RESUMO
Combining high efficiency with good radiation tolerance, perovskite solar cells (PSCs) are promising candidates to upend expanding space photovoltaic (PV) technologies. Successful employment in a Near-Earth space environment, however, requires high resistance against atomic oxygen (AtOx). This work unravels AtOx-induced degradation mechanisms of PSCs with and without phenethylammonium iodide (PEAI) based 2D-passivation and investigates the applicability of ultrathin silicon oxide (SiO) encapsulation as AtOx barrier. AtOx exposure for 2 h degraded the average power conversion efficiency (PCE) of devices without barrier encapsulation by 40% and 43% (w/o and with 2D-PEAI-passivation) of their initial PCE. In contrast, devices with a SiO-barrier retained over 97% of initial PCE. To understand why 2D-PEAI passivated devices degrade faster than less efficient non-passivated devices, various opto-electrical and structural characterications are conducted. Together, these allowed to decouple different damage mechanisms. Notably, pseudo-J-V curves reveal unchanged high implied fill factors (pFF) of 86.4% and 86.2% in non-passivated and passivated devices, suggesting that degradation of the perovskite absorber itself is not dominating. Instead, inefficient charge extraction and mobile ions, due to a swiftly degrading PEAI interlayer are the primary causes of AtOx-induced device performance degradation in passivated devices, whereas a large ionic FF loss limits non-passivated devices.
RESUMO
With a remarkable tolerance to high-energetic radiation and potential high power-to-weight ratios, halide perovskite-based solar cells are interesting for future space PV applications. In this work, we fabricate and test methylammonium-free, co-evaporated FA0.7Cs0.3Pb(I0.9Br0.1)3 perovskite solar cells that could potentially be fabricated in space or on the Moon by physical vapor deposition, making use of the available vacuum present. The absence of methylammonium hereby increased the UV-light stability significantly, an important factor considering the increased UV proportion in the extra-terrestrial solar spectrum. We then tested their radiation tolerance under high energetic proton irradiation and found that the PCE degraded to 0.79 of its initial value due to coloring of the glass substrate, a typical problem that often complicates analysis. To disentangle damage mechanisms and to assess whether the perovskite degraded, we employ injection-current-dependent electroluminescence (EL) and intensity-dependent VOC measurements to derive pseudo-JV curves that are independent of parasitic effects. This way we identify a high radiation tolerance with 0.96 of the initial PCE remaining after 1 × 1013 p+ cm-2 which is beyond today's space material systems (<0.8) and on par with those of previously tested solution-processed perovskite solar cells. Together our results render co-evaporated perovskites as highly interesting candidates for future space manufacturing, while the pseudo-JV methodology presents an important tool to disentangle parasitic effects.
RESUMO
It is current belief that numbers of CD8+ memory T lymphocytes in the memory phase of an immune response are maintained by homeostatic proliferation. Here, we compare the proliferation of CD8+ memory T lymphocytes, generated by natural infections and by intentional immunization, in spleen and bone marrow (BM). Fifty percent of CD8+ memory T lymphocytes in the spleen are eliminated by cyclophosphamide within 14 days, indicating that numbers of at least 50% of splenic CD8+ memory T lymphocytes are maintained by proliferation. The numbers of CD8+ memory T lymphocytes in the BM, however, were not affected by cyclophosphamide. This stability was independent of circulating CD8+ memory T cells, blocked by FTY720, showing that BM is a privileged site for the maintenance of memory T lymphocytes, as resident cells, resting in terms of proliferation.
