EAGER: Characterization of the Red-Shift Effect Observed in Solutions of Photoluminescent Down-Shifting Carbon Quantum Dots and CdTe/Carbon Quantum Dots

EAGER：光致发光下移碳量子点和 CdTe/碳量子点溶液中观察到的红移效应的表征

• 批准号: 1650571
• 负责人: Arturo Ayon
• 金额: $ 10万
• 依托单位: University of Texas at San Antonio
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1650571&HistoricalAwards=false
• 关键词: EAGER; Characterization; Red; Shift; Effect

The development of higher efficiency solar cells is considered a requirement to reduce the dependence on fossil fuels. This is the main impetus for a variety of research schemes including the utilization of nanoparticles for performance improvement, particularly in silicon because it remains the most widely employed material in solar cell manufacturing. However, one of the problems affecting silicon structures is associated with relatively high energy photons that tend to interact with phonons in the silicon lattice rather than producing electron-hole pairs. Thus, improving the capture of high energy photons that are otherwise lost, could lead to a dramatic increase in the efficiency of photovoltaic structures. In order to address this shortcoming a variety of quantum dots are frequently explored because of their ability to capture high energy photons and subsequently emitting lower energy photons more suitable for producing electron-hole pairs in silicon, i.e., down-shifting. In addition to the aforementioned red-shift of quantum dots, large red-shifts have been observed in solutions containing a collection of photoluminescent carbon quantum dots (CQDs) of different synthesized radii. The observed red-shift effect is anticipated to have a dramatic impact on the power conversion efficiency of solar cells since it can be construed as an enhancement of the down-shifting effect associated with photoluminescent quantum dots. Specifically, with an excitation wavelength of 390 nm, individual colloidal solutions of CQDs of a specific radius, exhibited down-shifted emission peaks centered at ~420 nm. However, the solution comprised of the mixture of the previously synthesized colloidal solutions of Carbon QDs of different radii, was observed to have an emission red-shifted to ~515 nm. Furthermore, the red-shift effect was also observed in CdTe QDs when added to the solution with the aforementioned collection of Carbon QDs. Thus, whereas a colloidal solution solely comprised of CdTe QDs of different radii, exhibited a down-shifted photoluminescence centered at ~555 nm, the peak was observed to be further red-shifted to ~580 nm when combined with the previously mentioned mixed solution of Carbon QDs of different radii. However, upon spin casting the quantum dot mixtures either directly on a silicon substrate, or dispersing the quantum dots in poly-methyl-methacrylate (PMMA) prior to spin casting, the red-shift effect is lost. Therefore, we propose the extensive utilization of spectroscopic methods to investigate (i.) the origin of the merged and shifted spectrum observed upon mixing the QDs (both different sized CQDs and mixed CQD/CdTe QDs), (ii.) the dependence and/or stability of the emission spectra on the temperature and gaseous atmosphere of the colloidal solutions and (iii.) the disappearance of the red-shift observed upon processing the QDs with different solvents either directly on silicon substrates or when dispersing the synthesized QDs in PMMA.

开发更高效率的太阳能电池被认为是减少对化石燃料依赖的一个要求。这是各种研究计划的主要推动力，包括利用纳米颗粒来提高性能，特别是在硅中，因为它仍然是太阳能电池制造中最广泛使用的材料。然而，影响硅结构的问题之一是与相对高能量的光子相关联，这些光子倾向于与硅晶格中的声子相互作用，而不是产生电子-空穴对。因此，改善对否则会损失的高能光子的捕获可以导致光伏结构的效率的显著增加。为了解决这个缺点，经常探索各种量子点，因为它们能够捕获高能量光子并随后发射更适合于在硅中产生电子-空穴对的较低能量光子，即，降档除了量子点的上述红移之外，在含有不同合成半径的光致发光碳量子点（CQD）的集合的溶液中已经观察到大的红移。观察到的红移效应预计对太阳能电池的功率转换效率具有显著影响，因为它可以被解释为与光致发光量子点相关的下移效应的增强。具体地，在390 nm的激发波长下，特定半径的CQD的单个胶体溶液表现出以~420 nm为中心的下移的发射峰。然而，观察到由先前合成的不同半径的碳QD的胶体溶液的混合物组成的溶液具有红移至约515 nm的发射。此外，当将CdTe量子点添加到具有上述碳量子点集合的溶液中时，也在CdTe量子点中观察到红移效应。因此，尽管仅由不同半径的CdTe QD组成的胶体溶液表现出以~555 nm为中心的下移的光致发光，但当与先前提到的不同半径的碳QD的混合溶液组合时，观察到峰进一步红移至~580 nm。然而，在将量子点混合物直接旋铸在硅衬底上或在旋铸之前将量子点分散在聚甲基丙烯酸甲酯（PMMA）中时，红移效应丧失。因此，我们建议广泛利用光谱方法来研究（i.）在混合QD（不同尺寸的CQD和混合的CQD/CdTe QD两者）时观察到的合并和移位的光谱的起源，（ii.）发射光谱对胶体溶液的温度和气体气氛的依赖性和/或稳定性，和（iii.）在用不同溶剂直接在硅衬底上处理QD时或在将合成的QD分散在PMMA中时观察到的红移消失。