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Pilar Espinet Gonzalez1 Michael Kelzenberg1 Nina Vaidya1 Qin Yang1 Rebecca Saive1 Samuel Loke1 Ali Naqavi1 Jing Shun1 Harry Atwater1

1, California Institute of Technology, Pasadena, California, United States

Perovskites are emerging as a promising photovoltaic technology for space applications. Not only can they be produced at dramatically lower cost than established space solar technologies, they can in fact achieve higher specific power (power output per mass > 20 W/g). We have recently found that they exhibit remarkable radiation resistance, suggesting that unshielded, ultralight perovskite solar cells could enable a 10x or higher breakthrough in specific power of space solar panels. We have fabricated cells and are experimentally evaluating several critical aspects of space operation: radiation resistance, stability under sunlight in vacuum, UV resistance, and extended thermal cycling.
We fabricated our cells on quartz superstrates, and achieved typical AM0 efficiencies of 13–16%. The device architecture adopted for our study is ITO/NiO/ MAPbI3/PCBM/Ag. Radiation testing has been performed with 1 MeV electrons and with 30 KeV, 50 KeV, and 350 KeV protons. To prevent the superstrate from shielding the cells, we irradiate the cells from the back side, through thin Ag contacts. Monte Carlo simulations predict that the 1MeV electrons and 350 KeV protons largely penetrate the entire perovskite structure. The 30 KeV and 50 KeV protons stop largely in the NiO and the ITO layers, respectively. Cell performance was measured before and after the radiation exposure. The 1 MeV electrons did not significantly damage the cells at fluence of 1013, 1014, and 1015 cm-3, and the remaining power at a fluence of 1016 e-/cm2 was 90 %. By comparison, this electron fluence in a III-V GaAs solar cell is reported to degrade efficiency by 50 %. The perovskite solar cells under 30, 50 and 350 KeV protons at a fluence of 1012 p+/cm2 maintained the open circuit voltage and short circuit current, while the fill factor degraded from 70%, to 37%, 42%, and 55%, respectively. However, after annealing the solar cells in a vacuum chamber at 90 oC for 3 days, the performance was completely recovered in all three cases, suggesting that the degradation in orbit would likely be negligible. We further tested the cells at the most damaging energy (30 KeV) at a higher fluence of 1013 p+/cm2. All efficiency parameters (Isc, Voc and FF) were degraded, resulting in a remaining efficiency of 2 %. However, annealing under vacuum restored the efficiency of the solar cells to 85 % of the initial value. In order to evaluate the light- and UV-stability of perovskite solar cells operating in space, we have loaded both irradiated and non-irradiated cells into a vacuum chamber where they can be continuously illuminated with simulated AM0 sunlight, or higher intensity UV light. A vacuum feedthrough permits us to periodically measure the cells’ efficiency parameters. We plan to monitor cell performance vs. time, over a range of anticipated operating temperatures (40–80°C), and under different steady-state load conditions (near maximum power point, open circuit, or short circuit).

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