ORGANOMETALLIC HALIDE PEROVSKITE SINGLE CRYSTALS HAVING LOW DEFFECT DENSITY AND METHODS OF PREPARATION THEREOF
Document Type and Number:
WIPO Patent Application WO/
Kind Code:
The present disclosure presents a method of making a single crystal organometallic halide perovskites, with the formula: AMX3, wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, and Eu, and X is a halide. The method comprises the use of two reservoirs containing different precursors and allowing the vapor diffusion from one reservoir to the other one. A solar cell comprising said crystal is also disclosed.
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JPJPH1172225JP3012088
Inventors:
BAKR, Osman, M. (4700 King Abdullah University Of, Science And TechnologyThuwal, , SA)
SHI, Dong (4700 King Abdullah University Of, Science And TechnologyThuwal, , SA)
Application Number:
Publication Date:
February 18, 2016
Filing Date:
August 12, 2015
Export Citation:
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KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY (4700 King Abdullah University of, Science And TechnologyThuwal, , SA)
International Classes:
C30B7/14; C30B29/12
Foreign References:
Other References:
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We claim at least the following:
1 . A method of making a single crystal, comprising:
providing a first reservoir including a first liquid, and a second reservoir including a second liquid, wherein the first reservoir and second reservoir are separated by a boundary so that the first liquid and the second liquid do not contact one another, wherein the first reservoir and the second reservoir ar
allowing for vapor diffusion of the second liquid into the first liquid to form a m and
precipitating out an organometallic halide perovskite single crystal in the first reservoir.
2. The method of claim 1 , wherein the organometallic halide perovskite single crystal has the following formula: AMX3, wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, and Eu, and X is a halide.
3. The method of claim 1 or 2, wherein the first liquid comprises: a first liquid solvent, a first precursor, and an organic cation precursor.
4. The method of claim 3, wherein the first liquid solvent is selected from the group consisting of: Ν,Ν-dimethylformamide (DMF), dimethylsulfoxide (DMSO), gamma-butylrolactone (GBR), and a combination thereof.
5. The method of claim 3 or 4, wherein the first precursor is a halide salt of M, wherein M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, and Eu.
6. The method of claim 6, wherein the first precursor is selected from PbBr2 or SnBr2.
7. The method of claim 3, 4, or 5, wherein the organic cation precursor is a halide salt of A, wherein A is an organic cation.
8. The method of claim 7, wherein the organic cation precursor is selected from the group consisting of: methylammonium bromide, methylammonium iodide, methylammonium chloride, formamidinium chloride, formamidinium bromide, ormamidinium iodide, and combination thereof.
9. The method of claim 1 or 2, wherein the second liquid comprises a second liquid solvent that has a lower boiling point than the first liquid solvent, and the first precursor and the organic cation precursor are not soluble in the second liquid solvent.
10. The method of claim 9, wherein the second liquid solvent is selected from the group consisting of: dichloromethane, chloroform, acetonitrile, toluene, and a combination thereof.
1 1 . The method of claim 1 , wherein the organometallic halide perovskite single crystal is selected from the group consisting of: methylammonium lead chloride (MAPbCI3), methylammonium lead iodide (MAPbl3), methylammonium lead bromide (MAPbBr3), formamidinium lead chloride (FAPbCI3), formamidinum lead bromide (FAPbBr3), formamidinum lead iodide (FAPbl3), methylammonium tin chloride (MASnCI3), methylammonium tin bromide (MASnBr3), methylammonium tin iodide (MASnl3), formamidinium tin chloride (FASnCI3), formamidinium tin bromide
(FASnBr3), and formamidinium tin iodide (FASnl3).
12. A composition, comprising:
a single crystal organometallic halide perovskite having a first dimension of about 1 mm to 8 mm and a thickness of about 0.2 to 2 mm, wherein the
organometallic halide perovskite single crystal has the following formula: AMX3, wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, and Eu, and X is a halide.
13. The composition of claim 12, wherein the single crystal organometallic halide perovskite has a trap-state density of about 1 x 1010 cm"3 to 2 x 1010 cm"3, wherein the single crystal organometallic halide perovskite has a long charge-carrier diffusion length of about 16 to 18 μιη.
14. The composition of claim 12 or 13, wherein the organometallic halide perovskite single crystal is selected from the group consisting of: methylammonium lead chloride (MAPbCI3), methylammonium lead iodide (MAPbl3), methylammonium lead bromide (MAPbBr3), formamidinium lead chloride (FAPbCI3), formamidinum lead bromide (FAPbBr3), formamidinum lead iodide (FAPbl3), methylammonium tin chloride (MASnCI3), methylammonium tin bromide (MASnBr3), methylammonium tin iodide (MASnl3), formamidinium tin chloride (FASnCI3), formamidinium tin bromide (FASnBr3), and formamidinium tin iodide (FASnl3).
15. A solar cell, comprising:
a single crystal organometallic halide perovskite having a first dimension of about 1 mm to 8 mm and a thickness of about 0.2 to 2 mm, wherein the
organometallic halide perovskite single crystal has the following formula: AMX3, wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, and Eu, and X is a halide, wherein the single crystal organometallic halide perovskite has a trap-state density of about 1 x 1010 cm"3 to 2 x 1010 cm"3, wherein the single crystal organometallic halide perovskite has a long charge-carrier diffusion length of about 16 to 18 μιη.
