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

技术概述：Davis & Santa Cruz太阳能团队将研究太阳能转换的一种变革性新范式：高效多激子生成（MEG）途径以及在全无机纳米结构太阳能电池中电荷提取的相应挑战。最近在纳米颗粒（NPs）中观察到MEG，并且不受31%的太阳能转换理论限制。太阳能团队将合成纯的、掺杂的和合金化的Si和Ge核壳NPs，以PbS NPs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。分析了NP表面的弛豫、核壳结构、激子-激子相互作用和NP-NP相互作用等复杂因素对NP的化学性质和光谱以及MEG的影响。分析工具将包括飞秒分辨率的光致发光和瞬态吸收研究；并形成全功能的基于NP的太阳能电池，完成嵌入电荷传输层。这些太阳能电池将通过优化保持量子约束的竞争设计原则来开发，以保持MEG的效率，同时将NPs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NPs的表面重构和能量学；时间依赖DFT和Bethe-Salpeter方法描述激子-激子相互作用；和非平衡速率方程来确定MEG的全部速率。数学项目将通过开发Lanczos系数外推法来协助这些工作，通过用矩阵向量积代替直接的矩阵操作来显著减少计算工作量；并通过开发全局统计方法，从光致发光和瞬态吸收获得的噪声、超高维光谱时间数据集中定性地改进隐藏动力学的分析和提取。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。最近的一项突破表明，在纳米颗粒中，一个光子可以激发几个电子，从而开辟了一个不受上述限制的新的能量转换范式。戴维斯太阳能小组将合成各种各样的纳米颗粒；进行超快速光学实验，表征这些粒子中的能量转换过程；并通过将纳米颗粒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，以加速计算技术到前所未有的速度，以极高的精度模拟能量转换过程。此外，将开发新的定性统计分析，以揭示光学实验产生的大量数据中隐含的复杂因素。该项目预计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发挥的作用。戴维斯太阳能团队不仅将开发这些基于纳米颗粒的新型太阳能电池，而且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，该团队在该委员会中发挥了早期的领导作用。团队吗?韩国的产业合作将通过在太阳能企业咨询委员会任职的pi进行。除了致力于纳米颗粒太阳能技术的广泛应用外，该团队还将通过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）分析和传播最新的学术研究，为太阳能社区提供服务。该团队还将开发一个？Solarwiki吗?作为一个平台，向有兴趣的公众提供广泛的电子外展服务。该小组将把它的工作同它在ACS SEED方案中的活动结合起来。研究生和博士后将与太阳能团队的小组合作，培养跨学科的思维，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.