Thick Charge Transport Layers Enable Amplified Spontaneous Emission and Enhanced Electroluminescence in Lossy Aluminum-Cathode Perovskite LEDs

The realization of electrically pumped perovskite lasers is currently hindered by a fundamental “cathode conflict”: noble metals like silver (Ag) are required for low optical modal loss but lack the proper work function for efficient electron injection, whereas the standard lithium fluoride/aluminum (LiF/Al) cathode ensures superior electron injection but introduces prohibitive optical absorption. Here, we present a device engineering strategy that decouples these constraints by utilizing the electron transport layer (ETL) as a geometric optical spacer. We demonstrate that increasing the ETL thickness from 40 to 200 nm effectively isolates the optical mode from the cathode interface, suppressing modal absorption. This optimization enables a perovskite LED with a standard, optically lossy LiF/Al cathode to achieve amplified spontaneous emission (ASE) under optical pumping, a milestone typically restricted to noble metal electrodes. Furthermore, under nanosecond pulsed electrical operation, the 200 nm ETL device exhibits superior electroluminescence intensity compared to conventional thin-ETL structures, attributed to enhanced charge balance and hole-blocking capabilities. This work establishes a viable pathway to integrate electrically efficient LiF/Al cathodes into low-loss optical cavities, addressing a critical trade-off toward the realization of perovskite laser diodes.