Sharma Dharmendar Kumar, Hirata Shuzo, Biju Vasudevanpillai, Vacha Martin
Department of Materials Science and Engineering , Tokyo Institute of Technology , Ookayama 2-12-1-S8-44 , Meguro-ku, Tokyo 152-8552 , Japan.
Department of Engineering Science and Engineering , The University of Electro Communications , 1-5-1 Chofugaoka, Chofu , Tokyo 182-8585 , Japan.
ACS Nano. 2019 Jan 22;13(1):624-632. doi: 10.1021/acsnano.8b07677. Epub 2019 Jan 9.
Organic-inorganic halide perovskites have emerged as promising materials for next-generation solar cells. In nanostructured form also, these materials are excellent candidates for optoelectronic applications such as lasers and light-emitting diodes for displays and lighting. While great progress has been achieved so far in optimizing the intrinsic photophysical properties of perovskite nanocrystals (NCs), in working optoelectronic devices, external factors, such as the effects of conducting environment and the applied electric field on exciton generation and photon emission, have been largely unexplored. Here, we use NCs of the all-inorganic perovskite CsPbBr dispersed polyvinyl carbazole, a hole-conductor, and in poly(methyl methacrylate), an insulator, to examine the effects of applied electric field and conductivity of the matrix on the perovskite photophysics at the single-particle level. We found that the conducting environment causes a significant decrease of photoluminescence (PL) brightness of individual NCs due the appearance of intermediate-intensity emitting states with significantly shortened lifetime. Applied electric field has a similar effect and, in addition, causes a nonlinear spectral shift of the PL maxima, a combination of linear and quadratic Stark effects caused by environment-induced polarity and field-related polarizability. The environment and electric-field effects are explained by ionization of the NCs through hole transfer and emission of the resulting negatively charged excitons.
有机-无机卤化物钙钛矿已成为下一代太阳能电池的有前途的材料。以纳米结构形式存在时，这些材料也是光电子应用的极佳候选材料，如用于显示器和照明的激光器和发光二极管。虽然到目前为止在优化钙钛矿纳米晶体（NCs）的固有光物理性质方面已经取得了很大进展，但在实际工作的光电器件中，外部因素，如导电环境和外加电场对激子产生和光子发射的影响，在很大程度上尚未得到探索。在这里，我们使用全无机钙钛矿CsPbBr的纳米晶体分散在空穴导体聚乙烯咔唑和绝缘体聚甲基丙烯酸甲酯中来研究外加电场和基质电导率对单粒子水平上钙钛矿光物理性质的影响。我们发现，由于出现了寿命显著缩短的中等强度发射态，导电环境导致单个纳米晶体的光致发光（PL）亮度显著降低。外加电场有类似的效果，此外，还会导致PL最大值的非线性光谱位移，这是由环境诱导的极性和场相关极化率引起的线性和二次斯塔克效应的组合。环境和电场效应可以通过纳米晶体通过空穴转移的电离以及由此产生的带负电激子的发射来解释。
