Carrier Transport Improvement of CH3NH3PbI3 Film by Methylamine

Subscriber access provided by University of Idaho Library

Article

The carrier transport improvement of CH3NH3PbI3 film by methylamine gas treatment Mingjia Zhang, Ning Wang, Shuping Pang, Qing Lv, Changshui Huang, Zhongmin Zhou, and Fuxiang Ji ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b10418 • Publication Date (Web): 31 Oct 2016 Downloaded from http://pubs.acs.org on November 2, 2016

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 Applied Materials & Interfaces 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 25

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 Applied Materials & Interfaces

The carrier transport improvement of CH3NH3PbI3 film by methylamine gas treatment Ming-Jia Zhang, Ning Wang, Shu-Ping Pang, Qing Lv, Chang-Shui Huang*, Zhong-Min Zhou and Fu-Xiang Ji Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P.R. China. KEYWORDS: Preferred orientation, Photovoltaic Efficiency, Mobility, Grain Size, Diffusion length

ABSTRACT: Recently, perovskite solar cells with high photovoltaic performance based on methyl ammonium lead halide have attracted great interest due to the superior physical properties of perovskite optical absorption layer. Here, we investigate the interface carrier transport properties of CH3NH3PbI3 film by applying the reported treatment with methylamine gas, to reveal the possible mechanism of high performance perovskite-sensitized solar cells results. It is found that the crystal structure and surface morphology are effectively improved by the room temperature repair of methylamine atmosphere. The preferred 110 orientation results in a slightly larger band gap, which may contribute to the better energy level matching and carrier transport. Further investigations on relaxation time and electron mobility confirm the significantly enhanced carrier diffusion length, revealing the important role of optimized

ACS Paragon Plus Environment

1


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 25

crystallization on charge transport properties, which may be helpful to seek high-powered perovskite solar cells by optimizing the perovskite synthetic process.

INTRODUCTION In recent years, the organolead halide perovskite has been considered as the most promising material in a new generation of solar cells due to its excellent performance such as large carrier mobility, long relaxation time and efficient light trapping.1-3 Since the first discovery of efficiency about 3.8 % in CH3NH3PbI3 perovskite solar cells,4 the highest efficiency in this system has been achieved to above 22 % in 2016.5 Theoretically, it is given that the efficiency limit of CH3NH3PbI3 perovskite solar cells is about 31 %,6 which is higher than that of commercialized silicon solar cell. Thus, much effort has always been down to improve the efficiency, such as optimizing the perovskite crystallinity and morphology, modulating the composition and doping, changing the device configuration and so on. Especially in 2015, postprocessing with raw material additive has been adopted to improve the perovskite film crystallinity and device performance. It has been reported that the methylamine gas induced defect-healing technique can be used to double the efficiency of one-step spin coating CH3NH3PbI3 perovskite solar cells to 15.1 %, which attracts much attention in defect-free organometal halide materials.7 Further, a solvent-bathing process is reported to prepare largegrain and high-crystallinity CH3NH3PbI3 films, and on this basis to realize over 15 % stabilized efficiency.8 Besides, excess PbI2 is also added into perovskite film to improve crystallinity and realize the PCE nearly 19 % from 16 %.9 Contrary to the TiO2-based perovskite solar cells, the methylamine gas is found to suppress the photoelectric conversion properties of the PEDOT:PSS-based solar cells due to chemically reduction of PEDOT:PSS films.10 Thus it will be interesting to investigate the regulatory mechanism for improved photovoltaic conversion


