Optical constants manipulation of formamidinium lead iodide perovskites: ellipsometric and spectroscopic twigging.

Unraveling the knowledge of the complex refractive index and photophysical properties of the perovskite layer is paramount to uncovering the physical process that occurs in a perovskite solar cell under illumination. Herein, we probed the optical and photophysical properties of FAPbI (FAPI) and CsFAPbI (CsFAPI) thin films deposited from pre-synthesized powder, by the spectroscopic ellipsometer and time-resolved fluorescence spectra. We determined the complex refractive index of perovskite films by fitting the measured spectroscopic ellipsometer data with the three-oscillator Tauc-Lorentz (T-L) model.

Lead-sulfur interaction induced damp and water stability in pure formamidinium lead triiodide.

Research efforts in various multitudes have been demonstrated to stabilize methylammonium (MA)- and bromide (Br)-free formamidinium lead triiodide (FAPI) perovskite thin films. Despite these commendable efforts, pure FAPI perovskite thin film is prone to critical phase-transition issues due to its thermodynamically stable non-perovskite phase (2H). Here, in this work, we propose a rational additivization strategy to overcome this challenge.

Molecular Tailoring of Pyridine Core-Based Hole Selective Layer for Lead Free Double Perovskite Solar Cells Fabrication.

To solve the toxicity issues related to lead-based halide perovskite solar cells, the lead-free double halide perovskite CsAgBiBr is proposed. However, reduced rate of charge transfer in double perovskites affects optoelectronic performance. We designed a series of pyridine-based small molecules with four different arms attached to the pyridine core as hole-selective materials by using interface engineering.

Overcoming Limitations in Water-Ethanol Sprayed Superstrate Solar Cells by Compositional Engineering of CuCdSn(S,Se).

The increasing demand for solar energy requires materials from earth-abundant elements to ensure cost-effective production. One such light harvester CuCdSn(S,Se) fulfills this property. We report the development of functional solar cells based on CuCdSn(S,Se), which has been previously unreported.

Uncovering the Role of Electronic Doping in Lead-free Perovskite (CH NH ) CuCl Br and Solar Cells Fabrication.

Lead halide perovskites are attractive pigments to fabricate solar cells in the laboratory, owing to their high power conversion efficiency. However, given the presence of Pb, such materials also have a high level of toxicity and are carcinogenic for humans and aquatic life. Arguably, this hampers their acceptability for immediate commercialization.

Probing proton diffusion as a guide to environmental stability in powder-engineered FAPbI and CsFAPbI perovskites.

Formamidinium lead iodide-based solar cells show promising device reliability. The grain imperfection can be further suppressed by developing powder methodology. The water uptake capability is critical for the stability of α-formamidinium lead triiodide (FAPbI) thin films, and elucidating the migration of hydrogen species is challenging using routine techniques such as imaging or mass spectroscopy.

Microstrain and Urbach Energy Relaxation in FAPbI-Based Solar Cells through Powder Engineering and Perfluoroalkyl Phosphate Ionic Liquid Additives.

Structural and electronic imperfections are the origin of defects and lead to nonradiative recombination that is detrimental to fabricating efficient perovskite solar cells. Here, we propose a powder engineering methodology for α-FAPbI as a precursor material. Our developed methodology of α-FAPbI synthesis mitigates the notorious structural and electronic imperfections evidenced by a significant decline in the microstrain and Urbach energy as compared to reported δ-FAPbI powder and conventional precursor routes.

Reducing the Trap Density in MAPbI Based Perovskite Solar Cells via Bromide Substitution.

The past decade has witnessed tremendous advancement in the field of halide perovskite (PSK) as a choice of material for high-performing solar cells fabrication. Here, we investigate the impact of the halide exchange through N-bromosuccinimide (NBS) treatment in MAPbI based solar cells. We observed the partial halide exchange (I to Br ) or the filling of halide (X ) vacancy upon treatment of different NBS concentrations experimentally by spectroscopic and diffractogram studies.

Leverage of Pyridine Isomer on Phenothiazine Core: Organic Semiconductors as Selective Layers in Perovskite Solar Cells.

To drive the development of perovskite solar cells (PSCs), hole-transporting materials are imperative. In this context, pyridine derivatives are being probed as small molecules-based hole-transporting materials due to their Lewis base and electron-deficient unit. Herein, we focused our investigation on pyridine isomer molecules 4,4'-(10-(pyridin--yl)-10-phenothiazine-3,7-diyl)bis(,-bis(4-methoxyphenyl)aniline) ( = , , or ), in which the pyridine nitrogen heteroatom is located at the 2, 3, and 4 positions, named as , , and , respectively.

