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7265957 
Journal Article 
Ultrafast Spectroscopy of Photoexcitations in Organometal Trihalide Perovskites 
Zhai, Y; Sheng, CX; Zhang, C; Vardeny, ZV; , 
2016 
Yes 
Advanced Functional Materials
ISSN: 1616-301X
EISSN: 1616-3028 
WILEY-V C H VERLAG GMBH 
WEINHEIM 
1617-1627 
WOS:000372309000013 
Studying the room temperature broadband ultrafast transient response of photoexcitations in three perovskite films, namely MAPbI(3), MAPbI(1.1)Br(1.9), and MAPbI(3-x)Cl(x) (MA = CH3NH3), allowed unravelling the branching ratio between photogenerated carriers and excitons, a key factor for optoelectronic applications of perovskites. An instantaneously generated mid-IR photoinduced absorption (PA) band, PA(1) is observed in all three perovskites, as well as a strong derivative-like band of photoinduced bleaching (PB) and PA (PA(2)) close to the corresponding absorption band edge. From the distinguished different decay dynamics of the PA bands in MAPbI(3), PA(1) is interpreted as due to the exciton transition, whereas PA(2) and PB are due to band-filling effect caused by the photocarriers. In contrast, all bands in MAPbI(1.1)Br(1.9) and MAPbI(3-x)Cl(x) share the same dynamics and are therefore due to the same species, namely photogenerated excitons. The transient photoinduced polarization memory (POM) for both excitons and photocarriers as well as the steady-state photoluminescence (PL) emission are observed in MAPbI(3), but not in MAPbI(1.1)Br(1.9) and MAPbI(3-x)Cl(x) because they possess cubic symmetry at room temperature. The estimated long excitons diffusion length (approximate to 150 nm) in MAPbI(3) opens up the possibility of photocarriers generation at interfaces and grain boundaries even when the exciton binding energy is large compare to k(B)T.