Publications by Year: 2017

2017
Tufan Ghosh, Sigalit Aharon, lioz etgar, and Sanford Ruhman. 12/5/2017. “Free carrier emergence and onset of electron-phononcoupling in methylammonium lead halide perovskite films.” Journal of the American Chemical Society, DOI: 10.1021/jacs.7b09508. free_carrier_emergence_and_onset_of_electron-phonon_coupling_in_methylammonium_lead_halide_perovskite_films.pdf
Daniel Amgar, Małgorzata Wierzbowska, Vladimir Uvarov, Vitaly Gutkin, and lioz etgar. 10/23/2017. “Novel Rubidium lead chloride nanocrystals: Synthesisand characterization.” Nano Futures, 1: 021002.Abstract

Alkali ternary lead halides have been studied intensively in the past few years, with great interest
focussed on perovskite materials. In this paper we report on novel rubidium lead chloride nanocrystals
(NCs) with the formula Rb6Pb5Cl16, which adopt a tetragonal symmetry. The NCs were characterized
and found to be active in theUVregion, with a band-gap of∼4.05 eV. The roles of the ligands, oleic
acid and oleylamine, were investigated and found to strongly affect the morphology and composition
of the NCs, through the stabilization of the facilitated crystallization of the ionic precursors. The
effective masses were observed by density functional theory (DFT) calculations, using the dielectric
function, and the the Bohr exciton radius and exciton binding energy of the NCs were estimated.
Moreover, the results were supported by the DFT calculations of the electronic properties and atomic
structure.

novel_rubidium_lead_chloride_nanocrystals.pdf
Stav Rahmany, Michael Layani, Shlomo Magdassi, and lioz etgar. 9/24/2017. “Fully functional semi-transparent perovskitesolar cell fabricated at ambient air.” Energy & Fuels, DOI: 10.1039/c7se00383h.Abstract

Organic–inorganic halide perovskite has excellent properties to function as light harvesters in solar cells
due to the possibility to tune its optical properties and to use it as thin film absorber, at a few hundrednanometer
thicknesses. Herein, we demonstrate the fabrication of perovskite solar cells with controlled
transparency, by the mesh assisted deposition process. Sequential fabrication of perovskite was
performed in air, wherein a PbI2 grid was formed in the first step, and in the second step, the grid
reacted selectively with methylammoniumiodide, resulting in a perovskite grid pattern. The best cells
were obtained with a photoanode composed of mesoporous TiO2 with Al2O3 nanoparticles. The
resulting semi-transparent perovskite solar cells, including a semi-transparent contact composed of
MoO3/Au/MoO3 yielded a power conversion efficiency of 5.5% with an average transparency of 26% and
efficiency of 8% for cells fabricated with a gold contact.

fully_functional_semi-transparent.pdf fully_functional.png
Ravi K. Misra, Bat-El Cohen, Lior Iagher, and lioz etgar. 8/28/2017. “Low-Dimensional Organic–Inorganic Halide Perovskite:Structure, Properties, and Applications.” ChemSusChem, 2017,10: 3712 – 3721.Abstract

Three-dimensional (3D) perovskite has attracted a lot of attention owing to its success in photovoltaic (PV) solar cells. However, one of its major crucial issues lies in its stability, which has limited its commercialization. An important property of organic–inorganic perovskite is the possibility of forming a layered material by using long organic cations that do not fit into the octahedral cage. These long organic cations act as a “barrier” that “caps” 3D perovskite to form the layered material.
Controlling the number of perovskite layers could provide a confined structure with chemical and physical properties that are different from those of 3D perovskite. This opens up a
whole new batch of interesting materials with huge potential for optoelectronic applications. This Minireview presents the synthesis, properties, and structural orientation of low-dimensional perovskite. It also discusses the progress of low-dimensional perovskite in PV solar cells, which, to date, have performance comparable to that of 3D perovskite but with enhanced stability. Finally, the use of low-dimensional perovskite in light-emitting diodes (LEDs) and photodetectors is discussed.
The low-dimensional perovskites are promising candidates for LED devices, mainly because of their high radiative recombination as a result of the confined low-dimensional
quantum well.

