Exciton Character and High‐Performance Stimulated Emission of Hybrid Lead Bromide Perovskite Polycrystalline Film

Abstract

optical communication, detecting, and photovoltaic applications, owing to their advantages of tunable bandgap, long car rier lifetime, and high light absorption. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] These advantages have arisen because of the distinctive semiconductor and photo physics properties that such materials possess, including ultrahigh bandedge density of states, [15] ultralow charge trap ping crosssection, [16] and low defect den sities. [17] Recent findings, including the ultraslow hot carrier cooling, [18,19] ultralong polarization memory, [20] giant spinorbit Rashba splitting, [21] and weak electronlattice coupling, [22] further increase mys tery of the perovskites. Underlying these alluring characteristics are intrinsic elec tronic states of the perovskite materials, while the electronic structure ultimately determines their photoelectric conversion mechanisms and performances. [23,24] As such, exploring electronic states of the hybrid perovskite pos sesses important implications for improving performance of current devices and expanding application horizons of these materials.Nonetheless, a clear understanding of the intrinsic elec tronic structure and chargecarrier characters of the perovskite remains lacking, and controversies on these properties have always been ongoing. These endless controversies arise because of the observed complicated photophysics characteristics and distinct scenarios proposed for interpreting them. For instance, the electronic origin for bandedge dual emission bands within both the single crystal and polycrystalline perovskites is one of the controversial focuses. [25][26][27][28][29][30][31][32] These dual emission bands pro vide important spectroscopic information for elucidating the fine structure of bandedge electronic states. Photon recycling provided a satisfied explanation for this phenomenon within the single crystal methylammonium lead bromide (MAPbBr 3 ). [25] Indirect band structure induced by a static or dynamical Rashba effect is another common interpretation [30][31][32] since a giant Rashba splitting within MAPbBr 3 was indeed observed using angular resolved photoelectron spectroscopy. [21] The indirect band structure scenario was also proposed to explain an unu sual temperature dependent secondorder radiative recombina tion velocity. [33] In contrast, an experimental result supporting the direct bandgap structure was observed recently. [34] Another controversial focus is on the charge character of perovskite. The bandedge emission of the bromide perovskite was once Electronic states of hybrid perovskites enable their exceptional optoelectronic applications. Herein, through heterojunction enhanced exciton dissociation and global tracing of multiple radiative electronic states across wide temperature regions, it has been found that excitons while not free carriers dominate the bandedge photoelectric properties of hybrid lead bromide perovskite (MAPbBr 3 ). MAPbBr 3 has exhibited two types of excitons with giant binding energies and superior phas...

Observation of Net Stimulated Emission in CsPbBr3 Thin Films Prepared by Pulsed Laser Deposition

“…The carrier behaviors behind stimulated emission ultimately determine optical amplification and device performance. [ 27 ] Whether stimulated emission arises from biexciton, [ 4 ] bound exciton, [ 28 ] EHP, [ 29,30 ] or exciton scattering process? [ 31,32 ] Through detailed photocurrent and temperature dependent measurement, we report exciton‐exciton inelastic scattering process induced stimulated emission in bulk‐like CsPbBr 3 film by PLD.…”

Polaron and Spin Dynamics in Organic–Inorganic Lead Halide Perovskite Nanocrystals

“…[ 7,11–15 ] These attributes led to extremely efficient solution‐processed cost‐effective solar cells (>25%), low‐threshold lasing, and light‐emitting diodes. [ 2,5,12,16–21 ] Recently demonstrated hot phonon bottleneck helps to establish the potential for hot carrier photovoltaic devices that can break the single‐junction Shockley–Queisser limit for solar cells. [ 22,23 ]…”

Toward stable lead halide perovskite solar cells: A knob on the A/X sites components

“…Meng et al. demonstrated that the Br ‒ -containing pure perovskites possessed dual exciton states dominated by excitons, not free carriers ( Shi et al., 2020 ). Levine et al.…”

“…proved that mixed A/X sites with a structure of (FA 0.85 MA 0.1 Cs 0.05 )Pb(I 0.83 Br 0.17 ) 3 did not detect deep trap states by surface photovoltage spectroscopy (SPS) and deep-level transient spectroscopy (DLTS) techniques ( Levine et al., 2019 ), which indicated that A/X sites alloying would be a promising channel to decrease defect level and optimize band level alignment. Based on the energy band structure and charge species in hybrid perovskites, there are several origins to explain the dual emission band such as mixed charge species within the perovskites in (e.g., free carrier, free and bound exciton) ( Shi et al., 2020 ; Wu et al., 2019 ).…”