Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , via R. Cozzi 55, 20125 Milano, Italy.
Nano Lett. 2017 Jun 14;17(6):3844-3853. doi: 10.1021/acs.nanolett.7b01253. Epub 2017 May 10.
Lead halide perovskite nanocrystals (NCs) are emerging as optically active materials for solution-processed optoelectronic devices. Despite the technological relevance of tracing rational guidelines for optimizing their performances and stability beyond their intrinsic resilience to structural imperfections, no in-depth study of the role of selective carrier trapping and environmental conditions on their exciton dynamics has been reported to date. Here we conduct spectro-electrochemical (SEC) experiments, side-by-side to oxygen sensing measurements on CsPbBr NCs for the first time. We show that the application of EC potentials controls the emission intensity by altering the occupancy of defect states without degrading the NCs. Reductive potentials lead to strong (60%) emission quenching by trapping of photogenerated holes, whereas the concomitant suppression of electron trapping is nearly inconsequential to the emission efficiency. Consistently, oxidizing conditions result in minor (5%) brightening due to suppressed hole trapping, confirming that electron traps play a minor role in nonradiative decay. This behavior is rationalized through a model that links the occupancy of trap sites with the position of the NC Fermi level controlled by the EC potential. Photoluminescence measurements in controlled atmosphere reveal strong quenching by collisional interactions with O, which is in contrast to the photobrightening effect observed in films and single crystals. This indicates that O acts as a scavenger of photoexcited electrons without mediation by structural defects and, together with the asymmetrical SEC response, suggests that electron-rich defects are likely less abundant in nanostructured perovskites than in the bulk, leading to an emission response dominated by direct interaction with the environment.
卤铅钙钛矿纳米晶体（NCs）作为用于溶液处理光电设备的光学活性材料而崭露头角。尽管在技术上需要追踪合理的指导方针，以优化其性能和稳定性，超越其对结构缺陷固有弹性的范围，但迄今为止，尚未有关于选择性载流子捕获和环境条件对其激子动力学影响的深入研究。在这里，我们首次对 CsPbBr NCs 进行了光谱电化学（SEC）实验和氧传感测量。我们表明，通过改变缺陷态的占据，应用 EC 电势可以控制发射强度，而不会使 NCs 降解。还原电势通过捕获光生空穴导致强烈的（60%）发射猝灭，而电子捕获的同时抑制对发射效率几乎没有影响。一致地，氧化条件导致由于抑制空穴捕获而导致的微小（5%）变亮，这证实了电子陷阱在非辐射衰减中作用较小。这种行为通过一个模型得到了合理化，该模型将陷阱位置的占据与由 EC 电势控制的 NC 费米能级的位置联系起来。在受控气氛中的光致发光测量显示，与在薄膜和单晶中观察到的光致增亮效应相反，与 O 的碰撞相互作用强烈猝灭。这表明 O 作为光激发电子的清除剂，而无需结构缺陷的介导，并且与非对称 SEC 响应一起，表明富电子缺陷在纳米结构钙钛矿中比在体相中不太丰富，导致发射响应主要由与环境的直接相互作用决定。
