Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Charged grain boundaries reduce the open circuit voltage of
  polycrystalline solar cells--An analytical description   Analytic expressions are presented for the dark current-voltage relation
$J(V)$ of a $pn^+$ junction with positively charged columnar grain boundaries
with high defect density. These expressions apply to non-depleted grains with
sufficiently high bulk hole mobilities. The accuracy of the formulas is
verified by direct comparison to numerical simulations. Numerical simulations
further show that the dark $J(V)$ can be used to determine the open circuit
potential $V_{\rm oc}$ of an illuminated junction for a given short-circuit
current density $J_{\rm sc}$ . A precise relation between the grain boundary
properties and $V_{\rm oc}$ is provided, advancing the understanding of the
influence of grain boundaries on the efficiency of thin film polycrystalline
photovoltaics like CdTe and $\mathrm{Cu(In,Ga)Se_2}$.

9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat