Carrier Decay Properties of Mixed Cation Formamidinium

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Carrier Decay Properties of Mixed Cation FormamidiniumMethylammonium Lead Iodide Perovskite [HC(NH)] [CHNH]PbI Nanorods 2

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1-x

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Jun Dai, Yongping Fu, Lydia H. Manger, Morgan T. Rea, Leekyoung Hwang, Randall H. Goldsmith, and Song Jin J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b01958 • Publication Date (Web): 23 Nov 2016 Downloaded from http://pubs.acs.org on November 24, 2016

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The Journal of Physical Chemistry Letters

Carrier Decay Properties of Mixed Cation Formamidinium-Methylammonium Lead Iodide Perovskite [HC(NH2)2]1-x[CH3NH3]xPbI3 Nanorods Jun Dai,a,b Yongping Fu,a Lydia H. Manger,a Morgan T. Rea,a Leekyoung Hwang,a Randall H. Goldsmith,a,* Song Jina,∗

a

Department of Chemistry, University of Wisconsin-Madison, Madison, 53705, USA

b

Department of Physics, Jiangsu University of Science and Technology, Zhenjiang, 212003,

China

Abstract Organic-inorganic lead iodide perovskites are efficient materials for photovoltaics and light-emitting diodes. We report carrier decay dynamics of nanorods of mixed cation formamidinium and methylammonium lead iodide perovskites [HC(NH2)2]1-x[CH3NH3]xPbI3 (FA1-xMAxPbI3) synthesized through a simple solution method. The structure and FA/MA composition ratio of the single-crystal FA1-xMAxPbI3 nanorods are fully characterized, which shows that the mixed cation FA1-xMAxPbI3 nanorods are stabilized in the perovskite structure. The photoluminescence (PL) emission from FA1-xMAxPbI3 nanorods continuously shifts from 821 to 782 nm as the MA ratio (x) increases from 0 to 1 and is shown to be inhomogeneously broadened. Time-resolved photoluminescence from individual FA1-xMAxPbI3 nanorods demonstrates that lifetimes of mixed cation FA1-xMAxPbI3 nanorods are longer than the pure FAPbI3 or MAPbI3 nanorods, and the FA0.4MA0.6PbI3 displays the longest average photoluminescence lifetime of about 2 µs. These results suggest that mixed cation FA1-xMAxPbI3 perovskites are promising for high-efficiency photovoltaics and other optoelectronic ∗

Corresponding authors: [email protected] (Prof. Song Jin); [email protected] (Prof. Randall Goldsmith)

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applications.

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Hybrid organic-inorganic lead halide perovskites have attracted tremendous attention as a new class of solution-processed semiconductors for optoelectronic applications, such as photovoltaics, lasers, light emitting diodes and photodetectors. In particular, methylammonium (MA) lead iodide CH3NH3PbI3 (MAPbI3) exhibits excellent photovoltaic performance with a power conversion efficiency of ~20%,1-9 as well as remarkable optically-pumped lasing performance.10-12 Compared to other conventional solution-processed semiconductors, MAPbI3 has extraordinary semiconductor properties such as a large absorption coefficient, low defect density, long carrier lifetime, and long carrier diffusion length that are essential for its remarkable optoelectronic performance. Despite these successes, a major hurdle for practical application of MAPbI3 is its instability, including poor thermal stability, photo-instability, and high moisture sensitivity. The lack of stability of MAPbI3 is consistent with the low formation energy of hybrid perovskites. In addition, MAPbI3 undergoes a phase transition from tetragonal to cubic phase at 55 °C, a temperature that can be realized in the outdoor environment or during operation of light-emitting devices, which might further affect the performance and long-term stability.13 Therefore, it is important to search for other perovskite candidates with improved stability while maintaining similar or better semiconductor properties. The crystal structure of lead halide perovskite with a general chemical formula APbX3 (where A is an organic or inorganic cation, X is a halide) consists of a network of corner-shared PbX6 octahedra with the cation occupying the 12-fold coordination site formed by eight octahedra. Similar to traditional oxide perovskites, this crystal structure provides great flexibility to modify the physical properties through chemical substitution. For example, there has been ongoing research interest in formamidinium (FA) lead iodide perovskites, HC(NH2)2PbI3 (α-FAPbI3), in which the organic cation is replaced by formamidinium.14-19 Due to the enhanced interaction between organic cation and PbI6 network, FAPbI3 perovskite shows improved thermal stability. Moreover, its room temperature band gap is slightly smaller than that of MAPbI3, which allows redder portions of solar radiation to be harvested. However, unlike MAPbI3, the larger radii of the FA cation results in a structural tolerance factor too high to maintain the perovskite 3 ACS Paragon Plus Environment


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structure.20 Indeed, at room temperature, FAPbI3 preferentially stabilizes in a yellow hexagonal phase (δ-FAPbI3) that shows negligible photovoltaic performance.21 Therefore, researchers have resorted to stabilizing the perovskite phase of FAPbI3 by partially replacing the FA cation with smaller-sized MA or Cs cations. Examples of mixed cation perovskite thin films, such as FA1-xMAxPbI3,22-25 FA1-xCsxPbI3,2 FA1-xCsxPbI3-yBry,26,

