Binary and Ternary Semiconductor Quantum Rods: A Computational Route to Next-Generation All-Inorganic Photovoltaic Materials

基于无机纳米晶体的光伏系统的效率可能远远超过目前使用的块状薄膜(如硅)结构，因为纳米晶体中的量子限制使其在将太阳光子转化为电子-空穴对(或激子)方面明显更好。然而，在激子解离为电子和空穴方面仍然存在重大挑战--这是有效地将太阳能整体转换为电能的必要条件。这一建议基于这样一个想法，即在量子棒中精心设计的正确类型材料之间的界面将有助于实现增强的激子解离，从而实现最佳的光伏性能。智能优点：这项提议的目标是使用一套基于密度泛函理论(DFT)的综合第一性原理计算来研究各种包含界面的二值和三值量子棒(QR)系统。被研究的二元系将包括CdSe和CdTe，三元系将包括CdSe1-xTex、Cd1-xZnxSe、CdTe1-xSx和ZnSe1-xTex。将考虑沿二元系长度的晶体结构变化，以及沿QR半径或长度的成分(即x值)变化，以导致核/壳或端部接触的界面。具体的系统选择是由它们在界面上产生交错的II型价态和导带边缘偏移的潜力(以及其他因素)所驱动的。设计这样的第二类带偏移对于增加激子解离的程度将是至关重要的。DFT计算将被用来评估这些系统的稳定性和电子结构作为量子限制(即QR半径)和界面成分变化速度的函数。DFT电子本征值和波函数将被用来研究与激子解离有关的临界性质，如界面带边位置的变化，电子-空穴结合能作为电子和空穴波函数位置的函数，激子解离的势垒和激子复合寿命。更广泛的影响：这项建议的一个重要组成部分是对学生的教育。PI的工业经验将加强学生的工程教育，并将通过与行业的互动(通过实习、访问和联合出版物)帮助扩大学生在学术环境之外的接触。PI将继续完善和教授他在2006年开发的一门计算材料科学课程，该课程正在填补康涅狄格州大学工程、物理和化学系当前课程的空白。将与致力于社区服务的当地机构(如公共图书馆和博物馆)合作，推动开展外联活动，以提高公众对替代能源解决方案和纳米技术领域的认识。特别是，Pi得到了托兰公共图书馆和当地初中/高中教师的大力支持，帮助他的外展工作，并将他的研究和整个科学与工程的兴奋打包和传播到当地社区。

The efficiency of photovoltaic systems based on inorganic nanocrystals could far surpass that of currently used bulk thin film (e.g., Si) based architectures, as the quantum confinement in nanocrystals makes them significantly better at converting solar photons to electron-hole pairs (or excitons). Nevertheless, major challenges remain, concerning the dissociation of the exciton into electrons and holes-a necessary condition for the efficient overall conversion of solar to electrical energy. This proposal rests on the idea that carefully designed interfaces between materials of the right type within a quantum rod will help achieve enhanced exciton dissociation and therefore optimal photovoltaic performance. Intellectual Merit: The objective of this proposal is to use an integrated set of first principles computations based on density functional theory (DFT) to study a variety of binary and ternary quantum rod (QR) systems containing interfaces. Binary systems to be studied will include CdSe and CdTe, and ternary systems will include CdSe1-xTex, Cd1-xZnxSe, CdTe1-xSx, and ZnSe1-xTex. Crystal structure variation along the length of the binary systems, and composition (i.e., x value) variation along the QR radius or length will be considered so as to result in core/shell or end-contacted interfaces. The specific system choices were motivated (among other factors) by their potential for the creation of staggered Type II valence and conduction band edge offsets at interfaces. Engineering such Type II band offsets will be critical to increasing the extent of exciton dissociation. DFT computations will be used to assess the stability and electronic structure of these systems as a function of quantum confinement (i.e., QR radius) and the rapidity of composition variations across the interface. The DFT electronic eigenvalues and wavefunctions will then be used to investigate critical properties related to exciton dissociation such as variations in the band edge positions across interfaces, electron-hole binding energy as a function of electron and hole wavefunction position, barriers to exciton dissociation and exciton recombination lifetime. Broader Impact: An important component of this proposal is the education of students. The industrial experience of the PI will enhance the engineering education of students and will aid in broadening student exposure beyond the academic environment through interactions with industry (via internships, visits and joint publications). The PI will continue to refine and teach a Computational Materials Science course he developed in 2006, which is filling a gap in the current curricula of the Engineering, Physics and Chemistry departments at the UConn. Outreach activities will be fostered to increase public awareness in the areas of Alternative Energy Solutions and Nanotechnology, in collaboration with local establishments committed to community services (e.g., public libraries and museums). In particular, the PI has the strong support of the Tolland Public Library and local middle/high school teachers, in aiding his outreach efforts, and in packaging and propagating the excitement of his research, and of Science & Engineering in general, to the local communities.