Precise Composition Tailoring of Mixed-Cation Hybrid Perovskites for

Subscriber access provided by PEPPERDINE UNIV

Article

Precise Composition Tailoring of Mixed-Cation Hybrid Perovskites for Efficient Solar Cells by Mixture Design Methods Liang Li, Na Liu, Ziqi Xu, Qi Chen, Xindong Wang, and Huanping Zhou ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.7b02867 • Publication Date (Web): 23 Aug 2017 Downloaded from http://pubs.acs.org on August 23, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Nano is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31

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

ACS Nano

Precise Composition Tailoring of Mixed-Cation Hybrid Perovskites for Efficient Solar Cells by Mixture Design Methods Liang Lia,b+, Na Liuc+, Ziqi Xua, Qi Chenc*, Xindong Wangb*, and Huanping Zhoua* a.

Department of Materials Science and Engineering& Department of Energy and

Resources Engineering, College of Engineering, Peking University, Beijing 100871, P.R.China. E-mail: [email protected] b.

Department of Physical Chemistry, University of Science and Technology Beijing,

Beijing 100083, P.R.China. E-mail: [email protected]. c.

School of Materials Science and Engineering, 5 Zhongguancun South Street, Beijing

Institute of Technology, Beijing 100081, P.R.China. E-mail: [email protected].

ABSTRACT

Mixed anion/cation perovskites absorber has been recently implemented to construct highly efficient single junction solar cells and tandem devices. However, considerable efforts are still required to map the composition-property relationship of the mixed perovskites absorber, which

ACS Paragon Plus Environment

1

ACS Nano

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 2 of 31

is essential to facilitate device design. Here we report the intensive exploration of mixed-cation perovskites in their compositional space with the assistance of a rational mixture design (MD) methods. Different from the previous linear search of the cation ratios, it is found that by employing the MD methods, the ternary composition can be tuned simultaneously follow simplex lattice designs or simplex-centroid designs, which enable significantly reduced experiment/sampling size to unveil the composition-property relationship for mixed perovskite materials, and to boost the resultant device efficiency. We illustrated the composition-property relationship of the mixed perovskites in multi-dimension, and achieved an optimized power conversion efficiency of 20.99% in the corresponding device. Moreover, the method is demonstrated to be feasible to help adjust the bandgap through rational materials design, which can be further extended to other materials systems, not limited in polycrystalline perovskites films for photovoltaic applications only.

KEYWORDS: mixture design, mixed cation, composition, perovskite solar cells, bandgap, structure

Organic/inorganic hybrid perovskites have been well recognized in both academia and industry thanks to their superior optoelectronic properties including long carrier lifetime, 1 high absorption coefficient,2 and exceptional defect tolerance.3 To date, this family of semiconductors have been intensively exploited in the fields of solar cells,4-8 light-emitting diodes,7 lasers,10 and field-effect transistors (FET).11 In particular, perovskite solar cells have achieved power conversion efficiencies (PCE) of 22.1%.12 Due to their extremely low cost and scalable processability, hybrid perovskites are regarded as one of the most promising photovoltaic (PV) materials that are potential to compete or integrate with c-silicon PVs. Moreover, the encouraging progress in


2

Page 3 of 31

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

ACS Nano

device fabrication has been accompanied by a persisting pursuit of fundamental understandings in materials composition, crystal structure, and defect associated optoelectronic properties. Hybrid perovskites share the chemical formula of ABX3, where often, A is a monovalent cation, B is a divalent metal ion, and X is a halide. Each ion serves as an independent constituent to occupy the corresponding site, obeying the tolerance factor rule.13 Therefore, possible combinations of elements and molecules are ready to create a diverse family of perovskites with distinct and tailorable properties. In the early stage, efforts were witnessed to exploit X site occupants, where “Br” were found to be effectively adjust the bandgap from 1.48 eV to 2.23 eV.14 Meanwhile, the myth of “Cl” has received quite hot discussions.1,15,16 Particularly, CH3NH3PbI3(Cl)15 (commonly denoted as CH3NH3PbI3-xClx) has been reported to exhibit a substantially longer carrier diffusion length of over 1 µm than that of its counterpart CH3NH3PbI3 (~100 nm).1 Device performance has consequently been elevated dramatically, mostly due to the improvement in the resultant absorber quality and the relevant interface.15 On the other hand, B site occupants have been systematically explored with the major purpose to find lead free perovskites. When replacing lead (Pb) by tin (Sn) in the perovskite, the optical absorption edge can be successfully red-shifted to over 1000 nm.17,18 While the stability is reported to be higher in the mixed Pb/Sn perovskites with comparison to the pure tin based materials.19 Meanwhile, the evolution of hybrid perovskites has occurred in A site, and received continuous attention among the community to improve PCE and stability in the resulted devices. Formamidinium (FA) has been firstly documented as a possible constituent to compose hybrid perovskites for PV cells.20,21 It was reported to modify Pb-I bonding length and/or corresponding bond angles that extends absorption edge of the resultant materials to 850 nm,14 corresponding to


3

ACS Nano

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 4 of 31

the bandgap of 1.45 eV. However, pure FAPbI3 is prone to transform into a yellow polymorph, which is not suitable for PV applications.22 Subsequently, the mixed-cation perovskites were reported, where α phase of FAPbI3 can be achieved/stabilized at room temperature by partial replacement of FA with (MA).23-25 One of the most successful recipe includes (FAPbI3)0.85(MAPbBr3)0.15, which has contributed to the device with certified PCE exceeding 20%.22,26 Compared to FA, pure cesium (Cs) based perovskites solar cells showed limited PCE, because the desired α phase of CsPbX3 endures phase transition even at room temperature.5 Encouraging results have been reported recently while the fabrication challenges remain.27-29 Interestingly, when cesium is partially incorporated to either FA or MA based perovskites, it endows astonishing phase stability and moisture resistance in the resultant mixed-cation perovskites.13,30 In particular, partial substitution of cesium successfully eliminates the halide segregation, and creates hybrid perovskites with a wider bandgap for tandem devices.31 Besides, other A site occupant candidates like ethylammonium (EA), Guanidinium (GA) and Rubidium have also been exploited.32-34 Indeed, material properties can be manipulated in a broad range through variable constituent combinations in the hybrid perovskites (ABX3), which enables a great compositional space for future development. However, it leads to further complexity in experimental design if taking account of various processing protocols. For instance, it is reported that a set of total 49 samples have been investigated to illustrate the effects of different substitution in certain range.35 The large sampling cost and time is not always affordable in most labs that hinders the research momentum. In addition, most relevant study in mixed perovskites is mainly based on independently tuning one site composition rather than the whole ternary composition plane. To our understanding, there is no study to exploit the composition-property relationship among the


