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Multilayered Perovskite Materials Based on Polymericammonium Cations for Stable Large-area Solar Cell Kai Yao, Xiaofeng wang, Yun-xiang Xu, Fan Li, and Lang Zhou Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b00711 • Publication Date (Web): 12 Apr 2016 Downloaded from http://pubs.acs.org on April 17, 2016

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Chemistry of Materials

Multilayered Perovskite Materials Based on Polymeric-ammonium Cations for Stable Large-area Solar Cell Kai Yao,†* Xiaofeng Wang,‡ Yun-xiang Xu,# Fan Li,‡* Lang Zhou† †

Institute of Photovoltaics, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China,

E-mail: [email protected] ‡

Department of Materials Science and Engineering, Nanchang University, 999 Xuefu Avenue,

Nanchang 330031, China, E-mail: [email protected] #

College of Polymer Science & Engineering, State Key Laboratory of Polymer Materials

Engineering, Sichuan University, Chengdu 610065, China

Abstract Despite the dramatic rise in power conversion efficiencies (PCEs) of perovskite solar cells (PeSCs), concerns surrounding the long-term stability as well as the poor reproducibility in the archetypal three-dimensional (3D) perovskite, MAPbI3 (MA = CH3NH3), have the potential to derail commercialization. We have reported the fabrication and properties of a series of 2D perovskite compounds (PEI)2(MA)n−1PbnI3n+1 (n = 3, 5, 7) by incorporating polyethylenimine (PEI) cations within the layered structure. The benefits of using intercalated polymer cations in the multilayered films are multiple: moisture resistance and film-quality are greatly enhanced compared to that of their 3D MAPbI3 analogue; charge transport within solar cells can also be improved compared to that of 2D materials using small-molecule bulky ammonium. The moisture-stable nature of the multilayered perovskite materials allow for the simple one-step fabrication of cells with an aperture area of 2.32 cm2 under ambient humidity that have a PCE up to 8.77%. Overall, the 2D perovskite family offers rich multitudes of substituent and crystal structures, defining a promising class of stable and efficient light-absorbing materials.

ACS Paragon Plus Environment


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Introduction Organic inorganic hybrid metal halide perovskites have been under intense investigation as lightabsorbing materials for next-generation photovoltaic devices.[1] Among the light absorber candidates, 3D perovskite materials are the most prominent choice owing to their outstanding properties for a solar cell absorber, including high extinction coefficient, medium band gap and small exciton binding energy as well as long charge diffusion lengths.[2-4] Purely inorganic perovskites methylammonium lead iodide (MAPbI3) or formamidinium lead iodide (FAPbI3) have been the most widely studied perovskite material with power conversion efficiencies (PCEs) exceeding 20% efficiency milestone.[5,

6]

From the commercial view, the large-scale

implementation of perovskite solar cells still requires high film-quality and stability. Both MAPbI3 and FAPbI3 showed severe degradation in ambient air subjected to environmental stresses humidities, due to their inherent vulnerability to moisture and heat,[7] thereby their longterm operational stability remains a bottleneck toward their practical deployment.[8] Besides normal external encapsulation strategies, great efforts for stability improvement of perovskite solar cells are focused on the interfacial layer modification, which are employed as an additional barrier as a “moisture-shielding” layer to protect the perovskite film beneath.[9-13] Nevertheless, only a handful of studies have been conducted to improve the stability of perovskite materials.[14, 15]

On the other side, the poor reproducibility and lack of uniformity of perovskite solar cells

make it challenging to control the deposition and obtain high efficiencies with large devices.[18,19] And actually the true PCE of reported high performance perovskite solar cells remain open to debate, because small-size PeSCs typically show a wide spread in their PCEs. Previous work has focused on improving the uniformity of the perovskite layer by optimizing its deposition methods but fewer studies have aimed at the material itself.[20, 21] As we know, tuning low dimensional perovskites have implications on critical issues on photophysical and electronic properties, as well as the moisture stability.[22] We can control the interlayer separation and thickness of the inorganic layers through the choice of organic cations. Large bulky cation cannot fit into the rigid 3D perovskite network and separates the system into layers, forming 2D perovskites. Moreover, low dimensional 2D analogues yield smooth, ultrahigh surface coverage films from a simple one-step spin-coating approach under ambient conditions without annealing. In comparison, MAPbI3 or FAPbI3 require more complex film fabrication methods to achieve high-quality films without pinholes even in small area.[23,


