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Using Deep Machine Learning to Understand the Physical Performance Bottlenecks in Novel Thin‐Film Solar Cells
摘要： There is currently a worldwide effort to develop materials for solar energy harvesting which are efficient and cost effective, and do not emit significant levels of CO2 during manufacture. When a researcher fabricates a novel device from a novel material system, it often takes many weeks of experimental effort and data analysis to understand why any given device/material combination produces an efficient or poorly optimized cell. It therefore takes the community tens of years to transform a promising material system to a fully optimized cell ready for production (perovskites are a contemporary example). Herein, developed is a new and rapid approach to understanding device/material performance, which uses a combination of machine learning, device modeling, and experiment. Providing a set of electrical device parameters (charge carrier mobilities, recombination rates, trap densities, etc.) in a matter of seconds thus offers a fast way to directly link fabrication conditions to device/material performance, pointing a way to further and more rapid optimization of light harvesting devices. The method is demonstrated by using it to understand annealing temperature and surfactant choice and in terms of charge carrier dynamics in organic solar cells made from the P3HT:PCBM, PBTZT-stat-BDTT-8:PCBM, and PTB7:PCBM material systems.
关键词： charge carrier mobility,machine learning,organic solar cells,thin film solar cells,drift diffusion
更新于2025-09-12 10:27:22
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Simulating nanocrystal-based solar cells: A lead sulfide case study
摘要： Nanocrystal-based solar cells are promising candidates for next generation photovoltaic applications; however, the most recent improvements to the device chemistry and architecture have been mostly trial-and-error based advancements. Due to complex interdependencies among parameters, determining factors that limit overall solar cell efficiency are not trivial. Furthermore, many of the underlying chemical and physical parameters of nanocrystal-based solar cells have only recently been understood and quantified. Here, we show that this new understanding of interfaces, transport, and origin of trap states in nanocrystal-based semiconductors can be integrated into simulation tools, based on 1D drift-diffusion models. Using input parameters measured in independent experiments, we find excellent agreement between experimentally measured and simulated PbS nanocrystal solar cell behavior without having to fit any parameters. We then use this simulation to understand the impact of interfaces, charge carrier mobility, and trap-assisted recombination on nanocrystal performance. We find that careful engineering of the interface between the nanocrystals and the current collector is crucial for an optimal open-circuit voltage. We also show that in the regime of trap-state densities found in PbS nanocrystal solar cells (～1017 cm?3), device performance exhibits strong dependence on the trap state density, explaining the sensitivity of power conversion efficiency to small changes in nanocrystal synthesis and nanocrystal thin-film deposition that has been reported in the literature. Based on these findings, we propose a systematic approach to nanocrystal solar cell optimization. Our method for incorporating parameters into simulations presented and validated here can be adopted to speed up the understanding and development of all types of nanocrystal-based solar cells.
关键词： nanocrystal-based solar cells,simulation,charge carrier mobility,lead sulfide,drift-diffusion models,trap states
更新于2025-09-12 10:27:22
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Identification and Characterization of ‘Killer-Modes’ in Organic Semiconductors with Terahertz Spectroscopy
摘要： Organic semiconductors are promising modern optoelectric materials, with countless potential applications ranging from ?exible displays to photovoltaics. The applicability of these materials is largely driven by their charge carrier mobility, which is strongly in?uenced by low-frequency vibrations. In this work, the speci?c low-frequency vibrations that exhibit strong electron-phonon coupling, deemed ‘killer-modes’, in organic semiconductors are determined using a combination of terahertz time-domain spectroscopy and solid-state density functional theory. The results of this study enable a concerted synthetic effort to rationally design novel materials, utilizing intermolecular forces to stiffen lattice dynamics, to ultimately improve charge carrier mobility.
关键词： electron-phonon coupling,organic semiconductors,charge carrier mobility,solid-state density functional theory,terahertz spectroscopy
更新于2025-09-11 14:15:04
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Modifying the electrical properties of graphene by reversible point-ripple formation
摘要： Strain, ripples and wrinkles in graphene reduce the charge-carrier mobility and alter the electronic behaviour. In few-layer graphene the anisotropy between the in-plane and cross-plane resistivity is altered and a band gap can be opened up. Here we demonstrate a method to reversibly induce point ripples in electrically isolated few-layer graphene with the ability to select the number of layers used for transport measurement down to single layer. During ripple formation the in-plane and cross-plane sheet resistances increase by up to 78% and 699% respectively, confirming that microscopic corrugation changes can solely account for graphene's non-ideal charge-carrier mobility. The method can also count the number of layers in few-layer graphene and is complimentary to Raman spectroscopy and atomic force microscopy when n ≤ 4. Understanding these changes is crucial to realising practical oscillators, nano-electromechanical systems and flexible electronics with graphene.
关键词： charge-carrier mobility,graphene,electrical properties,flexible electronics,nano-electromechanical systems,point-ripple formation
更新于2025-09-09 09:28:46
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Quantitative mobility evaluation of organic semiconductors using quantum dynamics based on density functional theory
摘要： We present an order-N methodology to evaluate mobilities of charge carriers coupled with molecular vibrations using quantum dynamics based on first-principles calculations that can be applied to micron-scale soft materials. As a demonstration, we apply it to several organic semiconductors and show that the calculated intrinsic hole mobilities and their temperature dependences are quantitatively in good agreement with those obtained in experiments. We also clarified which vibrational modes dominate the transport properties. The methodology paves the way for quantitative prediction of the transport properties of various soft materials.
关键词： quantum dynamics,density functional theory,charge-carrier mobility,organic semiconductors,molecular vibrations
更新于2025-09-04 15:30:14