4

Page 5 of 31

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

ACS Nano

abundant mixed cation perovskite materials (Cs,MA,FA)PbX3 to reveal the synergistic effects from multiple components (e.g. surface recombination, crystal lattice, bandgap, etc.) based on rational experimental design. Here we report the exploit of the compositional space of tertiary cation (FA/MA/Cs) perovskites and the relevant devices via mixture design methods. Particularly, we employ the simplex lattice designs36,37 and simplex-centroid designs36,38 by picking up only 16 conditions for three factors, which drastically decreases the number of experiment while keeping the uniformity through the entire compositional space of the mixed cation perovskites. More importantly, we conducted detailed material characterizations to bridge the materials optoelectronic properties to the resultant device performance. It proves the scientific soundness of this method, which is efficient to predict the optimum point from the experimental data independent of most theoretical models. Insights are revealed in the context of device efficiency, the tunability of materials properties (e.g. carrier lifetime and bandgap) when exploring the compositional space of the mixed-cation perovskites via MD method. In the materials perspective, this method is feasible to design hybrid perovskites in the forms of not only polycrystalline thin films, but also single crystals and nanostructures, in applications of solar cells and other optoelectronic devices. RESULTS AND DISCUSSION The MD methods, are one major design of experiment (DoE), is employed to decrease the number of experiments that has been proven to effectively reduce the cost and time for optimizing the process conditions.36 For instance, Bashiri et al. used DoE coupled with the response surface models to study optical properties of Cu and Ni-doped TiO2 in photocatalysts.39


5

ACS Nano

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 6 of 31

Here, we employed the simplex lattice designs and simplex-centroid designs to pick up samples within the newly developed mixed-cation perovskite system in solar cell application. The aim is to find the optimal composition and discover the relationship between component and photovoltaic characteristics. The compositional space is picked up from recent publications with high credibility (Table S1). In this study, we mainly focus on the impacts of materials composition on device performance by taking the advantage of MD method, whereas other parameters are decoupled intentionally, such as device configurations, and processing protocols/conditions. As shown in Figure S1, the optimized efficiency is estimated to locate at the compositional space where MA=0.16, FA=0.79, and Cs=0.05. In this case, we have screened out our target area (with FA cation prevailing) in the compositional space of mixed-cation perovskites (MA=0~0.4, FA=0.6~1.0, Cs=0~0.4, with fixed Cl:Br:I ratio) that is most likely to result in the best performance devices. When the compositional space of particular interest is identified, an ordinary Kriging interpolation method40,41 was used to predict their output function from the experimental data generated through MD methods. In this method, the input parameters are the concentrations of FA/MA/Cs in the precursor solutions, and the processing conditions are kept the same (Figure S2, Table S2&S3). The outputs of this experiment are set to be the most influential device parameters, namely, fill factor (FF), short circuit current density (JSC), open circuit voltage (VOC) and PCE. We collected the device data (as was summarized in Table S4), and applied quadratic model to conduct computational optimization by minilab.42,43 The detailed precursor formula, device fabrication and data processing can be found in supplementary information. The perovskite film was obtained via two-step process. Typically, a DMF solution containing PbI2, PbBr2 and CsI was deposited by spin coating and dried. A solution composed of HC(NH2)2I,


6

Page 7 of 31

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

ACS Nano

CH3NH3I and CH3NH3Cl was deposited by spin coating in nitrogen glovebox and dried in air with desired relative humidity. Figure 1 shows the output contour distribution of short circuit current (JSC), open circuit voltage (VOC), fill factor (FF) and PCE. From these contour plots, we can approximately predict the reasonable region of input parameters to reach the highest value of output. Figure 1(a) illustrates the PCE output in the mixed perovskite compositional space. To achieve PCE higher than 19.52%, the molar concentration reaches 0.2-0.3 for MA, 0.65-0.7 for FA, and 0.1-0.15 for Cs in the precursor solution. To obtain JSC higher than 22.5 mA/cm2, the region was approximated as 0.0-0.2 for MA, 0.6-0.8 for FA and 0.2-0.3 for Cs (Figure 1(b)). For VOC, higher than 1.11 V, the region was approximated as 0.35-0.4 for MA, 0.7-1.0 for FA and 0.0-0.05 for Cs (Figure 1(c)). And with respect to FF, we define the local maximum area in red as is approaching 80% (Figure 1(d)). The composition for the best efficiency in the present study is based on the precursor solution with molar ratio of FA=66.6%; MA=26.7%; Cs=6.6%. This composition ratio is different from the aforementioned best compositional space supported by other published reports, where MA=0.16, FA=0.79, and Cs=0.05. The difference could be associated to the fact that the final products of the perovskite materials are different from the precursor solution in two-step process, due to the different diffusivity, reaction kinetics, and volatile characteristic between MA and FA.


7

ACS Nano

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 8 of 31

Figure 1. Contour plot of the relationship between (Cs,MA,FA)Pb(Cl,Br,I)3 with different composition (MA=0-0.4, FA=0.6-1.0, Cs=0-0.4, with fixed Cl:Br:I) and outputs a) power conversion efficiency (PCE), b) short circuit current density (JSC), c) fill factor (FF) and d) open circuit voltage (VOC). By the employment of MD methods, the number of sampling has been greatly reduced when exploring the compositional space of tertiary mixed-cation perovskites to identify the best recipe. Figure 2 shows the reproducibility of the best composition (condition 8 in Table S2, FA=66.6%; MA=26.7%; Cs=6.6%). Over 43.9% of the cells show efficiencies above 18%, while ~80% of the cells show efficiencies above 17%. The average power conversion efficiency is 17.46%. Under the optimum conditions discussed in the experimental section, our best cell achieved a