16. The solar cell of claim 15, wherein the organometallic halide perovskite single crystal is selected from the group consisting of: methylammonium lead chloride (MAPbCI3), methylammonium lead iodide (MAPbl3), methylammonium lead bromide (MAPbBr3), formamidinium lead chloride (FAPbCI3), formamidinum lead bromide (FAPbBr3), formamidinum lead iodide (FAPbl3), methylammonium tin chloride (MASnCI3), methylammonium tin bromide (MASnBr3), methylammonium tin iodide (MASnl3), formamidinium tin chloride (FASnCI3), formamidinium tin bromide (FASnBr3), and formamidinium tin iodide (FASnl3).
Description:
ORGANOMETALLIC HALIDE PEROVSKITE SINGLE CRYSTALS HAVING LOW DEFFECT DENSITY AND METHODS OF PREPARATION THEREOF
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of and priority to U.S. Provisional
Application Serial No. 62/037,270, having the title ORGANOMETALLIC HALIDE PEROVSKITE SINGLE CRYSTALS HAVING LOW DEFFECT DENSITY AND METHODS OF PREPARATION THEREOF," filed on August 14, 2014, the disclosure of which is incorporated herein by reference in its entirety.
BACKGROUND
Solution-processed hybrid organolead trihalide (MAPbX 3 ) perovskite solar cells (PSCs) have now achieved 20.1 % certified power conversion efficiencies (PCE), following a rapid surge of development since perovskite-based devices were reported in 2009. A key to the success of PSCs is the long diffusion length of charge carriers in the absorber perovskite layer. This parameter is expected to depend strongly on film crystallinity and morphology, so it is expected that there may be room to improve upon already remarkable PSC efficiencies via the optimization of three key parameters: charge carrier lifetime, mobility, and diffusion length.
Embodiments of the present disclosure provide for single crystal
organometallic halide perovskites, methods of making, methods of use, devices incorporating single crystal organometallic halide perovskites, and the like.
An embodiment of the present disclosure provides for a method of making a single crystal, among others, that includes: providing a first reservoir including a first liquid, and a second reservoir including a second liquid, wherein the first reservoir and second reservoir are separated by a boundary so that the first liquid and the second liquid do not contact one another, wherein the first reservoir and the second reservoir ar allowing for vapor diffusion of the second liquid into the first liquid to form a m and precipitating out an organometallic halide perovskite single crystal in the first reservoir. In an embodiment, the organometallic halide perovskite single crystal has the following formula: AMX 3 , wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, or Eu, and X is a halide. In particular, the organometallic halide perovskite single crystal can be: methylammonium lead chloride (MAPbCI 3 ), methylammonium lead iodide (MAPbl 3 ), methylammonium lead bromide (MAPbBr 3 ), formamidinium lead chloride (FAPbCI 3 ), formamidinum lead bromide (FAPbBr 3 ), formamidinum lead iodide (FAPbl 3 ), methylammonium tin chloride (MASnCI 3 ), methylammonium tin bromide (MASnBr 3 ), methylammonium tin iodide (MASnl 3 ), formamidinium tin chloride (FASnCI 3 ), formamidinium tin bromide (FASnBr 3 ), and formamidinium tin iodide (FASnl 3 ).
An embodiment of the present disclosure provides for a composition, among others, that includes: a single crystal organometallic halide perovskite having a first dimension of about 1 mm to 8 mm and a thickness of about 0.2 to 2 mm, wherein the organometallic halide perovskite single crystal has the following formula: AMX 3 , wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, or Eu, and X is a halide. In an embodiment, the single crystal organometallic halide perovskite has a trap-state density of about 1 x 10 10
to 2 x 10 10
cm "3 , wherein the single crystal organometallic halide perovskite has a long charge-carrier diffusion length of about 16 to 18 μιη.
An embodiment of the present disclosure provides for a solar cell, among others, that includes: a single crystal organometallic halide perovskite having a first dimension of about 1 mm to 8 mm and a thickness of about 0.2 to 2 mm, wherein the organometallic halide perovskite single crystal has the following formula: AMX 3 , wherein A is an organic cation, M is selected from the group consisting of: Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, or Eu, and X is a halide, wherein the single crystal organometallic halide perovskite has a trap-state density of about 1 x 10 10
to 2 x 10 10
cm "3 , wherein the single crystal organometallic halide perovskite has a long charge-carrier diffusion length of about 16 to 18 μιη.
Other compositions, systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate
corresponding parts throughout the several views.
Figures 1 .1 A-D illustrates a schematic diagram of the crystallization process. (Fig. 1 .1 B) Photographic images of the as-grown MAPbBr 3
single-crystals. (Fig. 1 .1 C) Refined single-crystal structure of the as-grown MAPbBr 3
crystals. (Fig. 1 .1 D) Experimental and calculated powder XRD profile of the as-grown MAPbBr 3
crystals, confirming 100% phase (cubic) purity. Zoom-in view of experimental (300) diffraction was inserted.
Figures 1 .2A-B illustrate normalized absorption and PL spectra: Fig. 1 .2A) illustrates MAPbBr 3
single-crystal in mother liquor, Fig. 1 .2B) illustrates crystalline MAPbBr 3
thin films. The PL was recorded at excitation wavelength of 480 nm for each case. Insets in Fig. 1 .2A) illustrate photographs of the as-grown single-crystals.
