Highly Efficient Light Emitting Diodes Based on In Situ Fabricated FAPbI₃ Nanocrystals: Solvent Effects of On-Chip Crystallization

The in situ fabricated perovskite nanocrystals (PNCs) obtained through spin-coating a precursor solution are suitable candidates to achieve efficient perovskite light emitting diodes (PeLEDs). In this work, the solvent effects of on-chip crystallization are investigated by correlating the nucleation and growth process of in situ fabricated formamidinium lead iodide (FAPbI₃) nanocrystals with their optical and electronic properties. The FAPbI₃ nanocrystals obtained from a precursor solution in γ-butyrolactone (GBL) are smaller than those obtained from N,N-dimethylformamide and dimethyl sulfoxide, and the relatively weak coordination between GBL and the precursor molecules enables reduced defect states in the resulted PNCs with enhanced photoluminescence properties. A modified LaMer model is proposed to describe the solvent effects in the on-chip crystallization process. Based on these understandings, red emissive FA_0.87Cs_0.13PbI₃ nanocrystal films with absolute photoluminescence quantum yields up to 70% are realized. Finally, an efficient PeLED with maximum luminance of 218 cd m⁻² and peak external quantum efficiency of 15.8% is achieved with good reproducibility.