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.

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.

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.

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

We describe a general synthesis of conductive gold thin films doped with entrapped organic molecules,
and demonstrate, for the first time, the immobilization of a redox couple within an electrode in a single
step. The resulting film is of dual properties: conductivity arising from the gold, and redox behavior
originating from the entrapped molecule. Faster electron-transfer rates are found for the entrapped
case, compared to adsorption. The conductivity of the film affects the organic molecule–metal interactions,
as seen in resistivity measurements, in Raman spectroscopy of the metal-entrapped molecules and from
a remarkable red shift of 30 nm in emission spectroscopy. Doping is found to affect the work function
of gold. Thin conductive doped metal films are of relevance to a variety of applications such as
electrochemical detectors, electrode materials for electrochemical impedance spectroscopy, micro and
nano electronics interconnects for packaging and for printed circuit boards. The ability to fine-tune the
work function opens the possibility to design the desired energy level gaps for optoelectronic applications
such as light emitting diodes (LEDs), solar cells and transistors.

In recent years, hybrid organic–inorganic perovskite light absorbers have attracted much
attention in the field of solar cells due to their optoelectronic characteristics that enable high power
conversion efficiencies. Perovskite-based solar cells’ efficiency has increased dramatically from
3.8% to more than 20% in just a few years, making them a promising low-cost alternative for
photovoltaic applications. The deposition of perovskite into a mesoporous metal oxide is an
influential factor affecting solar cell performance. Full coverage and pore filling into the porous metal
oxide are important issues in the fabrication of highly-efficient mesoporous perovskite solar cells.
In this work, we carry out a structural and quantitative investigation of CH3NH3PbI3 pore filling
deposited via sequential two-step deposition into two different mesoporous metal oxides—TiO2
and Al2O3. We avoid using a hole conductor in the perovskite solar cells studied in this work to
eliminate undesirable end results. Filling oxide pores with perovskite was characterized by Energy
Dispersive X-ray Spectroscopy (EDS) in Transmission Electron Microscopy (TEM) on cross-sectional
focused ion beam (FIB) lamellae. Complete pore filling of CH3NH3PbI3 perovskite into the metal
oxide pores was observed down to X-depth, showing the presence of Pb and I inside the pores.
The observations reported in this work are particularly important for mesoporous Al2O3 perovskite
solar cells, as pore filling is essential for the operation of this solar cell structure. This work presents
structural and quantitative proof of complete pore filling into mesoporous perovskite-based solar
cells, substantiating their high power conversion efficiency.

Hybrid perovskite and all-inorganic perovskite have attracted much attention
in recent years owing to their successful use in the photovoltaic field.
Usually the perovskite is used in its bulk form, although recently, perovskites’
nanocrystalline form has received increased attention. Recent developments
in the evolving research field of nanomaterial-based perovskite are reviewed.
Both hybrid organic-inorganic and all-inorganic perovskite nanostructures are
discussed, as well as approaches to tune the optical properties by controlling
the size and shape of perovskite nanostructures. In addition, chemical modifications
can change the perovskite nanostructures’ band-gap, similar to their
bulk counterpart. Several applications, including light-emitting diodes, lasers,
and detectors, demonstrate the latent potential of perovskite nanostructures.

This review discusses various parameters that influence and control the organo-metal halide perovskite crystallization process. The effect of the perovskite morphology on the photovoltaic performance is a critical factor. Moreover, it has a dramatic effect on the stability of the perovskite, which has significant importance for later use of the organo-metal perovskite in assorted applications. In this review, we brought together several research investigations that describe the main parameters that significantly influence perovskite crystallization, for example, the annealing process, the precursor solvent, anti-solvent treatment, and additives to the iteite solutions.mechanisms. Control over morphology is a key parameter to understand this attractive material; morphology control will be an additional step throughout its commercialization process. The review is divided to four parts, presenting various parameters influencing perovskite crystallization and morphology. Section 2 discusses the effect of the annealing process; Section 3 describes the precursor solvent, presenting the possible solvents being used in the deposition process; Section 4 presents the anti-solvent treatment and its effect on the cell properties; and Section 5 discusses additives that can be added to the perovskite solution before deposition.

Spatial heterogeneities in the chemical makeup of thin film photovoltaic devices are pivotal in determining device efficiency. We report the in-plane spatial distribution and degree of chlorine incorporation in organic−inorganic lead halide perovskite absorbers by means of nondestructive synchrotronbased nanoprobe X-ray fluorescence. The presence of chlorine is positively identified in CH3NH3PbI3 films synthesized with Clcontaining precursors and as an impurity in some films synthesized with nominally Cl-free precursors. The impurity may be introduced from precursors or as contaminants during film synthesis. The films formed from Cl-containing precursors contain roughly an order of magnitude higher amount of chlorine, with Cl:I values greater than 0.02 found whether Cl is present in either the organic or the inorganic precursor for both one- and two-step fabrication processes. A spatial variation in the Cl incorporation is observed within single particles and as well as between particles within a given film, and the standard deviation of the Cl:I ratio across the films is up to 30% of the average
value. Understanding and controlling the heterogeneous distribution of chlorine in hybrid perovskite layers may offer a path to improve their photovoltaic performance.

We report a hybrid mesoporous–planar architecture of methylammonium lead iodide perovskite based solar cells, to combine the benefits of both the mesoporous and planar architectures in a single device. A mesoporous-TiO2 grid was fabricated on a compact TiO2 layer, through a self-assembly process based on directional wetting, providing regions with and without mesoporous-TiO2, followed by perovskite deposition and back contact evaporation (hybrid cells). The hybrid cells showed up to 10.7% power conversion efficiency (PCE) as compared to 13.5% and 6.3% for their mesoporous and planar counterparts, respectively. Interestingly, the hybrid cells are found to show a short circuit current density
(Jsc) as high as the Jsc of the mesoporous TiO2 based cells and proved to conserve the current density even in the absence of mesoporous-TiO2 from planar parts of the hybrid cells. The cells showed the best fill factor as compared to their mesoporous and planar counterparts. The areal variation in the meso to planar ratio has also been realized by changing the grid size to demonstrate the effect of the architecture on the cell performance. Charge extraction measurements have been used to obtain insight into the recombination inside different solar cells architectures. The hybrid cell structure emerged as a novel promising design for perovskite solar cells.