Figures 1 .3A-E illustrate carrier mobility and lifetime measurements. (Fig. 1 .3A) Time-of-flight traces showing the transient current I(t) following
photoexcitation at time t = 0 in a bi- the transit time z t
is identified by the corner in each trace and marked using the blue squares. Inset: transit time vs. inverse voltage V -1 . (Fig. 1 .3B) Mobility (red circles) and transit time (blue squares) vs. driving voltage, with different estimates of the mobility provided. (Fig. 1 .3C) Time- and wavelength-dependent photoluminescence (PL) color map I PL (t, X), with superimposed the time trace at λ = 580nm and the impulsive background signal at short times (full grey). (Fig. 1 .3D) Time-averaged PL as a function of wavelength for different time ranges. (Fig. 1 .3E) Background-subtracted PL time decay trace at λ = 580nm on a logarithmic scale, with bi-exponential fits showing a fast (τ~256 ns) and a slow dynamics (τ~833 ns).
Figure 1 .4 illustrates transient absorption spectra of the thin film (top panel) and single-crystal (middle panel) of MAPbX 3 . In the lower panel is the normalized time profile of transient absorption of the thin film (red dots) and single-crystal (black dots) of MAPbX 3
Measured at 440 nm excitation. The solid line is the calculated signal.
Figure 1 .5 illustrates the Current-Voltage trace and trap density. Characteristic current (/) vs. voltage (V) trace (purple markers) showing three different regimes: (i) Ohmic (0.1 -3 V), with linear voltage dependence (I~V, blue line); (ii) trap-filled limit (TFL, 3-7 V), with a steep power-like increase in current {I~V S - 9 , green line); (iii) space-charge-limited-current (SCLC, & 7 V), which is quadratic with the applied voltage {I~V 2
, gold line).
Figure 1 .6 illustrates a photograph of a batch of the as-grown MAPbBr 3
single- crystals obtained within one week using the method detailed in the text.
Figure 1 .7 illustrates a PES (left, showing valence band structures) and IPES (right, showing conduction band structures) spectra of MAPbBr3 single-crystal.
Figure 1 .8 illustrates a time- and wavelength-dependent photoluminescence (PL) color map I PL (t, X), with superimposed the time trace at λ = 560nm and the impulsive background signal at short times.
Figure 1 .9 illustrates photographs of the as-grown MAPbl 3
single-crystals at room temperature.
Figures 2.1A-B illustrate crystal growth and diffraction. (Fig. 2.1 A) Schematic diagram of the crystallization process. (Fig. 2.1 B) Experimental and calculated powder XRD profiles confirming the phase purity of the room-temperature grown MAPbX 3
crystals. Single crystal XRD data are given in SM.
Figures 2.2A-B illustrate steady state absorbance and photoluminescence. (Fig. 2.2A) MAPbBr 3
single crystal. (Fig. 2.2B) MAPbl 3
single crystal. Insets:
absorbance vs. photon energy and determination of band gap. PL excitation wavelength was 480 nm.
Figures 2.3A-F illustrate carrier mobility and lifetime measurements. (Fig. 2.3A) Time-of-flight traces showing the transient current I(t) following photoexcitation at time t=0 in
the transit time rt is identified by the corner in each trace and marked using the blue squares. (Fig. 2.3B) Linear fit of the transit time vs. inverse voltage V '
(Fig. 2.3C) Transient absorption in MAPbBr 3
crystals, evaluated at 590 nn, showing a fast component (τ~74±5 ns) together with a slower decay (τ~978±22 ns). (Fig. 2.3D) Time- and wavelength-dependent photoluminescence (PL) color map (t,), with superimposed the time trace at 1=580 nm (blue markers). (Fig. 2.3E) PL time decay trace on a MAPbBr 3
crystals at 1=580 nm, with bi-exponential fits showing a fast (τ~41 ±2 ns) and a slow dynamics
(τ~357±1 1 ns). (Fig. 2.3F) PL time decay trace on a MAPbl 3
crystals (1=820 nm, also showing a fast (τ~22±6 ns) and a slow (τ~ ns) component.
Figures 2.4A-B illustrate Current-Voltage traces and trap density.
Characteristic current (/) vs. voltage (V) trace (purple markers) showing three different regimes for (Fig. 2.4A) MAPbBr3 (at 300K) and (Fig. 2.4AB) MAPbl3 (at 225 K). A linear ohmic regime (I~V, blue line) is followed by the trap-filled regime, marked by a steep increase in current (I~V n&3 , green line). The MAPbBr3 trace shows a trap- free Child's regime (I~V 2 , green line) at high voltages.
Figures 2.5A-B illustrate photograph of a batch of the as-grown MAPbBr 3
(Fig. 2.5A) and MAPbl 3
(Fig. 2.5B) single crystals obtained within one week.
Figure 2.6 illustrates static absorbance and PL spectrum of MAPbl 3
thin films. Excitation wavelength of 480 nm was used to record the PL. The main peak occurring at 540 nm in thin films may stem from the low-dimensional structurally coherent units within the MAPbBr 3
film, whereas the noticeable peak at longer wavelength around 580 nm may be attributed to the intrinsic PL of the fully crystallized three-dimensional MAPbBr 3
lattice which is less tight in thin films than in single crystals. Other PL signals appearing around 620 nm and 650 nm may originate from sub gap trap states (43).
Figure 2.7 illustrates the extraction of the optical band gap of MAPbBr 3
single crystal. The optical bandgap is extracted by using the relation:
a = c {hf-E g ) V2
Where hf \s the photon energy, a is the optical absorption coefficient, E g
the energy bandgap and c a constant of the material. The exponent 1/2 in the right side of the equation applies for direct bandgap semiconductors. The measured bandgap, 2.21 eV, is in good agreement with the DFT computed value (2.2 eV) shown in Fig. 2.15.