27

have been reported with good

photovoltaic performance. While mixing with Cs+ might significantly improve thermal stability, the mixed FA-Cs+ cation perovskites are challenging and complicated due to the more complex phase behaviors of FAPbI3 and CsPbI3. Note that the CsPbI3 perovskite phase is also not stable at room temperature. For example, it is difficult to acquire a phase-pure FA1-xCsxPbI3 perovskite at room temperature,2 and FA1-xCsxPbI3-yBry potentially have phase segregation issues under long-term light exposure and the band gap slightly increases due to the doping of Br.27 In contrast, FA1-xMAxPbI3 was found to crystallize in the perovskite phase more readily at room temperature, because FA and MA are more similar in chemical property to each other than Cs+. Moreover, perovskite solar cells based on FA1-xMAxPbI3 thin films often showed comparable or even better performance than those based on α-FAPbI3 and MAPbI3 devices.24, 28 However, the photoexcited carrier dynamics that form the mechanistic basis for the better performance of the FA1-xMAxPbI3 solar cells remains unclear. Carrier lifetime is a key parameter of semiconductor materials; longer carrier lifetime usually results in longer diffusion lengths and better solar cell performance. Consequently, understanding carrier decay processes can help us to predict and improve solar cells’ performance. Previous reports on the photophysics of FA1-xMAxPbI3 materials mostly focus on polycrystalline thin films that were synthesized via spin-coating.24,

29

The quality of such

perovskite films can be highly variable and very sensitive to the preparation conditions, i.e. humidity, solvent and lead precursor, thus the ability to grow high-quality perovskite materials with well-defined morphology and good reproducibility for photophysical studies is highly desirable. Single crystals could be an attractive platform to explore the intrinsic properties of the semiconductors. In particular, high quality single-crystal nanostructures (i.e. nanowires, 4 ACS Paragon Plus Environment

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nanorods, and nanoplates) with well-controlled surface facets can be studied as excellent model systems30 and can also be used as building blocks for nanoelectronics and nanophotonics.10, 11, 31-33

Although the photoluminescence (PL) lifetimes of MAPbI3 and FAPbI3 thin films and bulk

single crystals have been investigated to explain the photovoltaic performance,34-41 a comprehensive and systematic study on the synthesis and photoexcited carrier decay properties of the whole series of FA1-xMAxPbI3 single crystal samples has not been reported. In this paper, we report the influence of chemical composition on the phase stability and photoluminescence lifetime of single-crystal nanorods of FA1-xMAxPbI3 (x = 0-1). We synthesized a complete series of mixed cation FA1-xMAxPbI3 nanostructures by reacting a lead acetate precursor film with a mixed cation iodide solution with various FA/MA ratios. The phase, nanoscale morphology, and chemical composition of these mixed cation FA1-xMAxPbI3 nanorods were examined by powder X-ray diffraction (PXRD), scanning electron microscopy, and 1H NMR. The emission peak of the photoluminescence for single objects of mixed cation FA1-xMAxPbI3 gradually red-shifts from 782 to 821 nm as the x value changes from 1 to 0. More importantly, time-resolved photoluminescence revealed that all FA1-xMAxPbI3 generally have longer photoluminescence lifetimes than FAPbI3 or MAPbI3, and FA0.4MA0.6PbI3 displays the longest photoluminescence lifetime, which could be attributed to their stable cubic perovskite structure with more favorable tolerance factors. Our results suggest that mixed cation hybrid perovskites could be more stable alternatives with excellent photophysical properties for photovoltaic and other optoelectronic applications. We synthesized a complete series of mixed cation FA1-xMAxPbI3 nanostructures by reacting a

lead

acetate

precursor

film

with

mixed

cation

iodide

solutions

through

a

dissolution-recrystallization mechanism.42, 43 The detailed experimental methods are described in the Supporting Information. Figure 1a shows optical images of various FA1-xMAxPbI3 samples grown on glass substrates by the solution method. The pictures show, from the left to the right, the samples grown in the precursor solution with the FA/(FA+MA) ratio of 1.0, 0.8, 0.6, 0.4, 0.2 and 0, respectively. In a pure formamidinium iodide (FAI) solution, FAPbI3 crystalizes in the 5 ACS Paragon Plus Environment


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hexagonal phase at room temperature, as confirmed by the yellow product shown in the far left in Figure 1a. The sample can be transformed into the black α-FAPbI3 phase with a perovskite structure after annealing at 160 °C for several minutes.43 We note all optical characterization of the FAPbI3 samples was taken on the converted samples. Figure 1b-g show the SEM images of FA1-xMAxPbI3 nanostructures with composition x changing from 0 to 1. The FAPbI3 sample shows bunches of nanowires with hexagonal cross sections, and the FA1-xMAxPbI3 samples mainly show nanorods and nanoplates with rectangular cross sections.

Figure 1. (a) Optical images of the as-grown FA1-xMAxPbI3 samples on glass substrates. From the left to the right, the FA ratio in the reaction solution is 1.0, 0.8, 0.6, 0.4, 0.2 and 0. (b-g) SEM images of (b) FAPbI3, (c) FA0.8MA0.2PbI3, (d) FA0.6MA0.4PbI3, (e) FA0.4MA0.6PbI3, (f) FA0.2MA0.8PbI3 and (g) MAPbI3 nanorods (and nanoplates).

