the formation of the solar system and was incorporated into planetesimal bodies. Consequently, if
the formation of the solar nebula was typical, our
work implies that interstellar ices from the parent
molecular cloud core—including the most fundamental life-fostering ingredient, water—are widely
available to all young planetary systems.
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L.I.C. and E.A.B. acknowledge support by NSF grant
AST-1008800. C.M.O’D.A. was partially supported by
NASA Astrobiology grant NNA09DA81A and by NASA
Cosmochemistry grant NNX11AG67G. F.D. was supported
by NASA grant NNX12A193G. T.J.H. was supported by U.K.
Science and Technology Facilities Council grant ST/J001627/1.
Materials and Methods
Figs. S1 to S4
Tables S1 to S4
30 June 2014; accepted 21 August 2014
Water photolysis at 12.3% efficiency
via perovskite photovoltaics and
Jingshan Luo,1,2 Jeong-Hyeok Im,1,3 Matthew T. Mayer,1 Marcel Schreier,1
Mohammad Khaja Nazeeruddin,1 Nam-Gyu Park,3 S. David Tilley,1
Hong Jin Fan,2 Michael Grätzel1*
Although sunlight-driven water splitting is a promising route to sustainable hydrogen fuel
production, widespread implementation is hampered by the expense of the necessary
photovoltaic and photoelectrochemical apparatus. Here, we describe a highly efficient and
low-cost water-splitting cell combining a state-of-the-art solution-processed perovskite tandem
solar cell and a bifunctional Earth-abundant catalyst. The catalyst electrode, a NiFe layered
double hydroxide, exhibits high activity toward both the oxygen and hydrogen evolution
reactions in alkaline electrolyte. The combination of the two yields a water-splitting
photocurrent density of around 10 milliamperes per square centimeter, corresponding to a
solar-to-hydrogen efficiency of 12.3%. Currently, the perovskite instability limits the cell lifetime.
Compared with other energy resources, so- lar energy is sustainable and far more abun- dant than our projected energy needs as a species; thus, it is considered as the most promising energy source for the future. Because of the diffuse nature of solar energy, large
arrays of solar cells will have to be implemented.
Currently, electricity produced by silicon (Si) solar cells is too costly to achieve grid parity. In
contrast, the dye-sensitized solar cell (DSSC) (1, 2)
uses cheap materials and facile solution processes.
A related type of low-cost solution-processed so-
lar cell based on a perovskite formulation has
recently emerged (3–10). The rapid rise of the
solar-to-electric power conversion efficiency (cur-
rently 17.9% certified) in less than 5 years makes
it highly promising for large-scale commerciali-
zation (11). Long-term stability, however, is cur-
rently a challenge with these solar cells.
The conversion of solar energy directly into
fuels is a promising solution to the challenge of
intermittency in renewable energy sources, addressing the issues of effective storage and transport. In nature, plants harvest solar energy and
convert it into chemical fuel via photosynthesis.
Inspired by nature, artificial photosynthesis has
been proposed as a viable way to store the solar
energy as fuel (12, 13). Hydrogen, which is the
simplest form of energy carrier, can be generated
renewably with solar energy through photoelectrochemical water splitting or by photovoltaic (PV)–
driven electrolysis. Intensive research has been
conducted in the past several decades to develop
efficient photoelectrodes, catalysts, and device architectures for solar hydrogen generation (14–20).
However, it still remains a great challenge to develop solar water-splitting systems that are both
low-cost and efficient enough to generate fuel at
a price that is competitive with fossil fuels (21).
Splitting water requires an applied voltage of at
least 1.23 V to provide the thermodynamic driving
1Laboratory of Photonics and Interfaces, Institute of
Chemical Sciences and Engineering, School of Basic
Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL),
CH-1015 Lausanne, Switzerland. 2Division of Physics and
Applied Physics, School of Physical and Mathematical
Sciences, Nanyang Technological University (NTU), 637371
Singapore. 3School of Chemical Engineering and Department
of Energy Science, Sungkyunkwan University (SKKU), Suwon
*Corresponding author. E-mail: email@example.com
Fig. 1. Performance of perovskite solar cell. (A) Current density–potential curve (J–V) of the perovskite
solar cell under dark and simulated AM 1.5G 100 mW cm−2 illumination. (B) IPCE spectrum of the
perovskite solar cell and the integrated photocurrent with the AM 1.5G solar spectrum.