Figure 2.8 illustrates the model comparison for the analysis of the PL decay time traces on a MAPbBr 3
single crystalline sample. Overlaid on top of the
experimental PL decay trace (grey markers, same as Fig. 2.3) are plotted the bi- exponential (blue) and tri-exponential (green) fit profiles. The values of the reduced chi-square χ
for the two models are also reported, demonstrating that a tri- exponential model does not perform better than a bi-exponential one.
Figure 2.9 illustrates time-resolved PL of MAPbBr 3
thin films, acquired at λ = 560 nm, showing the experimental time trace (grey markers) with bi-exponential fit (continuous lines) and corresponding time constants superimposed.
Figures 2.10A-C illustrate transient absorption spectra. Transient absorption spectra of the thin film (Fig. 2.1 OA) and single crystal (Fig. 2.1 OB) of MAPbBr 3 . (Fig. 2.10C) The normalized time profile of transient absorption of the thin film (red dots) and single crystal (black dots) of MAPbBr 3
Measured at 480 nm excitation. The solid line is the calculated signal. As can be clearly seen in Fig. 2.10, under the same experimental conditions, the decay of the excited state due to the electron hole recombination of single crystals is much longer than the thin film (Fig. 2.10C). The observed decay can be attributed to trap-assisted recombination of charge carriers, indicating that substantially fewer defect trap-states are present in the single crystal relative to the thin film. This finding is consistent with the long carrier lifetimes extracted from photoluminescence experiments on single crystals.
Fig. 2.1 1A illustrates time of flight measurements of MAPbBr 3 , while Fig. 2.1 1 B illustrates the lower mobility, which are shown for completeness. A small variability between the samples is seen.
Figure 2.12 illustrates the space charge limited current analysis for a MAPbl 3
single crystal of dimensions: 1 .63 mm x 2.74 mm x 2.74 mm.
Figure 2.13 illustrates the defect formation energies in case of Br-rich growth conditions. No vacancies are displayed due to their shallow nature.
Figure 2.14 illustrates the defect formation energies in case of Br-poor growth conditions. No vacancies are displayed due to their shallow nature.
Figure 2.15 illustrates the MAPbBr 3
Density of States (DOS).
Figure 2.16 illustrates the Hall effect results.
DETAILED DESCRIPTION
Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit (unless the context clearly dictates otherwise), between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described.
As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.
Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of chemistry, material science, synthetic organic chemistry, and the like, which are within the skill of the art. Such techniques are explained fully in the literature.
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the compositions and compounds disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C, and pressure is in bar. Standard temperature and pressure are defined as 0 °C and 1 bar. Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing
processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible.
It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a support" includes a plurality of supports. In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings unless a contrary intention is apparent.
General Discussion
Embodiments of the present disclosure provide for single crystal
organometallic halide perovskites, methods of making, methods of use, devices incorporating single crystal organometallic halide perovskites, and the like.
Embodiments of the present disclosure provide for methods of making single crystal organometallic halide perovskites that is simple and requires little or no energy input. In addition, other methods can not be used to form single crystal organometallic halide perovskites having dimensions at the micron-scale level.
Furthermore, single crystal organometallic halide perovskites formed using embodiments of the present disclosure can have superior characteristics as compared to state-of-the-art crystalline thin films prepared by other methods and these characteristic can include charge carrier mobility, lifetime, trap-state density, and/or diffusion length. In this regard, embodiments of the single crystal organometallic halide perovskite can be used in photovoltaic devices such as perovskite-type photovoltaic devices, where superior properties of the single crystal organometallic halide perovskite can be used to achieve enhanced photocurrent generation, collection, and overall power conversion efficiency.
Embodiments of the present disclosure provide for single crystal
organometallic halide perovskites. In an embodiment, the organometallic halide perovskite single crystal can have the following formula: AMX 3 . In an embodiment, A can be an organic cation such as alkyl-ammonium (e.g., methylammonium (MA)), formamidinum (FA), 5-ammoniumvaleric acid. In an embodiment, M can be a cation or divalent cation of an element such as Pb, Sn, Cu, Ni, Co, Fe, Mn, Pd, Cd, Ge, or Eu. In an embodiment, X can be a halide such as CI, Br, F, I, and At. The selection of the components of AMX 3
is made so that the organometallic halide perovskite has a neutral charge. In an embodiment, alkyl can refer to hydrocarbon moieties having one to six carbon atoms, linear or branched, substituted or substituted (e.g., a halogen).
In an embodiment, AMX 3
can be: methylammonium lead chloride (MAPbCI 3 ), methylammonium lead iodide (MAPbl 3 ), methylammonium lead bromide (MAPbBr 3 ), formamidinium lead chloride (FAPbCI 3 ), formamidinum lead bromide (FAPbBr 3 ), formamidinum lead iodide (FAPbl 3 ), methylammonium tin chloride (MASnCI 3 ), methylammonium tin bromide (MASnBr 3 ), methylammonium tin iodide (MASnl 3 ), formamidinium tin chloride (FASnCI 3 ), formamidinium tin bromide (FASnBr 3 ), or formamidinium tin iodide (FASnl 3 ).
