With the advent of metal halide perovskites into the world of emerging sustainablesemiconductors, a host of previously unprecedented applications has materialised. Aside from their ragingsuccess in photovoltaics, perovskites as applied to light emitting diodes (LEDs) and displays have gainedparticular interest due to their extremely facile bandgap tunability, directional and narrow-linewidth emissioncharacteristics, high brightness, superior efficiencies and colour purity among other desirable features.However, most of the world records in terms of device efficiency and stability have been achieved on lab-scalepixels processed using solution-based techniques, primarily spin-coating. However, with its inherentadvantages of scalability, reproducibility and precise thickness control, vacuum-based thermal evaporationprovides an edge over solution-processing for all optoelectronic applications.

Following recent advancements in vacuum thermal evaporation of perovskite solar cells in our group, we haveemployed this technique to fabricate highly luminescent red-emitting perovskite films for efficient andoperationally stable light emitting diodes (LEDs). By optimizing the growth conditions, we have been able toachieve previously unreported photoluminescence quantum efficiencies (PLQE) close to 20% under 1-sun-equivalent conditions for red emitters. Moreover, no sign of unwanted halide segregation has been observedunder continuous illumination, thereby resulting in stable PL emissions in the wavelength range of 630-640 nm(within CIE pure-red range). To understand the effect of deposition conditions on the resulting optoelectronicproperties of evaporated perovskites, a range of characterization including intensity-dependent PLQE, fluence-dependent TRPL, THz spectroscopy and transient photoconductivity measurements have also beenconducted. Furthermore, X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy(UPS) have been employed to obtain information on the chemical composition and electronic properties of theevaporated films. To gain deeper insight into the microscopic origins of device performance, we employphotoluminescence (PL) imaging to directly probe static and dynamic defect populations within the perovskitefilms. These measurements reveal pronounced spatial heterogeneity and provide insight into carrierrecombination pathways that remain poorly understood in vacuum-deposited perovskite emitters. Theoptimized LEDs exhibit negligible electroluminescence peak shifts with increasing drive voltage, indicative ofsuppressed phase segregation and spectral instability, while operational lifetimes (T₈₀) of several minutes areachieved under continuous operation. To further elucidate degradation mechanisms, fresh and aged devicestacks are investigated using a combination of STEM-EDX, ToF-SIMS, and PL microscopy. This multimodalanalysis tracks changes in structure, morphology, composition, and defect distributions throughout themultilayer architecture, enabling identification of the dominant degradation pathways responsible forperformance losses under sustained current-bias stress. Finally, by extensive screening of the charge injectionlayers, we have been able to demonstrate red LEDs with champion external quantum efficiency (EQE) ~5% and turn-on voltage~ 3 V which exhibit unprecedented high luminance of > 3000 cd/m².