Deciphering the Orientation of the Aromatic Spacer Cation in Bilayer Perovskite Solar Cells through Spectroscopic Techniques.

Slowing the degradation of perovskite-based solar cells (PSCs) is of substantial interest. We engineered the surface by introducing a hydrophobic overlayer on a three-dimensional (3D) perovskite using fluorinated or nonfluorinated aryl ammonium cation spacers. The placement of a fluoroarene cation allows the formation of a bilayer structure, that is, layered/3D perovskites.

Tailoring of a Phenothiazine Core for Electrical Conductivity and Thermal Stability: Hole-Selective Layers in Perovskite Solar Cells.

Hole-selective layers are an indispensable component for the fabrication of effective perovskite solar cells. We designed and developed two phenothiazine-based hole transport materials: with an electron-donating sulfur atom and with an electron-withdrawing sulfone group in the core. in contrast to possesses a unique molecular orbital distribution and lower dihedral angles, which endowed it with excellent optoelectrical properties, improved charge transportation, and thermal stability.

Protocol for deciphering the electrical parameters of perovskite solar cells using immittance spectroscopy.

Here, we present a protocol for the fabrication of inverted ()-type perovskite solar cells, unraveling its electrical merits via immittance spectroscopy. The immittance spectroscopy is a prevailing technique for both qualitative and quantitative analyses of charge carrier dynamics in working devices. This technique integrates the temperature-dependent capacitance-frequency () spectra, impedance spectra, and Mott-Schottky analyses.

A Machine Learning Approach for Metal Oxide Based Polymer Composites as Charge Selective Layers in Perovskite Solar Cells.

A library of metal oxide-conjugated polymer composites was prepared, encompassing WO -polyaniline (PANI), WO -poly(N-methylaniline) (PMANI), WO -poly(2-fluoroaniline) (PFANI), WO -polythiophene (PTh), WO -polyfuran (PFu) and WO -poly(3,4-ethylenedioxythiophene) (PEDOT) which were used as hole selective layers for perovskite solar cells (PSCs) fabrication. We adopted machine learning approaches to predict and compare PSCs performances with the developed WO and its composites. For the evaluation of PSCs performance, a decision tree model that returns 0.

Substance and shadow of formamidinium lead triiodide based solar cells.

The current decade has witnessed a surge of progress in the investigation of methyl ammonium lead iodide (MAPbI3) perovskites for solar cell fabrication due to their intriguing electro-optical properties, despite the intrinsic degradation of the material that has restricted its commercialisation. As a promising alternative, solar cells based on its formamidinium analogue, FAPbI3, are currently being actively pursued for having demonstrated a certified efficiency of 24.4%, while the room-temperature conversion to a non-perovskite δ-phase impedes its further commercialisation, and strategies have been adopted to overcome this phase instability.

Mechanistic origin and unlocking of negative capacitance in perovskites solar cells.

We have unlocked the mechanistic behavior of negative capacitance in perovskite solar cells (PSCs) by analyzing impedance spectra at variable photovoltage and applied bias, temperature-dependent capacitance versus frequency () spectra, and current-voltage () characteristics. We noted that type PSCs having PEDOT:PSS or PTAA as hole transport layer display negative capacitance feature at low and intermediate frequencies. The activation energies ( ) for the observance of negative capacitance were found to be in a similar order of magnitude required for the ionic migration.

Pyridine Bridging Diphenylamine-Carbazole with Linking Topology as Rational Hole Transporter for Perovskite Solar Cells Fabrication.

Developing cost-effective and rational hole transporting materials is critical for fabricating high-performance perovskite solar cells (PSCs) and to promote their commercial endeavor. We have designed and developed pyridine (core) bridging diphenylamine-substituted carbazole (arm) small molecules, named as and . The linking topology of core and arm on their photophysical, thermal, semiconducting, and photovoltaic properties were probed systematically.

Elucidating the Doping Mechanism in Fluorene-Dithiophene-Based Hole Selective Layer Employing Ultrahydrophobic Ionic Liquid Dopant.

Perovskite solar cells have set a new milestone in terms of efficiencies in the thin film photovoltaics category. Long-term stability of perovskite solar cells is of paramount importance but remains a challenging task. The lack of perovskite solar cells stability in real-time operating conditions erodes and impedes commercialization.

