Observation of Internal Photoinduced Electron and Hole. Separation in Hybrid 2-Dimentional Perovskite Films

Transcription

1 Supporting Information for Observation of Internal Photoinduced Electron and Hole Separation in Hybrid 2-Dimentional Perovskite Films Junxue Liu,,, Jing Leng,, Kaifeng Wu, Jun Zhang, *, Shengye Jin *, State Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation Center of Chemistry for Energy Materials (ichem), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Rd., Dalian, 11623, China. State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum, 66 Changjiang West Rd., Huangdao District, Qingdao, , China. Preparation of hybrid and multi-layered 2D perovskite thin films. CH 3 NH 3 I (MAI) and C 4 H 9 NH 3 I (BAI) were synthesized from the reaction of methylamine and n-butylamine with hydriodic acid (HI) (47wt% in water) at 0 C. The crude product was obtained by slowly evaporating the solvent under reduced pressure. Then the white precipitate was dissolved in ethanol and recrystallized by adding diethyl ether. The small crystals were further washed with diethyl ether several times before drying them in vacuum oven. After drying overnight, they were all sealed under nitrogen and transferred into a glove box for further use. Glass (or FTO) slides were cleaned using an ultra-sonication bath in soap water and rinsed progressively with distilled water, isopropyl alcohol and acetone, and finally treated with oxygen plasma for 20 min. (BA) 2 (MA) n1 Pb n I 3n+1 precursor solution was prepared by dissolving BAI, MAI and PbI 2 (99%) with respective stoichiometric ratio in DMF., The 2D layered perovskite thin films were fabricated via hot-casting process. 1 The sample films discussed in Figure 2, 3, S1, S5 and in Figure S3, S4 were prepared respectively by using (BA) 2 (MA) 3 Pb 4 I 13 (n = 4) and (BA) 2 (MA) 2 Pb 3 I 10 (n = 3) precursor solutions with a total Pb 2+ molar concentration of 0.45 M in anhydrous DMF. The solution was dissolved using an ultra-sonication bath before film fabrication. For the hot-casting process of (BA) 2 (MA) 3 Pb 4 I 13 film, the rinsed glass or S1

2 FTO slides were first preheated 130 C on a hot plate for 10 min right before spin-coating. These hot slides were immediately transferred to the spin-coated chunk (which is at room temperature), and 80 µl of precursor solution was dropped onto the hot slides. The spin-coater was immediately started with a spin speed of 5,000 r.p.m. for 20 s without ramp; the color of the thin film turned from pale yellow to brown in few seconds as the solvent escaped. The hot-casting process of (BA) 2 (MA) 2 Pb 3 I 10 film is similar to the (BA) 2 (MA) 3 Pb 4 I 13 film except that the substrates were preheated at 140 C. Preparation of 2D layered perovskite single crystals (single phase). The 2D layered lead iodide perovskite single crystals were synthesized following the liquid phase crystallization method reported previously. 2, 3, 4 Lead(II) iodide (99%), hydriodic acid (57 wt %, stabilizer free in water), n-butylamine (99.5%), and methylamine solution (33 wt % in ethanol) were purchased from Sigma-Aldrich and diethyl ether (BHT stabilized) was purchased from Tianjin Kemiou Chemical Reagent Co.. At 110 C, stoichiometric quantities of lead(ii) iodide, n-butylamine, and methylammonium iodide were dissolved in a minimum volume of hydriodic acid for the growth of (BAI) 2 (MAI) n1 (PbI 2 ) n, n = 1, 2, 3, 4 and 5. For each single crystal sample, plate-like bright-colored crystals with surface areas of a few square milimeters were obtained after the solution was slowly cooled to 10 C. The crystals were rinsed with cold diethyl ether and dried at 60 C under vacuum for 24 h before exfoliation. We mechanically exfoliated each crystal and transferred the flakes onto clean fused silica for TA and linear absorption measurements. Ultrafast transient absorption spectroscopy measurement. The femtosecond transient absorption setup is based on a regenerative amplified Ti:sapphire laser system from Coherent (800 nm, 35 fs, 6 mj/pulse, and 1 khz repetition rate), nonlinear frequency mixing techniques and the Helios spectrometer S2