2

Page 3 of 25

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


properties with postprocessing, which is important for further optimizing the device performance. Another important key in perovskite solar cells with different synthetic process is the charge transport characteristic, which is a major factor affecting the device performance and closely related with perovskite crystal structure.11-12 Especially the carrier recombination and diffusion length, have been recognized crucial for device conversion efficiency.13 For example, the bimolecular recombination of free charges has been found the major decay mechanism for device applications.14 In CH3NH3PbI3-xClx, the diffusion lengths is greater than 1 µm, which is one order of magnitude greater than the absorption depth and thus becomes a critical parameter to optimize for more efficient devices.15 On the other hand, many reports to date have proven the importance of crystal structure on charge transport and photoconversion properties. The preferred (110) orientation of CH3NH3PbI3 is found to contribute to not only reduce trap density but also increase the open circuit voltage as well as the fill factor.16 The improved crystallinity of CH3NH3PbI3 film by solvent annealing is also confirmed favorable for electron transport property and photovoltaic performance.17 Besides, reduced defects and larger grain have also been reported important for high efficient perovskite solar cells.18 As for the CH3NH2 gasassistant repairing technique, the change of carrier diffusion length as well as perovskite absorber layer crystallization is still not clear, and thus a better explanation is necessary to reveal the inner relationship between crystal structure and carrier transport for device after postprocessing. In this paper, we investigate the influence of CH3NH2 gas treatment on perovskite crystallinity and carrier transport properties, and reveal its relationship with device performance. It is found that the crystal structure trends to preferred 110-orientation by CH3NH2 gas treating, which increases the band gap as well as carrier relaxation time efficiently. Based on the mobility


3


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 25

measurement, we also found the important role of intergranular scattering for enhanced carrier transfer characteristic. More importantly, the carrier diffusion length for CH3NH2 treated solar cell can achieve three times longer than that for the raw device, contributing to the improvement of photovoltaic conversion properties from 6.26 % to 14.9 %. These results reveal the inner relationship between efficiency and crystal structure, which can further guide us to explore more efficient perovskite solar cell experimentally. EXPERIMENTAL SECTION Fabrication and characterization of perovskite solar cells The 1:1 molar CH3NH3I and PbI2 were dissolved in anhydrous DMF to prepare 40 % CH3NH3PbI3 (MAPbI3) precursor. MAPbI3 films were spin-coated on TiO2-coated FTO glass at 4000 rpm and annealed at 100 oC for 15 min. Subsequently, parts of these films were placed in CH3NH2 gas at room temperature for 3 s to repair the defects based on the previous studies7, 19 (here we define the terminology “raw” and ”repaired” to refer the CH3NH3PbI3 materials as without or with the methylamine gas exposure.), and then all the films were coated with spiroOMETAD at 1500 rpm for 1 minute. Au electrodes were thermally evaporated on the surfaces to complete the fabrication of the perovskite solar cells. XRD patterns were recorded with a Bruker D8 X-Ray diffractometer. Uv-vis measurement was performed using the Hitachi U-4100 spectrometer. The morphology was investigated by AFM and SEM. The solar cell performance was measured under an AAA solar simulator with one-sun AM 1.5G illumination. The J-V curves were obtained by using a Keithley 2400 sourcemeter starting from -0.2 V to 1.2 V.


4

Page 5 of 25

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


FET device preparation and measurement The MAPbI3 precursor was spin-coated on surface oxidation silicon wafer, and then Au electrodes were deposited on the surface to fabricate the Au/MAPbI3/SiO2/Si device. The channel length and width were 100 µm and 3 mm respectively. Electrical measurements were performed on back-gated field effect transistors at room temperature in air using a Keithly 4200 Semiconductor Characterization System and Signatonc Probe Station. Impedance spectroscopy A Zahner electrochemical workstation (Zahner IM6) was used to carry out the Electrochemical Impedance Spectroscopy (EIS) measurements with different DC bias from 0 V to 1 V. The frequency of applied ac voltage perturbation was in the range from 4 MHz to 100 Hz with amplitude of 25 mV. Impedance data were analyzed using Z-View software. RESULTS AND DISCUSSION Figure 1a shows the x-ray diffraction pattern of the CH3NH3PbI3 (MAPbI3) film on the TiO2/FTO substrate without and with CH3NH2 gas repairing, respectively. Both diffraction patterns display much higher intensity for the (110) plane than other peaks for the plane (202), (312), (224), (314) and so on, which is marked in Figure 1a. Especially for the repaired film, the preferred (110) orientation is more obvious. We can define the relative peak intensity P(hkl) to describe the preferred orientation as fellow,20 () = () /Σ ()

