiency is
reached and how it can be exceeded! The loss mechanisms - thermalization, angle
entropy, and below-bandgap transmission - explain the gap between Carnot
efficiency and the Shockley-Queisser limit. Wide varieties of techniques
developed to reduce these losses (e.g., solar concentrators, solar-thermal,
tandem cells, etc.) are reinterpreted by using a two level model. Remarkably,
the simple model appears to capture the essence of PV operation and reproduce
the key results and important insights that are known to the experts through
complex derivations.

23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org