8

Page 9 of 31

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

ACS Nano

PCE of 20.99% with a VOC of 1.103 V, a FF of 79.27% and a JSC of 24.02 mA/cm2.( Figure 2a) The stabilized efficiency is demonstrated by measuring current at the maximum power point at a slow scan, and the steady efficiency of our planar perovskite solar cell is reaching 18.57%.( Figure 2b) It is emphasized here the optimization process over the entire compositional space takes only 16 samples, which greatly improves the experimental efficacy. Typical incident photon-to-electron conversion efficiency (IPCE) spectrum of a representative cell are shown in Figure 2d, which reaches its maximum of 87% at 400–600 nm wavelengths and gradually drops at longer wavelength corresponding to its absorption spectrum. The integration of the IPCE spectra for the cell gives a current density of 22.56 mA/cm2, which is in good agreement with the current density obtained from J-V measurement. The relatively lower current density obtained from (EQE) measurement, compared to that from the J−V curve, probably indicates the presence of surface defects on the TiO2 transporting materials.44 In addition, we reveal the impacts of the single element (input parameters) on the device performance (output parameters) by carefully analysing the results from MD methods (Figure 1). It is found that upon the continuous increase of cesium concentration in the FA/MA mixed perovskites devices, JSC, FF and PCE show obviously enhancement at first, respectively. They reach the optimal concentration around 0.2, and show decrease when cesium is further increased. Interestingly, VOC follows a different pattern, which decreases when cesium is incorporated. Similar trends are observed when MA is incorporated in the FA/cesium system. It suggests the further use of the information generated by MD to guide the rational materials design to meet requirements for various applications.


9

ACS Nano

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 10 of 31

Figure 2. The photovoltaic properties of the best cell under condition 8 (MA=26.7%, FA=66.6%, Cs=6.6% in precursor solution): a) J−V curves obtained under AM1.5 illumination. b) Photocurrent density and power conversion efficiency as a function of time held at 0.90 V bias. c) The reproducibility of the perovskite solar cells. d) IPCE spectrum of the representative cell and its integrated current density. We conducted further characterizations to bridge the device performance to materials properties with the assistance of MD methods. Time resolved photoluminescence (TRPL) measurement is often used to probe the carrier dynamics within the perovskite films, which predominantly determines device performance. We obtained the lifetime decay curves for each sample, which was subsequently fitted with a bi-exponential function containing both fast (τ1) and slow components (τ2), as is summarized in Figure 3，Figure S4 and Table S5. It is generally believed that the fast component of the decay profile refers to the carrier recombination


10

Page 11 of 31

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

ACS Nano

dynamics at surface/grain boundaries and/or the associated carrier diffusion,45-48 and the slow one stands for that in bulk. The FA based perovskites exhibit the largest τ1 when a small amount of either MA and/or cesium is incorporated to form the mixed-cation system (Figure 3b). This is in accordance with the variation in VOC within the compositional space (Figure 1c). VOC Loss plot and is also in line with the recent reported respectable VOC in FA based perovskites with a small concentration of either cesium or FA. (Table S6) Interestingly, the contour plot pattern of the slow component τ2 within the compositional space exhibits great discrepancy to that of τ1 (Figure 3). It is more likely to correlates VOC loss in corresponding perovskite solar cells to the carrier recombination at the surfaces (τ1) rather than in bulk perovskites (τ2). It thus suggests improving the device performance based on current perovskite film growth technique, whereas efforts are appreciated to be focused on inhibiting the carrier recombination at the surfaces/interfaces. This also consistent with recent demonstrated work that surface recombination was more critical than bulk recombination in conventional perovskite.48 We attempt to reveal the insights of the carrier recombination profiles within the compositional space of mixed cation perovskites in the perspective of crystal structure. When fabricating polycrystalline absorbers for PVs, larger crystal/grain size is often preferred. It is because larger grain size is believed to possess better crystallinity and less grain boundaries that hosts more carrier recombination centers. However, decent PCEs have been observed in perovskite solar cells with grain sizes in both ends.49 X-ray diffraction (XRD) has thus been conducted to investigate the crystal properties (Figure S3). The grain size calculated from XRD pattern by Debye-Scherrer equation, which is summarized in Table S7 and plotted in Figure S5. To be noted, these are much smaller compared to that obtained from scanning electron microscopy (SEM), because Debye-Scherrer equation is accurate for the film with grain size less than 200


11

ACS Nano

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 12 of 31

nm. However, we are mainly interested in the trend. The grain size decreases upon the first addition of MA/cesium in FA-based perovskites, but increases when the cesium concentration is over 0.2. It clearly shows the crystal size is relevant to the carrier recombination lifetime at the surfaces/interfaces and in the bulk. It thus indicates that increase the grain size is an effective approach to reduce grain boundaries and hence to improve device performance. In our previous work, it has been argued that residual PbI2 phase within the perovskite absorber exhibit great impact on device performance. An appropriate amount of excessive PbI2 is able to passivate the defects and enhance the device performance.50 Followed by intensive research efforts recently, quite decent PCEs have been achieved by adopting this strategy.51 Herein, we explore the effects of residual PbI2 in the compositional space of mixed perovskite systematically with the assistance of MD (Figure S5b). First, we observed that it exhibited higher content of PbI2 mostly at the region with higher FA content, and the incorporation of other cations e.g. cesium decreased the PbI2 content in the as-prepared films. It is in consistent with the report that the addition of cesium will significantly decrease the transition temperature of the mixed perovskites, indicating the thermodynamics of crystallization changes due to the smaller size of cesium.33 Furthermore, we observed that the increase of PbI2 leads to the increase of τ1 in the resultant film. It is in line with our previous argument that residual PbI2 effectively passivates the defects to inhibit the carrier recombination at the grain boundaries in the polycrystalline perovskite films. Accordingly, the pattern of VOC loss is observed to follow the similar trend as that of residual PbI2 distribution in the compositional space of mixed-cation perovskite (Figure S5b). It thus infers that PbI2 serves as a native species that is able to lead to well-passivated absorbers at the grain boundaries to boost the corresponding device performance.


