多重纳米核壳结构的稀土上转换与活性高分子吸收光子匹配的研究

Photon upconversion(UC) of near-infrared photons is a promising way to overcome the Shockley–Queisser efficiency limit of organic solar cell. However, the mismatching of UC emission and photoactivable polymer absorption, extremely weak upconversion efficiency, poor compatibility and narrowband near-infrared absorption of UC nanomaterials are the most serious limitation for their practical applications. Here, the UC nanoparticles with multiple coating core-shell structure would be designed and synthesized by supercritical carbon dioxide-assisted method with other liquid phase methodes. The UC emission can be turned by adjusting the spatial location and concentration of rare-earth ions, which can be absorbed by photoactivable polymers. Especially, rare earth ions were doped at different doping levels, and the Yb3+/Tm3+ pair and activator (Ln3+) can be separated by hexagonal NaGdF4@NaGdF4 core/shell layer. Thus, the designed unique core/shell structure could effectively eliminate cross relaxation due to direct interaction between the Yb3+/Tm3+ pair and Ln3+, resulting in enhancement of the UC intensity. And the silica shell with various thicknesses can efficiently eliminate the fluorescent quenching and enhance the fluorescent intensity. After polymer modification of NaGdF4:Yb3+/Tm3+@NaGdF4:Ln3+@SiO2, the multiple coating core-shell UC nanoparticles are compatible with organic solar cell, it is useful to broaden the absorption spectrum and improve the photoelectric efficiency by photons matching. As an “inorganic antenna” system, the proposed concept can be extended to cover any part of the solar spectrum and overlap absorption spectra of photoactivable polymers by incorporating rare-earth ions into multiple core-shell nanoparticles.

将上转换纳米材料应用于太阳能电池，认为是突破Shockley–Queisser极限的有效途径。但上转换发射光谱与光活性分子吸收光谱不匹配，上转换效率低，与体系相容性差和红外光区的吸光范围窄等是制约其应用的主要因素。本项目拟制备上转换效率高的多重核壳结构的稀土掺杂上转换纳米粒子，稀土离子掺杂在NaGdF4@NaGdF4不同的壳层，使材料的上转换光子发射与光活性高分子吸收光子相匹配，减低了交叉弛豫；一定厚度的SiO2壳层有效消除荧光猝灭，提高其上转换效率；将制备的NaGdF4:Yb3+/Tm3+@NaGdF4:Ln3+@SiO2的纳米颗粒表面通过氯球化和烷基化修饰后，改善了在有机体系中的相容性和分散性，应用于有机太阳能电池,可拓宽光吸收范围，提高光电转换效率。本项目将稀土离子掺杂多重结构纳米粒子作为“天线”，通过调节上转换光子发射，使之与光活性高分子光子吸收区间相匹配，实现高效的上转换效率。

将上转换纳米材料应用于太阳能电池，认为是突破Shockley–Queisser极限的有效途径。上转换纳米粒子应用于太阳能电池的主要问题是：红外光密度小，光吸收范围窄，荧光效率低，稳定性差，光电效率低等。本项目主要研究内容是将稀土掺杂的上转换无机纳米粒子，通过同质层和异质层包裹，通过有机分子的修饰形成核壳结构，同时使其荧光发射与聚合物太阳能电池的光活性吸收层相匹配，最终可提高聚合物太阳能电池的光电转换效率。取得的成果主要包括以下三方面内容。第一、相对于文献报道的高温合成途径，可以在较低的温度下，通过控制实验条件，对上转换纳米粒子的形态、晶型和尺寸分布等进行设计和控制。制备的梭形GdF3(YF3):Yb3+/Tm3+ 和球形 NaGdF4(NaYF4):Yb3+/Tm3+具有了良好的上转换荧光性质，可通过调整基质材料对上转换荧光进行调控，证实了Gd3+在多晶结构中同样存在能量传递作用。此外，制备的单分散性的KGdF4:Yb3+/Er3+盘状纳米颗粒，具有高的比表面积，将其应用于聚合物太阳能电池，其能量电转换效率达到7.8%，增加效率达到8.5%。第二、相对于文献报道的油溶性上转换纳米粒子，通过两步法制备了多重复合的核壳结构水溶性的NaGdF4:Yb,Er@SiO2@Eu(TTA)3Phen纳米球形粒子。6纳米厚度SiO2层的包裹不仅避免了材料荧光淬灭，而且上转换荧光强度在542纳米和660纳米的发射强度分别增强了5倍和14倍。980纳米红外光激发下，材料可以发出特征的绿光；表层稀土络合物的修饰，使其在在外光的激发下可以发出特征的红光。因此制备的材料具备了灵敏的光响应性质，其水溶性的性质也是其在生物成像和诊断等方面更具潜在的应用空间。第三、制备了噻吩甲酰三氟丙酮（TTA）和邻菲罗啉（Phen）修饰的NaYbF4:Tb/Eu@Phen,TTA纳米粒子。上转换纳米粒子可以吸收红外线，有机分子吸收紫外线，这样相互补充，大大拓宽太阳光的吸收范围。发射光谱分别为绿光和红光与聚合物太阳能电池的活性层的活性层相匹配。将其应用于聚合物太阳能电池，电池的开路电压为0.77V，短路电流为16.48 mA•cm-2，相对于参比电池，电池的光电转换效率提高了10.2%。