24]

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However, spatial confinement of the 2D structure leads to higher exciton binding energies and poor conductivity in certain crystallographic directions.[25] We recently have described the compositional engineering of mixed perovskites of 3D perovskite and layered perovskite based on polymeric-ammonium.[26] (Figure S1A) Although the mixed resulting perovskite films showed a direct improvement of moisture tolerance, the device performance based on (MAPbI3)1-x[(PEI)2PbI4]x dropped significantly as the content of layered perovskite composition over 4% (Figure S1B). The increasing content of layered perovskite resulted in severe phase separation (inset image of Figure S2), which act as “barriers” for charge extraction.[27] The compromise method between the two extremes is the 2D multilayered halide perovskites with the generic structural formula of (A)2(CH3NH3)n−1PbI3n+1 (n is an integer, from 1 to ∞).[28] The unit layers are stacked together to maintain the structure integrity, with favorable electronic properties of the 3D structure. Nevertheless, all the photovoltaic cells based on the low dimensional perovskites yielded low performance with power conversion efficiencies less than 5%, to the best of our knowledge. Recently, Smith et al. reported the use of a 2D perovskite (PhC2H5NH3)2(MA)2Pb3I10 as a photovoltaic absorber with a PCE of 4.73%,[29] and Kanatzidis et al. chose n-butylammine (BA) to fabricate a series 2D perovskite (BA)2(MA)n−1PbnI3n+1 (n = 1, 2, 3, and 4) films, achieving PCE of 4.02%.[30] In the multidimensional perovskites, the key problems that would have to be addressed are relatively low charge carrier mobility and higher exciton binding energies, along with significantly increased band gap.[31, 32] In the search for new multifunctional hybrid perovskite compounds, the use of polymeric-ammonium has not been considered up to now. Such multi-functional organic entities would be able to anchor the adjacent perovskite layers via the cationic ammonium and then enhance their electronic interaction.[33] With all these considerations in mind, here we present a strategy that simultaneously addresses the scale-up and stability issues facing embodiments of perovskite solar cells. In this work, we have reported an intermediate multilayered perovskite (PEI)2(MA)n−1PbnI3n+1 (n = 3, 5, 7) by replacing partially MA in MAPbI3 with PEI cations. The intercalated polymer ammonium, acting as multi-ammonium cations, induce the tightly stacking of the separated inorganic unit layers, which improve the charge transfer. (Figure 1) To preserve the favorable electronic properties of the 3D structure, we also increase the inorganic slabs (indicated by n) to decrease the band gap. And the multilayered perovskites allow for high-quality films to be deposited without annealing.



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With this strategy, we have successfully fabricated large-size (aperture area of 2.32 cm2) solar cells based on (PEI)2(MA)6Pb7I22 thin films with an maximum efficiency of 8.77%. Moreover, the perovskite solar cells based on multilayered structures show high stability to moisture, rendering them attractive for future commercial application.

Results and Discussion 2D perovskite compounds (PEI)2(MA)n−1PbnI3n+1 (n = 3, 5, 7) was synthesized from a stoichiometric reaction between PbI2, MAI, and polyethylenimine hydriodide (PEI•HI). Details of the synthesis and preparation are presented in the experimental section. Figure 2 shows the Xray diffraction (XRD) patterns of 2D perovskite powder materials in comparison to with those of MAPbI3. In the case of (PEI)2(MA)2Pb3I10, its orientation not only reveals the vertical growth of the compound with the (111) and (202) reflections of MA perovskite structure, but also the growth of planar layered (PEI)2PbI4 shows the (0k0) reflections (Figures S3).[34] As the layers become thicker (n = 5, 7), the competition arises between the PEI cations, which try to confine the growth within the planar layer, and the MA ions, which try to expand the perovskite growth outside the layer. Therefore, the multilayered perovskites present desirable vertical growth rather than growth parallel to the substrate as that of (PEI)2PbI4. All perovskite films were fabricated using one-step spin-coating deposition method with DMF precursor solutions, unless specified otherwise. Simple one-step processing of MAPbI3 can not afford continuous films with high surface coverage and non-uniform crystal size, as shown in the scanning electron microscopy (SEM) images of Figure S4.[35] Under crude conditions with solvent engineering, we could improve the quality of the MAPbI3 (M) films with compact and better coverage morphology, as shown in Figure S5.[36] However, the (PEI)2(MA)n−1PbnI3n+1 (n = 3, 5, 7) perovskite films are superior to MAPbI3 films deposited by the modified method. All the multilayered perovskites grow into similar compact, pore-free films with small grain size. It is noteworthy that the 2D films are readily formed with high quality after the spin-coating process without requiring annealing steps. As the content of large cation PEI increases, the time for selfassemble to form well-defined films decreases (Figure S6), judging from the absorption feature. Actually, the (PEI)2(MA)2Pb3I10 are formed during the spin-coating process. For the (PEI)2(MA)n−1PbnI3n+1 (n ≥ 9), thermal annealing are required to generate the high quality film and thereby excluding these materials from this work. The morphologies differences caused by


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the incorporation of PEI cation can be further proved by the cross-sectional SEM image of perovskite films in Figure 3. In the MAPbI3 films, the annealed films generally feature loosely packed, larger crystals surrounding pores, similar with the surface feature. In contrast, all the 2D perovskites exhibit well packed and dense films. The evolution of continuous crystallites with few defect-related trap sites is highly desirable in photovoltaic devices because it avoids the shunt paths leading to leakage currents, and also depresses direct contact of adventitious water with the inner perovskite. The moisture-tolerance tests for perovskite materials were performed by monitoring the reflection of XRD patterns in the corresponding perovskite films after 30 days in air with a relative humidity of 50%. The changes in the XRD patterns of both the MAPbI3 and (PEI)2(MA)6Pb7I22 films are presented in Figure S7. Clearly from the optical images, 3D perovskite MAPbI3 started to decompose immediately after being exposed to moisture. After several days, most of the black films had decomposed and turned yellow with the formation of PbI2 (Figure 4A), because of the gradual loss of the MA+ cation.[37] However, no obvious changes could be observed for (PEI)2(MA)n−1PbnI3n+1 even after one month without color change. Previous calculations results of Yang et al.[38] has presented that the steric effects caused by tetramethyl ammonium and the change of surface Pb-I bonds can effectively hinder the adsorption of water on the reactive Pb sites. While our hydrophobic polymeric-ammonium can provide stronger steric hindrance, endowing perovskite crystals with considerably improved moisture stability. Moreover, the incorporation of PEI can form a more compact perovskite films, further minimized water intake of devices. Benefited from the improved moisture resistance and the dense-grained uniform morphology, our (PEI)2(MA)n−1PbnI3n+1 have demonstrated a stable perovskite structure for facile preparatory method. Decreasing the dimensionality of the inorganic components from the 3D structure causes an increase in the bandgap. As shown in Figure 4B, MAPbI3 (M) perovskite films show optical absorption spectra with a band edge (Eg) of 1.58 eV, in accord with previous reports. The band gap of (PEI)2(MA)6Pb7I22, (PEI)2(MA)4Pb5I16 and (PEI)2(MA)2Pb3I10 can be calculated as 1.62, 1.69 and 1.79 eV, respectively. For the multilayered perovskite (PEI)2(MA)n−1PbnI3n+1 (n = 3, 5, 7), their optical band gaps increase with decreasing n values, accompanying with the perovskite growth outside the planar layer. For the polymer ammonium PEI, we can consider it as multiammonium cations. The mono-ammonium cations, such as BA and PEA, can only bond to one