Single crystal organometallic halide perovskites having a dimension greater than the micron range have not been previously formed due to limitations in the known processes from making them. In an embodiment, the single crystal organometallic halide perovskite can have dimensions greater than 500 microns (e.g., about 500 microns to 10,000 microns or about 500 microns to 5000 microns) or greater than 1000 microns (e.g., about 1000 microns to 10,000 microns or about 1000 microns to 5000 microns). In an embodiment, the single crystal
organometallic halide perovskite can have one or more dimensions of about 0.1 mm to 10 mm or more. In an embodiment, the single crystal organometallic halide perovskite can have the following dimensions: one or more dimensions (e.g., length, width, diameter) of about 1 mm to 10 mm and a thickness of about 0.05 to 3 mm. In an embodiment, the single crystal organometallic halide perovskite can have a crustal volume of 100 mm 3
or more. In an embodiment, the single crystal organometallic halide perovskite can have the following dimensions: a length of about 1 mm to 10 mm or about 2 mm to 8 mm, a width of about 1 mm to 10 mm or about 2 mm to 8 mm and a thickness of about 0.2 to 2 mm. Embodiments of the single crystal organometallic halide perovskite can have one or more of the following characteristics: larger charge carrier mobility than state-of-the-art crystalline thin films prepared by other methods, larger lifetime than state-of-the-art crystalline thin films prepared by other methods, larger trap-state density than state-of-the-art crystalline thin films prepared by other methods, or longer diffusion length than state-of-the-art crystalline thin films prepared by other methods.
In an embodiment, the charge carrier mobility can be an order of magnitude larger than state-of-the-art crystalline thin films. In an embodiment, the charge carrier mobility can be about 70 to 150 cm 2 /Vs for MAPbBr 3 . In an embodiment, the expected charge carrier mobility may be about 40 to 100 cm 2 /Vs for MAPbCI 3 . In an embodiment, the expected charge carrier mobility may be about 100 to 220 cm 2 /Vs for MAPbl 3 .
In an embodiment, the lifetime can be an order of magnitude larger than state-of-the-art crystalline thin films. In an embodiment, the lifetime can be about 150 to 750 ns for MAPbBr 3 . In an embodiment, the expected lifetime may be about 100 to 450 ns for MAPbCl 3 . In an embodiment, the expected lifetime may be about 300 to 1000 ns for MAPbl 3 .
In an embodiment, the trap-state density can be an order of magnitude larger than state-of-the-art crystalline thin films. In an embodiment, the trap-state density can be about 1 x 10 10
to 3 x 10 10
for MAPbBr 3 . In an
embodiment, the expected trap-state density may be about 1 x 10 13
to 3 x 10 13
for MAPbCI 3 . In an embodiment, the expected trap-state density may be about 1 x 10 13
to 3 x 10 10
for MAPbl 3 .
In an embodiment, the charge-carrier diffusion length can be an order of magnitude larger than state-of-the-art crystalline thin films. In an embodiment, the charge-carrier diffusion length can be about 7 to 17 μιη for MAPbBr 3 . In an embodiment, the expected charge-carrier diffusion length may be about 1 to 10 μιη for MAPbCI 3 . In an embodiment, the expected charge-carrier diffusion length may be about 10 to 30 μιη for MAPbl 3 .
An embodiment of the present disclosure includes a method of making a single crystal, in particular organometallic halide perovskite single crystals as described herein. The method is simple, the component set up is not complex and does not require specialized equipment, the time of reaction is relatively time- efficient, and the reaction requires no-energy input.
An embodiment of the present disclosure includes a first reservoir and a second reservoir, each including a liquid (e.g., a first liquid and second liquid, respectively). In an embodiment, the first liquid can include a first liquid solvent, a first precursor, and an organic cation precursor. In an embodiment, the first liquid solvent can be Ν,Ν-dimethylformamide (DMF), dimethylsulfoxide (DMSO), gamma- butylrolactone (GBR), or a combination thereof.
In an embodiment, the first precursor can be a compound that supplies M for the organometallic halide perovskite single crystal (AMX 3 ), where M is defined herein. In an embodiment, the first precursor can be a halide salt of M, for example PbBr 2
or SnBr 2 . In an embodiment, the concentration of the first precursor in the first liquid can be about 1 to 20 weight %.
In an embodiment, the organic cation precursor can be a compound that supplies A for the organometallic halide perovskite single crystal (AMX 3 ), where A is defined herein. In an embodiment, the organic cation precursor can be a halide salt of A. In an embodiment, the organic cation precursor can be methylammonium bromide, methylammonium iodide, methylammonium chloride, formamidinium chloride, formamidinium bromide, or formamidinium iodide. In an embodiment, the concentration of the organic cation precursor in the first liquid can be about 1 to 30 weight %.
In an embodiment, the second liquid can be a second liquid solvent that has a boiling point that is less (e.g., about 70° C or more) than that of the first liquid solvent and is not a solvent for the first precursor or organic cation precursor. In an embodiment, the second liquid solvent can be: dichloromethane, chloroform, acetonitrile, toluene, or a combination thereof.
In an embodiment, the first reservoir and second reservoir are separated by a boundary so that the first liquid and the second liquid do not contact one another. In an embodiment, the first reservoir is positioned in the center of second reservoir with a boundary wall separating the first liquid and the second liquid. Other configurations can be used that include a plurality of first reservoirs and a plurality of second reservoirs as long as the first liquid and the second liquid are separated. In an embodiment, the first reservoir and the second reservoir can be a single structure or can be separate structures. In an embodiment, the first reservoir and the second reservoir can be made of materials that do not impede the formation of the organometallic halide perovskite single crystals, for example, metal, plastic, glass, and the like. In an embodiment, the first reservoir and the second reservoir can have dimensions on the millimeter scale to the centimeter scale or larger as needed. The shape of the first reservoir and the second reservoir can be constructed to control the rate formation of organometallic halide perovskite single crystals, dimensions of the organometallic halide perovskite single crystals, and the like.
