Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Enhanced Photovoltaic Performance of Perovskite Solar Cells by Co-Doped
  Spinel Nickel Cobaltite Hole Transporting Layer
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th