To quantitatively determine the composition of FA/MA in the as-synthesized FA1-xMAxPbI3 samples, the samples were dissolved in methanol-d4 solvent and the 1H NMR spectra were collected. Figure 2a shows the NMR spectra of the FA1-xMAxPbI3 samples (x = 0.2, 0.4, 0.6, 0.8), with the peak at a chemical shift (σ) of 7.89 ppm a signature of formamidinium and the peak at 6 ACS Paragon Plus Environment

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2.58 ppm a signature of methylammonium, chemical shifts at 4.86 ppm and 3.32 ppm are signatures of methanol-d4 solvent. The integrated intensities of these peaks yield the FA/MA ratios as 0.19 : 0.81, 0.4 : 0.6, 0.59 : 0.41, and 0.79 : 0.21 for the four mixed cation samples, which agree well with the FA/MA ratios (0.2 : 0.8, 0.4 : 0.6, 0.6 : 0.4, 0.8 : 0.2) in the precursor solutions. PXRD patterns were collected to determine the phase of these FA1-xMAxPbI3 samples, as shown in Figure 2b. The PXRD pattern of pure FAPbI3 can be indexed to a hexagonal phase (space group P63mc a = 0.868 nm, c = 0.793 nm) and MAPbI3 to a tetragonal perovskite phase (space group I4/mcm, a = 0.869 nm, c = 1.277 nm). Except for FA0.8M0.2PbI3, which shows the coexistence of both the hexagonal and the cubic perovskite phase, the PXRD patterns of FA0.6MA0.4PbI3, FA0.4MA0.6PbI3 and FA0.2M0.8PbI3 samples reveal only cubic perovskite phase. The reason why as-grown FAPbI3 has the non-perovskite hexagonal structure but the FA1-xMAxPbI3 are in the cubic perovskite phase is because mixing FAPbI3 with the MA cation with a smaller radius reduces the tolerance factor, which makes it acceptable for the perovskite structural type and thus stabilizes these compositions in the cubic perovskite phase.20, 43 Figure 2c further shows the enlarged (100) diffraction peak at 2θ ~14°, which continuously shifts from 13.96° to 13.86° as the FA/(MA+FA) ratio increases. Figure 2d shows the lattice spacing linearly increases with the increasing FA/(MA+FA) ratio, which agrees well with the Vegard’s law approximation.24, 44



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Figure 2. (a) NMR spectra of the mixed cation FA1-xMAxPbI3 samples. (b) PXRD patterns of the mixed cation FA1-xMAxPbI3 nanorods. (c) The enlarged area in PXRD patterns highlighted by the dash box in (b) that clearly shows the peak shift as a function of the composition (x). (d) Lattice spacing of different FA1-xMAxPbI3 samples as a function of the composition.

Figure 3a shows the room temperature photoluminescence (PL) spectra of the mixed cation FA1-xMAxPbI3 samples collected on ensembles of nanorods. Each FA1-xMAxPbI3 sample displays a single emission peak originating from near band edge radiative recombination, and no emission from deep defect levels can be observed. The center emission wavelength shifts from 821 nm to 782 nm as the FA/(MA+FA) ratio decreases. Such a continuous shift of PL emission peaks confirms the successful band gap tuning of these mixed cation FA1-xMAxPbI3 nanorods. The PL peak energy with respect to the FA/(MA+FA) ratio is shown in Figure 3b. The PL peak energy Eg increases almost linearly from 1.51 to 1.59 eV while the FA/(MA+FA) ratio decreases from 1 to 0, which is well fit by the equation: Eg(FA1-xMAxPbI3) = xEg(MAPbI3) + (1-x)Eg(α-FAPbI3). Here, PL peak energies of the MAPbI3 and FAPbI3 are a little different from those band gap values in the literature because they are estimated from PL center wavelength λcenter after the λ2 correction.


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Figure 3. (a) Room temperature PL spectra of ensemble FA1-xMAxPbI3 samples for each cation composition x, the excitation wavelength is 550 nm. (b) The PL peak energy of FA1-xMAxPbI3 samples as a function of the FA ratio. (c-f) µ-PL spectra of different individual FA1-xMAxPbI3 nanorods excited by CW 532 nm laser. (g-j) The statistical PL peak energy and the FWHM of the µ-PL in (c-f) (red dots). The black dots denote the PL peak energy and FWHM of the corresponding ensemble PL spectra in (a).

Micro-photoluminescence (µ-PL) spectra of different individual nanorods from the same batch of FA1-xMAxPbI3 sample were measured to confirm the homogeneous compositional distribution. Figures 3c-f display eight representative µ-PL spectra from eight different nanorods for four FA1-xMAxPbI3 samples with x = 0.8, 0.6, 0.4, and 0.2. These small differences of the PL peak energy in the µ-PL spectra of these nanorods may be attributed to subtle composition fluctuations, size effects, or surface defects. Figures 3g-j show the PL peak energy and FWHM 9 ACS Paragon Plus Environment


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of emission spectra of all nanorods examined for each FA1-xMAxPbI3 composition (red circles), and the PL peak energy and FWHM of the ensemble PL spectra collected on the samples (black square). As seen in Figure 3a and quantified by the rising black squares in Figure 3g-j, the bulk (ensemble) emission peak grows broader as the MA fraction rises, increasing from 87 to 104 meV. These scatter plots yield information on the relative contributions of homogeneous and inhomogeneous broadening to the bulk spectrum. The homogeneous photoluminescence linewidths of the individual nanorods remains nearly constant across the series at 80-85 meV, a value marginally smaller than the 103 meV homogenous linewidth in mixed halide MA perovskite thin films, and likely stemming from strong coupling of charge carriers to phonons.45 In contrast, the PL peak energy of many individual nanorods is tightly clustered for x = 0.2 and then more scattered at higher values of x. However, summation of the individual nanorod spectra still results in a FWHM lower than the bulk spectra (see Figure S7). But, it should be noted that the bulk spectra were collected on the as-grown substrates, which also consist of many smaller nanoparticles along with the nanorods. Thus, the increasing PL linewidth for ensemble samples likely originates from an increasing degree of inhomogeneous broadening at high MA fraction. Because the growth kinetics change when the FA fraction is increased in the precursor solution, the resulting morphology of products may vary among these samples. The size and crystalline quality of these nanoparticles may vary, contributing to the inhomogeneous broadening of the bulk PL. We then performed time-resolved photoluminescence (TRPL) on individual nanorod to investigate the influence of chemical composition on carrier dynamics. Figure 4a shows representative TRPL spectra of a representative FA0.4MA0.6PbI3 nanorod excited by 639 nm picosecond laser with increasing excitation intensity. Under the low excitation intensities of 1.09 × 10-9 (black) and 1.09 × 10-8 J/cm2/pulse (red), a first order process likely dominates. Consequently, the decay processes can be well fit by monoexponential profiles with photoluminescence lifetimes of 1950 and 1170 ns, respectively. The monoexponential decay at low excitation condition is caused by mono-molecular and trap-mediated recombination. Upon 10 ACS Paragon Plus Environment