(1)

where I(hkl) represents the intensity of (hkl) peak. The calculated relative change of preferred (110) orientation P(110) for the raw film and repaired film are 40.7 % and 59.5 % respectively,


5


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 25

Figure 1. (a) The XRD patterns of raw MAPbI3 film and methylamine gas repaired MAPbI3 film. (b), (c) Schematics of the MAPbI3 structure oriented along the (001) and (110) direction respectively. indicating that the repair process can significantly improve the crystallization orientation. Here, the schematics of the MAPbI3 crystal structure for the (001) and (110) orientation are also displayed in Figure 1b and c respectively. It has been reported that the dominating (110)-oriented

Figure 2. (a), (d) SEM micrographs of top surfaces of raw film and repaired film. (b), (e) The SEM cross-sectional images of mesoscopic PSCs with raw and repaired MAPbI3. (c), (f) AFM images of CH3NH3PbI3 film surfaces without and with CH3NH2 repairment.


6

Page 7 of 25

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


crystal structure may originate from the good structural matching between the halides of MAPbI3 layer and the titanium atoms of TiO2 layer21, thus we can draw a conclusion that CH3NH2 treatment can efficiently enhance this structural matching. Except for the crystal structure, the morphology of the two films is also investigated by SEM, which is shown in Figure 2a and d. It can be seen that the film surface of the raw film is composed of large aggregation, while for repaired film, at the same scale the film surface display a more smooth morphology with reduced voids or pinholes. Besides, the cross-section SEM shown in Figure 2b and e indicates that the film thickness is almost the same though the morphology varies obviously before and after methylamine gas treatment. AFM results indicate the surface roughness for repaired and raw CH3NH3PbI3 films are 109 nm and 16.9 nm respectively, which is shown in Figure 2c and f, confirming the improvement of surface morphology by CH3NH2 gas treatment, which may be due to more sufficient chemical reaction. Next, we measured high-resolution SEM and TEM22-23 in order to further clarify the change of crystallinity respectively. The average particle sizes shown by high-resolution SEM (see Figure S1 in supporting information) for the raw film and repaired film are 200 nm and 200-300 nm respectively, indicating the increased particle size by methylamine gas treatment. However, it should be noted that particle size is not grain size,24 thus we compare the TEM images (Figure S2) and find that the grain size of repaired film seems larger than that for the raw film. Furthermore, we determine the average grain size from the Williamson–Hall plots25 based on the XRD data (Figure S3), which are 48.7 nm and 72.4 nm for the raw and repaired film respectively. The increased grain size after CH3NH2 gas treatment means the reduction of grain boundary and thus also suggests optimized crystal structure. Figure 3 shows the J-V curves under 1 sun AM 1.5 G irradiation for the raw perovskite solar cell and the defect repaired device respectively. It can be seen that the raw solar cell presents


7


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 25

13.24 mA cm-2 of Jsc, 0.86 V of Voc and 58.68 of FF, while the repaired solar cell can present 19.3 mA cm-2 of Jsc, 1.06 V of Voc and 71.01 of FF, which is listed in the inset of Figure 3. Here, we also calculate the saturated photocurrent Jsc by IPCE (Figure S4), which are 11.98 and 18.35 mA/cm 2 respectively, further confirming the enhancement of saturation current after methylamine gas treatment. Most notably, 14.9 % PCE is obtained for the device with CH3NH2 gas repaired while the PCE for the raw device is only 6.26 %. The PSC device with CH3NH2 repaired MAPbI3 absorber layer displays more superior photoelectric properties, which is consistent with the early report. Both the larger Voc and FF indicate the improved carrier transport properties with lower recombination probability in repaired perovskite solar cell. Based on the single-diode model,26 we obtain the shunt resistance RSH by fitting the J-V curves, which is 1206 Ohm·cm 2 and 727 Ohm·cm 2 for repaired device and raw device respectively.