3 (Ultrafast Systems LLC). Briefly, the 800 nm output pulse from the regenerative amplifier was split in two parts with a 50% beam splitter. The transmitted part was used to pump a TOPAS Optical Parametric Amplifier (OPA) which generates a wavelength-tunable laser pulse from 250 nm to 2.5 µm as pump beam. The reflected 800 nm beam was split again into two parts. One part with less than 10% was attenuated with a neutral density filter and focused into a 2 mm thick sapphire window to generate a white light continuum (WLC) from 420 nm to 800 nm used for probe beam. The probe beam was focused with an Al parabolic reflector onto the sample. After the sample, the probe beam was collimated and then focused into a fiber-coupled spectrometer with CMOS sensors and detected at a frequency of 1 KHz. The intensity of the pump pulse used in the experiment was controlled by a variable neutral-density filter wheel. The delay between the pump and probe pulses was controlled by a motorized delay stage. The pump pulses were chopped by a synchronized chopper at 500 Hz and the absorbance change was calculated with two adjacent probe pulses (pump-blocked and pump-unblocked). All experiments were performed at room temperature. Time-resolved photoluminescence measurement. The fluorescence lifetime measurement setup used in this study was based on the time-correlated single photon counter technology. The excitation beam was picosecond pulse diode laser with 405 nm output wavelength and 50-ps pulse width. The optical detector was single photon counting module. References: 1. Tsai, H. H.; Nie, W. Y.; Blancon, J. C.; Toumpos, C. C. S.; Asadpour, R.; Harutyunyan, B.; Neukirch, A. J.; Verduzco, R.; Crochet, J. J.; Tretiak, S.; Pedesseau, L.; Even, J.; Alam, M. A.; Gupta, G.; Lou, J.; Ajayan, P. M.; Bedzyk, M. J.; Kanatzidis, M. G.; Mohite, A. D. Nature, 2016, 536, Mitzi, D. B. Prog. Inorg. Chem., John Wiley & Sons, Inc.: New York, 2007; pp S3

4 3. Depmeier, W.; Chapuis, G. Acta Crystallogr., Sect. B, 1979, 35, Wu, X.; Trinh, M. T.; Zhu, X. Y. J. Phys. Chem. C, 2015, 119, Figure S1. Top-view and cross-section SEM images of the (BA) 2 (MA) 3 Pb 4 I 13 (n = 4) multi-layered 2D perovskite films. The thickness of the film is ~358 nm. Figure S2. UV-Vis absorption spectra of (BA) 2 (MA) n1 Pb n I 3n+1 2D perovskite single crystals with n = 1, 2, 3, 4 and 5. S4

5 Figure S3. Top-view and cross-sectional SEM images of the (BA) 2 (MA) 2 Pb 3 I 10 (n = 3) multi-layered 2D perovskite films. The thickness of the film is ~523 nm. Figure S4. TA spectra at different delay times of a typical (BA) 2 (MA) n1 Pb n I 3n+1 2D perovskite film (~523 nm thickness, prepared as n = 3) under (a) back- and (b) frontexcitations. (c) TA kinetics probed at n = 2, 3, 4 and n bands under back-excitation. Solid lines are the fits of the kinetics by exponential function with fitting parameters listed in Table S3. (d) Comparison of the time-resolved PL and TA kinetics probed at the n band. The TA kinetics probed at n = 3, 4, 5 and n bands all show rising kinetics, whose time becomes longer as the n increases. This S5

6 observation further confirms the consecutive carrier transfer (majorly stemming from n = 2) from phase to phase. In the thicker film the different perovskites are more spatially separated than in the thin film (Figure 2 in main text), and therefore results in a slower carrier transfer time between adjacent phases. Figure S5. Comparison of TA kinetics probed at n band (with back-excitation) in (BA) 2 (MA) n1 Pb n I 3n+1 2D perovskite films before and after depositions of PCBM (electron acceptor) and Spiro-OMeTAD (hole acceptor). S6

7 Figure S6. TA spectra in Figure 3a after subtracting the PIA signal from n phase, showing clear bleach peaks that are attributed to n = 3 and 4 perovskite species.. Figure S7. PL decay of the (BA) 2 (MA) n1 Pb n I 3n+1 2D perovskite film (358 nm thickness) probed at 750 nm (emission from n band) under front-excitation at 405 nm. The solid line is the fit of the decay with an exponential function, yielding a lifetime of 680 ps. This lifetime is much faster than the intrinsic carrier lifetime (see S7