12

Page 13 of 31

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

ACS Nano

Figure 3. The optoelectronic properties of the cells/films: a) Response surfaces of the VOC loss of the solar cells; b) Response surfaces of the life time τ1 (fitted by the lifetime decay curves); c) Response surfaces of the life time τ2 (fitted by the lifetime decay curves) as a function of ternary methylamine, formamidinium and cesium mixture composition. For the interest in the mixed perovskites in tandem applications, it is highly appealing to tune the bandgap in a controllable manner by rational incorporation of different occupants in either A or X sites. To date, binary mixed-cation perovskites have already been studied to understand the bandgap tuning mechanism in both theoretical and experimental realm,35 but systematically


13

ACS Nano

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 14 of 31

experiments on the tertiary materials systems are still limited due to the heavy sampling loading. Therefore, we have thoroughly investigated the bandgap tunability of mixed-cation perovskites in the tertiary compositional space via MD method. Bandgaps of the 16 samples were determined by conducting the UV-vis and PL measurements to obtain necessary data for Kubellka–Munk equation, as is summarized in Table S5, and Figure 4. It shows the bandgaps varies from 1.56-1.65 eV by simultaneously adjusting the compositions in the tertiary space. The lowest value of bandgap is found to locate on the area with 100% FA occupancy, while the highest one sits on the composition of 6.6% MA, 66.6% FA and 26.7% Cs(Sample 7). When Cs and/or MA cation with small radius is incorporated in the FA based perovskites in certain range, the bandgap of the resultant mixed perovskites increases, respectively.

Figure 4. a) Static photoluminescence spectra and absorption of the sample 4 (Figure S2&Table S2, MA=30%, FA=60%, Cs=10%). b) Response surfaces for the bandgap (which was fitted by the static photoluminescence spectra and absorption curves) as a function of ternary methylamine, formamidinium and cesium mixture composition.


14

Page 15 of 31

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

ACS Nano

Interestingly, this slight increase in bandgap is correlated to the reduced crystal lattice parameters. Figure 5 represents the mapping of crystal lattice parameters and cell volumes within the tertiary compositional space, as were obtained from XRD measurements. It clearly shows that with the increasing loading of small cations, the crystal lattice constants and cell volumes decrease consistently. The sample 7 (6.6% MA, 66.6% FA and 26.7% Cs) providing the largest bandgap, possess the smallest crystal lattice constant and cell volume. This phenomenon is quite similar to that the incorporation of Br to affect the bandgap of perovskite materials.52 Theoretical simulation has predicted that the bandgap of the hybrids perovskites decreases with the lattice constant, which is opposite to the behaviour in most semiconductors.53-55 The bandgap change is probably due to the enlargement, tilting, and/or deformation of the octahedral network. In the tertiary mixed-cation perovskites, the change in the lattice constant is attributed to the incorporation of much smaller ionic radius of Cs+ (1.81 Å) and/or MA+(2.7 Å) as compared to that of FA+ (FA+=HC(NH2)2+, 2.79 Å).33 It leads to the reduction of cubo-octahedral volume for A-site cation surrounded by corner shared eight PbI6 octahedral in unit cell. Consequently, the shrinkage of cubo-octahedral volume for A-site cation results in stronger interaction between Asite cation and iodide, which further affects the electronic configuration within the entire octahedral network and the bandgap of the materials. Our results provide abundant experimental evidence via MD method to further elaborate the mechanism that governs the bandgap by different cation occupants in the mixed hybrid perovskites materials.


15

ACS Nano

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 16 of 31

Figure 5. a) Response surfaces of the unit cell parameter a (fitted by the XRD curves); b) Response surfaces for the unit cell volume (fitted by the XRD curves) as a function of ternary methylamine, formamidinium and cesium mixture composition (the film composition obtained from Table S2 and 3). Among all tandem PV techniques, perovskite/c-silicon tandem is of particular interest by capitalizing the 50-year silicon industry. To serve as the front cell in this system, the perovskite absorber is required to equip with a bandgap of ~1.7 eV to match c-silicon (mostly ~1.1 eV). In previous work, the compositional space of the (MA/FA)Pb(I/Br)3 perovskite system has been systematically explored, and independently changing the MA/FA and I/Br ratios in the precursor solutions used in the film synthesis.35 However, the higher loading of Br, though effectively changes the bandgap, is reported to result in severe phase segregation and decreased PCE in the corresponding device. In this study, we deliver the report to investigate the compositional space in the tertiary mixed-cation perovskites with the assistance of the MD methods, which creates the mixed perovskites of 1.7 eV bandgap by simultaneously adjusting the A site occupants with relatively low loading of Br. As an illustration, we fabricated device based on perovskites with the bandgap of 1.7 eV(Figure S6&Table S9 ), which is optimized by further exploring the I/Br


16

Page 17 of 31

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

ACS Nano

composition based on the previous findings.(Table S8&S10) We found that the device based on Sample 8 (FA=66.6%; MA=26.7%; Cs=6.6%) exhibits the highest PCE with the same processing protocol (Figure 6a). Subsequently, we optimize the processing conditions with the focus on annealing temperature and time via the central composite design (Figure S7 and Table S11). In statistics, a central composite design is an experimental design, for building a quadratic model for the response variable without needing to use a complete three-level factorial experiment. It clearly shows that the PCE increases with the increasing temperature, but is irrelevant to the annealing time in the particular regime of interest. (Figure 6b) The increase of PCE is mainly attributed to the increase in VOC and FF, which follow the similar pattern. (Figure 6c & S8) Interestingly, the JSC decreases with the increase of annealing temperature, which is not fully understood yet. At relatively low temperature, the optimized annealing time is around 15 minutes. Either increasing or decreasing the annealing time will hamper the JSC. Possibly, it first undergoes crystallization to form the perovskites and then decomposition along with the annealing treatment. As shown in Figure 6d, our best cell achieved a PCE of 16.64% with a VOC of 1.088 V, a FF of 73.96% and a JSC of 20.04 mA/cm2, which is close to the recent report for that of the mixed perovskites with a bandgap of 1.74 eV.56-58 Therefore, the MD methods successfully reduce the experimental sampling numbers, and are demonstrated to be feasible to extend on even more complex system by simply adding a few more layers of parameters.