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inorganic layer and then the formation of a van der Waals gap between the layers, while the intercalated multi-ammonium cations span the entire distance between and bond to two adjacent inorganic sheets.[39] The strong interactions between the organic-inorganic structures can influence the overall structure in the solid state with reduced band gap.[40] It is consistent with the results that the multilayered perovskite (BA)2(MA)2Pb3I10 (n = 3), with mono-ammonium cations BA, shows an larger Eg of 1.89 eV (Figure S8). Furthermore, we have sought to confirm this optical property of the 2D perovskite series by performing photoluminescence (PL) measurements. As shown in Inset of Figure 4B, the PL spectra of 2D materials show blue-shift PL emission energy as the decreasing of n values. For instance, the PL emission shifted from 783 nm of MAPbI3 to 720 nm of (PEI)2(MA)2Pb3I10. This distinct feature is fully consistent with the absorption spectra. To understand the kinetics of excitons and free carriers in various perovskite films and how the presence of bulky cations affects the PL lifetime, we conducted time-resolved PL measurement (Figure 4C).[41,

42]

The

lifetimes of (PEI)2(MA)6Pb7I22 films exhibit a increasing time-constant of τe = 8.9 ns, when compared with that of (BA)2(MA)6Pb7I22 films. Moreover, we have observed a bimolecular recombination process of free electrons and holes for the MAPbI3 (M) and (PEI)2(MA)6Pb7I22 films. And this is in contrast to a mono-exponential decay observed in (BA)2(MA)6Pb7I22 films, which is representative of non-radiative decay.[43] These indicates that interaction induced by the polymeric-ammonium improve the charge transfer between the separated inorganic layers and restrain the strong non-radiative recombination.[4, 44] More studies are underway to understand the mechanisms of relative structure influence on energy transfer and charge separation in lowdimensional perovskites. To gain further insights into the energy level of the 2D perovskite materials, we determined the position of the valence band maxima (VBM) and conduction band maxima (CBM), using ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) of Figure 5, respectively. Figure 5A shows the secondary cut-offs of UPS spectra and all energies were referenced to a common Fermi level (EF) of 0 eV. The work functions (WFs) are calculated by subtracting the energies at secondary cut-offs from the ultraviolet radiation energy of 21.2 eV (Figure S9). For 3D perovskite MAPbI3, the WF is measured to be 4.16 eV, similar with other groups’ reports.[45] And it gradually increases with the decreasing n values, finally to 4.50 eV for (PEI)2(MA)2Pb3I10. Figure 5B presents the UPS data of the highest lying valence band regions, in


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which the valence band maximum (VBM) of all the perovskite films displayed a similar value of 1.2 eV. Therefore, the ionization energy (IP = Φ + VBM) of the perovskite films, which increase from 5.36 eV of MAPbI3 (n = ∞) to 5.52 eV of (PEI)2(MA)2Pb3I10 (n = 3), exhibit the same tendency as the WFs. The IPES spectra yield CBM positions 0.45 eV in MAPbI3 and 0.75 eV in (PEI)2(MA)2Pb3I10 above EF, respectively. Hence, no barrier for photo-generated charge extraction at interfaces using the same device structures and a small loss in the open-circuit voltage (Voc) is expected in all perovskite devices. We proceeded to fabricate and characterize photovoltaic devices with an inverted planar structure (Figure S10). The devices were constructed employing PCBM ([6,6]-phenyl-C61butyric acid methyl ester) as the electron-selective layer and PEDOT:PSS [poly(3,4ethylenedioxythiophene) polystyrene sulfonate] as the hole-selective contact. Figure 6A shows photocurrent density–voltage (J-V) curves of perovskite solar cell using different absorber materials and the photovoltaic parameters short-circuit current (Jsc), Voc, FF, and PCE data are listed in Table 1. For the 3D perovskite MAPbI3, the cells based on normal one step approach exhibit low performance characteristics with large deviation, while the deposition with solvent annealing of MAPbI3 (M) show a higher PCE of 15.4%. On the other hand, we can obtain reasonable performance based on the 2D materials in a simple one step spin-coating without any treatment. The Voc values obtained from (PEI)2(MA)n−1PbnI3n+1 compounds are in line with the bandgap, but the Jsc and FF are significantly lower comparing with MAPbI3 (M), resulting in a substantially lower conversion efficiency. In the cells fabricated with (PEI)2(MA)2Pb3I10, Voc increased to 1.21 V, while the Jsc and FF decrease to 6.53 mA cm-2 and 0.53, respectively. As the decreasing of n value, the external quantum efficiency (EQE) spectrum (Figure 6B) is blueshifted with lower efficiency, confirming the reduction of photocurrent. The decreasing Jsc for the 2D perovskite devices could be attributed from many aspects: larger optical band gaps, higher exciton binding energies and unfavorable charge transfer between separated inorganic layers.[22] In such case, we expect less light absorption and severe charge recombination within the solar cell. We recently have also demonstrated that the coexistence of layered perovskite (PEI)2PbI4 (in small amount) in the MAPbI3 caused substantially poor device performance, as shown in Figure S1B. However, it was remarkable that the device based on (PEI)2(MA)6Pb7I22 afforded a maximum PCE of 10.08%, with a Jsc of 13.63 mA cm-2, a Voc value of 1.12 V, and a FF of 0.66. All the parameters of performance are much better than that of



