Anneal Recovery Post-Proton Irradiation of Hybrid Organic-Inorganic Metal Halide Perovskite Solar Cells and Study of Radiation Effects on Each Component Material

Nina Vaidya*¹ and Samuel Loke*¹, Jing-Shun Huang¹, Michael D. Kelzenberg¹, Pilar Espinet-Gonzales¹, Arky Yang¹, Jonathan Grandidier^1,2, Stepan Demchyschyn^1,3, Martin Kaltenbrunner³, Harry A. Atwater ¹<br/>* shared first authors<br/>¹ California Institute of Technology, Pasadena, CA, 91125, United States<br/>²Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109, United States<br/>³Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria<br/>We propose the recently expanding field of hybrid organic-inorganic metal halide perovskites solar cells to offer avenues to achieve high specific power (power/mass) needed for space-based power systems. These perovskites present tuneable band gaps ideal for a solar cell absorber layer, when combined with their favourable carrier diffusion lengths arising from high carrier mobility and lower ease of formation of deep-band defects, have thus far resulted in single-junction record efficiencies of 25.7% -perovskite solar cell have over taken efficiencies of thin-film Silicon solar cells. The ability to process the perovskite family of materials at temperatures below 473K via solution processing techniques such as spin-coating, spray coating, and even printing offers avenues for low-cost fabrication of perovskite solar cells. Moreover, work has been done to investigate the viability of perovskite solar cells on a flexible substrate, and it has been shown to be robust enough for flexible and ultralightweight cells, achieving power densities as high as 23Wg^-¹ [1]. As such, perovskite solar cells present themselves as a potential candidate for the high specific power technology necessary to enable space based solar power. More critically, perovskites are sensitive to oxygen and water vapor, both of which are not present in space and hence they inevitably become an extremely important opto-electronic energy materials to investigate for space applications.<br/>Hybrid organic-inorganic lead halide perovskite solar cells and their constituent device material layers were irradiated to examine their viability for space energy applications. Perovskites cells, hole and electron transport material films, and transparent conducting films were irradiated with 30keV and 75keV protons at fluences ranging from 4.3 x 10¹³ p⁺ cm^-2 to 1.7 x 10¹⁴ p⁺ cm^-2. The optical transmission and electrical resistances of the charge-transport material films were characterized before and after irradiation to deconvolve and assess the individual contribution of these materials on the degradation of perovskite devices. We conclude, some materials like PEDOT do become more opaque. Apart from these, electrically, the damage to many of these materials is low enough that there is only a small impact on the perovskite cell performance. The results of this proton irradiance study can serve as material selection guide for space cells. Furthermore, we characterized the perovskite solar cells through light-IV curves and EQE spectra before and after irradiation. Further to our initial study [2], we observed large scale degradation trends post large doses of proton irradiation. However, we demonstrate temperature-dependent anneal recovery post irradiation. We note that while heating a cell can recover most of its performance, this recovery peaks at 80°C and this reversible recovery starts reaching its limit when proton irradiation energy gets high, up to 75KeV.<br/>References:<br/>1) M. Kaltenbrunner, et al., “Flexible high power-per-weight perovskite solar cells with chromium oxide–metal contacts for improved stability in air,” Nature Materials, vol. 14, no. 10, pp. 1032-1039, 2015.<br/>2) J.-S. Huang, et al., “Effects of electron and proton radiation on perovskite solar cells for space solar power application,” in 2017 IEEE 44th Photovoltaic Specialist Conference, 2017.