17

ACS Nano

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 31

Figure 6. a) Contour plot of the relationship between 1.7 eV bandgap (Cs,MA,FA)Pb(Cl,Br,I)3 with different composition and PCE. The processing condition and device performance for sample 8 in Table S8 (MA=26.7%, FA=66.6%, Cs=6.6%, Br:I=0.38:0.62): b) Contour plot of the relationship between experimental parameters and PCE c) Contour plot of the relationship between experimental parameters and VOC. d) J−V curves obtained under AM1.5 illumination for the best cell under optimized annealing condition. So far, we have already shown the MD methods serve as a powerful tool to help probe the compositional space of mixed perovskite, which facilitates to optimize the device performance and adjust the bandgap with significantly reduced sampling size. Furthermore, it successfully correlates the crystal lattice parameters, the materials optoelectronic properties and the device


18

Page 19 of 31

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

ACS Nano

performance, which provides insights in deep understanding the mixed perovskites materials and pertaining devices. In addition, it is useful to inspect the effects of the single occupant on crystal size in the tertiary cation perovskites via MD methods (Figure S5). The primary results show that the incorporation of Cs significantly influences the crystal size, while the MA does not. It clearly indicates the crystal size is determined by at least two factors, given the identical processing condition. The investigation is undergoing to understand the underlying mechanism that affects the crystal size in the mixed perovskite film. CONCLUSIONS In summary, we have demonstrated the employment of MD to exploit the perovskites absorbers in solar cells, mainly in the tertiary-cation compositional space. Different from the previous endeavour by independently adjusting the cation ratios, it is found that MD serves as an effective and rational approach 1) to probing composition-property relationship of the mixed perovskites in a multi-dimension manner, 2) to optimization of the device performance by adjusting various components simultaneously with significantly reduced sampling size. We achieved the best device exhibiting the VOC of 1.103 V, FF of 79.27%, JSC of 24.02 mA/cm2 and PCE of 20.99% with the assistance of MD. Furthermore, we obtained the perovskites with the bandgap of 1.7 eV to fabricate single junction device for tandem applications, whose PCE reaches 16.64%. In the perspective of materials design, the MD methods show great feasibility and effectiveness in use for data analysis and device optimization, which provide sufficient insights to guide future research and design for perovskite solar cells. Moreover, it can be adopted in mixed perovskites systems, such as polycrystalline thin films, single crystals and nanostructures, for various optoelectronic devices.


19

ACS Nano

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 20 of 31

METHODS Materials The commercial materials used are listed as follows: acetone (AR Beijing Chemical Works), dimethyl sulfoxide (AR Beijing Chemical Works), Aminomethane (CP Beijing Chemical Works), Formamidinium acetate(CP Beijing Chemical Works), Hydrogen iodide (57%, Alfa Aesar), Hydrochloric acide(48 %, Alfa Aesar), thanol (AR Beijing Chemical Works), N,Ndimethylformamide (99.99%, Sigma-Aldrich), isopropanol (99.99%, Aladdin Industrial Corporation), PbI2 (99.999%, Sigma-Aldrich), PbBr2 (99.999%, Sigma-Aldrich), CsI (Aladdin Industrial Corporation), TiAc2 (75 wt% in isopropanol, Sigma-Aldrich), spiro-OMeTAD (Lumtec), and ITO substrates. Precursor synthesis CH3NH3I (MAI) was synthesized by stirring 27.8 mL of CH3NH2 and 30 mL of HI at 0 °C for 2 hours.59 Using a rotary evaporator, the precipitate was collected by removing the solvents at 50 °C. The product was dissolved in 100 mL anhydrous ethanol and precipitated with the addition of 500 mL diethyl ether. This procedure was repeated twice. The final product was collected and dried at 60 °C in a vacuum oven for one day. Synthesis of methylammonium chloride (CH3NH3Cl): 33.7 ml of methylamine and 21.6 ml of hydrochloric acid were mixed in a round bottomed flask at room temperature, and then kept stirring for 2 hours. The precipitate was recovered using the vacuum rotary evaporator. The product, methylammonium chloride (CH3NH3Cl), was collected after several washings with diethyl ether, and then dried at 60 °C in vacuum oven for one day. Synthesis of HC(NH2)2I: Formamidinium acetate powder was dissolved in a 1.4X molar excess of 57% w/w hydroiodic acid (for FAI). After the addition of HI, the solution was left stirring for 2 hours at 0°C. The products were then dissolved in ethanol, recrystallized using diethylether, and finally dried at 60 °C in a vacuum oven for 24 h. The TiO2 nanocrystals were synthesized by a non-hydrolytic sol–gel approach,60 where the entire synthetic procedure was performed in ambient air. In a typical synthesis, 1 mL TiCl4 was added into 4 mL ethanol slowly with stirring, followed by adding 20 mL benzyl alcohol, leading to a


20

Page 21 of 31

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

ACS Nano

yellow solution. The solution was heated at 80 °C for a period of 6 hours, forming a slightly milky suspension, which was then mixed with 250 mL diethyl ether and centrifuged to collect the precipitate. The obtained product was re-dissolved in 40 mL absolute ethanol and precipitated with the addition of 300 mL diethyl ether, and this step was repeated twice. The final TiO2 was collected and dispersed in ethanol to make a suspension with a concentration of 5 mg mL-1. Afterward, TiAc2 was added to the solution, resulting in a solution of 1:1 weight percent of TiO2 to TiAc2. Device fabrication The ITO substrate was sequentially washed with isopropanol, acetone, distilled water and ethanol. The ETL was subsequently coated on ITO substrate with the Titanium diisopropoxide bis(acetylacetonate) stabilized TiO2 nanocrystal solution, and annealed at 150 °C for 30 min in air. The thickness of the ETL layer is around 40 nm. After gradually cooling the substrates to room temperature (25 °C), a mixture solution containing PbI2, PbBr2 and CsI (different amount of PbI2, PbBr2 and CsI were dissolved in 1 mL DMF according Table S3) was deposited by spin coating at 3000 rpm for 30 s (6,500 rpm/s accelerating speed) and dried at 70 °C for 30 min. After the PbI2 coated substrates cooling to room temperature (25 °C) in nitrogen glovebox, a solution composed of HC(NH2)2I, CH3NH3I and CH3NH3Cl (different amount of HC(NH2)2I, CH3NH3I and CH3NH3Cl were dissolved in 1 mL isopropanol according Table S3) was deposited by spin coating at 3000 rpm for 30 s (6,500 rpm/s accelerating speed) in nitrogen glovebox and dried at 135 °C for 18.5 min in air (Relative Humidity 30 %). The HTM solution was then deposited by spin coating at 2,000 r.p.m. for 30 s. The HTM solution was prepared by dissolving

72.3

mg

(2,2’,7,7’-tetrakis-(N,N-dimethoxyphenyl-amine)-9,9’-spirobifluorene)

(Spiro-OMeTAD), 28.8 µL 4-tert-butylpyridine (99.9%, Sigma-Aldrich) and 17.5 µL of a stock solution of 520 mg/mL lithium bis(trifluoromethylsulphonyl)imide in acetonitrile (99.9%, Sigma-Aldrich) in 1 mL chlorobenzene (99.9%, Sigma-Aldrich). It is important to note that the samples in this work were aged under pure oxygen condition for ~12 hours. Finally, the counter electrode was deposited by thermal evaporation of gold under a pressure of 5 × 10−5 Pa. The active area was 0.102 cm2. The as-fabricated device consist five functional layers, including 150 nm thick ITO electrode, a 40 nm of TiO2, 350 nm of perovskite, 200 nm of spiro-OMeTAD, and 100 nm of gold.