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more intense excitation at 1.09 × 10-6 J/cm2/pulse, the photoluminescence exhibits non-monoexponential decay with a much shorter effective lifetime likely due to electron-hole recombination and other higher order processes.10, 46 The photoluminescence decay dynamics of other FA1-xMAxPbI3 show a similar trend when the excitation intensity is increased.

Figure 4. (a) Representative TRPL decays of a FA0.4MA0.6PbI3 nanorod under different laser excitation energy densities. (b) TRPL decays of various mixed cation FA1-xMAxPbI3 nanorods with different composition (x) at the excitation energy density of 1.09×10-9 J/cm2/pulse with the right panel showing the corresponding nanorod imaged during excitation. (c) The average photoluminescence lifetime from multiple nanorods at each composition plotted vs. FA/(FA+MA) at the 1.09×10-9 J/cm2/pulse. Error bars represent standard deviation of the mean.

Here we focus our attention on the carrier decay dynamics of FA1-xMAxPbI3 perovskite nanorods measured under the lowest excitation intensity of 1.09×10-9 J/cm2/pulse, where the behaviors can be well-modeled with a monoexponential fit. We focused on this regime because 11 ACS Paragon Plus Environment


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at typical solar irradiance, photoexcited carrier densities are expected to be low, and trap-mediated recombination is likely the dominant decay pathway.47 The trap states are usually shallow subgap states very close to the conductance band because the deep trap state around the middle of the band gap is hard to form due to its high formation energy.48 In addition, we did not find PL from the deep trap states whose PL center would show longer wavelength than the near band gap recombination. Baumann et al. pointed out that the electrons in the shallow trap states can be released and have no obvious effect on device performance.49 Representative TRPL spectra of the FA1-xMAxPbI3 samples at 1.09×10-9 J/cm2/pulse excitation are shown in Figure 4b along with the corresponding images of the excited perovskite nanorods (right panel). PL decays sometimes present a fast initial decay component, which is likely caused by carrier diffusion or surface defects,39, 50, 51 with surface defects playing a more exaggerated role due to the high surface-to-volume ratio of our nanorods. For our samples, all of the FAPbI3 nanorods show non-monoexponential decay curves (Fig. S6), whereas most of the FA1-xMAxPbI3 nanorods only present a slow decay process. In our subsequent analysis, we will mainly concentrate on the longer timescale decays which are more relevant to achieving long carrier diffusion lengths and monoexponential decay kinetics. Different nanorods in the same batch of sample with the same composition (x) show only some variations in PL lifetime. Several nanorods from the same batch of sample were examined to obtain their average PL lifetime for each composition and representative TRPL spectra of the FA1-xMAxPbI3 samples can be found in Figures S1-6 in the Supporting Information. Figure 4c shows the average photoluminescence lifetime with respect to the FA/MA ratio. The average lifetimes are 490 ± 110 ns, 1240 ± 190 ns, 1940 ± 130 ns, 1730 ± 280 ns and 1010 ± 180 ns for the MAPbI3, FA0.2MA0.8PbI3, FA0.4MA0.6PbI3, FA0.6MA0.4PbI3 and FA0.8MA0.2PbI3 nanorods, respectively. For the FAPbI3 nanorods, we fit the TRPL curves to a biexponential decay. All of the FAPbI3 nanorods show a short lifetime τ1 and long lifetime τ2, with the weight of the long lifetime varying from 30% to 50%. The average τ1 and τ2 are 32 ± 9 ns and 390 ± 95 ns, respectively, with the short carrier lifetime component likely originating from recombination at surface defects. FA0.6MA0.4PbI3 nanorods also show a fast initial decay 12 ACS Paragon Plus Environment

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more often than the other compositions, suggesting a higher incidence of surface defects. Only the longer lifetimes of the nanorods were plotted in Fig. 4c in order to maintain a fair comparison between

mixed

FA1-xMAxPbI3

samples.

All

FA1-xMAxPbI3

samples

have

longer

photoluminescence lifetimes than pure FAPbI3 or MAPbI3, and FA0.4MA0.6PbI3 displays the longest photoluminescence lifetime. The FAPbI3 nanorods show the the shortest average photoluminescence lifetime, which is probably also due to the polycrystalline nature and the many crystal domain boundaries after the phase conversion from the hexagonal non-perovskite phase. The PL lifetime of FAPbI3, MAPbI3 and mixed cation FA1-xMAxPbI3 show longer lifetimes than the reported polycrystalline thin films, indicating that single crystal FA1-xMAxPbI3 photovoltaic devices should suffer less from defects and thus potentially demonstrate better performance. The reported carrier lifetime of bulk MAPbI3 and FAPbI3 single crystals are 1 µs and 480 ns, respectively.21, 39 Because of the high surface-to-volume ratio in nanostructures, MAPbI3 and FAPbI3 nanorods likely have more surface defects than that in their bulk single crystals, which results in a shorter PL lifetime. Photoexcited carriers can be strongly confined in our FA1-xMAxPbI3 nanorods with their size much smaller than the carrier diffusion length.52, 53 This observed dependence of photoluminescence decay dynamics on composition is interesting and suggests that FA1-xMAxPbI3, especially the composition around FA0.4MA0.6PbI3, could be promising for improved solar and other optoelectronic devices. One can also relate this observed trend to the perovskite structural stability and defect levels. The Goldschmidt tolerance factor (t) is an empirical index for predicting stable crystal structures of perovskite materials and has been shown to correlate with changes in photoluminescence lifetime.29 The tolerance factor is defined as t =

