Unraveling the Energy Landscape and Energy Funneling Modulated by Hole Transport Layer for Highly Efficient Perovskite LEDs

Abstract Previous reports have demonstrated significant effects of hole transport layer (HTL) on the morphology of quasi‐2 dimensional (2D) perovskites, hole injection, and interfacial defect density. However, the effects of HTL on energy landscape and energy funneling of quasi‐2D perovskites have not been revealed so far. Herein, the PEA 2 Cs n −1 Pb n Br 3 n +1 perovskite films are fabricated on four types of HTLs including poly(9‐vinylcarbazole):poly(ethylene oxide) (PVK:PEO), PVK, poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and nickel oxide (NiO x ). The steady‐state and transient absorption spectroscopies reveal that the energy landscape and energy funneling of quasi‐2D perovskites vary significantly on different HTLs. All domains with n = 1, 2, 3, and higher order ( n ≥ 4) are formed with desired population ratios on the PVK:PEO HTL, leading to the most efficient energy funneling. Furthermore, the interfacial passivation effect of PEO on the energy funneling process is studied. The light‐emitting diodes (LEDs) based on PEA 2 Cs n −1 Pb n Br 3 n +1 and PVK:PEO (with an optimized ratio of 5.3:0.7 w/w) HTL result in a maximum luminescence of ≈23 110 cd m –2 and maximum external quantum efficiency of ≈11.5%, respectively. This is the best performance reported so far using pure PEA 2 Cs n −1 Pb n Br 3 n +1 without perovskite composition modifications. This study provides new insights into the HTL for the development of highly efficient quasi‐2D perovskite LEDs.