The first reservoir and second reservoir are enclosed by a structure(s) to form a closed system. In an embodiment, the structure can be designed to reduce or eliminate exposure of the first liquid and the second liquid to light. In an embodiment, the structure can be used to reduce or prevent exposure of the first liquid and the second liquid to contaminants. In an embodiment the structure can be configured to control the temperature and/or pressure to which the first and second liquids are subjected. In general, the temperature is room temperature and the pressure is 1 atm, however, the structure can include equipment (e.g. pumps, pressure gauges, heating devices, cooling device, and the like) to adjust the temperature and/or pressure to control the rate of formation of the organometallic halide perovskite single crystals, the size of the organometallic halide perovskite single crystals, and the like. In an embodiment, the structure can be made of materials that do not impede the formation of the organometallic halide perovskite single crystals for example, metal, plastic, glass, and the like.
Now referring to the method, initially the first liquid and the second liquid are disposed in the first reservoir and second reservoir, respectively. In an
embodiment, the second liquid solvent vaporizes more readily than the first liquid solvent, so that the second liquid solvent diffuses into the first liquid over time (e.g., hours to days) to form a modified first liquid. Typically, the vaporization is allowed to occur at room temperature and pressure. In other embodiments, the
temperature and/or pressure can be adjusted to control the rate of formation of the organometallic halide perovskite single crystals. Since the first precursor and the organic cation precursor are not soluble or only slightly soluble in the second liquid solvent, the first precursor and the organic cation precursor precipitate (e.g., stoichiometrically precipitate) from the modified first liquid as the second liquid solvent diffuses into the first liquid. In an
embodiment, the diffusion rate can be controlled by selection of the first liquid solvent, the second liquid solvent, the temperature, and pressure. In a particular embodiment, the diffusion rate can be controlled by selection of the first liquid solvent and the second liquid solvent. After a time frame, the organometallic halide perovskite single crystals are formed. In an embodiment, the time frame can be about a few hours to about fourteen days or about a day to a about seven days.
In an embodiment, the single crystal organometallic halide perovskite can be used in a solar cell. Use of single crystal organometallic halide perovskites of the present disclosure in a solar cell can lead to enhanced photocurrent generation and/or collection or the overall power conversion efficiency upon use in
photovoltaic devices.
Now having described the embodiments of the disclosure, in general, the examples describe some additional embodiments. While embodiments of the present disclosure are described in connection with the example and the
corresponding text and figures, there is no intent to limit embodiments of the disclosure to these descriptions. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure.
Example 1 :
Brief Introduction:
Despite the staggering advances in the efficiency of solar cells based on methylammonium lead trihalide (MAPbXs) perovskites within the past two years, the perovskites' fundamental properties and ultimate performance limits remain obscured by the extensive disorder in crystalline MAPbX 3
films. Researchers have thus far relied on such films for their studies because of the difficulty in growing appropriately sized MAPbX3 single-crystals. Here we show a simple room- temperature vapor diffusion-assisted route to obtain sizable crack-free MAPbX 3
single-crystal wafers (up to 8 * 8 * 2 mm). Only by reaching such scales did it become practical to measure their optical and transport characteristics, which we demonstrate by revealing the exceptionally low (ultra-high-quality crystalline siliconlike) trap-state densities (ca. 1.4 x 10 w cm ~3
) and long charge-carrier diffusion- lengths (-16.8 μπι) of MAPbBr 3
crystals. The room-temperature growth of these well- ordered high-performing semiconductors, suitable for device studies, is a
groundbreaking advancement towards realizing the ultimate efficiency of perovskite photovoltaics.
Introduction:
Recent advancements in hybrid organo-lead trihalide perovskite solar cells (PSCs) have made the union between 'low-cost' and 'high-efficiency' suddenly seem within reach. Since the first report of low-cost solution-processed photovoltaics (PVs) incorporating hybrid organo-lead halide perovskites in 2009,
the technology has seen a meteoric rise in its power conversion efficiency (PCE). 2, 3| 4| 5| 6| 7| 8| 9
To-date certified PCEs of 17.9% have been reached, 10
with a strong expectation that further substantial improvements will be reached before the end of 2014. 10, 11 , 12, 13
In contrast, traditional crystalline Si and thin film chalchogenide (e.g., CIGS, CdTe) PVs, the dominant technologies of today, took decades to achieve this benchmark, and yet remain at a substantial cost disadvantage vis-a-vis traditional energy sources due to their expensive fabrication methodologies - such as high-vacuum vapor-assisted deposition methods.