Figure 3. J-V characteristics of the PSCs with (a) raw and (b) repaired perovskite absorber layer respectively. Inset displays the schematic illustration of MAPbI3 perovskite hybrid solar cell.


8

Page 9 of 25

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


The increased RSH also suggests suppressed recombination at the interface between the perovskite and the HTM layer, which may be attributed to the improved crystallization such as preferred 110-orientation and larger grain size. To provide insight into the influence of absorber layer microstructure on the optical and electrical properties of the devices, we measured the ultraviolet-visible absorbance spectra for the two perovskite films with and without repairmen, as shown in Figure 4a. It can be seen that

Figure 4. (a) Uv-vis absorption spectra of raw and repaired perovskite films. (b), (c) The Kubelka–Munk spectrum for raw and repaired MAPbI3 films. (d) Energy level diagram of the perovskite solar cells.


9


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 25

both the films show the similar absorption band with slight discrepancy, while absorbance intensity for repaired MAPbI3 film is much higher than the raw film especially in the visible region 400 nm-760 nm. In order to obtain the difference in the band gaps, we transformed the absorbance spectrum to Kubelka-Munk spectrum, as shown in Figure 4b and c. Eg of the bare MAPbI3 films are gained as 1.564 eV and 1.595 eV for the raw and repaired device, respectively. This enhanced band gap is closely related with preferred (110) orientation indicated by XRD, since the density functional theory calculations has proven that the energy gap for (110) surface is larger than that for (001) or other surface.27 Besides, it has been reported that for Br-doped MAPbI3, the preferred 110-orientation is more obvious and meanwhile the valence band maximum (VBM) decreases significantly with nearly unchanged EF and conduction band minimum (CBM).28 Thus we can assume the Fermi energy and LUMO are nearly constant for our repaired MAPbI3 film, and the HOMO is reduced to support better energy level matching between MAPbI3 and HTM. Furthermore, we can give a qualitative schematic diagram of energy level in related device as shown in Figure 4d. It can be anticipated that the larger band gap for repaired MAPbI3 films is beneficial to charge transport due to better energy level matching. More importantly, this increasing band gap can suppress the direct recombination, such as decreasing Auger recombination rate,29 and thus enhance the recombination lifetime τ. In order to obtain the carrier relaxation characteristics, we performed electronic impedance spectroscopy (EIS) from 100 Hz to 4 MHz under illuminated conditions for our solar cell devices. The high-frequency time constant has been reported to use to provide a good approximation of the free-carrier lifetime within the PSC device.30 Figure 5a presents representative Nyquist plots at zero bias voltage for the raw and repaired MAPbI3/TiO2 films respectively. Carrier lifetime can be obtained from the angle frequency of characteristic peak fp, and calculated as τ=1/2πfp,31


10

Page 11 of 25

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


Figure 5. (a) Nyquist plots for perovskite solar cell devices with different MAPbI3 absorber layer at zero-bias. (b) Bias voltage dependent carrier relaxation time. which is 1.15 µs and 5.58 µs for the raw and repaired MAPbI3 films respectively. Besides, the impedance spectroscopies with different applied bias voltage were also measured to obtain the voltage dependent carrier lifetime, as shown in Figure 5b. Compared with the raw film, carrier lifetime for repaired MAPbI3 film shows a relatively weak decrease with increasing bias voltage, suggesting the excellent persistence characteristics of carrier diffusion. Though the measured bulk carrier lifetime may be underestimated due to the presence of surface charge recombination,32 we investigate the high-frequency time constant of raw and repaired devices with the same batch samples just intending to obtain the relative difference of carrier lifetime.


