All polymer ligand strategy enables highly stable spectra-pure green-emitting perovskites

Stabilizing perovskite nanocrystals (PNCs) has been a hot topic since last decade. To avoid defect formation under ambient conditions it is crucial to protect crystal lattice using enhanced surface passivation. Polymers are one of the most promising materials for protection of PNCs and generally used along with conventional ligands. In this work we demonstrate all polymer ligands-based strategy to achieve highly stable, spectra-pure green-emitting PNCs of CsPbBr₃ at room temperature. We employ combination of Polyvinylpyrrolidone (PVP) and Polyethylene glycol (PEG) polymers without the use of conventional Oleic acid and Oleylamine ligands. PNCs synthesized with only PVP emit bluish green weak PL intensity. Upon addition of PEG, PNCs exhibit giant PL enhancement and PL spectra shifted towards pure green region. Xray diffraction (XRD) and Transmission Electron Microscopy (TEM) confirms the formation of CsPbBr₃ lattice. We also studied the effect of PEG concentration and obtained an optimized sample with peak PL intensity. As an effect of proper passivation, optimized sample delivered 76% of Photoluminescence Quantum Yield (PLQY). It remained stable with up to one year under ambient conditions. It possessed robust thermal and UV stabilities. Sample retained 92.6% PL after 15 cycles of heating and cooling between 27 °C and 85 °C. Under extreme environmental conditions of 80% relative humidity and high intensity UV irradiation, sample retained 96.81% of original PL after 50 h testing. Further, we fabricated a Light Emitting Diode (LED) using optimized sample. The LED delivered outstanding performance with peak luminous efficiency of 104.33 lm.W^{- 1} (20 mA, 2.54 V) and high spectral stability after 500 h of continuous operation with 94% of PL retention. We believe this all-polymer passivation strategy could be beneficial for stabilization of perovskite materials for the next generation display devices.