Hot Carrier Trapping and It's Influence to the Carrier Diffusion in CsPbBr3 Perovskite Film Revealed by Transient Absorption Microscopy

Abstract The defects in perovskite film can cause charge carrier trapping which shortens carrier lifetime and diffusion length. So defects passivation has become promising for the perovskite studies. However, how defects disturb the carrier transport and how the passivating affects the carrier transport in CsPbBr3 are still unclear. Here the carrier dynamics and diffusion processes of CsPbBr3 and LiBr passivated CsPbBr3 films are investigated by using transient absorption spectroscopy and transient absorption microscopy. It's found that there is a fast hot carrier trapping process with the above bandgap excitation, and the hot carrier trapping would decrease the population of cold carriers which are diffusible, then lower the carrier diffusion constant. It's proved that LiBr can passivate the defect and lower the trapping probability of hot carriers, thus improve the carrier diffusion rate. The finding demonstrates the influence of hot carrier trapping to the carrier diffusion in CsPbBr3 film.

We have measured the TRPL decay curves for CsPbBr3 and LiBr-CsPbBr3 films with initial carrier density n0 ~1.5×10 16 cm -3 .The PL lifetime of passivated perovskite film is significantly longer than Figure S25.High energy tails on the normalized bleaching spectra of (a, b, c) CsPbBr3 and (e, f, g) LiBr-CsPbBr3 films under 400 nm excitation with different initial carrier density n0.The blue lines are the normalized TA signals to 1 (-ΔA) for different time delays.The higher energy tails are well fitted by an exponential function corresponding to Maxwell-Boltzmann distribution to extract the hot carrier temperature Tc. [2,7] (d, h) The extracted carrier temperature with delay time at different carrier density.The cooling lifetimes are obtained by using a monoexponential fitting.

Figure S4 .
Figure S4.The TAM synchronous scanning images of (a) CsPbBr3 and (b) LiBr-CsPbBr3 films.Pump and probe beams are overlapped in space (pump at 400 nm, probe at 520 nm).The pump probe delay is at 0 ps.

Figure S5 .
Figure S5.The scanning electron microscope (SEM) images of the cross-section of CsPbBr3 and LiBr-CsPbBr3 films.

Figure S7 .
Figure S7.The TA spectra of CsPbBr3 at several delay times under 514 nm excitation with different initial carrier density (n0).

Figure S8 .
Figure S8.The TA spectra of LiBr-CsPbBr3 at several delay times under 514 nm excitation with different initial carrier density (n0).

Figure S10 .
Figure S10.Linear fits to the bimolecular recombination rate equation n0/nt -1 = Bn0t for (a) CsPbBr3 and (b) LiBr-CsPbBr3 with different initial carrier density under 514 nm excitation (probed at 520 nm).The slope is equal to Bn0, where n0 is the initial photogenerated carrier density and B is the rate constant for the bimolecular recombination.

Figure S11 .
Figure S11.The TA spectra of CsPbBr3 at several delay times under 400 nm excitation with different initial carrier density (n0).

Figure
Figure S12.(a-e) The TA spectra of LiBr-CsPbBr3 at several delay times under 400 nm excitation with different initial carrier density (n0).(f) Normalized kinetic profiles probed at 520 nm in the early time with different initial carrier density for LiBr-CsPbBr3 film under 400 nm excitation.

Figure S13 .
Figure S13.Normalized early time PB kinetics of CsPbBr3 with different excitation wavelength at lower initial carrier density.Probed at 520 nm.

Figure
Figure S14.TAM images of (a) CsPbBr3 and (b) LiBr-CsPbBr3 pumped at 490 nm (n0 ~3.0×10 18 cm - 3 ) and probed at 520 nm.The color scale represents the intensity of pump-induced differential transmission (ΔT) of the probe, and every image has been normalized by the peak value.The images show the spatial distribution of the ΔT signal measured at pump−probe delay times as labeled.

Figure
Figure S15.TAM images of (a) CsPbBr3 and (b) LiBr-CsPbBr3 pumped at 400 nm (n0 ~1.9×10 18 cm - 3 ) and probed at 520 nm.The color scale represents the intensity of pump-induced differential transmission (ΔT) of the probe, and every image has been normalized by the peak value.The images show the spatial distribution of the ΔT signal measured at pump−probe delay times as labeled.

Figure S16 .
Figure S16.Time evolution of  2 = () 2 − (0) 2 of CsPbBr3 and LiBr-CsPbBr3 films.Error bars are the standard error estimated from the 2D Gaussian fitting to the spatial intensity distribution.The linear fitting to eq 3 yields the diffusion constant D. The inset of (b) displays the early time evolution of L 2 .

Figure S17 .
Figure S17.One-dimensional TAM images of CsPbBr3 fitted by Gaussian function at different delay times, with the maximum ΔT signal normalized.Pumped at 490 nm with different initial carrier density n0.

Figure S18 .
Figure S18.One-dimensional TAM images of LiBr-CsPbBr3 fitted by Gaussian function at different delay times, with the maximum ΔT signal normalized.Pumped at 490 nm with different initial carrier density n0.

Figure S19 .
Figure S19.Time evolution of  2 = () 2 − (0) 2 of (a) CsPbBr3 and (b) LiBr-CsPbBr3 films pumped at 490 nm with different initial carrier density.Error bars are the standard error estimated from the 1D Gaussian fitting to the spatial intensity distribution.The linear fitting to eq 3 yields the diffusion constant D.

Figure S20 .
Figure S20.One-dimensional TAM images of CsPbBr3 fitted by Gaussian function at different delay times, with the maximum ΔT signal normalized.Pumped at 400 nm with different initial carrier density n0.

Figure S21 .
Figure S21.One-dimensional TAM images of LiBr-CsPbBr3 fitted by Gaussian function at different delay times, with the maximum ΔT signal normalized.Pumped at 400 nm with different initial carrier density n0.

Figure S22 .
Figure S22.Time evolution of  2 = () 2 − (0) 2 of (a) CsPbBr3 and (b) LiBr-CsPbBr3 films pumped at 400 nm with different initial carrier density.Error bars are the standard error estimated from the 1D Gaussian fitting to the spatial intensity distribution.The linear fitting to eq 3 yields the diffusion constant D.

Figure S23 .
Figure S23.Normalized TAM dynamics of (a, c) CsPbBr3 and (b, d) LiBr-CsPbBr3 films with different initial carrier density n0 under different excitation wavelength.The pump beam spatially overlapped with the probe beam.

Table S1 .
The fitted diffusion constant D of CsPbBr3 and LiBr-CsPbBr3 with different initial carrier density under 490 nm and 400 nm excitation.