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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Systematic Characterization on Optical and Phonon Properties of Cs[Pb x Sn 1– x ]I 3 Alloyed Perovskites via First-Principles Modeling

Here, understanding the optical properties and phonon thermodynamic features of materials enables the determination of their viability for optoelectronic applications including optical-based gas sensors. Metal halide perovskites ABX 3 as well as their mixed alloys can be attractive in applications of this kind. In particular, the formation of alloyed perovskites A[B x B’ 1–x ]X 3 modulates the functional characteristics that can overtake the single-halide ABX 3 . To this end, we use the first-principles simulations to model the effect of B-site alloying on the optical and phonon properties of cubic Cs[Pb x Sn 1–x ]I 3 (x = 0.75, 0.50, and 0.25). We identified the systematic shifts of optical properties as a function of alloying concentration, such as dielectric constants, refraction indices, and absorption coefficients. It was also found that a linear correlation exists between the optical constants and the band gaps of these materials, which satisfies the Penn model. Modeling of phonons in Cs[Pb x Sn 1–x ]I 3 showed that dissipating the dynamically unstable phonons can be feasible at a carefully chosen alloying concentration, which are originally present in their single-halide Pb- and Sn-ends. Our findings pave a way to optimize the alloying conditions of the alloyed perovskite systems of interest for tuning their optical and phonon stability characteristics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Water-Dispersible CsPbBr 3 Perovskite Nanocrystals with Ultra-Stability and its Application in Electrochemical CO 2 Reduction

Thanks to the excellent optoelectronic properties, lead halide perovskites (LHPs) have been widely employed in high-performance optoelectronic devices such as solar cells and light-emitting diodes. However, overcoming their poor stability against water has been one of the biggest challenges for most applications. Herein, we report a novel hot-injection method in a Pb-poor environment combined with a well-designed purification process to synthesize water-dispersible CsPbBr 3 nanocrystals (NCs). The as-prepared NCs sustain their superior photoluminescence (91% quantum yield in water) for more than 200 days in an aqueous environment, which is attributed to a passivation effect induced by excess CsBr salts. Thanks to the ultra-stability of these LHP NCs, for the first time, we report a new application of LHP NCs, in which they are applied to electrocatalysis of CO 2 reduction reaction. Noticeably, they show significant electrocatalytic activity (faradaic yield: 32% for CH 4 , 40% for CO) and operation stability (> 350 h).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Moisture-Induced Structural Degradation in Methylammonium Lead Iodide Perovskite Thin Films

Methylammonium lead iodide (CH 3 NH 3 PbI 3 , MAPbI 3 ) belongs to the group of organic–inorganic halide perovskites (OIHPs) that exhibit exceptional electrical and optical behavior suitable for photovoltaic applications. However, improving its structural and chemical stability and robustness remains a challenge for OIHPs to be considered a feasible active material in optoelectronic devices. This is due to the fact that this material is very susceptible to degrade under various intrinsic and extrinsic factors. Therefore, it is crucial to understand the mechanisms through which MAPbI 3 undergoes chemical degradation under operating conditions such as a relatively humid environment. We present the structural characteristics of MAPbI 3 under working conditions that suggest the routes of phase segregation as a result of exposing to highly moist media. We use dark pulse discharge behavior and current–voltage (I–V) variations of MAPbI 3 under different moisture levels to investigate the nature of structural degradation in OIHPs. Here we show that while relatively lower levels of humidity (~60% RH) have a limited impact on the structural stability of MAPbI 3 , exposure to higher levels of moisture (~100% RH) results in the formation of PbI 2 and aqueous CH 3 NH 3 I, which fundamentally change the charge transport characteristics in MAPbI 3 . Our findings explain the ongoing debate on the presence of a threshold for the humidity that triggers irreversible structural transformation and leads to full degradation of MAPbI 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Implications of Electron Transport Layer and Back Metal Contact Variations in Tin–Lead Perovskite Solar Cells Assessed by Spectroscopic Ellipsometry and External Quantum Efficiency

The structural and optical properties of hybrid organic–inorganic metal halide perovskite solar cells are measured by spectroscopic ellipsometry to reveal an optically distinct interfacial layer among the back contact metal, charge transport, and absorber layers. Understanding how this interfacial layer impacts performance is essential for developing higher performing solar cells. Here, this interfacial layer is modeled by Bruggeman effective medium approximations (EMAs) to contain perovskite, C 60 , BCP, and metal. External quantum efficiency (EQE) simulations that consider scattering, electronic losses, and the formation of nonparallel interfaces are created with input derived from ellipsometry structural-optical models and compared with experimental EQE to estimate optical losses. This nonplanar interface causes optical losses in short circuit current density (JSC) of up to 1.2 mA cm –2 . A study of glass/C 60 /SnO 2 /Ag or Cu and glass/C 60 /BCP/Ag film stacks shows that C 60 and BCP mix, but replacing BCP with SnO 2 can prevent mixing between the ETLs to prevent contact between C 60 and back contact metal and enable the formation of a planar interface between ETLs and back contact metals.

