量子限制纳米结构太阳能电池的前景与挑战 The Promise and Challenge of Quantum Confined Nanostructured Solar Cells

报告摘要：

Nanoscale systems as opposed to bulk or thin film versions of the same compounds exhibit some profoundly different properties and have dramatically changed the picture of how solar cells convert sunlight into free energy. In general there are two broad approaches based on nanostructures that are being explored for PV; (1) significantly reduce material usage and/or associated final costs; and (2) target PV approaches that have a higher limiting efficiency than that determined by the Shockley-Queisser analysis. One approach to higher limiting efficiencies is the process of multiple exciton generation (MEG) where absorption of high-energy photons can lead to the production of multiple electron-hole pairs that can contribute to an enhanced photocurrent in appropriately designed solar cells. However, there are challenges associated with achieving the highest MEG efficiencies needed for enhanced power conversion efficiencies and with the incorporation of nanocrystals into viable solar energy conversion technologies. To address those challenges, we have studied MEG in a variety of spherical semiconductor nanocrystals, or QDs, including PbSe, PbS, and Si and find that MEG is enhanced over impact ionization that occurs in bulk semiconductors. From these studies we have developed guidelines to further enhance MEG efficiencies and are developing new types of nano-heterostructures designed to increase MEG efficiencies.

We are developing approaches to overcome challenges in incorporating these structures into exploratory-based solar cells. We have studied MEG in quantum-confined semiconductors and show that for both solar cells and photo electrochemical (PEC) cells that produce hydrogen (H2) that multiple carriers per photon can be harvested when the photon energy is larger than about 3 times the semiconductor band gap. We are exploring new synthesis and QD surface treatments that show improvements in the PV performance. We correlate the improved performance to reduced defect density and show that through increased photoluminescence.

报告人介绍：

作为量子点中高效载流子倍增的提出者，美国国家可再生能源实验室的Beard和同组的Nozik教授长期致力于用瞬态吸收表征量子点中CM性能的研究，并开发其在太阳能电池中的应用，一直是此领域的国际权威。在美国能源部的资助下，Beard与量子点载流子倍增的另一位国际权威Klimov组建了先进太阳光物理前沿研究中心(Center for Advanced Solar Photophysics, CASP)，并担任副主任。2011年，Bead研究组首次在PbSe量子点太阳能电池中观察到了外量子效率大于100%的现象，证实了CM在器件应用中的有效性，相关工作发表于Science (Science 2011, 334, 1530)。近期，Beard组再次在Science发文(Science 2015, 350, 1061)，提出了用瞬态光调制反射技术研究半导体界面载流子动力学的新方法。

As a Senior Scientist at National Renewable Energy Laboratory, Dr. Beard has been working on the multiple exciton generation (MEG) in quantum dots using transient absorption and their application in solar cells, in which field Dr. Beard is the pioneer. Founded by Department of Energy of U. S., Dr. Beard and Klimov create the Center for Advanced Solar Photophysics (CASP). In 2001, Beard’s group observed an EQE of above 100% in PbSe quantum dot solar cell which was published on Science, demonstrating the feasibility of in working solar cells. Recently, Bearde’s group pubished another Science paper, developing a new way to study the carrier dynamics at the interface of semiconductors using time-resolved photoinduced reflectance.