Blade-coated perovskite nanoplatelet polymer composites for sky-blue light-emitting diodes

Abstract

Colloidal perovskite nanoplatelets (NPLs) have shown promise in tackling blue light-emitting diode challenges based on their tunable band gap and high photoluminescence efficiencies. However, high quality and large area dense NPL films have been proven to be very hard to prepare because of their chemical and physical fragility during the liquid phase deposition. Herein, we report a perovskite-polymer composite film deposition strategy with fine morphology engineering obtained using the blade coating method. The effects of the polymer type, solution concentration, compounding ratio and film thickness on the film quality are systematically investigated. We found that a relatively high-concentration suspension with an optimized NPL to polymer ratio of 1 : 2 is crucial for the suppression of phase separation and arriving at a uniform film. Finally, sky-blue NPL-based perovskite light-emitting diodes were fabricated by blade coating showing an EQE of 0.12% on a device area of 16 mm².

Fig. 1. (a) Absorption and PL spectra of CsPbBr₃ NPLs. (b) Schematic representation for polymer/NPLs composite solution preparation (ink) and the doctor-blading process for deposition.

Fig. 2. AFM surface topography of the blade-coated films with different ratios of polymers at 10 mg mL⁻¹ NPL concentration. (a) PVK at 5 mg mL⁻¹; (b) PVK at 30 mg mL⁻¹; (c) P-TPD at 5 mg mL⁻¹ and (d) P-TPD at 30 mg mL⁻¹. All the white scale bars represent 2 μm.

Fig. 3. AFM surface morphologies of the blade-coated composite films under fixed NPLs to P-TPD ratio (1 : 2), with NPL concentration of (a) 2.5 mg mL⁻¹, (b) 5 mg mL⁻¹, (c) 10 mg mL⁻¹ and (d) 15 mg mL⁻¹. All white scale bars represent 2 μm.

Fig. 4. AFM images showing surface morphologies of the blade-coated films using a solution with constant NPL concentration (15 mg mL⁻¹) and NPLs to P-TPD ratio of (a) 1 : 1.6, (b) 1 : 1.8, (c) 1 : 2.0 and (d) 1 : 2.2 with a fixed thickness of 45 nm. All white scale bars represent 2 μm.

Fig. 5. Under a fixed concentration of NPLs (15 mg mL⁻¹) and a ratio of NPL to P-TPD (1 : 2), AFM surface morphologies of the blade-coated films with different thicknesses of (a) 15 nm, (b) 20 nm, (c) 30 nm, and (d) 45 nm. All white scale bars represent 2 μm.

Fig. 6. (a) Normalized PL spectra and (b) time-resolved photoluminescence measurement (495 nm) of the composite film prepared by constant NPLs concentration (15 mg mL⁻¹) and NPLs to P-TPD ratio of 1 : 1.6, 1 : 1.8, 1 : 2.0, and 1 : 2.2.

Fig. 7. (a) Device structure, (b) EL spectra of the optimized device with the active layer thickness 45 nm and prepared from a 15 mg mL⁻¹ NPL suspension with a polymer mixing ratio of 1 : 2. (c) Current density–luminance–voltage curves and (d) EQE–V curves of sky-blue LED with different ratios of NPLs to P-TPD.