11


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 25

This enhanced carrier lifetime further confirm the influence of enlarged band gap on carrier diffusion discussed above, which also should be attributed to the preferred (110) orientation with CH3NH2 gas repairmen. Furthermore, to gain a deeper insight into the carrier transport properties, we also measured the mobility of MAPbI3 films by fabricating the thin film field effect transistor (FET) devices, as shown in Figure 6 a-c. The mobility at Vsd =1V was calculated as 10.03 cm2/V·s and 22.75 cm2/V·s for the raw MAPbI3 film and repaired film respectively. It is obvious that the mobility for repaired MAPbI3 film is much higher than the raw film, indicating more superior carrier transport characteristics. The reasons of increased mobility can be attributed to two aspects. Firstly, it has been calculated in theory that the mobility along (110)-orientation is larger than that along (001) or other directions.33 Secondly, the carrier migrates in crystalline grain faster than that across the grain boundary, 34 and thus both large grain size and reduced voids/pinholes can suppress the interface scattering coming from grain boundary or heterointerface between voids/pinholes and crystals. As for our FET device, the carriers migrate along the lateral, while the preferred (110) orientation is along the vertical direction, thus the enhanced mobility in repaired MAPbI3 film means that increased grain size as well as accompanying reduction of pinholes/voids rather than crystal orientation plays a more important role for carrier migration in our samples, which is sketched in Figure 6d in detail.


12

Page 13 of 25

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


Figure 6. (a) Schematic illustration of the FET device for the mobility measurement. (b), (c) Transfer output FET characteristics obtained at different VSD for raw and repaired MAPbI3 films. (d) Sketch of carrier scattering across the grain boundary in MAPbI3 films with small and large grain size respectively. Combining the measured mobility and lifetime mentioned above, we obtain the carrier diffusion length LD as LD = ( k BT µτ r / e)1/ 2

(2)

where kB, T and τr are Boltzmann constant, temperature and carrier lifetime.32 The calculated LD for repaired and raw films are 18.10 and 5.45 µm respectively, indicating the effectively improved carrier transport properties and suppressed recombination in PSCs with CH3NH2 gas treatment. Here it should be noted that both the diffusion length are larger than previous reports,


13


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 25

Table 1. Carrier transport properties for perovskite solar cells with and without CH3NH2 treatment.

Device

η (%)

Eg (eV)

Raw device

6.26

1.564

Repaired device

14.9

1.595

µ (cm2/V·s)

τ (µs)

Ld (µm)

10.03

1.15

5.45

22.75

5.58

18.10

since the charge diffusion length is closely related with film thickness and in thicker film above 300 nm it can be as long as several micrometers.35 All the carrier transport characteristics for raw device and repaired device are summarized in Table 1. Based on the analysis on relaxation time and mobility, the increased diffusion length in CH3NH2 repaired MAPbI3 can be ascribed to the optimization of crystal microstructure in lattice orientation and grain size, contributing to the carrier transport across the interfaces. Meanwhile, larger crystals with fewer surfaces and voids/pinholes possibly lower recombination at grain boundaries.31 Both these two reasons may be beneficial to enhance the photoelectric properties of CH3NH2 repaired perovskite solar cells. These results can not only help us deeply understand the regulatory mechanism in MAPbI3 film with postprocessing technology, but also promote the further process optimization to realize more efficient perovskite solar cell devices. CONCLUSIONS In conclusion, we investigated the photovoltaic conversion and interfacial carrier transport properties in methylamine repaired MAPbI3 film, and found that the carrier diffusion length can be dramatically increased to above three times as compared with the raw film before restoration. Based on the structural characterization, we found that the perovskite crystallization properties,


