Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modelling of limitations of bulk heterojunction architecture in organic
  solar cells II: 3d model   Polymer solar cells are considered as very promising candidates for
development of photovoltaics of the future. They are cheap and easy to
fabricate. However, up to now, they possess fundamental drawback: low
effectiveness. In the most popular BHJ (bulk heterojunction) architecture the
actual long-standing top efficiency is about 12\% (recent achievements about
15\%). One ask the question how fundamental this limitation is, as certain
theoretical considerations suggest that it should be about two times higher. In
our paper we analyze the `geometric factor' as one of possible explanation of
relatively low efficiency of BHJ architecture. More precisly, we calculate the
effective area of the donor-acceptor border in the random mixture of donor and
acceptor nanocrystals and further compare it with an ideal 'brush'
architecture. In our previous calculation for the two dimensional model, we
have found that the maximal value of geometric factor was about 40\%. In the
actual three dimensional model, it turned out that both architectures give very
close value of the effective area. So the geometric factor seems to be not
significant as a factor limiting efficiency. Implications of this fact are
discussed: we list two other factors (mentioned but not thoroughly discussed in
literature) which can be responsible for limitations of efficiency of BHJ
architecture. We estimate their scale, and suggest that these limitations are
inevitable, or at least very hard to overcome. We suggest that return to layer
architecture could radically improve efficiency limitations -- however, to make
breakthrough, materials with large exciton diffusion length have to be
invented.

13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th