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(BA)2(MA)6Pb7I22 cells (Figure S11). Moreover, it is noticeable that the FF of multilayered perovskite-devices show a steady increase when the light-absorber layers get thinner. It can achieve comparable FF (~ 70%) values with those of 3D devices in Figure S12, suggesting that building the hybrid structure using polymeric-ammonium cations to covalently link adjacent perovskite layers present a potential way of addressing the limitation of poor charge transport in multidimensional

perovskites.

Moreover,

although

the

devices

based

on

the

(PEI)2(MA)n−1PbnI3n+1 yield relatively high open-circuit voltages over 1.1 V (for example, 1.21 V for (PEI)2(MA)2Pb3I10), much higher Voc values are expected, closer to the actual perovskite band gap. In addition, utilizing conjugated polymer cations with the appropriate molecular energy levels can further improve the charge transfer. Therefore, material and device optimization should afford improvements in Jsc and Voc values, and then further enhancements in efficiency can be achieved in 2D perovskite solar cell. For all the devices discussed above, the illuminated size is 0.04 cm2. Such a small device size is possibly to cause measurement errors and an obligatory minimum cell area of >1 cm2 is required for certified PCEs. And it is highly desirable to fabricate perovskite solar cell devices at centimeter sizes with high-efficiency for future large-scale adoption of perovskite photovoltaics. Herein, we further fabricated cells with large active areas toward the scale-up of the practical deployment. The Figure S14 presents the perovskite films fabricated by one-step approach with substrate size of 3.5 cm × 3.5 cm. For the layered perovskite (PEI)2(MA)6Pb7I22, we demonstrated the uniformity of the perovskite in various scale, as shown in Figure 7. The optical image (500 µm × 500 µm) in Figure 7B shows a pore-free perovskite films and the AFM image (5 µm × 5 µm) in Figure 7D reveals the formation of a smooth film with a root-mean-square roughness of 4.59 nm. Taking 3D MAPbI3 as the reference, it was not surprise that we observed almost all the 50 large size devices in short circuit conditions. Although we applied solvent engineering to enhance the quality of MAPbI3 perovskite films, its relatively poor reproducibility and lack of uniformity still made it challenging to achieve high efficiencies with large devices. In the Table 2, we observe that the MAPbI3 (M) device exhibits a wide spread in their PCEs, and the deviation increases with the increasing cell sizes. The MAPbI3 (M) devices with large size of 2.32 cm2 from the large perovskite films show an average PCE of 4.26% (Figure 8A and 8B) with a deviation of ± 1.06% for 50 cells, retaining only 30% of its initial performance. In contrast, for the device