, where rA is the radius of the A-cation (FA+, MA+ in this case, rMA =

√( )

217 pm, rFA = 253 pm), rB = 119 pm is the radius of the B-cation (Pb2+) and r0 = 220 pm is the radius of the anion (I-). The perovskite materials tend to form an orthorhombic perovskite structure for t < 0.8, cubic perovskite structure for 0.8 < t < 1, and hexagonal non-perovskite structure for t > 1.20

Recent reports show that the stable cubic perovskites tend to display a 13 ACS Paragon Plus Environment


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longer photoluminescence lifetime.29, 54 The PXRD patterns of mixed cation perovskites (Figure 2) show that even though pure FAPbI3, with a tolerance factor very close to the critical value 1.0, is stable as a non-perovskite hexagonal structural at room temperature, the cubic perovskite forms when the smaller MA+ cation is mixed in the structure. The replacement of the large cation, FA+, with the smaller cation, MA+, decreases the tolerance factor and improve the stability of the cubic perovskite phase. The calculated tolerance factor for the FA1-xMAxPbI3 is shown in Figure 5. Li and co-workers20 found that inorganic-organic lead iodide perovskite solar cells show better performance if the tolerance factor of the mixed cation perovskite is in the region of 0.94-0.98, displayed as the gray area in Figure 5. The corresponding FA ratio region for better solar cell performance is 37.5%-91%, as shown by the dashed line in Figure 5, with our observed maximum photoluminescence lifetime falling within this range. The perovskite structure stability of the FA1-xMAxPbI3 increases initially and then decreases when the FA ratio increases from 0 to 1. Consequently, we find that the better perovskite structure stability is correlated with the longer photoluminescence lifetime, which results in better solar cell performance. The polycrystalline black perovskite α-FAPbI3 samples converted from yellow hexagonal δ-FAPbI3 contains surface defects and grain boundaries, which results in a faster decay process than MAPbI3 and FA1-xMAxPbI3. A similar trend of PL lifetime was also observed by Pellet et al. in polycrystalline FA1-xMAxPbI3 thin films, with the PL of MAPbI3 and FAPbI3 thin films decaying much faster than the mixed cation FA1-xMAxPbI3 thin films and FA0.4MA0.6PbI3 showing the longest PL lifetime, although their PL decays showed a non-monoexponential decay profile which might be related to their higher excitation intensity.24 This similarity suggests that defects stemming from structural mismatch are also present in the thin films. The PL lifetimes of the FA1-xMAxPbI3 nanorods observed here are longer than those of the FA1-xMAxPbI3 thin films by Pellet et al., which may be attributed to less prevalent boundary defects in the single-crystal nanorods. One possible mechanism of the improved PL lifetime for the FA1-xMAxPbI3 may be that the rapid rotation of MA+ in a larger cubic FA1-xMAxPbI3 unit cell than in a distorted tetragonal MAPbI3 unit cell can influence the photoexcited carrier decay.55, 56 More studies are needed to fully 14 ACS Paragon Plus Environment

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explain the deeper physical mechanisms behind this observed correlation between photoluminescence lifetime and perovskite structure stability.

Figure 5. The correlation between the Goldschmidt tolerance factor (black dot) and photoluminescence lifetime (blue squares) of the mixed cation FA1-xMAxPbI3 perovskites.

In summary, a series of mixed cation FA1-xMAxPbI3 nanorods were synthesized with a simple solution method and the PL emission wavelength was effectively tuned from 782 nm to 821 nm as the FA content increased from 0 to 1. Moreover, FA1-xMAxPbI3 displayed longer PL lifetimes than either pure MAPbI3 or FAPbI3. The stable cubic phase with higher symmetric structure tends to have a longer PL lifetime than those with the tetragonal phase. Therefore, the PL lifetime increases as the FA content increases from 0 to 0.6. However, the FA0.8MA0.2PbI3 nanorods may be structurally unstable due to the high FA content and show short PL lifetimes. The converted FAPbI3 samples are polycrystalline and contain many crystal boundaries formed after the phase transition. Therefore, FAPbI3 sample show much shorter PL lifetime. The intermediate FA0.4MA0.6PbI3 perovskites with the longest average photoluminescence lifetime, about 2 µs, could be promising active material in solar cells and other optoelectronic devices.



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Acknowledgement This materials synthesis and structural characterization was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award DE-FG02-09ER46664 (to S.J.). The optical microscopy and spectroscopic studies were supported by the National Science Foundation through the University of Wisconsin Materials Research Science and Engineering Center (UW-MRSEC, DMR-1121288, to R.H.G.). J.D. also thanks the financial support by the China Scholarship Council (CSC).

Supporting Information Detailed synthesis method, characterization method, TRPL setup parameters and experiment method, and more representative TRPL data of FA1-xMAxPbI3 nanorods.