14

Page 15 of 25

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


such as preferred (110) orientation and enlarged grain size, are significantly improved in repaired film, which should be responsible for the enhanced relaxation time and charge mobility respectively. These results clarify the contribution of preferred 110-orientation and increased grain size on carrier transport characteristics, and further reveal the relationship between crystallization and device photovoltaic performance, which may help open a new route to explore high-efficiency perovskite solar cells. AUTHOR INFORMATION Corresponding Author * Email: [email protected] Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This study was supported by the “100Talents” program of the Chinese Academy of Sciences, the National Natural Science Foundation of China Youth Science Fund Project (Contract No. 21301184) and China Postdoctoral Science Foundation Funded Project (Contract No. 2016M592264). REFERENCES (1) Brenner, T. M.; Egger, D. A.; Kronik, L.; Hodes, G.; Cahen, D. Hybrid Organic-Inorganic Perovskites: Low-Cost Semiconductors with Intriguing Charge-Transport Properties. Nat. Rev. Mater. 2016, 1, 15007. (2) Kim, J.; Kim, G.; Back, H.; Kong, J.; Hwang, I. W.; Kim, T. K.; Kwon, S.; Lee, J. H.; Lee, J.; Yu, K.; Lee, C. L.; Kang, H.; Lee, K. High-Performance Integrated Perovskite and Organic Solar Cells with Enhanced Fill Factors and Near-Infrared Harvesting. Adv. Mater. 2016, 28, 31593165. (3) Lee, Y. H.; Luo, J.; Son, M. K.; Gao, P.; Cho, K. T.; Seo, J.; Zakeeruddin, S. M.; Gratzel, M.; Nazeeruddin, M. K. Enhanced Charge Collection with Passivation Layers in Perovskite Solar Cells. Adv. Mater. 2016, 28, 3966-3972.


15


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 25

(4) 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. (5) NREL Best Research-Cell Photovoltaic Efficiency Chart. https:// upload.wikimedia.org/wikipedia/commons/archive/3/35/20160317201049%21Best_ResearchCell_Efficiencies.png (accessed Apr 13, 2016). (6) Sha, W. E. I.; Ren, X.; Chen, L.; Choy, W. C. H. The efficiency limit of CH3NH3PbI3 perovskite solar cells. Appl. Phys. Lett. 2015, 106, 221104. (7) Zhou, Z.; Wang, Z.; Zhou, Y.; Pang, S.; Wang, D.; Xu, H.; Liu, Z.; Padture, N. P.; Cui, G. Methylamine-Gas-Induced Defect-Healing Behavior of CH3NH3PbI3 Thin Films for Perovskite Solar Cells. Angew. Chem. Int. Ed. Engl. 2015, 54, 9705-9709. (8) Yang, M.; Zhou, Y.; Zeng, Y.; Jiang, C. S.; Padture, N. P.; Zhu, K. Square-Centimeter Solution-Processed Planar CH3NH3PbI3 Perovskite Solar Cells with Efficiency Exceeding 15. Adv. Mater. 2015, 27, 6363-6370. (9) Roldan-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. (10) Liu, T. F.; Jiang, F. Y.; Tong, J. H.; Qin, F.; Meng, W.; Jiang, Y. Y.; Li, Z. F.; Zhou, Y. H. Reduction and Oxidation of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Induced by Methylamine (CH3NH2)-Containing Atmosphere for Perovskite Solar Cells. J. Mater. Chem. A 2016, 4, 4305-4311. (11) Shi, J.; Wei, H.; Lv, S.; Xu, X.; Wu, H.; Luo, Y.; Li, D.; Meng, Q. Control of Charge Transport in the Perovskite CH3NH3PbI3 Thin Film. Chem. Phys. Chem. 2015, 16, 842-847. (12) Zhang, B.; Zhang, M. J.; Pang, S. P.; Huang, C. S.; Zhou, Z. M.; Wang, D.; Wang, N.; Cui, G. L. Carrier Transport in CH3NH3PbI3 Films with Different Thickness for Perovskite Solar Cells. Adv. Mater. Interfaces 2016, DOI: 10.1002/admi.201600327. (13) Adhikari, N.; Dubey, A.; Khatiwada, D.; Mitul, A. F.; Wang, Q.; Venkatesan, S.; Iefanova, A.; Zai, J.; Qian, X.; Kumar, M.; Qiao, Q. Interfacial Study to Suppress Charge Carrier Recombination for High Efficiency Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 26445-26454. (14) Blancon, J. C.; Nie, W.; Neukirch, A. J.; Gupta, G.; Tretiak, S.; Cognet, L.; Mohite, A. D.; Crochet, J. J. The Effects of Electronic Impurities and Electron-Hole Recombination Dynamics on Large-Grain Organic-Inorganic Perovskite Photovoltaic Efficiencies. Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201505324. (15) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J.; 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. (16) Lian, J. R.; Wang, Q.; Yuan, Y. B.; Shao, Y. C.; Huang, J. S. Organic Solvent Vapor Sensitive Methylammonium Lead Trihalide Film Formation for Efficient Hybrid Perovskite Solar Cells. J. Mater. Chem. A. 2015, 3, 9146-9151. (17) Xiao, Z.; Dong, Q.; Bi, C.; Shao, Y.; Yuan, Y.; Huang, J. Solvent Annealing of Perovskiteinduced Crystal Growth for Photovoltaic-device Efficiency Enhancement. Adv. Mater. 2014, 26, 6503-6509. (18) Nie, W.; Tsai, H.; Asadpour, R.; Blancon, J.-C.; Neukirch, A. J.; Gupta, G.; Crochet, J. J.; Chhowalla, M.; Tretiak, S.; Alam, M. A. High-efficiency Solution-processed Perovskite Solar Cells with Millimeter-scale Grains. Science 2015, 347, 522-525.


