to considerably suppress the organic signature.
Thus, although it cannot be excluded that part
of an organic cometary material could survive
the impact, we expect the organic signature to
be strongly reduced and, when mixed with the
original Ceres material, the organic signature
should be even more subdued, making its recognition very difficult. Thus, it seems unlikely that
a chondritic or cometary impactor can explain
the observed organic signature.
The geological settings of the organic-rich
areas provide additional information. The Ernutet
area is heavily cratered and appears to be ancient
[it is adjacent to the heavily cratered terrains
(29)], as many large craters are subdued. The
Ernutet crater, however, exhibits relatively fresh
rims, but the distribution and character of the
OR areas are not associated with any single crater.
The largest concentration appears to drape discontinuously across the southwest floor and rim
of Ernutet crater and onto an older, highly degraded crater. Other OR areas are scattered independently to the northwest.
The organic-rich area appears to be admixed
with additional carbonate and ammoniated-species
concentrations, at least close to the main location (Fig. 4). As carbonates and ammoniated
phyllosilicates are clearly Ceres’ endogenous material (12, 14, 30), this Ceres-like mineralogy
would add difficult constraints for delivery by
an impactor of different composition. Alternatively, because Ceres shows clear signatures of
pervasive hydrothermal activity and aqueous alteration (12, 14, 30, 31), the OR areas may be the
result of internal processes, which is also supported by the concentration of carbonate and
ammoniated species in the same Ernutet area.
The difficulty of an endogenous origin for the
observed OR regions on Ceres, however, is identifying a viable method for transporting such material from the interior to the surface in the
Some of the organic compounds in carbonaceous chondrites may be the result of hydrothermal processing within the meteorite parent
bodies (19), although exotic stable isotope ratios
also indicate the possible formation of organic
precursors in interstellar space (32). Organic
matter is most abundant in those carbonaceous
chondrites that display the greatest amount of
inorganic aqueous alteration products as phyllosilicates and carbonates (33). Clay minerals are
known to adsorb organic species and actively
participate as catalysts in their syntheses and
reactions (33, 34). In this sense, we expect that
Ceres is a perfect world to develop substantial
indigenous organic material formed by hydrothermal alteration, given the widespread presence of other hydrothermal products.
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We thank the Italian Space Agency (ASI) and NASA for supporting
this work. The VIR instrument was funded and coordinated by the
ASI and built by Selex ES, with the scientific leadership of the
Institute for Space Astrophysics and Planetology, Italian National
Institute for Astrophysics, Italy. The VIR is operated by the Institute
for Space Astrophysics and Planetology, Rome, Italy. A portion of
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Materials and Methods
Figs. S1 to S4
Tables S1 and S2
16 September 2016; accepted 17 January 2017
Efficient and stable solution-processed
planar perovskite solar cells via
Hairen Tan,1 Ankit Jain,1 Oleksandr Voznyy,1 Xinzheng Lan,1
F. Pelayo García de Arquer,1 James Z. Fan,1 Rafael Quintero-Bermudez,1
Mingjian Yuan,1 Bo Zhang,1 Yicheng Zhao,1 Fengjia Fan,1 Peicheng Li,2 Li Na Quan,1
Yongbiao Zhao,2 Zheng-Hong Lu,2 Zhenyu Yang,1
Sjoerd Hoogland,1 Edward H. Sargent1*
Planar perovskite solar cells (PSCs) made entirely via solution processing at low
temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible
substrates, and perovskite-based tandem devices. However, these PSCs require an
electron-selective layer that performs well with similar processing. We report a
contact-passivation strategy using chlorine-capped TiO2 colloidal nanocrystal film that
mitigates interfacial recombination and improves interface binding in low-temperature
planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for
active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature
solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after
dark recovery) of their initial performance after 500 hours of continuous room-temperature
operation at their maximum power point under 1-sun illumination (where 1 sun is defined
as the standard illumination at AM1.5, or 1 kilowatt/square meter).
Metal halide perovskite solar cells (PSCs) have attracted extensive research inter- est for next-generation solution-processed photovoltaic (PV) devices because of their high solar-to-electric power conversion
efficiency (PCE) and low fabrication cost (1–4).
The top-performing PSCs, which have reached
a certified PCE of 22.1%, have relied on high-
temperature–sintered (450° to 550°C) mesopo-
rous TiO2 as the electron-selective layer (ESL)
(5–7). However, this high-temperature processing
makes manufacture more complex and hampers
722 17 FEBRUARY 2017 • VOL 355 ISSUE 6326
1Department of Electrical and Computer Engineering,
University of Toronto, 35 St. George Street, Toronto, Ontario
M5S 1A4, Canada. 2Department of Materials Science and
Engineering, University of Toronto, 184 College Street,
Toronto, Ontario M5S 3E4, Canada.
*Corresponding author. Email: firstname.lastname@example.org