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fabricated from multilayered perovskite compounds, both the device performances of (PEI)2(MA)6Pb7I22 and (PEI)2(MA)4Pb5I16 drop slightly with small deviation in large-size cells. The champion (PEI)2(MA)6Pb7I22 cell (2.32 cm2) presents a PCE of 8.77%, and the slight decrease of the PCE values in larger area can be attributed to the relatively large series resistance of electrodes. Moreover, the hysteresis effect[46] for the large-area devices of (PEI)2(MA)6Pb7I22 is also small, as shown in Figure 8C. The average PCEs obtained from the two opposite scan directions are 7.81% and 8.06%, respectively. Besides the uniform morphology, another favorable property of the 2D perovskite materials that benefits their potential application is their extremely high moisture stability. As shown in Figure 8D, both the (PEI)2(MA)6Pb7I22 and (PEI)2(MA)4Pb5I16 large cells show excellent stability without sealing and the PCE of (PEI)2(MA)4Pb5I16 only decreases by ~5% of its initial value after 500 hrs light soaking at short–circuit condition. This negligible degradation is generally consistent across 20 devices. In comparison, the MAPbI3 (M)-based cell degraded significantly fast, decreasing from its initial PCE by >50% after 5 day. Thus, it confirms that the inherent stability to moisture of the multilayered perovskite is obviously enhanced since the hydrophobicity of the large polymer cation may protect the inner perovskite from reaction with water. Moreover, the dense nature of the 2D perovskite films can further increase the stability by preventing direct contact of adventitious water with the perovskite.

Conclusions In summary, we have developed the fabrication of (PEI)2(MA)n−1PbnI3n+1 (n = 3, 5, 7) perovskite with intermediate multilayered structure along with their detailed characterization of crystallinity and optoelectronic properties. Polymer ammonium cation (PEI) has been adopted to facilitate electronic interaction between separated inorganic layers of the structure, which allows an enhancement in the charge transport within solar cells. Moreover, the multilayered perovskite provides a facile access to ultrasmooth, pinhole-free and highly dense thin films that show greater moisture resistance compared to their 3D MAPbI3 analogue. All of these particular strengths enable them more attracting for large-scale industrial implementation. The solar cell based on (PEI)2(MA)6Pb7I22 exhibits power conversion efficiency over 10% in small-area (0.04 cm2) and an impressive efficiency up to 8.77% with area of 2.32 cm2. And the corresponding



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cells are stable, retaining over 90% of the initial PCE remaining after 500 hours of light illumination, demonstrating the up-scalability of our 2D materials in fabricating efficient and stable perovskite film solar cells. Further improvements of device performance are expected by proper material/device architectural design.

Supporting Information Detailed methods and additional figures of the perovskite materials and device fabrication. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgements This work was supported by the National Natural Science Foundation of China (61504053, 51172103 and 61464006) and Natural Science Foundation of Jiangxi Province, China (20151BAB217023).


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Figure 1. Schematic representation of the stacking structures of multilayered perovskites based on different ammonium cations.

Figure 2. XRDs of bulk powder of MAPbI3 and (PEI)2(MA)n−1PbnI3n+1 perovskites, with the illustration (Right) of their respective diffraction planes.



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Figure 3. Cross-sectional SEM images of MAPbI3 and (PEI)2(MA)n−1PbnI3n+1 films.

Figure 4. (A) Images of various perovskite films before and after exposure to 50% relative humidity; (B) UV-visible absorption spectra of spin-coated MAPbI3 and (PEI)2(MA)n−1PbnI3n+1 films and the corresponding PL spectra (Inset); (C) Comparison of the PL decay of the three perovskites (with PMMA) on a longer time scale, with lifetimes τe quoted as the time taken to reach 1/e of the initial intensity. Time-resolved PL measurements are taken at the peak emission wavelength of the corresponding perovskite films.


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Figure 5. UPS spectra of MAPbI3 and (PEI)2(MA)n−1PbnI3n+1 layers (A) showing secondary cutoffs and (B) offset between WFs and IEs; (C) IPES spectra of the bottom of unoccupied states of MAPbI3 and (PEI)2(MA)n−1PbnI3n+1 perovskite films; (D) Energy band diagram of the solar cells using various perovskite materials.

2

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A Current Density(mA/cm )

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Figure 6. (A) Current–voltage (J-V) curves and (B) EQE spectra for the 2D (PEI)2(MA)n−1PbnI3n+1 perovskites and MAPbI3 (M) based devices in small area.



