Universal,predominant exciton transfer in perovskite nanocrystal solids

钙钛矿纳米晶固体中普遍存在的、显著的激子转移

Perovskite nanocrystal(PNC)solids are promising materials for optoelectronic applications.Recent studies have shown that exciton diffusion in PNC solids occurs via alternate exciton hopping(EH)and photon recycling(PR).The energy disorder induced by the size distribution is a common factor in PNC solids,and the impact of this energy disorder on the exciton diffusion remains unclear.Here,we investigated the exciton diffusion in CsPbBr3 NC solids with a Gaussian size distribution of 11.2±6.8 nm via steady and time-resolved photoluminescence(PL)spectroscopy with multiple detection bands in transmission mode.Our results indicated that exciton diffusion was controlled by a downhill transfer among the different energy sites through the disordered energy landscape,as confirmed by the accompanying low-temperature PL analysis.A detailed examination revealed that the acceptor distribution in tandem with the reabsorption coefficient determined the contribution of EH and PR to exciton transfer between different energy sites.Consequently,the exciton diffusion mechanism varied in PNC solids of different thicknesses:in a thin solid with a thickness of several hundred nanometers,the exciton transfer was dominated by efficient EH and PR from the high-energy sites to the lower-energy sites;in a few-micrometer-thick solid,transfer from the medium-energy sites toward the lower-energy sites also became prominent and occurred mainly through PR.These findings enhance the understanding of the vital role that the acceptor distribution plays in the exciton diffusion process in PNC solids,providing important insights for optoelectronic applications based on PNC solids.Our work also exploits the use of commonly available tools for in-depth exciton diffusion studies,which reveals the interior diffusion information that is usually hidden in surface sensitive PL imaging methods.

钙钛矿纳米晶(PNC)固体是很有前景的光电应用材料.最近的研究表明,PNC固体中的激子扩散通过交替的激子跳跃(EH)和光子循环(PR)而实现.PNC固体中尺寸分布引起的能量不均一性是普遍存在的,目前尚不清楚该因素对激子扩散的影响.在这里,我们通过透射模式的多波段稳态和瞬态光致发光(PL)光谱学测试,研究了尺寸呈高斯分布(边长约为11.2±6.8 nm)的CsPbBr_(3)NC固体中的激子扩散.我们的研究结果表明,激子沿着能量降低的方向在不同能量位点之间进行转移,这一过程支配着PNC固体的激子扩散,低温PL分析结果进一步证实了这一点.更为详细的研究揭示出,受体分布与吸收系数共同决定了EH和PR在不同能量位点之间的激子转移中所做的贡献.因此,在不同厚度的PNC固体中,激子扩散机制有所不同:高能位点向较低能位点的EH和PR效率高,主导着几百纳米薄膜中的激子转移;在数微米的厚膜中,从中等能量位点向低能位点的、主要通过PR而进行的激子转移也变得明显起来.这些发现不仅使我们进一步理解了受体分布在PNC固体的激子扩散过程中所起的关键作用,也为基于PNC固体的光电应用提供了重要基础和指导.我们的工作还利用常规的测试手段来深入研究激子扩散过程,有利于揭示以往的表面PL成像方法所隐藏了的关于材料内部激子扩散的信息.