8 Figure S8b), and is consistent with the observed hole transfer time of 193 to 987 ps observed in the TA measurement (Figure 3 in the main text). Figure S8. (a) TA kinetics probed at the maximum bleach band of 2D perovskite single crystals (single phase) with n = 2 and 3. The solid lines are the exponential fits of the kinetics yielding intrinsic lifetime (averaged) of 5.4 ns for n = 3 and 14.1 ns for n = 4 crystals (at 480 nm, 0.7 µj/cm 2 /pulse). Using these intrinsic carrier lifetimes and an electron transfer time of 477 ps, the theoretical efficiency of charge separation by electron transfer (back-excitation) is calculated to be 97% from n = 3 to n phase and 92% from n = 2 to n phase in the hybrid 2D perovskite films discussed in the main text. (b) TA kinetics probed at the maximum bleach band of a perovskite film with n single phase. In order to obtain the intrinsic carrier lifetime of n phase (bleach peak at ~740 nm), we fabricated an almost pure n perovskite film by adjusting the molar ratio of BA + in the precursor mixture. The inset shows the TA spectra of the film with only single bleach band at ~740 nm. Solid line is the fit of the kinetics by exponential function, yielding the carrier lifetime of 2.3 ns. Using this intrinsic carrier lifetime and an hole transfer time of 987 ps, the theoretical efficiency of charge separation by hole transfer (front-excitation) is calculated to be 70% from n to n = 3 phase in the hybrid 2D perovskite films discussed in the main text. S8

9 Figure S9. (a) UV-vis absorption spectra of (BA) 2 (MA) n1 Pb n I 3n+1 2D perovskite films (prepared as n = 4) with the thinness of ~358 nm and < 100 nm. (b) PL spectra of the films in (a) with the same back-excitation power at 450 nm. After normalizing the absorption at the excitation wavelength of 450 nm, the relative PL quantum yield (PLQY) between two films is PLQY 100 nm /PLQY 358 nm = 6.9 (back-excitation) and 4.0 (front excitation). (c) PL spectra of the 2D perovskite film (thickness < 100 nm) and a 3D perovskite film with a similar thickness (after normalizing the absorption). The relative PLQY 100 nm (2D) / PLQY 100 nm (3D) = 1.8 (back-excitation) and 2.1 (front-excitation). S9

10 Figure S10. (a) TA spectra of the (BA) 2 (MA) n1 Pb n I 3n+1 2D perovskite film (prepared as n = 4) with the thickness of ~100 nm. The electron transfer from small-n to large-n perovskite phases is observed. (b) TA kinetics probed the maximum of n bleach band. Solid line is the fit of the kinetics with exponential function, yielding the electron transfer time of 142 ps. Table S1. Fitting parameters for the kinetics shown in Figure 2c. The kinetics are fit by an multiple-exponential function, A(t) = a 1 exp(-t/τ 1 ) + a 2 exp(-t/τ 2 ) + a 3 exp(-t/τ 3 ) - c 1 exp(-t/τ et ), where a 1,a 2, a 3 and c 1 are the amplitudes; τ 1, τ 2 and τ 3 are the decay time constants and τ et is the electron transfer time constant. τ et /ps (c 1 ) τ 1 /ps (a 1 ) τ 2 /ps (a 2 ) τ 3 /ps (a 3 ) n = ±5.8 (30.8%) ±61.1 (42.5%) ± (26.7%) n = ± 29.5 (15.2%) ± (64.8%) ± (20.0%) n = ± 80.1 (78.9%) ± (21.1%) n ± 23.5 (70.1%) ± (100%) S10

11 Table S2. Fitting parameters for the kinetics shown in Figure 3b. The kinetics are fit by an multiple-exponential function, A(t) = a 1 exp(-t/τ 1 ) -c 1 exp(-t/τ ht ), where a 1 and c 1 are the amplitudes; τ 1 is the decay time constant and τ ht is the hole transfer time constant. τ ht /ps (c 1 ) τ 1 /ps n = ± (84.3%) > n = ± 30.2 (71.9%) ± Table S3. Fitting parameters for the kinetics shown in Figure S4c. The kinetics are fit by an multiple-exponential function, A(t) = a 1 exp(-t/τ 1 ) + a 2 exp(-t/τ 2 ) - c 1 exp(-t/τ et ), where a 1,a 2 and c 1 are the amplitudes; τ 1 and τ 2 are the decay time constants and τ et is the electron transfer time constant. τ et /ps (c 1 ) τ 1 /ps (a 1 ) τ 2 /ps (a 2 ) n = ± 7.2 (35.5%) ± 42.4 (64.5%) n = ± 11.3 (12.3%) ± (45.9%) ± (54.1%) n = ± 12.4 (55.6%) ± n = ± 57.9 (82.3%) ± n ± S11