SOLAR COLLABORATIVE: Multiple Exciton Generation and Charge Extraction in All-Inorganic Nanostructured Solar Cells

技术总结戴维斯圣克鲁斯太阳能团队将研究太阳能转换的变革性新范式：高效多激子生成（MEG）途径和全无机纳米结构太阳能电池中电荷提取的相应挑战。MEG最近在纳米颗粒（NPs）中被观察到，并且不受太阳能转换的31%理论极限的影响。 太阳能团队将合成纯的、掺杂的和合金化的Si和Ge核壳纳米粒子，以PbS纳米粒子为参考，分析它们在各种尺寸、掺杂和结构下的化学、量子态和能量学。 复杂的因素，如NP表面的弛豫，各种核壳结构，激子-激子相互作用和NP-NP相互作用对NP的化学和光谱以及MEG的影响将被分析。 分析的工具将包括飞秒分辨率的光致发光和瞬态吸收研究;以及形成功能齐全的NP基太阳能电池，包括嵌入的电荷传输层。 这些太阳能电池将通过优化保持量子限制的竞争设计原则来开发，以保持MEG的效率，同时将NP嵌入适当的导电层中以实现有效的电荷提取和传输。 强有力的理论工作将补充该小组的实验工作。密度泛函理论（DFT）将用于捕获的表面重建和能量的NP;时间依赖性DFT和Bethe-Salpeter方法来描述激子-激子相互作用;和非平衡速率方程，以确定全速率的MEG。数学项目将协助这些努力，开发Lanczos系数外推法，用矩阵乘矢量积取代直接矩阵运算，从而大大减少计算工作量;以及通过开发全局统计方法来定性地改进从噪声、超高维谱时数据集中对隐藏动态的分析和提取，通过光致发光和瞬态吸收获得。非技术概述即使在理论上，太阳能电池的效率也被限制在令人失望的31%。然而，这一限制是基于太阳能电池的传统操作，其中入射的太阳光子仅激发单个电子。最近的突破表明，在纳米颗粒中，一个光子可以激发多个电子，从而打开了一个新的能量转换范式，而不受上述限制。 戴维斯太阳能团队将合成各种各样的纳米粒子;进行超快光学实验来表征这些粒子中的能量转换过程;并通过将纳米粒子嵌入电荷传输层来构建功能齐全的太阳能电池。将进行开创性的数学工作，以将计算技术加速到前所未有的速度，以非常准确地模拟能量转换过程。此外，将开发新的定性统计分析，以揭示嵌入在光学实验产生的大量数据中的复杂因素。 预计该项目将提高太阳能转换效率，这将大大提高太阳能技术在美国向可再生能源过渡中的作用。 戴维斯太阳能团队不仅将开发这些新的基于纳米粒子的太阳能电池，还计划将这项技术推向市场。这将通过与加州能源委员会（SC-CEC）的太阳能合作来实现，该团队在其中发挥了早期的领导作用。团队？的工业合作将通过一个在太阳能公司顾问委员会的PI来发展。除了致力于纳米颗粒太阳能技术的广泛接受外，该团队还将通过分析和传播最新的学术研究成果，并通过SC-CEC向太阳能利益相关者：光伏制造商，公用事业公司和监管机构提供服务。该小组还将制定一项？Solarwiki？作为向感兴趣的公众进行广泛电子宣传的平台。 该小组将把它的工作与它在ACS SEED计划中的活动结合起来。 研究生和博士后研究员将与太阳能团队的小组共同努力，以促进跨学科思维，并为他们加入太阳能革命做好准备。

TECHNICAL SUMMARYThe Davis & Santa Cruz Solar Team will investigate a transformative new paradigm of solar energy conversion: the high efficiency Multiple Exciton Generation (MEG) pathway and the corresponding challenge of charge extraction in all-inorganic nanostructured solar cells. MEG was recently observed in nanoparticles (NPs) and is not subject to the 31% theoretical limit of solar energy conversion. The Solar Team will synthesize pure, doped and alloyed Si and Ge core-shell NPs to analyze their chemistry, quantum states and energetics in a wide range of sizes, dopings, and structures, using PbS NPs as reference. The impact of complex factors such as the relaxation of the NP surface, the various core-shell structures, the exciton-exciton interaction and the NP-NP interaction on the chemistry and spectra of the NPs as well as on the MEG will be analyzed. The tools of the analysis will include photoluminescence and transient absorption studies with femtosecond resolution; and forming fully functional NP based solar cells, complete with embedding charge transport layers. These solar cells will be developed by optimizing the competing design principles of maintaining quantum confinement to preserve the efficiency of the MEG while embedding the NPs into suitably conducting layers for efficient charge extraction and transport. A strong theoretical effort will complement the Team's experimental work. Density functional theories (DFT) will be used to capture the surface reconstruction and the energetics of NPs; time dependent DFT and Bethe-Salpeter methods to describe the exciton-exciton interaction; and non-equilibrium rate equations to determine the full rate of MEG. Mathematical projects will assist these efforts by developing a Lanczos coefficient extrapolation method, dramatically reducing the computational workload by replacing direct matrix manipulations with matrix by vector products; and by developing global statistical methods to qualitatively improve the analysis and extraction of the hidden dynamics from the noisy, ultra-high dimensional spectrotemporal dataset, obtained by the photoluminescence and transient absorption.NON-TECHNICAL SUMMARYEven in theory, the efficiency of solar cells is limited to a disappointing 31%. However, this limit was based on the traditional operation of solar cells, where an incoming solar photon excites only a single electron. A recent breakthrough showed that in nanoparticles one photon may excite several electrons, thus opening a new energy conversion paradigm not constrained by the above limit. The Davis Solar Team will synthesize a wide variety of nanoparticles; perform ultra-fast optical experiments to characterize the energy conversion process in these particles; and construct fully functional solar cells by embedding the nanoparticles into charge transport layers. Path-breaking mathematical work will be performed to accelerate the computational techniques to unprecedented speeds to simulate the energy conversion process with great accuracy. Further, qualitatively new statistical analyses will be developed to uncover the complex factors embedded in the vast amount of data produced by the optical experiments. The improvement of the solar energy conversion efficiency expected to emerge from this project can considerably increase the role solar technologies will play in the US transitioning towards renewable energy sources. The Davis Solar Team will not only develop these new nanoparticle based solar cells, but also plans to chaperon this technology towards the marketplace. This will be pursued through working with the Solar Collaborative of the California Energy Commission (SC-CEC), where the Team played an early leadership role. The Team?s industrial collaboration will be developed through one of the PIs who is on the advisory board of a solar company. Besides working toward a wide acceptance of nanoparticle solar technologies, the Team will reach out and serve the solar community at large by analyzing and disseminating the latest academic research to the solar stakeholders: the PV manufacturers, utilities and the regulatory bodies through the SC-CEC. The Team will also develop a ?Solarwiki? as a platform for a broad electronic outreach to the interested public. The Team will integrate its work with its activity in the ACS SEED program. Graduate students and postdoctoral fellows will work jointly with the groups of the Solar Team to foster interdisciplinary thinking and to prepare them to join the solar revolution.