Aryl-Acetylene Layered Hybrid Perovskites in Photovoltaics.

Metal halide perovskites have shown exceptional potential in converting solar energy to electric power in photovoltaics, yet their application is hampered by limited operational stability. This stimulated the development of hybrid layered (two-dimensional, 2D) halide perovskites based on hydrophobic organic spacers, templating perovskite slabs, as a more stable alternative. However, conventional organic spacer cations are electronically insulating, resulting in charge confinement within the inorganic slabs, thus limiting their functionality.

Linking Nanoscopic Insights to Millimetric-Devices in Formamidinium-Rich Perovskite Photovoltaics.

Halide-perovskite semiconductors have a high potential for use in single-junction and tandem solar cells. Despite their unprecedented rise in power conversion efficiencies (PCEs) for photovoltaic (PV) applications, it remains unclear whether perovskite solar modules can reach a sufficient operational lifetime. In order to make perovskite solar cells (PSCs) commercially viable, a fundamental understanding of the relationship between their nanostructure, optoelectronic properties, device efficiency, and long-term operational stability/reliability needs to be established.

Assessing the Influence of Illumination on Ion Conductivity in Perovskite Solar Cells.

Whether illumination influences the ion conductivity in lead-halide perovskite solar cells containing iodide halides has been an ongoing debate. Experiments to elucidate the presence of a photoconductive effect require special devices or measurement techniques and neglect possible influences of the enhanced electronic charge concentrations. Here, we assess the electronic-ionic charge transport using drift-diffusion simulations and show that the well-known increase in capacitance at low frequencies under illumination is caused by electronic currents that are amplified due to the screening of the alternating electric field by the ions.

Blade-Coating of High Crystallinity Cesium-Formamidinium Perovskite Formulations.

Up-scalable coating processes need to be developed to manufacture efficient and stable perovskite-based solar modules. In this work, we combine two Lewis base additives (N,N'-dimethylpropyleneurea and thiourea) to fabricate high-quality CsFAPbI perovskite films by blade-coating on large areas. Selected-area electron diffraction patterns reveal a minimization of stacking faults in the α-FAPbI phase for this specific cesium-formamidinium composition in both spin-coated and blade-coated perovskite films, demonstrating its scaling potential.

Alleviating nanostructural phase impurities enhances the optoelectronic properties, device performance and stability of cesium-formamidinium metal-halide perovskites.

The technique of alloying FA with Cs is often used to promote structural stabilization of the desirable α-FAPbI phase in halide perovskite devices. However, the precise mechanisms by which these alloying approaches improve the optoelectronic quality and enhance the stability have remained elusive. In this study, we advance that understanding by investigating the effect of cationic alloying in CsFAPbI perovskite thin-films and solar-cell devices.

A Universal Perovskite/C60 Interface Modification via Atomic Layer Deposited Aluminum Oxide for Perovskite Solar Cells and Perovskite-Silicon Tandems.

The primary performance limitation in inverted perovskite-based solar cells is the interface between the fullerene-based electron transport layers and the perovskite. Atomic layer deposited thin aluminum oxide (AlO) interlayers that reduce nonradiative recombination at the perovskite/C interface are developed, resulting in >60 millivolts improvement in open-circuit voltage and 1% absolute improvement in power conversion efficiency. Surface-sensitive characterizations indicate the presence of a thin, conformally deposited AlO layer, functioning as a passivating contact.

Interface passivation for 31.25%-efficient perovskite/silicon tandem solar cells.

Silicon solar cells are approaching their theoretical efficiency limit of 29%. This limitation can be exceeded with advanced device architectures, where two or more solar cells are stacked to improve the harvesting of solar energy. In this work, we devise a tandem device with a perovskite layer conformally coated on a silicon bottom cell featuring micrometric pyramids-the industry standard-to improve its photocurrent.

Understanding and Mitigating the Degradation of Perovskite Solar Cells Based on a Nickel Oxide Hole Transport Material during Damp Heat Testing.

The development of stable materials, processable on a large area, is a prerequisite for perovskite industrialization. Beyond the perovskite absorber itself, this should also guide the development of all other layers in the solar cell. In this regard, the use of NiO as a hole transport material (HTM) offers several advantages, as it can be deposited with high throughput on large areas and on flat or textured surfaces via sputtering, a well-established industrial method.

Revealing the Role of Tin Fluoride Additive in Narrow Bandgap Pb-Sn Perovskites for Highly Efficient Flexible All-Perovskite Tandem Cells.

Tin fluoride (SnF) is an indispensable additive for high-efficiency Pb-Sn perovskite solar cells (PSCs). However, the spatial distribution of SnF in the perovskite absorber is seldom investigated while essential for a comprehensive understanding of the exact role of the SnF additive. Herein, we revealed the spatial distribution of the SnF additive and made structure-optoelectronic properties-flexible photovoltaic performance correlation.

Static Disorder in Lead Halide Perovskites.