21

ACS Nano

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 31

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.xxxxx. The composition distribution area of the published perovskite solar cell with high power conversion efficiency, as well as detailed data for the composition tuning, bandgap tuning, TRPL, XRD analysis in the present work. AUTHOR INFORMATION Corresponding Author *Email: (H.Z.) [email protected]. * Email: (X.W.) [email protected]. * Email: (Q.C.) [email protected]. Author Contributions + L.L. and N.L. contributed equally to this work. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT The authors acknowledge funding support from the National Natural Science Foundation of China (51672008) (U1508202) (51673025), National Key Research and Development Program of China Grant No. 2016YFB0700700, Young Talent Thousand Program and ENN Group. REFERENCES


22

Page 23 of 31

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

ACS Nano

(1) 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. (2) Chen, Q.; De Marco, N.; Yang, Y.; Song, T.-B.; Chen, C.-C.; Zhao, H.; Hong, Z.; Zhou, H.; Yang, Y., Under the Spotlight: The Organic–Inorganic Hybrid Halide Perovskite for Optoelectronic Applications. Nano Today 2015, 10, 355-396. (3) Yin, W. J.; Shi, T.; Yan, Y., Unique Properties of Halide Perovskites as Possible Origins of the Superior Solar Cell Performance. Adv. Mater. 2014, 26, 4653-4658. (4) Yi, C.; Luo, J.; Meloni, S.; Boziki, A.; Ashari-Astani, N.; Grätzel, C.; Zakeeruddin, S. M.; Röthlisberger, U.; Grätzel, M., Entropic Stabilization of Mixed A-Cation ABX3 Metal Halide Perovskites for High Performance Perovskite Solar Cells. Energy Environ. Sci. 2016, 9, 656-662. (5) Saliba, M.; Matsui, T.; Seo, J. Y.; Domanski, K.; Correa-Baena, J. P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Gratzel, M., Cesium-Containing Triple Cation Perovskite Solar Cells: Improved Stability, Reproducibility and High Efficiency. Energy Environ. Sci. 2016, 9, 1989-1997. (6) Tsai, H.; Nie, W.; Blancon, J. C.; Stoumpos, C. C.; Asadpour, R.; Harutyunyan, B.; Neukirch, A. J.; Verduzco, R.; Crochet, J. J.; Tretiak, S.; Pedesseau, L.; Even, J.; Alam, M. A.; Gupta, G.; Lou, J.; Ajayan, P. M.; Bedzyk, M. J.; Kanatzidis, M. G., High-Efficiency TwoDimensional Ruddlesden-Popper Perovskite Solar Cells. Nature 2016, 536, 312-316. (7) 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.


23

ACS Nano

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 24 of 31

(8) Kim H.S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.; Moon, S. J.; Humphry-Baker, R.; Yum, J. H.; Moser, J. E.; Gratzel, M.; Park, N. G., Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (9) Tan, Z.-K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler, R.; Deschler, F.; Price, M.; Sadhanala, A.; Pazos, L. M.; Credgington, D.; Hanusch, F.; Bein, T.; Snaith, H. J.; Friend, R. H., Bright Light-Emitting Diodes Based on Organometal Halide Perovskite. Nat. Nanotech. 2014, 9, 687-692. (10) Saliba, M.; Wood, S. M.; Patel, J. B.; Nayak, P. K.; Huang, J.; Alexander-Webber, J. A.; Wenger, B.; Stranks, S. D.; Horantner, M. T.; Wang, J. T.; Nicholas, R. J.; Herz, L. M.; Johnston, M. B.; Morris, S. M.; Snaith, H. J.; Riede, M. K., Structured Organic-Inorganic Perovskite Toward a Distributed Feedback Laser. Adv. Mater. 2016, 28, 923-929. (11) Chin, X. Y.; Cortecchia, D.; Yin, J.; Bruno, A.; Soci, C., Lead Iodide Perovskite LightEmitting Field-Effect Transistor. Nat. Commun. 2015, 6, 7383. (12) Yang, W. S.; Park, B.-W.; Jung, E. H.; Jeon, N. J.; Kim, Y. C.; Lee, D. U.; Shin, S. S.; Seo, J.; Kim, E. K.; Noh, J. H., Iodide Management in Formamidinium-Lead-Halide–Based Perovskite Layers for Efficient Solar Cells. Science 2017, 356, 1376-1379. (13) Li, Z.; Yang, M.; 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.


24

Page 25 of 31

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

ACS Nano

(14) 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 Heterojunction Solar Cells. Energy Environ. Sci. 2014, 7, 982. (15) Chen, Q.; Zhou, H.; Fang, Y.; Stieg, A. Z.; Song, T.-B.; Wang, H.-H.; Xu, X.; Liu, Y.; Lu, S.; You, J.; Sun, P.; McKay, J.; Goorsky, M. S.; Yang, Y., The Optoelectronic Role of Chlorine in CH3NH3PbI3(Cl)-Based Perovskite Solar Cells. Nat. Commun. 2015, 6, 7269. (16) Lian, Z.; Yan, Q.; Gao, T.; Ding, J.; Lv, Q.; Ning, C.; Li, Q.; Sun, J. L., Perovskite CH3NH3PbI3(Cl) Single Crystals: Rapid Solution Growth, Unparalleled Crystalline Quality, and Low Trap Density toward 10(8) cm(-3). J. Am. Chem. Soc. 2016, 138, 9409-9412. (17) Liu, X.; Yang, Z.; Chueh, C.-C.; Rajagopal, A.; Williams, S. T.; Sun, Y.; Jen, A. K. Y., Improved Efficiency and Stability of Pb–Sn Binary Perovskite Solar Cells by Cs Substitution. J. Mater. Chem. A 2016, 4, 17939-17945. (18) Noel, N. K.; Stranks, S. D.; Abate, A.; Wehrenfennig, C.; Guarnera, S.; Haghighirad, A.-A.; Sadhanala, A.; Eperon, G. E.; Pathak, S. K.; Johnston, M. B., Lead-Free Organic-Inorganic Tin Halide Perovskites for Photovoltaic Applications. Energy Environ. Sci. 2014, 7, 3061-3068. (19) Yang, Z.; Rajagopal, A.; Jo, S. B.; Chueh, C. C.; Williams, S.; Huang, C. C.; Katahara, J. K.; Hillhouse, H. W.; Jen, A. K., Stabilized Wide Bandgap Perovskite Solar Cells by Tin Substitution. Nano Lett. 2016, 16, 7739-7747. (20) Koh, T. M.; Fu, K.; Fang, Y.; 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.


