Quantitative Correlation of Perovskite Film Morphology to Light Emitting Diodes Efficiency Parameters

Abstract

This paper reports quantitative correlation of CH3NH3PbBr3 (MAPbBr3) thin film morphology to light emitting diode efficiency parameters. Sequential (spin coating) deposition is used for highly reproducible and dense film morphology of MAPbBr3 thin‐film. In this fabrication process using an orthogonal solvent approach, control of morphology, coverage, thickness, and optical properties in these compact thin‐films is demonstrated. Optical studies show direct correlation between morphology to dynamics of photoluminescence (PL) and absolute PL yield. Perovskite light emitting diodes (PeLEDs) are fabricated from these films to find the best ratio of PbBr2 versus MABr for optimal performance. This study demonstrates PeLEDs with high brightness, ≈1050 cd m−2 at 4.7 V (luminance efficiency ≈0.1 cd A−1), for optimal thin‐film process with state‐of‐the‐art device performance. This quantitative analysis suggests that these state‐of‐the‐art PeLEDs suffer from poor charge carrier balance (≈2%) and out‐coupling efficiency (≈6%). Interestingly, charge carrier balance and PL yield together can explain the change in PeLED efficiency modulation with film morphology. Studies on single carrier devices show that these PeLEDs are electron current dominated and charge carrier balance increases with operating bias voltage.

Record High External Quantum Efficiency of 19.2% Achieved in Light‐Emitting Diodes of Colloidal Quantum Wells Enabled by Hot‐Injection Shell Growth

“…For solution‐processed LEDs, the film morphology of the active layer has a significant influence on the device performance . Thus, the EQE of solution‐processed LEDs (EQE') can be written as follows where α represents the factor of film morphology extracted out from the charge balance factor to emphasize the effect of film roughness on the leakage current, γ' thus is the ratio of γ over α such that γ = α γ'. In OLEDs, α is not considered due to the very smooth film formed by the vacuum‐evaporated procedure .…”

Recent Advances in Metal Halide‐Based Perovskite Light‐Emitting Diodes

“…To improve out coupling photonic solutions such as index grids, microlenses, and patterning of substrates can be used. Separately tackling these three efficiency parameters can easily give a substantial boost to existing out‐coupling efficiencies, which is close to 5.7 % at present for bulk MAPbBr 3 ‐based PeLEDs . Optimally balanced charge‐carrier injection into the emissive layer requires smooth and pinhole‐free interfaces between perovskite emitter and electron‐ or hole‐transport layers.…”

Enhanced Coverage of All‐Inorganic Perovskite CsPbBr3 through Sequential Deposition for Green Light‐Emitting Diodes

“…This is ascribed to the combined effect of increased thickness and reduced surface coverage, which gives rise to more non‐radiative recombination pathways. The resulting drops in both L max and efficiency thus emphasize the importance of film morphology and coverage on device performance …”