Kshirsagar Anuraj S, Koch Katherine A, Srimath Kandada Ajay Ram, Gangishetty Mahesh K
Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762, United States.
Department of Physics and Center for Functional Materials, Wake Forest University, 2090 Eure Drive, Winston Salem, North Carolina 27109, United States.
JACS Au. 2024 Mar 6;4(3):1229-1242. doi: 10.1021/jacsau.4c00083. eCollection 2024 Mar 25.
Luminescence quenching by hole transport layers (HTLs) is one of the major issues in developing efficient perovskite light-emitting diodes (PeLEDs), which is particularly prominent in blue-emitting devices. While a variety of material systems have been used as interfacial layers, the origin of such quenching and the type of interactions between perovskites and HTLs are still ambiguous. Here, we present a systematic investigation of the luminescence quenching of CsPbBr by a commonly employed hole transport polymer, poly[(9,9-dioctylfluorenyl-2,7diyl)-co-(4,4'-(N-(4-sec-butylphenyl) diphenylamine)] (TFB), in LEDs. Strong and weak quantum-confined CsPbBr (nanoplatelets (NPLs)/nanocrystals (NCs)) are rationally selected to study the quenching mechanism by considering the differences in their morphology, energy level alignments, and quantum confinement. The steady-state and time-resolved Stern-Volmer plots unravel the dominance of dynamic and static quenching at lower and higher concentrations of TFB, respectively, with a maximum quenching efficiency of 98%. The quenching rate in NCs is faster than that in NPLs owing to their longer PL lifetimes and weak quantum confinement. The ultrafast transient absorption results support these dynamics and rule out the involvement of Forster or Dexter energy transfer. Finally, the 1D H and 2D nuclear overhauser effect spectroscopy nuclear magnetic resonance (NOESY NMR) study confirms the exchange of native ligands at the NCs surface with TFB, leading to dark CsPbBr-TFB ensemble formation accountable for luminescence quenching. This highlights the critical role of the triarylamine functional group on TFB (also the backbone of many HTLs) in the quenching process. These results shed light on the underlying reasons for the luminescence quenching in PeLEDs and will help to rationally choose the interfacial layers for developing efficient LEDs.
空穴传输层（HTLs）导致的发光猝灭是高效钙钛矿发光二极管（PeLEDs）开发过程中的主要问题之一，这在蓝色发光器件中尤为突出。虽然多种材料体系已被用作界面层，但这种猝灭的起源以及钙钛矿与HTLs之间相互作用的类型仍不明确。在此，我们对发光二极管中常用的空穴传输聚合物聚[(9,9 - 二辛基芴 - 2,7 - 二基)-co-(4,4'-(N-(4 - 仲丁基苯基)二苯胺)]（TFB）引起的CsPbBr发光猝灭进行了系统研究。通过考虑其形态、能级排列和量子限制的差异，合理选择了强量子限制和弱量子限制的CsPbBr（纳米片（NPLs）/纳米晶体（NCs））来研究猝灭机制。稳态和时间分辨的斯特恩 - 沃尔默图分别揭示了在较低和较高TFB浓度下动态猝灭和静态猝灭的主导地位，最大猝灭效率为98%。由于纳米晶体（NCs）的荧光寿命更长且量子限制较弱，其猝灭速率比纳米片（NPLs）更快。超快瞬态吸收结果支持了这些动力学过程，并排除了福斯特或德克斯特能量转移的参与。最后，一维氢和二维核Overhauser效应光谱核磁共振（NOESY NMR）研究证实了纳米晶体（NCs）表面的天然配体与TFB发生了交换，导致形成了导致发光猝灭的暗CsPbBr - TFB聚集体。这突出了TFB上的三芳基胺官能团（也是许多HTLs的主链）在猝灭过程中的关键作用。这些结果揭示了PeLEDs中发光猝灭的潜在原因，并将有助于合理选择界面层以开发高效发光二极管。
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