Hybrid organo-lead trihalide perovskites have the crystal structural formula APbX 3 , where the A-site is occupied by an organic cation (e.g. methylammonium, MA; or formamidinium, FA) and the X-site is occupied by a halide (typically I, Br, and CI). 14
Key to the success of PSCs is the long charge-carrier diffusion length in the absorber perovskite layer, which is a result of the material's high crystalllinity, despite its low-temperature solution-processability. 15, 16, 17, 18
This property has enabled hybrid PSCs to go through several structural evolutions 2, 3, 4, 5, 19, 20, 21
resulting in a thick perovksite absorber layer sandwiched between planar n-type and p-type layers, without sacrificing charge collection efficiency in the device. Numerous investigations have focused on the perovskite layer's nanocrystallinity as the crucial factor toward the overall performance and a major avenue for the further improvement of PSCs. 22, 23, 24
Recently, it was found that improving the crystallinity and homogeneity of perovskite thin films resulted in a dramatic enhancement in the carrier mobility and diffusion length (beyond 1 μιη
Yet, according to a recent study as well, only ~ 30% of complete crystallinity was realized inside solution-processed perovskite layers, while the remainder material was comprised of a coherent structure of short-range order. 25
Consequently, the dominating level of disorder in perovksite films prepared using currently available methods makes it difficult to experimentally study and theoretically model the materials system in order to gain key insights into its remarkable efficiency.
Promisingly, it also suggests that drastic improvement in the crystallinity and reduction of disorder and defect states in the material will enable PSCs to easily surpass all current or expected PCE benchmarks (~ 20%) that are set by the existing state of the perovskite layer. 25
Here we show a straightforward room-temperature solution-based vapor- assisted diffusion crystallization method - inspired by vapor diffusion approaches commonly used by crystallographers to grow high-quality but micron-sized
macromolecular single-crystals - 26
to grow appreciable quantities of
methylammonium lead bromide (MAPbBr 3 ) semi-transparent square-shaped single- crystal wafers approaching centimeter dimensions. Because these wafers were of high-quality and large enough size for practical experimental measurements as well as device applications, we were able to uncover their remarkable properties:
extraordinarily low electronic defect trap- a sharp
narrow photoluminescence (PL) peak o and extremely high charge-carrier mobility, lifetime, and diffusion lengths in comparison to the state- of-the-art solution processed crystalline perovskite films. Our findings reveal that single-crystal hybrid perovskites are high-performance optoelectronic grade semiconductors on par with ultra-high-quality crystalline Si (c-Si), which - combined with the simplicity of our growth scheme - provides impetus for PV researchers to pursue device architectures based on completely crystalline perovskites and heralds further breakthroughs for the PSC technology. Results and Discussions:
With the motivation to obtain sizeable, yet high quality, MAPbX 3
single- crystals for practical charge carrier mobility and lifetime characterizations, and steady-state optical and electronic measurements, we devised a vapor diffusion technique, which is here used for the first time in organo-lead halides. The apparatus used for the crystallization is comprised of two simple vials (or crystallizing dishes) as schematically described in Fig. 1 .1 A. The inner vial (or crystallizing dish) contains a solution of the two precursors MABr and PbBr 2
fully dissolved in a solvent with relatively high boiling point such as Ν,Ν-dimethylformamide (DMF), while the outer vial (or crystallizing dish) contains a more volatile solvent such as dichloromethane (DCM) which is a non-solvent for the two precursors. Vapor from the outer volatile non-solvent slowly diffuses into the inner solvent at room temperature, gradually decreasing the overall solubility of the two precursors and forcing the product out of the solution in the form of MAPbBr 3
crystals. Through the careful selection of solvents and control of the diffusion rate - so that both precursors are precipitated from solution stoichiometrically - large and high quality MAPbBr 3
single-crystals were grown in the mixed mother liquid within the inner vial. The crystallization was performed in a closed system and kept in the dark. Within one-week of initiating the crystallization with this method, dozens of high quality cubic MAPbBr3 single-crystals in the shape of square wafers (between ~ 1 mm χ 1 mm χ 0.2 mm and ~ 8 mm χ 8 mm x 2 mm as shown in Fig. 1 .6) formed in the inner crystallizing dish (O.D. χ H ~ 125 mm χ 65 mm). This unattended crystallization scheme is simple, relatively time- efficient, and requires no energy input and no specialized equipment.
Figure 1 .1 B is a representative image of some of the large MAPbBr3 single- crystals we routinely obtained. The overall square shape of the as-grown large single-crystals is in excellent agreement with the room-temperature cubic crystal system of MAPbBr 3
perovskite as was confirmed decades ago. The excellent state of the as-grown MAPbBr 3
single-crystals, facilitated the collection of high quality single- crystal X-ray diffraction (XRD) data, acquired using a Cu-Και excitation (E =
8047.8 eV), and the accurate refinement (R=0.0349) of the crystal structure (Fig. 1 .1 C). The phase purity of the as-grown MAPbBr 3
crystals was further confirmed from the powder XRD spectra acquired from material ground from a large batch of single-crystals (~ 50 pieces of crystals ranging from hundreds of micrometers to several millimeters). The experimental powder XRD is in perfect agreement with the calculated XRD pattern of the cubic MAPbBr 3
crystal phase as shown in Fig. 1 .1 D, confirming 100% phase purity of the as-grown crystals. A slight peak splitting was noticed in the experimental XRD spectrum (see inserted zoom-in view of the (300) diffraction mode in Fig. 1 .1 D). This is caused by incomplete removal of the closely- lying Cu Kan radiation (E = 8027.8 eV). Any remnant discrepancies in the relative peak intensities between the experimental and calculated powder XRD profiles stem from the specific surface orientation of the as-measured powders when exposed to the X-ray beam.
