Researchers from Tianjin University, Tianjin Institute of Power Sources, Beijing Institute of Technology, the Shanghai Institute of Micro-System and Information Technology (Chinese Academy of Sciences), the Ningbo Institute of Materials Technology and Engineering (Chinese Academy of Sciences), and Harbin Institute of Technology have developed a perovskite/silicon tandem solar cell for space applications that reached a certified 27.49% power conversion efficiency (PCE) under AM0 (zero air mass) illumination - which the team describes as the highest certified AM0 efficiency reported to date for this type of tandem - while also demonstrating strong resistance to electron and proton radiation and stable output during a real high-altitude balloon flight to nearly 30 km.
Perovskite/silicon tandems are attractive for space power because they combine perovskite's radiation tolerance with silicon's mature manufacturing and near-infrared response, but most previous work has focused on efficiency under standard terrestrial (AM1.5G) conditions rather than the radiation resilience and extreme thermal cycling that low Earth orbit (LEO) actually demands. In LEO, devices cycle between roughly +90°C and -90°C more than 15 times a day and face continuous bombardment by high-energy electrons and protons, which damage semiconductors through ionization and atomic displacement. In a monolithic, series-connected tandem, damage to either subcell drags down the whole device - and the researchers found that the silicon bottom cell is usually the weak link.
To test this, the team irradiated both conventional n-type and p-type silicon heterojunction cells with 1 MeV electrons. The n-type cells were nearly wiped out: short-circuit current density collapsed from 47.08 to 1.96 mA/cm², a 97.58% efficiency loss at the highest fluence tested. P-type silicon held up far better, losing between 16.8% and 31.8% of its efficiency across the same fluence range - which is why the team built its tandem on a 100-μm-thick p-type silicon bottom cell instead of the n-type silicon used in most state-of-the-art tandems.
The team also tuned the top cell's bandgap specifically for radiation survival rather than just peak efficiency. Radiation damage in silicon shows up mainly as reduced response to longer-wavelength light, so the researchers widened the perovskite top cell's bandgap from the more commonly used 1.68 eV to 1.72 eV, letting more near-infrared light reach the silicon cell and keeping the two subcells' currents better matched even after the silicon degrades. After electron irradiation at 1x1014 e-/cm², the 1.72 eV tandem retained nearly 80% of its initial PCE, compared with a 27% efficiency loss for an otherwise identical 1.68 eV tandem.
To stabilize the wide-bandgap (1.72 eV) perovskite itself - a composition that normally suffers from phase segregation and non-radiative losses - the team added a multifunctional ionic liquid, 1,3-bis(cyanomethyl)imidazolium chloride ([Bcmim]Cl), to the perovskite precursor. The additive coordinates with Pb2+ ions during crystallization, producing larger, more uniform grains, reduced surface roughness, and lower trap density in both electron- and hole-only test devices. These improvements translated directly into device performance: single-junction 1.72 eV perovskite cells reached a champion PCE of 24.0% (certified steady-state efficiency of 23.58%), with reduced hysteresis and improved thermal and photostability compared with untreated control devices.
Built into the full monolithic tandem, the technology reached PCEs of 32.07% on a 0.95 cm² device and 30.58% on a 12.56 cm² device under standard AM1.5G illumination - a small drop that the team attributes to excellent process uniformity when scaling up. Under the AM0 spectrum relevant to actual space operation, an independently certified 12.56 cm² device reached 27.49% PCE, with an open-circuit voltage of 2.003 V, short-circuit current density of 22.44 mA/cm², and fill factor of 82.74%.
Beyond that headline efficiency figure, the tandem held up well under stress testing. Six thermal-shock cycles between -90°C and 90°C, with transitions of about 36°C per second, left the device at 96.8% of its initial PCE. Under 150 keV proton irradiation at a fluence of 1x1012 p+/cm², the unencapsulated tandem retained 93% of its initial PCE. Under continuous 1-sun illumination at 45±5°C and 70±10% relative humidity, an encapsulated device retained about 95% of its initial PCE after 550 hours, compared with roughly 60% retention for a control device over the same period.
Finally, the team took the test out of the lab: a 12.56 cm² encapsulated tandem, protected by a radiation-resistant cover glass, space-grade silicone and a thin moisture-blocking SiOx layer, was flown on a high-altitude balloon to an altitude of about 29.7 km, exposing it to real near-space conditions including low pressure, intense AM0 solar irradiance, rapid thermal swings and platform vibration. During the flight's high-altitude segments, the device delivered a stable, reproducible power output, reaching a maximum of 387.4 mW, with no signs of monotonic decay or encapsulation failure - direct evidence, the researchers say, that the design can survive authentic near-space operating conditions rather than just simulated ones in the lab.