References (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050-6051. (2) Lee, J. W.; Kim, D. H.; Kim, H. S.; Seo, S. W.; Cho, S. M.; Park, N. G. Formamidinium and Cesium Hybridization for Photo- and Moisture-Stable Perovskite Solar Cell. Adv. Energy Mater. 2015, 5, 1501310. (3) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science. 2012, 338, 643-647. (4) Liu, M. Z.; Johnston, M. B.; Snaith, H. J. Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501, 395-398. (5) Etgar, L.; Gao, P.; Xue, Z.; Peng, Q.; Chandiran, A. K.; Liu, B.; Nazeeruddin, M. K.; Graetzel, M. Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells. J. Am. Chem. Soc. 2012, 134, 17396-17399. 16 ACS Paragon Plus Environment

Page 17 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Zhou, H. P.; Chen, Q.; Li, G.; Luo, S.; Song, T. B.; Duan, H. S.; Hong, Z. R.; You, J. B.; Liu, Y. S.; Yang, Y. Interface Engineering of Highly Efficient Perovskite Solar Cells. Science. 2014, 345, 542-546. (7) Gao, P.; Graetzel, M.; Nazeeruddin, M. K. Organohalide Lead Perovskites for Photovoltaic Applications. Energy Environ. Sci. 2014, 7, 2448-2463. (8) Sum, T. C.; Mathews, N. Advancements in Perovskite Solar Cells: Photophysics Behind the Photovoltaics. Energy Environ. Sci. 2014, 7, 2518-2534. (9) Wang, W.; Tade, M. O.; Shao, Z. P. Research Progress of Perovskite Materials in Photocatalysis- and Photovoltaics-Related Energy Conversion and Environmental Treatment. Chem. Soc. Rev. 2015, 44, 5371-5408. (10) Zhu, H. M.; Fu, Y. P.; Meng, F.; Wu, X. X.; Gong, Z. Z.; Ding, Q.; Gustafsson, M. V.; Trinh, M. T.; Jin, S.; Zhu, X. Y. Lead Halide Perovskite Nanowire Lasers with Low Lasing Thresholds and High Quality Factors. Nat. Mater. 2015, 14, 636-642. (11) Xing, J.; Liu, X. F.; Zhang, Q.; Ha, S. T.; Yuan, Y. W.; Shen, C.; Sum, T. C.; Xiong, Q. H. Vapor Phase Synthesis of Organometal Halide Perovskite Nanowires for Tunable Room-Temperature Nanolasers. Nano. Lett. 2015, 15, 4571-4577. (12) Xing, G. C.; Mathews, N.; Lim, S. S.; Yantara, N.; Liu, X. F.; Sabba, D.; Gratzel, M.; Mhaisalkar, S.; Sum, T. C. Low-Temperature Solution-Processed Wavelength-Tunable Perovskites for Lasing. Nat. Mater. 2014, 13, 476-480. (13) Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties. Inorg. Chem. 2013, 52, 9019-9038. (14) Koh, T. M.; Fu, K. W.; Fang, Y. N.; Chen, S.; Sum, T. C.; Mathews, N.; Mhaisalkar, S. G.; Boix, P. P.; Baikie, T. Formamidinium-Containing Metal-Halide: An Alternative Material for Near-IR Absorption Perovskite Solar Cells. J. Phys. Chem. C 2014, 118, 16458-16462. (15) Eperon, G. E.; Stranks, S. D.; Menelaou, C.; Johnston, M. B.; Herz, L. M.; Snaith, H. J. Formamidinium Lead Trihalide: a Broadly Tunable Perovskite for Efficient Planar 17 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 22

Heterojunction Solar Cells. Energy Environ. Sci. 2014, 7, 982-988. (16) Aharon, S.; Dymshits, A.; Rotem, A.; Etgar, L. Temperature Dependence of Hole Conductor Free Formamidinium Lead Iodide Perovskite Based Solar Cells. J. Mater. Chem. A 2015, 3, 9171-9178. (17) Pang, S. P.; Hu, H.; Zhang, J. L.; Lv, S. L.; Yu, Y. M.; Wei, F.; Qin, T. S.; Xu, H. X.; Liu, Z. H.; Cui, G. L. NH2CH=NH2PbI3: An Alternative Organolead Iodide Perovskite Sensitizer for Mesoscopic Solar Cells. Chem. Mater. 2014, 26, 1485-1491. (18)Lee, J. W.; Lee, S. H.; Ko, H. S.; Kwon, J.; Park, J. H.; Kang, S. M.; Ahn, N.; Choi, M.; Kim, J. K.; Park, N. G. Opto-electronic Properties of TiO2 Nanohelices with Embedded HC(NH2)2PbI3 Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 9179-9186. (19) Seol, D. J.; Lee, J. W.; Park, N. G. On the Role of Interfaces in Planar-Structured HC(NH2)2PbI3 Perovskite Solar Cells. Chemsuschem 2015, 8, 2414-2419. (20) Li, Z.; Yang, M. J.; Park, J. S.; Wei, S. H.; Berry, J. J.; Zhu, K. Stabilizing Perovskite Structures by Tuning Tolerance Factor: Formation of Formamidinium and Cesium Lead Iodide Solid-State Alloys. Chem. Mater. 2016, 28, 284-292. (21) Han, Q. F.; Bae, S. H.; Sun, P. Y.; Hsieh, Y. T.; Yang, Y.; Rim, Y. S.; Zhao, H. X.; Chen, Q.; Shi, W. Z.; Li, G.; et al. Single Crystal Formamidinium Lead Iodide FAPbI3: Insight into the Structural, Optical, and Electrical Properties. Adv. Mater. 2016, 28, 2253-2258. (22) Hu, M.; Liu, L. F.; Mei, A. Y.; Yang, Y.; Liu, T. F.; Han, H. W. Efficient Hole-Conductor-Free, Fully Printable Mesoscopic Perovskite Solar Cells with a Broad Light Harvester NH2CH=NH2Pbl3. J. Mater. Chem. A 2014, 2, 17115-17121. (23) Liu, J.; Shirai, Y.; Yang, X. X.; Yue, Y. F.; Chen, W.; Wu, Y. Z.; Islam, A.; Han, L. Y. High-Quality Mixed-Organic-Cation Perovskites from a Phase-Pure Non-stoichiometric Intermediate (FAI)1-x-PbI2 for Solar Cells. Adv. Mater. 2015, 27, 4918-4923. (24) Pellet, N.; Gao, P.; Gregori, G.; Yang, T. Y.; Nazeeruddin, M. K.; Maier, J.; Graetzel, M. Mixed-Organic-Cation Perovskite Photovoltaics for Enhanced Solar-Light Harvesting. Angew. Chem. Int. Ed. 2014, 53, 3151-3157. 18 ACS Paragon Plus Environment

