Samuel Erickson1,William; Delmas1,2,Calista Lum1,3,Jorge Arteaga1,Kyle Crowley4,Jennifer Williams5,6,Lyndsey McMillon-Brown4,Timothy Peshek4,Sayantani Ghosh1
University of California, Merced1,Sandia National Laboratories2,University of California, Irvine3,NASA Glenn Research Center4,Wilberforce University5,Ohio Aerospace Institute6
Samuel Erickson1,William; Delmas1,2,Calista Lum1,3,Jorge Arteaga1,Kyle Crowley4,Jennifer Williams5,6,Lyndsey McMillon-Brown4,Timothy Peshek4,Sayantani Ghosh1
University of California, Merced1,Sandia National Laboratories2,University of California, Irvine3,NASA Glenn Research Center4,Wilberforce University5,Ohio Aerospace Institute6
The high defect tolerance and potential for extremely high specific power in metal-halide perovskite (MHP) solar cells make them promising materials for space-based photovoltaics. Additionally, moisture, by far the most significant variable in MHP degradation, is negligible outside of the earth’s atmosphere. In this work, we examine the effects of low earth orbit (LEO) on an MHP sample through high-resolution spectroscopic characterization. An encapsulated methylammonium lead iodide film was flown to the International Space Station as part of the 13<sup>th</sup> Materials International Space Station Experiment (MISSE-13) and exposed to the LEO environment for 10 months. Placed at zenith orientation, the sample underwent 45 minutes of AM0 illumination followed by 45 minutes of darkness a total of 4800 times, cycling between 100° C and -100° C each revolution. By comparing the spectral behavior, recombination lifetime, and phase transition temperature to a control sample, we quantified the changes in the flight sample.<br/> <br/>Overall, the flight sample emitted a strong photoluminescence signal and showed little sign of degradation. The film was encapsulated with Dow Corning 93-500 silicone elastomer and a 1 mm borosilicate cover glass. Glass of this thickness blocked protons with energies up to 13 MeV in simulation, so galactic cosmic rays were unlikely to have affected the sample. The flight sample also showed no visual changes or significant lead iodide (PbI<sub>2</sub>) formation under confocal microscopy, indicating that ultraviolet light transmitted through the cover glass was not damaging. Our analysis showed that the most significant and advantageous change in the film was a decreased tetragonal to orthorhombic phase transition temperature, likely caused by tensile strain from rapid temperature cycling. Calculations reveal in-plane tensile strain in the perovskite film at low temperatures due to the thermal expansion mismatch with its glass substrate. When this strain was relaxed through light soaking following 15 hours of AM1.5 illumination from a solar simulator, the flight sample’s low phase transition temperature (56 K) increased to nearly match its control (130 K). The slightly larger bandgap of the MISSE-13 sample (1.612 eV) also red-shifted to match that of its control sample (1.594 eV). Likewise, confocal microscopy revealed a reduction in lead iodide regions of the flight film. Finally, the average charge recombination lifetime of the flight sample tripled after this illumination. These behaviors indicate a combination of photo-annealing and strain relaxation within the film, further improving its performance. Altogether, the excellent optical response and stability of the flight sample demonstrates that MHPs can be properly encapsulated to withstand space stressors.<br/> <br/>*This work was supported by NASA grants no. NNX15AQ01 and NNH18ZHA008CMIROG6R