 

low_dimensional_organic_inorganic.png low-dimensional_organic-inorganic_halide_perovskite.pdf
Bat-El Cohen, Malgorzata Wierzbowska, and lioz etgar. 8/10/2017. “High efficiency quasi 2D lead bromide perovskitesolar cells using various barrier molecules.” Sustainable Energy & Fuels, 2017,1: 1935–1943.Abstract

This work reports on the high power conversion efficiency (PCE) and high open circuit voltage (Voc) of
bromide-based quasi 2D perovskite solar cells. A Voc of more than 1.4 V and, at the same time, a PCE of
9.5% for cells with hole transport material (HTM) were displayed, whereas a Voc value of 1.37 V and a PCE
of 7.9% were achieved for HTM-free cells. Bromide quasi 2D perovskites were synthesized using various
long organic barriers (e.g., benzyl ammonium, BA; phenylethyl ammonium, PEA; and propyl phenyl
ammonium, PPA). The influence of different barrier molecules on the quasi 2D perovskite's properties
was studied using absorbance, X-ray diffraction, and scanning electron microscopy. No change was
observed in the exciton binding energy as a result of changing the barrier molecule. Density functional
theory (DFT) with spin–orbit coupling calculations showed that in the case of BA, holes are delocalized
over the whole molecule, whereas for PEA and PPA, they are delocalized more at the phenyl ring. This
factor influences the electrical conductivity of holes, which is highest for BA in comparison with the
other barriers. In the case of electrons, the energy onset for the nonzero conductivity is lowest for BA.
Both calculations support the better PV performance observed for the quasi 2D perovskite based on BA
as the barrier. Finally, using contact angle measurements, it was shown that the quasi 2D perovskite is
more hydrophobic than the 3D perovskite. Stability measurements showed that cells based on the quasi
2D perovskite are more stable than cells based on the 3D perovskite.

high_efficiency_quasi_2d_lead_bromide_perovskite.pdf high_efficiency_quasi_2d_1.png
Y. Huang, S. Aharon, A. Rolland, L. Pedesseau, O. Durand, L. Etgar, and J. Even. 5/19/2017. “Influence of Schottky contact on the C-V and J-V characteristicsof HTM-free perovskite solar cells.” EPJ Photovoltaics, 2017,8: 85501.Abstract

Abstract The influence of the Schottky contact is studied for hole transport material (HTM) free
CH3NH3PbI3 perovskite solar cells (PSCs), by using drift-diffusion and small signal models. The basic
current-voltage and capacitance-voltage characteristics are simulated in reasonable agreement with experimental
data. The build in potential of the finite CH3NH3PbI3 layer is extracted from a Mott-Schottky
capacitance analysis. Furthermore, hole collector conductors with work-functions of more than 5.5 eV are
proposed as solutions for high efficiency HTM-free CH3NH3PbI3 PSCs.

influence_of_schottky_contact_on_the_c-v_and_j-v_characteristics.pdf
Chongwen Li, Yuanyuan Zhou, Yue Chang Li Wang, Yingxia Zong, lioz etgar, Guanglei Cui, Nitin P. Padture, and Shuping Pang. 5/19/2017. “Methylammonium-Mediated Evolution of Mixed-Organic-CationPerovskite Thin Films: A Dynamic Composition-Tuning Process.” Angew. Chem. Int. Ed., 2017,56: 7674 –7678.Abstract

Methylammonium-mediated phase-evolution
behavior of FA1@xMAxPbI3 mixed-organic-cation perovskite
(MOCP) is studied. It is found that by simply enriching the
MOCP precursor solutions with excess methylammonium
cations, the MOCPs form via a dynamic composition-tuning
process that is key to obtaining MOCP thin films with superior
properties. This simple chemical approach addresses several
key challenges, such as control over phase purity, uniformity,
grain size, composition, etc., associated with the solutiongrowth
of MOCP thin films with targeted compositions.

methylammonium.png methylammonium-mediated_evolution_of_mixed-organic-cation.pdf
Yue Chang, Li Wang, Jiliang Zhang, Zhongmin Zhou, Chongwen Li, Bingbing Chen, lioz etgar, Guanglei Cui, and Shuping Pang. 2/10/2017. “CH3NH2 gas induced (110) preferred cesiumcontainingperovskite films with reduced PbI6octahedron distortion and enhanced moisturestability.” J. Mater. Chem. A, 2017,5: 4803–4808.Abstract