Page 19 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Bai, S. H.; Cheng, N.; Yu, Z. H.; Liu, P.; Wang, C. L.; Zhao, X. Z. Cubic: Column Composite

Structure

(NH2CH=NH2)x(CH3NH3)1-xPbI3

for

Efficient

Hole-Transport

Material-Free and Insulation Layer Free Perovskite Solar Cells with High Stability. Electrochimi. Acta 2016, 190, 775-779. (26) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Hoerantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; et al. A Mixed-Cation Lead Mixed-Halide Perovskite Absorber for Tandem Solar Cells. Science. 2016, 351, 151-155. (27) Yi, C. Y.; Luo, J. S.; Meloni, S.; Boziki, A.; Ashari-Astani, N.; Graetzel, C.; Zakeeruddin, S. M.; Roethlisberger, U.; Graetzel, M. Entropic Stabilization of Mixed A-Cation ABX3 Metal Halide Perovskites for High Performance Perovskite Solar Cells. Energy Environ. Sci 2016, 9, 656-662. (28) Deng, Y. H.; Dong, Q. F.; Bi, C.; Yuan, Y. B.; Huang, J. S. Effi cient Mixed-Cation Perovskite Solar Cells with Cu Electrode by Scalable Fabrication of Active Layer. Adv. Energy Mater. 2016, 6, 1600372. (29) Binek, A.; Hanusch, F. C.; Docampo, P.; Bein, T. Stabilization of the Trigonal High-Temperature Phase of Formamidinium Lead Iodide. J. Phys. Chem. Lett. 2015, 6, 1249-1253. (30) Zhu, H. M.; Miyata, K.; Fu, Y. P.; Wang, J.; Joshi, P. P.; Niesner, D.; Williams, K. W.; Jin, S.; Zhu, X. Y. Screening in Crystalline Liquids Protects Energetic Carriers in Hybrid Perovskites. Science. 2016, 353, 1409-1413. (31) Wong, A. B.; Lai, M. L.; Eaton, S. W.; Yu, Y.; Lin, E.; Dou, L. T.; Fu, A.; Yang, P. D. Growth and Anion Exchange Conversion of CH3NH3PbX3 Nanorod Arrays for Light-Emitting Diodes. Nano. Lett. 2015, 15, 5519-5524. (32) Liang, D.; Peng, Y. L.; Fu, Y. P.; Shearer, M. J.; Zhang, J. J.; Zhai, J. Y.; Zhang, Y.; Hamers, R. J.; Andrew, T. L.; Jin, S. Color-Pure Violet-Light-Emitting Diodes Based on Layered Lead Halide Perovskite Nanoplates. ACS. Nano. 2016, 10, 6897. (33) Fu, Y.; Zhu, H.; Stoumpos, C. C.; Ding, Q.; Wang, J.; Kanatzidis, M. G.; Zhu, X.; Jin, S. 19 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Broad Wavelength Tunable Robust Lasing from Single-Crystal Nanowires of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). ACS. Nano. 2016, 10, 7963. (34) Piatkowski, P.; Cohen, B.; Ponseca, C. S., Jr.; Salado, M.; Kazim, S.; Ahmad, S.; Sundstrom, V.; Douhal, A. Unraveling Charge Carriers Generation, Diffusion, and Recombination in Formamidiniurn Lead Triiodide Perovskite Polycrystalline Thin Film. J. Phys. Chem. Lett. 2016, 7, 204-210. (35) D'Innocenzo, V.; Kandada, A. R. S.; De Bastiani, M.; Gandini, M.; Petrozza, A. Tuning the Light Emission Properties by Band Gap Engineering in Hybrid Lead Halide Perovskite. J. Am. Chem. Soc. 2014, 136, 17730-17733. (36) Saidaminov, M. I.; Abdelhady, A. L.; Maculan, G.; Bakr, O. M. Retrograde Solubility of Formamidinium and Methylammonium Lead Halide Perovskites Enabling Rapid Single Crystal Growth. Chem. Commun. 2015, 51, 17658-61. (37) Wehrenfennig, C.; Liu, M.; Snaith, H. J.; Johnston, M. B.; Herz, L. M. Charge-Carrier Dynamics in Vapour-Deposited Films of the Organolead Halide Perovskite CH3NH3PbI3-xClx. Energy Environ. Sci 2014, 7, 2269-2275. (38) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science. 2013, 342, 341-344. (39) Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; et al. Low Trap-State Density and Long Carrier Diffusion in Organolead Trihalide Perovskite Single Crystals. Science. 2015, 347, 519-522. (40) Yamada, Y.; Nakamura, T.; Endo, M.; Wakamiya, A.; Kanemitsu, Y. Photocarrier Recombination Dynamics in Perovskite CH3NH3PbI3 for Solar Cell Applications. J. Am. Chem. Soc. 2014, 136, 11610-11613. (41) Suarez, B.; Gonzalez-Pedro, V.; Ripolles, T. S.; Sanchez, R. S.; Otero, L.; Mora-Sero, I. Recombination Study of Combined Halides (Cl, Br, I) Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 1628-1635. 20 ACS Paragon Plus Environment