14 SOLAR ENERGY↗
DOE OSTI2022

Low-energy electronic structure of perovskite and Ruddlesden-Popper semiconductors in the Ba-Zr-S system probed by bond-selective polarized x-ray absorption spectroscopy, infrared reflectivity, and Raman scattering

Chalcogenides in perovskite and the related layered Ruddlesden-Popper crystal structures ( chalcogenide perovskites for brevity) are an exciting family of semiconductors but remain experimentally little studied. Chalcogenide perovskites share crystal structures and some physical properties with ionic compounds such as oxide and halide perovskites, but the metal-chalcogen bonds responsible for semiconducting behavior are substantially more covalent than in these more-studied perovskites. In this study, we use complementary experimental and theoretical methods to study how the mixed ionic-covalent Zr-S bonds support the electronic structure and physical properties of perovskite BaZrS 3 and Ruddlesden-Popper Ba 3 Zr 2 S 7 . We apply theoretical methods to assign features of experimentally measured x-ray absorption spectroscopy (XAS) to particular orbital transitions, enabling a clear physical interpretation of angle-dependent, polarized XAS data measured on single-crystal samples, and an atomistic view of the covalent bonding network that facilitates charge transport. Polarized Raman measurements identify signatures of crystalline anisotropy in Ba 3 Zr 2 S 7 and enable the first assignments of mode symmetry in this material. Infrared reflectivity reveals electronic transport properties that augur well for the use of chalcogenide perovskites in optoelectronic and energy-conversion technologies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Chapter 1: Halide Organic Photovoltaics for Energy: Hybrid Perovskites for Solar Cells

The following sections are included: Fundamentals of Photovoltaics, What Limits PV Device Efficiencies?, Traditional Photovoltaics, Perovskite Halide-Based Hybrid Semiconductors for Photovoltaics: Novel Materials in a League of Their Own, Solution Processability, Tunability, Perovskite Solar Cell Architectures, Pairing Perovskite Absorbers, Reduction/Oxidation and Electrochemical Reactivity Considerations for High-Performance Halide Perovskite Solar Cells, Metal Electrode Corrosion, Proton-Mediated Reduction of Ni3+ at NiOx Interfaces, Electrochemistry in Solid-State Perovskite Devices, Overview of Stability Considerations for High Performance Perovskite Solar Cells, Moisture-Induced Degradation, Oxygen-Mediated Degradation, Illumination-Dependent Degradation, Bias-Dependent Degradation, Stability Considerations for Charge Selective Contacts, Electrode-Induced Degradation Modes, Conclusion, and References.

absorbers↗
DOE OSTI2021

Nonadiabatic molecular dynamics analysis of hybrid Dion–Jacobson 2D leads iodide perovskites

The past six years have witnessed the rapid growth of interest in Dion–Jacobson (DJ) phase two-dimensional (2D) hybrid halide perovskites as optoelectronic materials with considerable intrinsic stability. The precise relationships between structural variations and the resulting charge carrier dynamics at finite temperature in these materials are keys to practical applications and are not yet completely understood. Here, we study 3-(aminomethyl) piperidinium (3AMP) and 4-(aminomethyl) piperidinium (4AMP) spacer cation-based lead iodide DJ phase systems and find these spacer cations to have a profound impact on the structural dynamics. Particularly, large conformational dynamics of the 3AMP-based perovskite compared to that of the 4AMP at room temperature leads to pronounced state energy fluctuation near band edges and further results in a shorter quantum coherence. The faster quantum decoherence of the 3AMP spacer-based perovskite underpins a longer nonradiative lifetime, offering insight into its superior performance as an optoelectronic material. This work sheds light on the relationship between structural fluctuations and charge carrier dynamics that can help in designing 2D perovskites with superior photophysical properties.

Wang, Ying (ORCID:0000000349048227)↗
DOE OSTI2020

Flash Formation of I-Rich Clusters during Multistage Halide Segregation Studied in MAPbI 1.5 Br 1.5