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Figure 7. The morphology of perovskite in large area: (A) optical image of MAPbI3 (M); optical images of (PEI)2(MA)6Pb7I22 in large scale (B) and small scale (C); (D) top-surface AFM image of (PEI)2(MA)6Pb7I22. The inset image of figure A shows the optical image of MAPbI3. The inset image of figure B shows the photograph of (PEI)2(MA)6Pb7I22 film.


2

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PCE Values (%)

(PEI)2(MA)6Pb7I22 (PEI)2(MA)4Pb5I16

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0.4

0.6

0.8

1.0

10

1.2

(PEI)2(MA)6Pb7I22

C

0.5

8.5

9.0

1.0

1.5

2

2.0

Cell Area (cm ) Area = 2.32 cm

1.0 0.8

MAPbI3 (M)

0.6

(PEI)2(MA)6Pb7I22 (PEI)2(MA)4Pb5I16

0.4 0.2 0.0

0 8.0

0.0

B

2

Normalized PCE (%)

10

7.5

(PEI)2(MA)4Pb5I16

1.2

Reverse scan 30 Forward scan (PEI)2(MA)6Pb7I22 2 20 Area = 2.32 cm

7.0

MAPbI3 (M)

5

0

Voltage (V) Counts (Device Number)

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Current Density(mA/cm )

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D 0

100

Device PCE (%)

200

300

400

500

Time (h)

Figure 8. (A) J–V curve for the (PEI)2(MA)n−1PbnI3n+1 perovskites and MAPbI3 (M) based devices in aperture area of 2.32 cm2; (B) Graph showing the corresponding PCE value changes of three materials as the device areas; (C) A histogram comparing the difference in the PCEs of large area solar cells obtained from scanning in the forward and reverse bias directions; (D) Stability of unsealed cells under simulated solar light (AM 1.5; 100 mW cm-2) during a shelf-life investigation for 500 h.



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Table 1 Performance of perovskite devices under AM 1.5G illumination (100 mW cm-2) with small-size cells (0.04 cm2). The fabrication procedure was similar for all devices in optimized condition. Device

Jsc (mA cm-2)

Voc (V)

FF

PCE (%)a

MAPbI3

16.80 ± 1.14

0.83 ± 0.04

0.52 ± 0.04

7.25 ± 0.94b (8.89)c

MAPbI3 (M)

19.22 ± 0.54

1.05 ± 0.02

0.71 ± 0.02

14.31 ± 0.52 (15.42)

(PEI)2(MA)6Pb7I22

13.12 ± 0.41

1.10 ± 0.02

0.65 ± 0.01

9.39 ± 0.42 (10.08)

(PEI)2(MA)4Pb5I16

10.22 ± 0.35

1.16 ± 0.01

0.59 ± 0.01

6.98 ± 0.36 (7.63)

(PEI)2(MA)2Pb3I10

6.63 ± 0.31 1.21 ± 0.01 0.53 ± 0.01 4.23 ± 0.33 (4.81) b Maximum PCE in the brackets; Error values represent the standard deviation of the mean of 50 devices. c The best device performance values of the PeSCs.

a

Table 2 Performance of perovskite devices under AM 1.5G illumination (100 mW cm-2) with small-size cells (2.32 cm2). The fabrication procedure was similar for all devices in optimized condition. Device

Jsc (mA cm-2)

Voc (V)

FF

PCE (%)a

MAPbI3 (M)

9.22 ± 0.94

0.94 ± 0.06

0.50 ± 0.04

4.26 ± 1.06b (5.82)c

(PEI)2(MA)6Pb7I22

11.74 ± 0.53

1.08 ± 0.02

0.63 ± 0.02

8.06 ± 0.47 (8.77)

(PEI)2(MA)4Pb5I16

9.72 ± 0.48 1.13 ± 0.02 0.57 ± 0.02 6.29 ± 0.42 (6.99) b Maximum PCE in the brackets; Error values represent the standard deviation of the mean of 50 devices. c The best device performance values of the PeSCs.

a


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Table of Content Multilayered Perovskite Materials Based on Polymeric-ammonium Cations for Stable Large-area Solar Cell Kai Yao, Xiaofeng Wang, Yun-xiang Xu, Fan Li, Lang Zhou


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