Page 20 of 22

Page 21 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(42) Fu, Y. P.; Meng, F.; Rowley, M. B.; Thompson, B. J.; Shearer, M. J.; Ma, D.; Hamers, R. J.; Wright, J. C.; Jin, S. Solution Growth of Single Crystal Methylammonium Lead Halide Perovskite Nanostructures for Optoelectronic and Photovoltaic Applications. J. Am. Chem. Soc. 2015, 137, 5810-5818. (43) Fu, Y. P.; Zhu, H. M.; Schrader, A. W.; Liang, D.; Ding, Q.; Joshi, P.; Hwang, L.; Zhu, X. Y.; Jin, S. Nanowire Lasers of Formamidinium Lead Halide Perovskites and Their Stabilized Alloys with Improved Stability. Nano. Lett. 2016, 16, 1000-1008. (44) Pan, J.; Utama, M. I. B.; Zhang, Q.; Liu, X. F.; Peng, B.; Wong, L. M.; Sum, T. C.; Wang, S. J.; Xiong, Q. H. Composition-Tunable Vertically Aligned CdSxSe1-x Nanowire Arrays via van der Waals Epitaxy: Investigation of Optical Properties and Photocatalytic Behavior. Adv. Mater. 2012, 24, 4151-4156. (45) Wehrenfennig, C.; Liu, M. Z.; Snaith, H. J.; Johnston, M. B.; Herz, L. M. Homogeneous Emission Line Broadening in the Organo Lead Halide Perovskite CH3NH3PbI3-xClx. J. Phys. Chem. Lett. 2014, 5, 1300-1306. (46)Saba, M.; Cadelano, M.; Marongiu, D.; Chen, F.; Sarritzu, V.; Sestu, N.; Figus, C.; Aresti, M.; Piras, R.; Lehmann, A. G.; et al. Correlated Electron-Hole Plasma in Organometal Perovskites. Nat. Commun. 2014, 5, 5049. (47) Johnston, M. B.; Herz, L. M. Hybrid Perovskites for Photovoltaics: Charge-Carrier Recombination, Diffusion, and Radiative Efficiencies. Acc. Chem. Res. 2016, 49, 146-154. (48) Stranks, S. D.; Burlakov, V. M.; Leijtens, T.; Ball, J. M.; Goriely, A.; Snaith, H. J. Recombination Kinetics in Organic-Inorganic Perovskites: Excitons, Free Charge, and Subgap States. Phys. Rev. Appl. 2014, 2, 034007. (49) Baumann, A.; Vath, S.; Rieder, P.; Heiber, M. C.; Tvingstedt, K.; Dyakonov, V. Identification of Trap States in Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 2350-2354. (50) Yamada, Y.; Yamada, T.; Phuong, L. Q.; Maruyama, N.; Nishimura, H.; Wakamiya, A.; Murata, Y.; Kanemitsu, Y. Dynamic Optical Properties of CH3NH3Pbl3 Single Crystals As Revealed by One- and Two-Photon Excited Photoluminescence Measurements. J. Am. Chem. 21 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 22

Soc. 2015, 137, 10456-10459. (51) Tian, W. M.; Zhao, C. Y.; Leng, J.; Gui, R. R.; Jin, S. G. Visualizing Carrier Diffusion in Individual Single-Crystal Organolead Halide Perovskite Nanowires and Nanoplates. J. Am. Chem. Soc. 2015, 137, 12458-12461. (52) Semonin, O. E.; Elbaz, G. A.; Straus, D. B.; Hull, T. D.; Paley, D. W.; van der Zande, A. M.; Hone, J. C.; Kymissis, I.; Kagan, C. R.; Roy, X.; et al. Limits of Carrier Diffusion in n-Type and p-Type CH3NH3PbI3 Perovskite Single Crystals. J. Phys. Chem. Lett. 2016, 7, 3510-3518. (53) Xiao, R.; Hou, Y.; Fu, Y.; Peng, X.; Wang, Q.; Gonzalez, E.; Jin, S.; Yu, D. Photocurrent Mapping in Single-Crystal Methylammonium Lead Iodide Perovskite Nanostructures. Nano Letters 2016, 16, ASAP. DOI: 10.1021/acs.nanolett.6b03782. (54) Zhumekenov, A. A.; Saidaminov, M. I.; Haque, M. A.; Alarousu, E. Formamidinium Lead Halide Perovskite Crystals with Unprecedented Long Carrier Dynamics and Diﬀusion Length. ACS Energy Lett. 2016, 1, 2189-2194. (55) Peng, W.; Miao, X. H.; Adinolfi, V.; Alarousu, E.; Tall, O. E.; Emwas, A.-H.; Zhao, C.; Walters, G.; Liu, J.; Olivier, O.; et al. Engineering of CH3NH3PbI3 Perovskite Crystals by Alloying Large Organic Cations for Enhanced Thermal Stability and Transport Properties. Angew. Chem. Int. Ed. 2016, 55, 10686-10690. (56) Motta, C.; El-Mellouhi, F.; Kais, S.; Tabet, N.; Alharbi, F.; Sanvito, S. Revealing the Role of Organic Cations in Hybrid Halide Perovskite CH3NH3PbI3. Nat. Commun. 2015, 6, 7026.


Carrier Decay Properties of Mixed Cation Formamidinium

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