Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Perovskite-perovskite tandem photovoltaics with optimized bandgaps   We demonstrate four and two-terminal perovskite-perovskite tandem solar cells
with ideally matched bandgaps. We develop an infrared absorbing 1.2eV bandgap
perovskite, $FA_{0.75}Cs_{0.25}Sn_{0.5}Pb_{0.5}I_3$, that can deliver 14.8 %
efficiency. By combining this material with a wider bandgap
$FA_{0.83}Cs_{0.17}Pb(I_{0.5}Br_{0.5})_3$ material, we reach monolithic two
terminal tandem efficiencies of 17.0 % with over 1.65 volts open-circuit
voltage. We also make mechanically stacked four terminal tandem cells and
obtain 20.3 % efficiency. Crucially, we find that our infrared absorbing
perovskite cells exhibit excellent thermal and atmospheric stability,
unprecedented for Sn based perovskites. This device architecture and materials
set will enable 'all perovskite' thin film solar cells to reach the highest
efficiencies in the long term at the lowest costs.

19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga