Material synthesis is one of the most important aspects in humankinds’ endeavor to discover and create new materials for energy applications. One strategy to tailor materials with desired functions ...in a rational way is by knowing how functions relate to structure, synthetic variables, arrangement of atoms and molecules, and how functions evolve during synthesis. In order to accelerate materials synthesis, discovery, and optimization by 10 times it is the right time now to integrate computational tools, synthesis, and characterization. One particular barrier to realizing this concept is the understanding of when and how phases form in real time during synthesis, which is challenging to asses by existing theoretical frameworks. In addition, transient or metastable phases with positive free energy above the lowest‐free energy ground state can be revealed by such real time (in situ) measurements. Metastable materials are ubiquitous in condensed matter and can show superior properties compared to their equilibrium form. This essay discusses the value of emerging multimodal in situ characterizations exemplified on hybrid halide perovskites. Finally, the ways in which the implementation of in situ measurements can advance the materials science synthesis field as well as their role to enable close‐loop feedback control and autonomous synthesis are discussed.
Multimodal in situ characterization during the fabrication of functional materials or device testing enables the correlation of complementary properties. Understanding the relevant mechanisms builds the foundation to tailor and engineer superior materials and devices. This essay reviews recent correlative studies that shed light on the formation of halide perovskites as well as device characterization to gain insights into failure mechanisms.
Halide perovskites have emerged as materials for high‐performance optoelectronic devices. Often, progress made to date in terms of higher efficiency and stability is based on increasing material ...complexity, i.e., formation of multicomponent halide perovskites with multiple cations and anions. In this review article, the use of in situ optical methods, namely, photoluminescence (PL) and UV‐vis, that provide access to the relevant time and length scales to ascertain chemistry–property relationships by monitoring evolving properties is discussed. Additionally, because halide perovskites are electron/ion conductors and prone to solid‐state ion transport under various external stimuli, application of these optical methods in the context of ionic movement is described to reveal mechanistic insights. Finally, examples of using in situ PL and UV‐vis to study degradation and phase transitions are reviewed to demonstrate the wealth of information that can be obtained regarding many different aspects of ongoing research activities in the field of halide perovskites.
This review summarizes the advances in the field of halide perovskites making use of optical in situ photoluminescence and UV‐vis measurements to investigate dynamic processes including synthesis, ionic movement, degradation, and phase changes.
Non-fullerene acceptors based organic solar cells represent the frontier of the field, owing to both the materials and morphology manipulation innovations. Non-radiative recombination loss ...suppression and performance boosting are in the center of organic solar cell research. Here, we developed a non-monotonic intermediate state manipulation strategy for state-of-the-art organic solar cells by employing 1,3,5-trichlorobenzene as crystallization regulator, which optimizes the film crystallization process, regulates the self-organization of bulk-heterojunction in a non-monotonic manner, i.e., first enhancing and then relaxing the molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided and we have achieved efficient organic solar cells with reduced non-radiative recombination loss. In PM6:BTP-eC9 organic solar cell, our strategy successfully offers a record binary organic solar cell efficiency of 19.31% (18.93% certified) with very low non-radiative recombination loss of 0.190 eV. And lower non-radiative recombination loss of 0.168 eV is further achieved in PM1:BTP-eC9 organic solar cell (19.10% efficiency), giving great promise to future organic solar cell research.
Hybrid organic–inorganic halide perovskite based semiconductor materials are attractive for use in a wide range of optoelectronic devices because they combine the advantages of suitable ...optoelectronic attributes and simultaneously low-cost solution processability. Here, we present a two-step low-pressure vapor-assisted solution process to grow high quality homogeneous CH3NH3PbI3–x Br x perovskite films over the full band gap range of 1.6–2.3 eV. Photoluminescence light-in versus light-out characterization techniques are used to provide new insights into the optoelectronic properties of Br-containing hybrid organic–inorganic perovskites as a function of optical carrier injection by employing pump-powers over a 6 orders of magnitude dynamic range. The internal luminescence quantum yield of wide band gap perovskites reaches impressive values up to 30%. This high quantum yield translates into substantial quasi-Fermi level splitting and high “luminescence or optically implied” open-circuit voltage. Most importantly, both attributes, high internal quantum yield and high optically implied open-circuit voltage, are demonstrated over the entire band gap range (1.6 eV ≤ E g ≤ 2.3 eV). These results establish the versatility of Br-containing perovskite semiconductors for a variety of applications and especially for the use as high-quality top cell in tandem photovoltaic devices in combination with industry dominant Si bottom cells.
Low‐resistance contact to lightly doped n‐type crystalline silicon (c‐Si) has long been recognized as technologically challenging due to the pervasive Fermi‐level pinning effect. This has hindered ...the development of certain devices such as n‐type c‐Si solar cells made with partial rear contacts (PRC) directly to the lowly doped c‐Si wafer. Here, a simple and robust process is demonstrated for achieving mΩ cm2 scale contact resistivities on lightly doped n‐type c‐Si via a lithium fluoride/aluminum contact. The realization of this low‐resistance contact enables the fabrication of a first‐of‐its‐kind high‐efficiency n‐type PRC solar cell. The electron contact of this cell is made to less than 1% of the rear surface area, reducing the impact of contact recombination and optical losses, permitting a power conversion efficiency of greater than 20% in the initial proof‐of‐concept stage. The implementation of the LiFx/Al contact mitigates the need for the costly high‐temperature phosphorus diffusion, typically implemented in such a cell design to nullify the issue of Fermi level pinning at the electron contact. The timing of this demonstration is significant, given the ongoing transition from p‐type to n‐type c‐Si solar cell architectures, together with the increased adoption of advanced PRC device structures within the c‐Si photovoltaic industry.
Exceptionally low contact resistivity is demonstrated on lightly doped (5 × 1015 cm−3) n‐type silicon via a nanometer thin lithium fluoride (LiFx) interlayer. This advancement enables the fabrication of a first‐of‐its‐kind n‐type silicon solar cell with a LiFx/Al partial rear contact made to less than 1% of the cell's area. An efficiency of over 20% is achieved at the proof‐of‐concept stage.
The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor ...is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI
PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI
as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.
Postfabrication surface treatment strategies have been instrumental to the stability and performance improvements of halide perovskite photovoltaics in recent years. However, a consensus ...understanding of the complex reconstruction processes occurring at the surface is still lacking. Here, we combined complementary surface-sensitive and depth-resolved techniques to investigate the mechanistic reconstruction of the perovskite surface at the microscale level. We observed a reconstruction toward a more PbI2-rich top surface induced by the commonly used solvent isopropyl alcohol (IPA). We discuss several implications of this reconstruction on the surface thermodynamics and energetics. Particularly, our observations suggest that IPA assists in the adsorption process of organic ammonium salts to the surface to enhance their defect passivation effects.
This work introduces a simplified deposition procedure for multidimensional (2D/3D) perovskite thin films, integrating a phenethylammonium chloride (PEACl)‐treatment into the antisolvent step when ...forming the 3D perovskite. This simultaneous deposition and passivation strategy reduces the number of synthesis steps while simultaneously stabilizing the halide perovskite film and improving the photovoltaic performance of resulting solar cell devices to 20.8%. Using a combination of multimodal in situ and additional ex situ characterizations, it is demonstrated that the introduction of PEACl during the perovskite film formation slows down the crystal growth process, which leads to a larger average grain size and narrower grain size distribution, thus reducing carrier recombination at grain boundaries and improving the device's performance and stability. The data suggests that during annealing of the wet film, the PEACl diffuses to the surface of the film, forming hydrophobic (quasi‐)2D structures that protect the bulk of the perovskite film from humidity‐induced degradation.
A facile method for depositing multidimensional perovskite thin films is presented, incorporating phenethylammonium chloride (PEACl) treatment into the antisolvent step for 3D perovskite formation. Using multimodal in situ characterization, it is shown that PEACl slows crystal growth, resulting in reduced grain boundary recombination and improved device efficiency. PEACl also forms hydrophobic 2D structures, protecting the film from humidity‐induced degradation.
Metal halide perovskite solar cells (PSCs) are infamous for their batch‐to‐batch and lab‐to‐lab irreproducibility in terms of stability and performance. Reproducible fabrication of PSCs is a critical ...requirement for market viability and practical commercialization. PSC irreproducibility plagues all levels of the community; from institutional research laboratories, start‐up companies, to large established corporations. In this work, the critical function of atmospheric humidity to regulate the crystallization and stabilization of formamidinium lead triiodide (FAPbI3) perovskites is unraveled. It is demonstrated that the humidity content during processing induces profound variations in perovskite stoichiometry, thermodynamic stability, and optoelectronic quality. Almost counterintuitively, it is shown that the presence of humidity is perhaps indispensable to reproduce phase‐stable and efficient FAPbI3‐based PSCs.
Atmospheric humidity control during the fabrication process crucially influences the phase formation and stability of formamidinium perovskites. This work reveals that controlled humidity during the fabrication process is a key to achieving reproducible fabrication of high‐quality and stable perovskite films. Thus, precise humidity management is essential to ensure the reproducible, efficient, and stable perovskite solar cells.
The in‐plane packing of gold (Au), polystyrene (PS), and silica (SiO2) spherical nanoparticle (NP) mixtures at a water–oil interface is investigated in situ by UV–vis reflection spectroscopy. All NPs ...are functionalized with carboxylic acid such that they strongly interact with amine‐functionalized ligands dissolved in an immiscible oil phase at the fluid interface. This interaction markedly increases the binding energy of these nanoparticle surfactants (NPSs). The separation distance between the Au NPSs and Au surface coverage are measured by the maximum plasmonic wavelength (λmax) and integrated intensities as the assemblies saturate for different concentrations of non‐plasmonic (PS/SiO2) NPs. As the PS/SiO2 content increases, the time to reach intimate Au NP contact also increases, resulting from their hindered mobility. λmax changes within the first few minutes of adsorption due to weak attractive inter‐NP forces. Additionally, a sharper peak in the reflection spectrum at NP saturation reveals tighter Au NP packing for assemblies with intermediate non‐plasmonic NP content. Grazing incidence small angle X‐ray scattering (GISAXS) and scanning electron microscopy (SEM) measurements confirm a decrease in Au NP domain size for mixtures with larger non‐plasmonic NP content. The results demonstrate a simple means to probe interfacial phase separation behavior using in situ spectroscopy as interfacial structures densify into jammed, phase‐separated NP films.
The assembly of mixed plasmonic and non‐plasmonic nanoparticles is characterized using UV–vis reflection spectroscopy, Grazing incidence small angle X‐ray scattering (GISAXS), and scanning electron microscopy (SEM). Small gold NP clusters form quickly, while NP rearrangements at later times allow for additional NP recruitment and subsequent ordering within the domain. Gold NP domains coarsen over time, but mixtures with intermediate non‐plasmonic content exhibit spectral narrowing, indicating an increase in order.
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