After ascertaining the quality and phase of the as-grown MAPbBr 3
single- crystals we proceeded to investigate their optical and charge transport properties. Figures 1 .2A-B display a typical normalized absorption and PL spectra of a single- crystal in its mother liquor (Fig. 1 .2Aa) and a crystalline thin film prepared by a solution-processed two-step deposition approach (Fig. 1 .2B). 4
A MAPbBr 3
single- crystal, stocked in its mother liquor, displays astonishing transparency in spite of its millimeter-scale thickness (inset images in Fig. 1 .2A), which is thousands of times thicker than crystalline MAPbX 3
thin films (200 ~ 400 nm) normally used for high efficiency planar heterojunction PSCs. The high transparency of the crystal enabled us to record its UV-Vis absorption spectrum in transmission mode, while the colorless mother liquor did not absorb in the wavelength region defined in Figs. 1 .2A- B, and thus was used as a reference for the absorption measurements. Storing the single-crystals in the mother liquor also protects the surface from reconstructions caused by prolonged dewetting or exposure to air. The surface structural
reconstruction upon dewetting results in the crystal wafers losing their optical sheen, as well as discrepancies in measured transport properties between surface- dominated techniques, such as Hall Effect, and bulk-dominated methods, such as time of flight measurements (vide infra).
The absorption of the MAPbBr 3
single-crystals exhibits an onset around 575 nm (Fig. 1 .2A) - a red-shift of ~ 25 nm compared to that of crystalline thin films (Fig. 1 .2B) that were produced in this work and reported in the literature. 27, 28
The single- crystal's steep absorption band edge - resembling a step-function above the band gap - is indicative of a clear band structure with low density of in-gap defect and trap states. The rather flat absorption band in the visible region that is energetically above the bandgap for the single-crystal is also a consequence of the clear band structure and the high symmetry of the room-temperature cubic crystal phase. In contrast, the absorption of the nanocrystalline thin films (Fig. 1 .2B) presented a differing trend: a noticeably decreasing absorption to lower energy, reaching a valley at 500 nm followed by a strong absorption peak right before the band gap edge. The edge being less steep than its counterpart in the single-crystal spectra (inset in Fig. 1 .2B), as well as the strong peak close to the edge are indicative of the high defect and trap states densities in the thin films as a result of decreased crystallinity. These observations are consistent with a recent study which revealed that close to 70% of the solution-processed MAPbX 3
perovskite thin film material is comprised of a short- range-ordered structural bonding motif rather than a well-ordered crystal state. The diminished crystallinity may also contribute to a decreased dimensionality of the perovskite structure, which can cause a widening of the bandgap and a consequent blue-shift to the absorption edge. As MAPbX 3
is a direct bandgap material, the bandgap may be calculated from the absorption spectra by extrapolating the linear region of the absorption edge to the wavelength-axis intercept, as is
diagrammatically shown in the insets of Fig. 1 .2A and 1 .2B. A band gap of 2.3 eV was determined for the crystalline thin films - in agreement with previous reports, 27, 29
while 2.2 eV was found for the single-crystals. The observation of a narrower band gap in single-crystals provides more incentive for seeking additional improvements in the crystallinity of the perovskite layer in PSCs, as it further sensitizes the absorption spectrum of the cells to harvest a broader range of photons and hence enhance photocurrent generation.
The bandgap of the as-grown MAPbBr 3
single-crystals was also studied by photoelectron spectroscopy (PES) and inverse photoelectron spectroscopy (IPES) methods. The complete electronic structures of MAPbBr3 single-crystals obtained by a combination of PES and IPES are shown in Fig. 1 .7. The electronic structure is comprised of four spectral features located at -2.3, -2.8, -3.9, and -5.7 eV with the valence band maximum at -3.93eV. The valence band edge appears significantly sharper than that of the respective thin films, 29
whereas the conduction band consists of three spectral features observed at 2.6, 4, and 5.1 eV, and is somewhat look similar to that of the thin films. The electronic bandgap of the crystal is estimated to be 2.37 eV, with the valence band maximum (VBM) positioned at - 1 .82eV and conduction band minimum (CBM) at 0.55eV above the Fermi level, and in a good agreement with the optically estimated bandgap (Fig. 1 .2A-B). A slightly larger bandgap value via photoemission spectroscopies is to be expected. Optical absorption measurements may result in a slightly underestimate of the actual ground state bandgap because optical excitations leave a hole in the valence band, which through Couiombic interaction, may decrease the observed gap.
In addition to absorption, the emission behavior of MAPbBr 3
single-crystals is also markedly different than thin films (Fig.1 .2A-B). The crystal's PL spectrum shows a single narrow peak at 570 nm with a stokes-shift of only 20 nm from the first absorption peak. The relatively small shift is likely a consequence of the highly restricted vibrational relaxation within the [PbBr 6 ] 4"
octahedra which are connected via a corner-sharing network in the three-dimensional cubic lattice. 14
In contrast, the PL of the MAPbBr 3
thin films reveals multiple features that have qualitatively different origins than the ones observed in the emission spectra of single-crystals. The main peak occurring at 540 nm in thin films, with an apparently narrow stokes-shift of 18 nm, likely originates from the low-dimensional structurally coherent units within the MAPbBr 3
film, whereas the noticeable peak at longer wavelength around 580 nm is probably resultant from the intrinsic photoluminescence of the three-dimensional crystalline component of the MAPbBr3 lattice. The increased defect and trap state densities in the nanocrystalline thin films, relative to single-crystals, provide more degrees of freedom for vibronic relaxation resulting in a larger stokes shift of 58 nm (Fig. 1 .2B). The weak PL signals below the bandgap, appearing around 620 nm 645 nm, are probably originating from transitions directly involving defect trap-states within the thin films.
Spurred by the steady-state optical characteristics of the MAPbBr 3
single- crystals, we investigated various key quantities that }