We report here the discovery of a fancy interaction between cesium iodide (CsI) and methylamine (CH3NH2) due to the presence of the hydrogen bond. The formed CsI$xCH3NH2 is a liquid phase, which facilitates the large scale fabrication of highly uniform cesium-containing perovskite films with strong (110) preferred orientation by the CH3NH2 gas healing process. With this method, at most 10% nonpolar Cs cations could fully dope into the crystal lattice and extremely enhance the interaction of the inorganic framework with a more
symmetrical PbI6 octahedron, resulting in obvious improvement in moisture stability under continuous illumination.

ch3nh2_gas_induced_110_preferred_cesiumcontaining.pdf ch3.png
Bat-El Cohen, Małgorzata Wierzbowska, and lioz etgar. 2/3/2017. “High Efficiency and High Open Circuit Voltage in Quasi 2DPerovskite Based Solar Cells.” Advanced Functional Materials, 2017: 1604733.Abstract

An important property of hybrid layered perovskite is the possibility to reduce
its dimensionality to provide wider band gap and better stability. In this work,
2D perovskite of the structure (PEA)2(MA)n–1PbnBr3n+1 has been sensitized,
where PEA is phenyl ethyl-ammonium, MA is methyl-ammonium, and using
only bromide as the halide. The number of the perovskite layers has been
varied (n) from n = 1 through n = ∞. Optical and physical characterization
verify the layered structure and the increase in the band gap. The photovoltaic
performance shows higher open circuit voltage (Voc) for the quasi 2D perovskite
(i.e., n = 40, 50, 60) compared to the 3D perovskite. Voc of 1.3 V without
hole transport material (HTM) and Voc of 1.46 V using HTM have been
demonstrated, with corresponding efficiency of 6.3% and 8.5%, among the
highest reported. The lower mobility and transport in the quasi 2D perovskites
have been proved effective to gain high Voc with high efficiency, further
supported by ab initio calculations and charge extraction measurements. Bromide
is the only halide used in these quasi 2D perovskites, as mixing halides
have recently revealed instability of the perovskite structure. These quasi 2D
materials are promising candidates for use in optoelectronic applications that
simultaneously require high voltage and high efficiency.

high_efficiency_and_high_open_circuit_voltage.png hight_efficiency_and_hight.pdf
Daniel Amgar, Avigail Stern, Dvir Rotem, Danny Porath, and lioz etgar. 1/17/2017. “Tunable Length and Optical Properties of CsPbX3 (X = Cl, Br, I)Nanowires with a Few Unit Cells.” Nano Letters, 2017, 17: 1007−1013.Abstract

Perovskite nanostructures, both hybrid organo−metal
and fully inorganic perovskites, have gained a lot of interest in the past
few years for their intriguing optical properties in the visible region. We
report on inorganic cesium lead bromide (CsPbBr3) nanowires (NWs)
having quantum confined dimensions corresponding to 5 unit cells. The
addition of various hydrohalic acids (HX, X = Cl, Br, I) was found to
highly affect the NW length, composition, and optical properties.
Hydrochloric (HCl) and hydroiodic (HI) acids mixed in the reaction
solution influence the crystal structure and optical properties and
shorten the NWs, while the hydrobromic acid (HBr) addition results
solely in shorter NWs, without any structural change. The addition of HX increases the acidity of the reaction solution, resulting
in protonation of the oleylamine ligands from oleylamine into oleyl-ammonium cations that behave similarly to Cs+ during
crystallization. Therefore, the positions of the Cs+ at the growing surface of the NWs are taken by the oleyl-ammonium cations,
thus blocking further growth in the favored direction. The emission of the NWs is tunable between ∼423−505 nm and possesses
a potential in the optoelectronic field. Moreover, electrical conductivity measurements

tunable_length_and_optical_properties_of_few.png tunable_length_and_optical_properties_of_cspbx3.pdf
lioz etgar and Sigalit Aharon. 2017. “TWO DIMENSIONAL ORGANO-METAL HALIDE PEROVSKITENANORODS.” WIPO (World Intellectual Prop Org) WO 2017/153994 Al.
David P. Fenning, Mariana I. Bertoni, Yang Shao-Horn, lioz etgar, and Shany Gamliel. 2017. “Environmental sensors using metal halide perovskites.” United States of America Provisional application.
lioz etgar and Daniel Amgar. 2017. “Rubidium Lead Chloride Nanocrystals.” United States of America Provisional.