Electrical Methods to Elucidate Charge Transport in Hybrid Perovskites Thin Films and Devices.

The panchromatic light absorption and excellent charge carrier transport properties in organo lead halide perovskites allowed to achieve an unprecedented power conversion efficiency in excess of 25 % for thin film photovoltaics fabrication. To understand the underlying phenomena, various comprehensive set of optical and electrical techniques have been employed to investigate the charge carrier dynamics in such devices. In this perspective, we aim to summarize the electrical transport properties of perovskite thin films by using (i) impedance spectroscopy (IS), (ii) space charge limited current (SCLC), (iii) field-effect transistors (FETs) and (iv) time-of-flight (TOF) methods.

Lead-Free Perovskites: Metals Substitution towards Environmentally Benign Solar Cell Fabrication.

Perovskite solar cells have attracted significant attention during the current decade owing to their efficacy and photovoltaics performance, which has reached a new milestone in the thin-film category. Perovskite solar cells have witnessed a remarkable 25.2 % light-to-electricity conversion efficiency; however, the toxicity of the commonly employed Pb counterpart towards humans as well as the environment, in addition to material instability, are current bottlenecks towards commercial application.

Appraisement of Crystal Expansion in CH NH PbI on Doping: Improved Photovoltaic Properties.

Three-dimensional hybrid perovskite materials (CH NH PbI ) suffer from intrinsic instability owing to organic cation evaporation and ion migration. The inclusion of a large organic cation such as guanidinium has been probed to stabilize the structure. This work proposes the inclusion of imidazolium iodide (C N H I) as an organic cation inside the CH NH PbI matrix, as a reservoir to control the spontaneous loss of iodide.

Understanding the Influence of Interface Morphology on the Performance of Perovskite Solar Cells.

In recent years, organo-halide perovskite solar cells have garnered a surge of interest due to their high performance and low-cost fabrication processing. Owing to the multilayer architecture of perovskite solar cells, interface not only has a pivotal role to play in performance, but also influences long-term stability. Here we have employed diverse morphologies of electron selective layer (ESL) to elucidate charge extraction behavior in perovskite solar cells.

Oxazolium Iodide Modified Perovskites for Solar Cell Fabrication.

Perovskites solar cells are gaining interest due to their attractive solar-to-electricity conversion efficiencies; however, they suffer from certain problems, such as suboptimal ion migration and stability issues. We report here on the inclusion of a phenyloxazolium salt (2-phenyl-3-methyloxazolium iodide) in perovskite solar cells based on methyl ammonium lead triiodide (MAPbI ). The fabricated solar cells not only displayed improved photovoltaic properties, but importantly the oxazolium cations can protect the perovskite layers from UV exposure as they down-convert electromagnetic irradiation; that is, the photons in the UV are absorbed and re-emitted at a different wavelength.

Identifying the charge generation dynamics in Cs-based triple cation mixed perovskite solar cells.

Triple cation based perovskite solar cells offer enhanced moisture tolerance and stability compared to mixed perovskites. Slight substitution of methyl ammonium or formamidinium cation by cesium (Cs), was also reported to eliminate halide segregation due to its smaller size. To elucidate the device kinetics and understand the role of the Cs, we undertook different modes of scanning probe microscopy and electrochemical impedance spectroscopy (EIS) experiments.

Towards Extending Solar Cell Lifetimes: Addition of a Fluorous Cation to Triple Cation-Based Perovskite Films.

Organohalide perovskites have emerged as highly promising replacements for thin-film solar cells. However, their poor stability under ambient conditions remains problematic, hindering commercial exploitation. The addition of a fluorous-functionalized imidazolium cation during the preparation of a highly stable cesium-based mixed perovskite material Cs (MA FA ) Pb(I Br ) (MA=methylammonium; FA=formamidinium) has been shown to influence its stability.

Cesium power: low Cs levels impart stability to perovskite solar cells.

Towards increasing the stability of perovskite solar cells, the addition of Cs is found to be a rational approach. Recently triple cation based perovskite solar cells were found to be more effective in terms of stability and efficiency. Heretofore they were unexplored, so we probed the Cs/MA/FA (cesium/methyl ammonium/formamidinium) cation based perovskites by X-ray photoelectron spectroscopy (XPS) and correlated their compositional features with their solar cell performances.