25

ACS Nano

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 26 of 31

(21) Pang, S.; Hu, H.; Zhang, J.; Lv, S.; Yu, Y.; Wei, F.; Qin, T.; Xu, H.; Liu, Z.; Cui, G., NH2CH═NH2PbI3: An Alternative Organolead Iodide Perovskite Sensitizer for Mesoscopic Solar Cells. Chem. Mater. 2014, 26, 1485-1491. (22) Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I., Compositional Engineering of Perovskite Materials for High-Performance Solar Cells. Nature 2015, 517, 476480. (23) Pellet, N.; Gao, P.; Gregori, G.; Yang, T. Y.; Nazeeruddin, M. K.; Maier, J.; Gratzel, M., Mixed-Organic-Cation Perovskite Photovoltaics for Enhanced Solar-Light Harvesting. Angew. Chem. 2014, 53, 3151-3157. (24) Hu, M.; Liu, L.; Mei, A.; Yang, Y.; Liu, T.; Han, H., Efficient Hole-Conductor-Free, Fully Printable Mesoscopic Perovskite Solar Cells with a Broad Light Harvester NH2CH=NH2PbI3. J. Mater. Chem. A 2014, 2, 17115-17121. (25) Binek, A.; Hanusch, F. C.; Docampo, P.; Bein, T., Stabilization of the Trigonal HighTemperature Phase of Formamidinium Lead Iodide. J. Phys. Chem. Lett. 2015, 6, 1249-1253. (26) Bi, D.; Tress, W.; Dar, M. I.; Gao, P.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Correa Baena, J. P.; Decoppet, J. D.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Gratzel, M.; Hagfeldt, A., Efficient Luminescent Solar Cells Based on Tailored Mixed-Cation Perovskites. Sci. Adv. 2016, 2, e1501170. (27) Eperon, G. E.; Paternò, G. M.; Sutton, R. J.; Zampetti, A.; Haghighirad, A. A.; Cacialli, F.; Snaith, H. J., Inorganic Caesium Lead Iodide Perovskite Solar C ells. J. Mater. Chem. A 2015, 3, 19688-19695.


26

Page 27 of 31

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

ACS Nano

(28) Liang, J.; Wang, C.; Wang, Y.; Xu, Z.; Lu, Z.; Ma, Y.; Zhu, H.; Hu, Y.; Xiao, C.; Yi, X.; Zhu, G.; Lv, H.; Ma, L.; Chen, T.; Tie, Z.; Jin, Z.; Liu, J., All-Inorganic Perovskite Solar Cells. J. Am. Chem. Soc. 2016, 138, 15829-15832. (29) Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, D. T.; Christians, J. A.; Chakrabarti, T.; Luther, J. M., Quantum Dot–Induced Phase Stabilization of aCsPbI3 Perovskite for High-Efficiency Photovoltaics. Science 2016, 354, 92-95. (30) 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. (31) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Horantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; Johnston, M. B.; Herz, L. M.; Snaith, H. J., A Mixed-Cation Lead Mixed-Halide Perovskite Absorber for Tandem Solar Cells. Science 2016, 351, 151-155. (32) Saliba, M.; Matsui, T.; Domanski, K.; Seo, J.-Y.; Ummadisingu, A.; Zakeeruddin, S. M.; Correa-Baena, J.-P.; Tress, W. R.; Abate, A.; Hagfeldt, A., Incorporation of Rubidium Cations into Perovskite Solar Cells Improves Photovoltaic Performance. Science 2016, 354, 206-209. (33) Mittal, M.; Jana, A.; Sarkar, S.; Mahadevan, P.; Sapra, S., Size of the Organic Cation Tunes the Band Gap of Colloidal Organolead Bromide Perovskite Nanocrystals. J. Phys. Chem. Lett. 2016, 7, 3270-3277.


27

ACS Nano

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 28 of 31

(34) De Marco, N.; Zhou, H.; Chen, Q.; Sun, P.; Liu, Z.; Meng, L.; Yao, E. P.; Liu, Y.; Schiffer, A.; Yang, Y., Guanidinium: A Route to Enhanced Carrier Lifetime and Open-Circuit Voltage in Hybrid Perovskite Solar Cells. Nano Lett. 2016, 16, 1009-1016. (35) Jesper Jacobsson, T.; Correa-Baena, J.-P.; Pazoki, M.; Saliba, M.; Schenk, K.; Grätzel, M.; Hagfeldt, A., Exploration of the Compositional Space for Mixed Lead Halogen Perovskites for High Efficiency Solar Cells. Energy Environ. Sci. 2016, 9, 1706-1724. (36) D. C. Montgomery, Design and Analysis of Experiment, (Editor: Biometrics), Wiley-VCH, Weinheim, Germany, 2012, pp. 478-553. (37) Scheffé, H., Experiments with Mixtures. J. R. Stat. Soc. 1958, 20, 344-360. (38) Scheffé, H., The Simplex-Centroid Design for Experiments with Mixtures. J. R. Stat. Soc. 1963, B, 235-263. (39) Bashiri, R.; Mohamed, N. M.; Kait, C. F.; Sufian, S.; khatani, M.; Hanaei, H., Effect of Preparation Parameters on Optical Properties of Cu and Ni Doped TiO2 Photocatalyst. Procedia Eng. 2016, 148, 151-157. (40) Gao, Y.; Wang, X., An Effective Warpage Optimization Method in Injection Molding Based on the Kriging Model. Int. J. Adv. Manuf. Tech. 2007, 37, 953-960. (41) Teixeira, A. L.; Falcao, A. O., Structural Similarity Based Kriging for Quantitative Structure Activity and Property Relationship Modeling. J. Chem. Inf. Model. 2014, 54, 1833-1849. (42) Deb, K.; Pratap, A.; Agarwal, S.; Meyarivan, T., A Fast and Elitist Multiobjective Genetic Algorithm: NSGA-II. IEEE Trans. Evolut. Comput. 2002, 6, 182-197.