Wide band gap mixed halide perovskites such as MAPb(I 1–x Br x ) 3 sparked great research interest because of their outstanding optoelectronic properties, ease of fabrication, and band gap tunability. Their application thus far is however limited by light-induced halide segregation in which microscopic clusters with a high iodide content are formed and act as recombination centers. The key mechanism(s) underlying this halide segregation process are still debated. Here, we present a study on the photoluminescence evolution in MAPb(I 1.5 Br 1.5 ) perovskites with varying microstructures under constant illumination at room temperature and at elevated temperature. Our findings reveal a more complicated picture of the segregation mechanism occurring in three stages instead of two as commonly reported. The process starts with a flash formation of I-rich domains. Following is a rapid blue shift before the gradual and typically observed red shift occurs. The evolution of the three stages is fully reversible in the dark and is also present at elevated temperatures (50 °C). We explain the existence of multiple stages during light-induced halide segregation by natural compositional fluctuations of the halides and the formation of halide clusters with a dynamically changing distribution in I–Br content. The variation in the I–Br ratio depends on the grain size and film heterogeneity. Overall, these findings add further details in the quest of unraveling the underlying segregation mechanism(s), which need to be identified to stabilize halides in wide band gap perovskites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Accelerated Stress Testing of Perovskite Photovoltaic Modules: Differentiating Degradation Modes with Electroluminescence Imaging

Herein, electroluminescence (EL) and thermal imaging are used to examine p–i–n metal halide perovskite (MHP) photovoltaic (PV) mini-modules (MA0.6FA0.4PbI3, 20 cells, 78 cm2) before and after indoor-accelerated stress testing or outdoor deployment. Distinct spatial patterns in the EL images emerge, which depend on the external stress conditions experienced by the mini-module. Imaging results highlight a distribution of dark speckle features that dominate after UV stress, attributed to widespread interfacial contact degradation. Lateral intensity gradients across cells dominate after thermal cycling (TC) stress, attributed to current crowding near scribe defects. While current–voltage analysis alone does not give full insight on the degradation process, this study shows that distinct degradation modes can be further defined by multimodal electro-optical imaging (i.e., EL combined with photoluminescence and dark lock-in thermography). Neither UV exposure nor TC-accelerated stress testing alone replicates the same degradation signatures observed after outdoor deployment, suggesting that multiple degradation modes occur under concurrent stressors outdoors. Finally, spatial characterization of degradation modes in MHP PV mini-modules before and after accelerated stress testing lays the groundwork for developing targeted accelerated stress testing procedures through comparison with outdoor aging.

14 SOLAR ENERGY↗
DOE OSTI2025

Explainable artificial intelligence relates perovskite luminescence images to current-voltage metrics

As the demand for low-cost, high-efficiency solar energy technologies grows, metal halide perovskite (MHP) solar cells have emerged as a promising candidate for next-generation photovoltaics due to their high power conversion efficiencies. However, their poor durability and issues with manufacturing consistency remain significant barriers to commercialization. In this work, we develop deep learning models to support materials characterization and provide insight into features and processes influencing performance. The models are trained using transfer learning of a pretrained model to predict relevant current-voltage (IV) metrics based on different combinations of input electroluminescence (EL) and photoluminescence (PL) images of MHP devices. We examine which image types are most informative in accurately predicting different IV metrics. Additionally, we use explainable artificial intelligence (XAI) techniques to provide insights into specific spatial features in the devices that drive differences in performance. We find that stabilized luminescence images (e.g. those collected after biasing the devices for at least 1 min) are better for predicting metrics of open-circuit voltage (by PL) and short-circuit current (by PL with EL), but that predicting fill factor and overall power output may use the time-evolution of EL images. Based on attribution masks generated by integrated gradients for each device performance metric, we further suggest different loss mechanisms associated with categories of large and small spatial defects. Overall, this case study highlights the potential applicability of XAI methodology for streamlining MHP device analysis and accelerating detailed understanding of the relationships between spatial defects and impacts on performance.

14 SOLAR ENERGY↗
DOE OSTI2024

In-Situ Luminescence Imaging of Perovskite Solar Cells Demonstrates Increasing Spatial Nonuniformity Upon Light-Soaking Degradation

In this work we investigate degradation rates of triplecation mixed-halide perovskite p-i-n solar cells. We present an accelerated stress testing procedure using periodic blue light-soaking at elevated temperatures until devices reach ~80% of their initial efficiency. We track light-induced degradation via in-situ: photoluminescence (PL), current-voltage (I-V) curves, and transient photovoltage. Devices underwent 165 hours of light bias at 65degrees C. Results suggest that spatial uniformity in PL intensity decreases as device degradation increases. This investigation lays the groundwork to address the current gap in understanding the interplay between device performance and the evolution of macroscopic features in perovskite solar cells. Thus, we believe spatial characterization techniques will play a crucial role in the commercialization of perovskite solar cells.

imaging↗
DOE OSTI2020

Nucleation-controlled growth of superior lead-free perovskite Cs 3 Bi 2 I 9 single-crystals for high-performance X-ray detection

The organic-inorganic hybrid lead halide perovskites have emerged as a series of star materials for solar cells, lasers and detectors. However, the issues raised by the toxic lead element and marginal stability due to the volatile organic components have severely limited their potential applications. In this work, we develop a nucleation-controlled solution method to grow large size high-quality Cs 3 Bi 2 I 9 perovskite single crystals (PSCs). Using the technique, we harvest some centimeter-sized single crystals and achieved high device performance. We find that X-ray detectors based on PSCs exhibit high sensitivity of 1652.3 μC Gy air -1 cm -2 and very low detectable dose rate of 130 nGy air s -1 , both desired in medical diagnostics. In addition, its outstanding thermal stability inspires us to develop a high temperature X-ray detector with stable response at up to 100 °C. Furthermore, PSCs exhibit high X-ray imaging capability thanks to its negligible signal drifting and extremely high stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Nanotechnology for catalysis and solar energy conversion

This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure–property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society.

