Critical Role of Low-Energy Protons in Radiation Testing of Perovskite Space Solar Cells

While perovskite solar cells (PSCs) appear attractive for space power applications, a true radiation tolerance assessment requires development of proper radiation testing protocols. A basic criterion is that protons normally incident on a PSC during ground-based testing should create a uniform damage profile, mimicking the profile that the omnidirectional and polyenergetic proton spectrum in a space orbit would create in the PSC. However, given the low thicknesses of PSCs, proton energies above 0.05 MeV can meet this criterion, leading to ambiguity regarding the precise energy needed for testing. Here, we address this ambiguity by highlighting another major criterion: the optimal proton energy should also closely mimic the <i>elemental vacancy distribution</i> created in the perovskite layer by space protons. To arrive at this conclusion, we use Monte-Carlo ion-solid simulations to first calculate the elemental vacancies in a PSC resulting from low-Earth orbit (LEO) protons. We then show that only ~0.07 MeV protons normally-incident on a PSC result in a similar elemental vacancy distribution. Higher energies (~1 MeV) lead to 25% more iodine vacancies, 33% more lead vacancies, and 50% less hydrogen vacancies, and therefore do not represent the space radiation environment. Our study offers more precise guidelines for PSC radiation testing, paving the way for more accurate, reliable, and comparable radiation tolerance assessments.