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solar cells could maximize performance under the AM0 environment in space, potentially achieving
efficiencies beyond the single-junction limit of 30%-35% . In addition, another important strategy in device
[108]
engineering is the introduction of integrated UV filters or UV-tolerant charge transport layers, since
photo-induced degradation of perovskite thin films occurs at short wavelengths, including the UV range .
[109]
For example, metal-oxide electron transport layers, such as TiO or SnO were widely used to filter out the
2
2,
most damaging UV wavelengths and protect the chemical bonds in the perovskite film from direct exposure
to high-energy UV light due to their wide bandgap and cutting UV region [110] . In addition, recent studies
have raised concerns that oxygen-vacancy-related Ti ions of TiO under UV illumination can lead to
2
photocarrier losses [100] , and SnO often exhibits more severe charge recombination due to its lower
2
conduction band , along with degradation during high-temperature processes . Accordingly, emerging
[112]
[111]
research efforts are underway to develop innovative charge transport materials with improved UV
durability [113,114] . Thus, compositional engineering of perovskites allows their absorption to be tuned for the
space solar spectrum, while PSCs can selectively absorb a broad range of wavelengths with high device
stability through appropriate choice of materials and device architecture.

Temperature coefficients and thermal cycling performance
Due to unpredictable solar phenomena, such as solar flares and coronal mass ejections, as well as the orbital
motion of spacecraft alternating between light and dark environments, thermal fluctuations become more
intense. The space temperature range of -185 to -150 °C, as specified by the American Institute of
Aeronautics and Astronautics in AIAA S-111A-2014, “Qualification and Quality Requirements for
Space-Qualified Solar Cells” [115] , requires that solar cells possess high thermal tolerance across a broad
operational range (-150 to +120 °C) to maintain stable and reliable performance in orbit. The temperature
coefficient (T ) is an important parameter for evaluating and improving the thermal cycling performance
PCE
of PSCs. It is defined as the change in efficiency or voltage with temperature. For example, c-Si solar cells
have a relatively low T of about -0.4 to -0.25%°C , indicating a significant efficiency drop with increasing
-1
PCE
temperature due to their high sensitivity to thermal effects. GaAs-based solar cells, commonly used in
current space applications, have a T of approximately 0.1 ~ -0.05%°C [Figure 4C]. PSCs generally exhibit
-1
PCE
a less negative T of around -0.2%°C -1[116] . Notably, Moot et al. reported a significantly improved T of
PCE
PCE
-0.08%°C for PSCs, achieved through compositional engineering of the perovskite and optimization of the
-1
charge transport layers . This interesting result can be attributed to the unique properties of perovskites, as
[117]
discussed below. (1) The bandgap of lead-halide perovskites typically increases with temperature, resulting in
an improvement in the open-circuit voltage (V ) of PSCs or a smaller V drop compared to other solar cells.
oc
oc
Consequently, PSCs exhibit reduced thermal voltage losses upon heating, partially offsetting the performance
degradation commonly observed in any commercial solar cells; (2) Although the carrier density in
perovskites varies depending on film engineering, device architecture [118,119] , and application, high-quality
MAPbI perovskites have a lower carrier density [120] compared to Sn-based narrow-bandgap, highly doped
3
perovskites [121] . This lower carrier density contributes to suppressed charge recombination and reduced
performance loss with increasing temperature. From a practical view, PSCs have high potential for thermal
tolerance with increased environmental temperatures [122,123] , such as prolonged sunlight exposure up to
~85 °C and repeated thermal cycling, compared with conventional solar cells [124-126] . Reportedly, the PCE of
PSCs decreased by only 5%-10% at 65 °C conditions, whereas silicon solar cells showed a PCE reduction of
approximately 20% relative to their initial room-temperature performance .
[117]
Basically, the perovskite PV materials undergo phase transitions in response to temperature variations,
leading to changes in crystal structure, structural disorder, and charge-carrier dynamics. For example,
MAPbI undergoes well-known phase transitions from the orthorhombic (γ) phase below ~-115 °C, to the
3
tetragonal (β) phase between -115 and ~60 °C, and finally to the cubic (α) phase above ~60 °C [127,128] . As
temperature increases, lattice symmetry increases, leading to enhanced dynamic disorder and stronger