Engineering topics

Vagott, Jacob N.

Publications and source records attributed to Vagott, Jacob N..

4 records

DOE OSTI2023

Vapor Phase Infiltration Improves Thermal Stability of Organic Layers in Perovskite Solar Cells

Despite the rapid increase in power conversion efficiency (PCE) of perovskite solar cells (PSCs) over the past decade, stability remains a major roadblock to commercialization. Here, this work shows vapor phase infiltration (VPI) as a tool to create hybrid organic–inorganic layers that improve the stability of organic charge transport layers, such as hole-selective spiro-OMeTAD in PSCs and in other organic electronic devices. Using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and grazing incident wide-angle X-ray scattering (GIWAXS), we identify that infiltration of TiO x via VPI hinders the crystallization of the spiro-OMeTAD layer by likely preventing the π–π stacking of the molecules. Infiltrated PSCs retained more than 80% of their original efficiency after an operando stability test of 200 h at 75 °C, double the efficiency retained by devices without infiltration, in which the efficiency rapidly decreases in the first 50 h. This work provides a blueprint for using VPI to stabilize organic charge transport layers via prevention of π–π stacking leading to deleterious crystallization that shortens device lifetimes.

14 SOLAR ENERGY↗

DOE OSTI2022

Formation of a Secondary Phase in Thermally Evaporated MAPbI 3 and Its Effects on Solar Cell Performance

Thermal evaporation is a promising deposition technique to scale up perovskite solar cells (PSCs) to large areas, but the lack of understanding of the mechanisms that lead to high-quality evaporated methylammonium lead triiodide (MAPbI 3 ) films gives rise to devices with efficiencies lower than those obtained by spin coating. Here this work investigates the crystalline properties of MAPbI 3 deposited by the thermal coevaporation of PbI 2 and MAI, where the MAI evaporation rate is controlled by setting different temperatures for the MAI source and the PbI 2 deposition rate is controlled with a quartz crystal microbalance (QCM). Using grazing incident wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD), we identify the formation of a secondary orthorhombic phase (with a Pnma space group) that appears at MAI source temperatures below 155 °C. With synchrotron-based X-ray fluorescence (XRF) microscopy, we show that the changes in crystalline phases are not necessarily due to changes in stoichiometry. The films show a stochiometric composition when the MAI source is heated between 140 to 155 °C, and the samples become slightly MAI rich at 165 °C. Increasing the MAI temperature beyond 165 °C introduces an excess of MAI in the film, which promotes the formation of films with low crystallinity that contain low-dimensional perovskites. When they are incorporated in solar cells, the films deposited at 165 °C result in the champion power conversion efficiency, although the presence of a small amount of low-dimensional perovskite may lead to a lower open-circuit voltage. We hypothesize that the formation of secondary phases in evaporated films limits the performance of PSCs and that their formation can be suppressed by controlling the MAI source temperature, bringing the film toward a phase-pure tetragonal structure. Control of the phases during perovskite evaporation is therefore crucial to obtain high-performance solar cells.

36 MATERIALS SCIENCE↗

DOE OSTI2022

PbI 2 Nanocrystal Growth by Atomic Layer Deposition from Pb(tmhd) 2 and HI

Atomic layer deposition (ALD) allows for fine control over the thickness, stoichiometry, and structural defects of materials. ALD provides a suitable route to deposit lead halides, which can further be converted to perovskites for photovoltaics, photoemission, and photodetection, among other applications. Deposition of lead halides by ALD has already begun to be explored; however, the precursors used in published processes are highly hazardous, require expensive fabrication processes, or contain impurities that can jeopardize the optoelectronic properties of metal halide perovskites after conversion. In this work, we deposited lead iodide (PbI 2 ) by a facile ALD process involving only two readily accessible and low-cost precursors. PbI 2 nanocrystals were grown on soda-lime glass (SLG), silicon dioxide support grids, and silicon wafer substrates and provided the groundwork for further investigation into developing lead halide perovskite processes by ALD. Further, the ALD-grown PbI 2 was characterized by annular dark-field scanning transmission electron microscopy (ADF-STEM), atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM), X-ray fluorescence (XRF), and X-ray photoemission spectroscopy (XPS), among other methods. This work presents the first step to synthesize lead halide perovskites with atomic control for applications such as interfacial layers in photovoltaics and for deposition in microcavities for lasing.

36 MATERIALS SCIENCE↗

DOE OSTI2021

An open-access database and analysis tool for perovskite solar cells based on the FAIR data principles

Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42,400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences.

14 SOLAR ENERGY↗