Poly(ethylene oxide)-assisted energy funneling for efficient perovskite light emission

Poly(ethylene oxide) (PEO) has been demonstrated as an effective polymer additive for fabrication of organic-inorganic hybrid perovskite light emitting devices due to its properties enabling pinhole-free film morphology, improved charge injection, and defect passivation. In this paper, we report a new aspect of PEO in assisting the energy funneling in formamidinium lead bromide (FAPbBr) thin films, leading to a very high photoluminescence quantum yield of ∼62.1%. By mixing PEO with FAPbBr at a desired ratio, self-assembled 3D polycrystals with sizes from ∼20 to ∼1500 nm were formed. The polycrystals contain inhomogeneous domains with a range of energetic excited states. Through fluorescence lifetime image microscopy, the in situ fluorescence emissions and the lifetimes of the domains were measured simultaneously, indicating energy funneling from the wide-bandgap domains (with small-size grains) into the narrow-bandgap domains (with large-size grains). PL spectroscopy on the nano-second scale was used to study the dynamics of charge transfer, which shows a reduced short-wavelength emission and narrowed full width at half maximum with increasing time. Our results also indicate that the optimal PEO doping ratio of 0.35:1 can facilitate the most efficient charge carrier cascade for energy funneling. This study establishes the role of PEO-assisted energy funneling avoiding the defect-quenching effect in perovskites, for potential applications in perovskite LEDs and lasers.