14 SOLAR ENERGY↗
DOE OSTI2021

Photophysical properties of zero-dimensional perovskites studied by PBE0 and GW+BSE methods

Due to the exceptional photophysical properties and great potential applications in solid state lighting, zero-dimensional halide perovskites with broadband emitting have recently attracted much attention. In this work, to reveal the origin of the broadband absorption and emission spectra of 0D (C 4 N 2 H 14 Br) 4 SnBr x I 6-x (x = 3), the ground state and exciton dynamics properties have been studied by hybrid PBE0 functional and the GW+BSE method. Different self-trapped excitons (STEs) are obtained, and their emission energies by PBE0 are consistent well with experimental data. By considering the vibrational broadening of emission, our calculated full width at half maximum of emission accords well with the experiment. The absorption of free exciton and STEs is also calculated by considering the quasiparticle and excitonic effect. Our results show that these light-induced trapped states can be observed by experiments, as confirmed in other similar systems by the femtosecond transient absorption spectra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Rational design of Lewis base molecules for stable and efficient inverted perovskite solar cells

Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.5 illumination at the maximum power point and at ~40°C for >3500 hours. DPPP-treated devices showed a similar increase in PCE after being kept under open-circuit conditions at 85°C for >1500 hours.

14 SOLAR ENERGY↗
DOE OSTI2022

PACT Perovskite PV Module Stress Testing Protocol (Version 0.0)

The purpose of this protocol is to use accelerated stress testing to assess the durability of metal halide perovskite (MHP) photovoltaic (PV) modules. The protocol aims to apply field relevant stressors to packaged MHP modules to screen for early failures that may be observed in the field. The current protocol has been designed with a glass/glass-PIB edge seal, no encapsulant package in mind. PACT anticipates adding additional testing sequences to evaluate additional stressors (e.g., PID, reverse bias) in the future.

42 ENGINEERING↗
DOE OSTI2020

Wide Band-Gap Perovskites for Tandem Photovoltaics

This research was aimed at development of a mechanically-stacked, perovskite Multi-Junction Solar Cell in which (1) at least one Junction is made of metal-halide perovskite and (2) the Junctions are manufactured in parallel and then stacked to create the final module. This technology presented significant advanced manufacturing challenges and opportunities in getting to scale, including materials scale-up and the development of novel roll-to-roll processing and encapsulation methods. Research conducted was also applicable to a monolithically-integrated perovskite Multi-Junction Solar Cell, in which the two or more Junctions are integrated and electrically connected. The project explored the following technical opportunities in conjunction with the Cyclotron Road mentored entrepreneurial research experience: Fabrication of inorganic heterojunction layers on both sides of a perovskite semiconductor, and modification of interfaces; developed transparent electrode layers on both sides of a perovskite semiconductor; and developed a prototype and optimized perovskite Junction Solar Cell.

14 SOLAR ENERGY↗
DOE OSTI2020

Establishing charge-transfer excitons in 2D perovskite heterostructures

Charge-transfer excitons (CTEs) immensely enrich property-tuning capabilities of semiconducting materials. However, such concept has been remaining as unexplored topic within halide perovskite structures. Here, we report that CTEs can be effectively formed in heterostructured 2D perovskites prepared by mixing PEA 2 PbI 4 :PEA 2 SnI 4 , functioning as host and guest components. Remarkably, a broad emission can be demonstrated with quick formation of 3 ps but prolonged lifetime of ~0.5 μs. This broad PL presents the hypothesis of CTEs, verified by the exclusion of lattice distortion and doping effects through demonstrating double-layered PEA 2 PbI 4 /PEA 2 SnI 4 heterostructure when shearing-away PEA 2 SnI 4 film onto the surface of PEA 2 PbI 4 film by using hand-finger pressing method. The below-bandgap photocurrent indicates that CTEs are vital states formed at PEA 2 PbI 4 :PEA 2 SnI 4 interfaces in 2D perovskite heterostructures. Electroluminescence shows that CTEs can be directly formed with electrically injected carriers in perovskite LEDs. Clearly, the CTEs presents a new mechanism to advance the multifunctionalities in 2D perovskites.

36 MATERIALS SCIENCE↗