tert-Butyl Chalcogenides as Useful Synthetic Tools for the Synthesis and Surface Modification of Semiconductor Nanocrystals

技术概述：本研究由固态和材料化学项目资助，目的是利用一般和合理的合成方法进行半导体纳米晶体的固相合成。PI开发了一种简单的低温合成方法，在现成的金属盐存在下，使用热（和光解）不稳定的二氯化二叔丁基前体来制造半导体纳米晶体。这种方法可以合成各种各样的半导体纳米晶体，并且这种方法提供的高水平的动力学控制有助于发现几种新的半导体纳米晶体相。本项目将重点研究利用该合成方法控制合成SnSe和Cu2SnSe3纳米晶体及其衍生物。这些IV-VI和I-IV-VI半导体的带隙（Eg = 1.0-1.5 eV）在太阳能转换的最佳范围内，吸收系数高，载流子迁移率高，并且由相对丰富的元素组成；然而，这两种系统都没有在明确定义的纳米晶体或太阳能电池方面进行详细的探索。一旦到手，将努力从纳米晶体表面去除绝缘配体外壳，用小的、热不稳定的配体代替，这些配体仍然可以提供足够的胶体稳定性来形成可用的纳米晶体墨水。这些油墨将被浇铸成纳米晶体薄膜，经过温和的热退火将产生无机薄膜，其中大部分没有绝缘的有机材料。利用固态器件和光电化学测量快速筛选配体交换的效果，并进一步探索在全无机纳米晶体太阳能电池中最有前途的纳米晶体/配体组合。尽管固体化学和材料化学领域有了50多年的发展，但合理地、可重复地合成无机材料的方法仍然有限，其中大多数需要耗费大量能量和苛刻的条件。因此，有必要开发新的方法，使用合理的化学设计原则，在廉价和可扩展的条件下可持续地合成材料。这将最终实现一种“设计材料”的方法，在这种方法中，新的功能材料可以合理地合成以满足特定的应用。PI将利用他的研究小组开发的一种方法，用于动力学控制，低温合成半导体纳米晶体。这些纳米晶体可以作为墨水分散，并以极其廉价的方法沉积为太阳能电池活性层的薄膜。特别的重点将放在纳米晶体的合成具有最佳带隙的太阳能转换，也由地球丰富和可持续的元素。纳入这项研究计划的是一个专门针对当地社区大学生的外展计划。在传统的化学拓展项目中，社区大学的学生是最没有针对性的；然而，大洛杉矶地区是美国社区大学生人数最多的地区。PI与Cerritos社区学院合作，提供太阳能电池研究方面的实习机会。Cerritos社区学院拥有大量未被充分代表的学生。这项为期8周的年度拓展计划的目标是为这些学生提供在社区大学通常无法获得的研究机会，从而提高他们转学到四年制大学的几率。

TECHNICAL SUMMARYThe goal of this research funded by the Solid State and Materials Chemistry program is to utilize general and rational synthetic methods for the solution-phase synthesis of semiconductor nanocrystals. The PI developed a facile, low-temperature synthesis method to make semiconductor nanocrystals using thermally (and photolytically) unstable di-tert-butyl dichalcogenide precursors in the presence of readily available metal salts. This method allows for the synthesis of a wide variety of semiconductor nanocrystals, and the high level of kinetic control offered by this approach has been instrumental in the discovery of several new crystal phases of semiconductor nanocrystals. This project will focus on the controlled synthesis of SnSe and Cu2SnSe3 nanocrystals and their derivatives using this synthesis method. These IV-VI and I-IV-VI semiconductors posses band gaps (Eg = 1.0-1.5 eV) in the optimal range for solar energy conversion, in addition to having high absorption coefficients, high carrier mobilities, and being comprised of relatively earth abundant elements; however, neither of these systems has been explored in great detail with respect to well-defined nanocrystals or solar cells. Once in hand, efforts will be placed on removing the insulating ligand shell from the nanocrystal surface and replacing it with small, thermally labile ligands that can still provide enough colloidal stability to form usable nanocrystal inks. These inks will be cast to give nanocrystal films, which upon mild thermal annealing will yield inorganic films that are largely devoid of insulating organic material. The efficacy of the ligand exchange will be rapidly screened using solid-state device and photoelectrochemical measurements, and the most promising nanocrystal/ligand combinations will be further explored in all-inorganic nanocrystal solar cells.NON-TECHNICAL SUMMARYDespite over fifty years of developments in the field of solid-state and materials chemistry, there are still only a limited number of ways to rationally and reproducibly synthesize inorganic materials - the majority of which require energetically costly and harsh conditions. As such, there is a need to develop new methodologies, using rational chemical design principles, for the sustainable synthesis of materials under inexpensive and scalable conditions. This will ultimately enable a 'materials by design' approach to be taken, in which new functional materials can be rationally synthesized to meet specific applications. The PI will utilize a method developed in his research group for the kinetically controlled, low-temperature synthesis of semiconductor nanocrystals. These nanocrystals can be dispersed as an ink, and deposited as films for solar cell active layers using extremely inexpensive methods. Particular focus will be placed on the synthesis of nanocrystals with optimal band gaps for solar energy conversion that are also comprised of earth abundant and sustainable elements. Integrated into this research plan is an outreach program specifically aimed at local community college students. The community college student demographic is among the least targeted in traditional chemistry outreach programs; however, the greater Los Angeles area is home to the largest number of community college students in the United States. The PI has partnered with Cerritos Community College, an institution with a large number of underrepresented students, to provide internships on solar cell research. The objective of this annual 8-week outreach program is to provide these students with research opportunities that are typically not afforded to them at the community college level, and thereby increase their transfer rate to 4-year institutions.