In crystalline and amorphous semiconductors, the temperature-dependent Urbach energy can be determined from the inverse slope of the logarithm of the absorption spectrum and reflects the static and dynamic energetic disorder. Using recent advances in the sensitivity of photocurrent spectroscopy methods, we elucidate the temperature-dependent Urbach energy in lead halide perovskites containing different numbers of cation components. We find Urbach energies at room temperature to be 13.

Position-locking of volatile reaction products by atmosphere and capping layers slows down photodecomposition of methylammonium lead triiodide perovskite.

The remarkable progress of metal halide perovskites in photovoltaics has led to the power conversion efficiency approaching 26%. However, practical applications of perovskite-based solar cells are challenged by the stability issues, of which the most critical one is photo-induced degradation. Bare CHNHPbI perovskite films are known to decompose rapidly, with methylammonium and iodine as volatile species and residual solid PbI and metallic Pb, under vacuum under white light illumination, on the timescale of minutes.

How To Quantify the Efficiency Potential of Neat Perovskite Films: Perovskite Semiconductors with an Implied Efficiency Exceeding 28.

Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1-sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non-radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell.

Barrierless Free Charge Generation in the High-Performance PM6:Y6 Bulk Heterojunction Non-Fullerene Solar Cell.

Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy.

Perfluorinated Self-Assembled Monolayers Enhance the Stability and Efficiency of Inverted Perovskite Solar Cells.

Perovskite solar cells are among the most exciting photovoltaic systems as they combine low recombination losses, ease of fabrication, and high spectral tunability. The Achilles heel of this technology is the device stability due to the ionic nature of the perovskite crystal, rendering it highly hygroscopic, and the extensive diffusion of ions especially at increased temperatures. Herein, we demonstrate the application of a simple solution-processed perfluorinated self-assembled monolayer (p-SAM) that not only enhances the solar cell efficiency, but also improves the stability of the perovskite absorber and, in turn, the solar cell under increased temperature or humid conditions.

Nonradiative Recombination in Perovskite Solar Cells: The Role of Interfaces.

Perovskite solar cells combine high carrier mobilities with long carrier lifetimes and high radiative efficiencies. Despite this, full devices suffer from significant nonradiative recombination losses, limiting their V to values well below the Shockley-Queisser limit. Here, recent advances in understanding nonradiative recombination in perovskite solar cells from picoseconds to steady state are presented, with an emphasis on the interfaces between the perovskite absorber and the charge transport layers.

The Role of Bulk and Interface Recombination in High-Efficiency Low-Dimensional Perovskite Solar Cells.

2D Ruddlesden-Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite-based cells. Herein, 2D (CH (CH ) NH ) (CH NH ) Pb I perovskite cells with different numbers of [PbI ] sheets (n = 2-4) are analyzed.

Recombination between Photogenerated and Electrode-Induced Charges Dominates the Fill Factor Losses in Optimized Organic Solar Cells.

Charge extraction in organic solar cells (OSCs) is commonly believed to be limited by bimolecular recombination of photogenerated charges. However, the fill factor of OSCs is usually almost entirely governed by recombination processes that scale with the first order of the light intensity. This linear loss was often interpreted to be a consequence of geminate or trap-assisted recombination.

Unraveling the Electronic Properties of Lead Halide Perovskites with Surface Photovoltage in Photoemission Studies.

The tremendous success of metal-halide perovskites, especially in the field of photovoltaics, has triggered a substantial number of studies in understanding their optoelectronic properties. However, consensus regarding the electronic properties of these perovskites is lacking due to a huge scatter in the reported key parameters, such as work function (Φ) and valence band maximum (VBM) values. Here, we demonstrate that the surface photovoltage (SPV) is a key phenomenon occurring at the perovskite surfaces that feature a non-negligible density of surface states, which is more the rule than an exception for most materials under study.

Mixtures of Dopant-Free Spiro-OMeTAD and Water-Free PEDOT as a Passivating Hole Contact in Perovskite Solar Cells.

Doped spiro-OMeTAD at present is the most commonly used hole transport material (HTM) in n-i-p-type perovskite solar cells, enabling high efficiencies around 22%. However, the required dopants were shown to induce nonradiative recombination of charge carriers and foster degradation of the solar cell. Here, in a novel approach, highly conductive and inexpensive water-free poly(3,4-ethylenedioxythiophene) (PEDOT) is used to replace these dopants.

Constructing the Electronic Structure of CHNHPbI and CHNHPbBr Perovskite Thin Films from Single-Crystal Band Structure Measurements.

Photovoltaic cells based on halide perovskites, possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single-crystal band structure data from angle-resolved photoemission measurements.

Lead Halide Perovskites as Charge Generation Layers for Electron Mobility Measurement in Organic Semiconductors.

Hybrid lead halide perovskites are introduced as charge generation layers (CGLs) for the accurate determination of electron mobilities in thin organic semiconductors. Such hybrid perovskites have become a widely studied photovoltaic material in their own right, for their high efficiencies, ease of processing from solution, strong absorption, and efficient photogeneration of charge. Time-of-flight (ToF) measurements on bilayer samples consisting of the perovskite CGL and an organic semiconductor layer of different thickness are shown to be determined by the carrier motion through the organic material, consistent with the much higher charge carrier mobility in the perovskite.