Impact Of Auger Recombination On Device Stability In Quasi-2D Perovskite Light Emitting Diodes

Metal halide perovskite has become a star material in the field of electroluminescence due to it has the advantage of inorganic and organic semiconductors.Just in a few years,the external quantum efficiency of perovskite light emitting diode（Pe LEDs）has rapidly increased from less than 1%to 20%.However,the instability of perovskite materials and Pe LEDs de vices is a big challenge for the commercialization.Among them,quasi-two-dimensional perovskite has become a research hotspot due to its high external quantum efficiency,but it also faces the problem of device stability,especially caused by non-radiation Auger Recombination.This is because the effective energy transfer causes the carrier density accumulation in the recombination center,which improves the probability of Auger Recombination,leading to a sharp decline in the efficiency,brightness and stability of Pe LEDs devices under h igh current operation.However,we note that the distribution of excited states and carriers in space is an important factor affecting Auger recombination in quasi-2D perovskite.Therefore,modulating and optimizing the MQWs structure,reducing the spatial density of excited states and carriers is an effective means for suppressed Auger Recombination to improve stability.Such strategies have not yet been reported.Above all the problems,this paper carried out the following work:In this study,we introduce the molecules of phenylethyl ammonium acetate（PEAAc）to modulate the MQWs distribution in the quasi-2D PEA₂Csn-1Pb_nBr_3n+1 to solve the efficiency roll-off and poor stability of the device caused by Auger recombination under high carrier density.The mechanism is that COO^-preferentially coordinates with the perovskite skeleton because it has low formation enthalpy and twice as large ionic radius as-NH₃⁺.As a result,the formation of small n phase by PEA⁺replacing Cs⁺site is significantly inhibited when COO^-binds to Pb²⁺site,then promotes the formation of large n phase.To demonstrate the increase of n≥4 phase in PEAAc assisted films,the steady-state absorption spectrum,transient absorption spectrum and photoluminescence spectrum are tested.The K elvin probe force microscopy and confocal laser scanning fluorescence microscopy were performed to reveal the distribution of excited states and carriers in the film.The results show that the space distribution of excited states and carriers is more evenl y with the increase of n≥4 phase,and the laser intensity increases by 10 times in the optimized thin film before the transition from two-photon to three-photon occurs.However,we found that the exciton binding energy decreased with the increase of n≥4 phase,leading to decreased radiation recombination efficiency.Therefore,To balance the positive effect of Auger Recombination suppression and the negative effect of decreased binding energy,the PEAAc:PEABr molar ratio is adjusted.At the optimal molar ratio,the maximum PLQE of PEA₂Csn-1Pb_nBr_3n+1film reaches 76%.Based on this film,the L_max and EQE_max of Pe LEDs are～29942 cd/m² and 20.2%,respectively.It is the most efficient Pe LEDs of PEA₂Csn-1Pb_nBr_3n+1 Pe LEDs without passivation reported at that time.Meanwhile,the efficiency roll-off of Pe LEDs devices is significantly mitigated with the threshold of the roll-off reaching 3.51 m A/cm².Finally,at the initial luminance is 100 cd/cm²,the maximum luminance and the maximum external quantum efficiency half-life of the optimized device are increased by～10 times.In summary,this strategy not only provides a feasible approach to o ptimize the MQWs structure,but also provides a valuable idea that improves the stability of Pe LEDs devices by suppressing the Auger Recombination in the MQWs structure.For the first time,the distribution of different n phases is related to Auger recombination and the stability of Pe LEDs devices,promotes the commercialization process of Pe LEDs devices.