Unraveling Luminescence Quenching Mechanism in Strong and Weak Quantum-Confined CsPbBr3 Triggered by Triarylamine-Based Hole Transport Layers

Luminescence quenching by hole transport layers (HTLs) is one of the major issues in developing efficient perovskite light-emitting diodes (PeLEDs); particularly, it is more prominent in blue LEDs. Often, various interfacial layers are used to overcome this issue. However, 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 CsPbBr3 by a commonly employed hole transport polymer, Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB) in LEDs. Strong and weak quantum-confined CsPbBr3 (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 maximum quenching efficiency of 98 %. The quenching rate in NCs is faster than 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 1H and 2D NOESY NMR study confirms the exchange of native ligands at the NCs surface with TFB, leading to dark CsPbBr3-TFB ensemble formation accountable for luminescence quenching. This highlights the critical role of the triarylamine functional group on TFB (which is 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 choose the interfacial layers rationally for developing efficient LEDs.