National Science Review
10: nwad071, 2023
https://doi.org/10.1093/nsr/nwad071
Advance access publication 14 March 2023
RESEARCH HIGHLIGHT
MATERIALS SCIENCE
Peter Müller-Buschbaum
Since the big success of the Vanguard
1 mission, being the first solar-powered
satellite, the use of solar cells in space
developed very rapidly. Today, conventional solar cell technologies for space
are based on silicon and GaAs modules.
If significantly higher power conversion
efficiencies (PCEs) are required,
sophisticated multiple junction devices
are in use such as III–V triple-junction
GaInP/GaAs/GaInAs modules. However, such inorganic solar cells are
expensive and supported on rigid substrates, not flexible and rather heavy,
also considering the massive deployment
systems typically needed. Accordingly,
the specific power or power-per-weight,
i.e. the ratio of generated power per mass
(measured in W kg−1 ), is very limited
despite high PCE values [1].
Due to high launch costs and payload
weight limits, a strong increase in the specific power of solar cells for space use is
highly desirable. Moreover, truly flexible
Figure 1. (a) Sketch of inverted device structure of AgNWs/α-ZnO/ZnO NPs/PBDB-T-2F : BTP-4F/C60/MoO3 /Al with an area of 0.64 cm2 fabricated
on 125- or 38-μm thin flexible PET substrates; (b) schematic diagram of the high-altitude balloon measurement system including photographs of the
balloon and device test system; (c) efficiency before and after balloon flight and at AM0 for six solar cells; (d) temporal evolution of open-circuit voltage
VOC , short-circuit current JSC , fill factor FF and PCE during the balloon flight. Reprinted from Ref. [8].
C The Author(s) 2023. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original
work is properly cited.
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Testing flexible polymer solar cells in near-space
Natl Sci Rev, 2023, Vol. 10, nwad071
stratospheric environment [8]. It is
to highlight that fully flexible organic
solar cells (for device geometry, see
Fig. 1a) were studied in situ with respect
to performance and stability at 35-km
altitude with a high-altitude balloon
measurement system (Fig. 1b). These
balloon flight data were compared with
systematic terrestrial investigations on
the performance under thermal cycling
and intense UV irradiation. Before and
after flying in near-space as well as under
terrestrial conditions, the PCEs were
compared (Fig. 1c) and the authors
concluded that flexible organic solar cells
can resist the extreme environment of
near-space. Of special value are the rich
solar cell device data collected during
the flight, probing different conditions
in terms of temperature and irradiation
intensity as seen in Fig. 1d. Here, a
single balloon flight is capable of probing
different conditions, thereby being an
excellent test platform.
In summary, this timely research
article demonstrates the power of using
near-space balloon studies for probing
next-generation solar cells and highlights
Page 2 of 2
the large potential of flexible organic
solar cells for use in the stratosphere.
Conflict of interest statement. None declared.
Peter Müller-Buschbaum
Department of Physics, TUM School of Natural
Sciences, and Heinz Maier-Leibnitz-Zentrum
(MLZ), Technical University of Munich, Germany
E-mail: muellerb@ph.tum.de
REFERENCES
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solar cells will enable completely different
deployment strategies. Novel solar cell
technologies based on organic solar cells
or perovskite solar cells offer these advantages of being lightweight, potentially
cheap and fully flexible [2]. Together
with a wide range of tunability, these
novel technologies become highly attractive for space use, after terrestrial tests
demonstrated a very promising stability in laboratory space simulations (testing vacuum & AM0/radiation tolerance)
[3,4]. First conceptual tests were realized
with balloon [5,6] and rocket flights [7],
which explored 35- and 240-km altitudes,
respectively.
In particular, the near-space region
has gained high interest for high-altitude
pseudo satellites or near-space aircrafts
in recent years and organic solar cells
or perovskite solar cells appear highly
promising to power objects in the
stratosphere. Recently, a team led by
Chang-Qi Ma, Zhixiang Wei, Qun Luo
and Guoning Xu published excellent
and solid work on in situ performance
and stability tests of large-area flexible polymer solar cells in the 35-km