28

Page 29 of 31

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

ACS Nano

(43) Li, H.; Zhang, Q., Multiobjective Optimization Problems with Complicated Pareto Sets, MOEA/D and NSGA-II. IEEE Trans. Evolut. Comput. 2009, 13, 284-302. (44) Hendry, E.; Koeberg, M.; O'Regan, B.; Bonn, M., Local Field Effects on Electron Transport in Nanostructured TiO2 Revealed by Terahertz Spectroscopy. Nano Lett. 2006, 6, 755-759. (45) Peng, W.; Yin, J.; Ho, K. T.; Ouellette, O.; De Bastiani, M.; Murali, B.; El Tall, O.; Shen, C.; Miao, X.; Pan, J.; Alarousu, E.; He, J. H.; Ooi, B. S.; Mohammed, O. F.; Sargent, E.; Bakr, O. M., Ultralow Self-Doping in Two-Dimensional Hybrid Perovskite Single Crystals. Nano lett. 2017, 17, 4759-4767.

(46) Murali, B.; Dey, S.; Abdelhady, A. L.; Peng, W.; Alarousu, E.; Kirmani, A. R.; Cho, N.; Sarmah, S. P.; Parida, M. R.; Saidaminov, M. I.; Zhumekenov, A. A.; Sun, J.; Alias, M. S.; Yengel, E.; Ooi, B. S.; Amassian, A.; Bakr, O. M.; Mohammed, O. F., Surface Restructuring of Hybrid Perovskite Crystals. ACS Energy Lett. 2016, 1, 1119-1126.

(47) Yang, Y.; Yan, Y.; Yang, M.; Choi, S.; Zhu, K.; Luther, J. M.; Beard, M. C., Low Surface Recombination Velocity in Solution-Grown CH3NH3PbBr3 Perovskite Single Crystal. Nat. Commun. 2015, 6, 7961.

(48) Yang, Y.; Yang, M.; Moore, David T.; Yan, Y.; Miller, Elisa M.; Zhu, K.; Beard, Matthew C., Top and Bottom Surfaces Limit Carrier Lifetime in Lead Iodide Perovskite Films. Nat. Energy 2017, 2, 16207.

(49) Li, L.; Chen, Y.; Liu, Z.; Chen, Q.; Wang, X.; Zhou, H., The Additive Coordination Effect on Hybrids Perovskite Crystallization and High-Performance Solar Cell. Adv. Mater. 2016, 28, 9862–9868.


29

ACS Nano

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 30 of 31

(50) Chen, Q.; Zhou, H.; Song, T. B.; Luo, S.; Hong, Z.; Duan, H. S.; Dou, L.; Liu, Y.; Yang, Y., Controllable Self-Induced Passivation of Hybrid Lead Iodide Perovskites Toward High Performance Solar Cells. Nano Lett. 2014, 14, 4158-4163. (51) Roldán-Carmona, C.; Gratia, P.; Zimmermann, I.; Grancini, G.; Gao, P.; Graetzel, M.; Nazeeruddin, M. K., High Efficiency Methylammonium Lead Triiodide Perovskite Solar Cells: the Relevance of Non-Stoichiometric Precursors. Energy Environ. Sci. 2015, 8, 3550-3556. (52) Cui, D.; Yang, Z.; Yang, D.; Ren, X.; Liu, Y.; Wei, Q.; Fan, H.; Zeng, J.; Liu, S., ColorTuned Perovskite Films Prepared for Efficient Solar Cell Applications. J. Phys. Chem. C 2016, 120, 42-47. (53) Borriello, I.; Cantele, G.; Ninno, D., Ab Initio Investigation of Hybrid Organic-Inorganic Perovskites Based on Tin Halides. Phys. Rev. B 2008, 77, 235214. (54) Huang, L.-y.; Lambrecht, W. R. L., Electronic Band Structure, Phonons, and Exciton Binding Energies of Halide Perovskites CsSnCl3, CsSnBr3, and CsSnI3. Phys. Rev. B 2013, 88， 165203. (55) Fang, H.; Jena, P., Molecular Origin of Properties of Organic-Inorganic Hybrid Perovskites: The Big Picture from Small Clusters. J. Phys. Chem. Lett. 2016, 7, 1596-1603. (56) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Hörantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B., A mixed-Cation Lead Mixed-Halide Perovskite Absorber for Tandem Solar Cells. Science 2016, 351, 151-155.


30

Page 31 of 31

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

ACS Nano

(57) Chen, B.; Zheng, X.; Bai, Y.; Padture, N. P.; Huang, J., Progress in Tandem Solar Cells Based on Hybrid Organic-Inorganic Perovskites. Adv. Energy Mater. 2017, 7, 1602400. (58) Zhao D.; Yu, Y.; Wang, C.; Liao, W.; Shrestha, N.; Grice, C. R.; Cimaroli, A. J.; Guan, L.; Ellingson, R. J.; Zhu, K.; Zhao, X.; Xiong, R.-G.; Yan, Y., Low-Bandgap Mixed Tin–Lead Iodide Perovskite Absorbers with Long Carrier Lifetimes for All-Perovskite Tandem Solar Cells. Nat. Energy 2017, 2, 17018. (59) Heo, J. H.; Im, S. H.; Noh, J. H.; Mandal, T. N.; Lim, C.-S.; Chang, J. A.; Lee, Y. H.; Kim, H.-j.; Sarkar, A.; NazeeruddinMd, K.; Gratzel, M.; Seok, S. I., Efficient Inorganic-Organic Hybrid Heterojunction Solar Cells Containing Perovskite Compound and Polymeric Hole Conductors. Nat. Photon. 2013, 7, 486-491.

(60) Wang, J.; Polleux, J.; Lim, J.; Dunn, B., Pseudocapacitive Contributions to Electrochemical Energy Storage in TiO2 (anatase) Nanoparticles. J. Phys. Chem. C 2007, 111, 14925–14931.

Table of Contents Graphic


31

Precise Composition Tailoring of Mixed-Cation Hybrid Perovskites for

Recommend Documents