16

Page 17 of 25

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


(19) Pang, S.; Zhou, Y.; Wang, Z.; Yang, M.; Krause, A. R.; Zhou, Z.; Zhu, K.; Padture, N. P.; Cui, G. Transformative Evolution of Organolead Triiodide Perovskite Thin Films from Strong Room-Temperature Solid-Gas Interaction between HPbI3-CH3NH2 Precursor Pair. J. Am. Chem. Soc 2016, 138, 750-753. (20) Malek, M. F.; Mamat, M. H.; Khusaimi, Z.; Sahdan, M. Z.; Musa, M. Z.; Zainun, A. R.; Suriani, A. B.; Md Sin, N. D.; Abd Hamid, S. B.; Rusop, M. Sonicated Sol–Gel Preparation of Nanoparticulate ZnO Thin Films with Various Deposition Speeds: The Highly Preferred c-axis (002) Orientation Enhances the Final Properties. J. Alloys Comp. 2014, 582, 12-21. (21) Mosconi, E.; Ronca, E.; De Angelis, F. First-Principles Investigation of the TiO2/Organohalide Perovskites Interface: The Role of Interfacial Chlorine. J. Phys. Chem. Lett. 2014, 5, 2619-2625. (22) Zhou, Y.; Vasiliev, A. L.; Wu, W.; Yang, M.; Pang, S.; Zhu, K.; Padture, N. P. Crystal Morphologies of Organolead Trihalide in Mesoscopic/Planar Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 2292-2297. (23) Zhou, Y.; Game, O. S.; Pang, S.; Padture, N. P. Microstructures of Organometal Trihalide Perovskites for Solar Cells: Their Evolution from Solutions and Characterization. J. Phys. Chem. Lett. 2015, 6, 4827-4839. (24) Liu, D.; Gangishetty, M. K.; Kelly, T. L. Effect of CH3NH3PbI3 Thickness on Device Efficiency in Planar Heterojunction Perovskite Solar Cells. J. Mater. Chem. A 2014, 2, 1987319881. (25) Patterson, A. L. The Scherrer Formula for X-Ray Particle Size Determination. Phys. Rev. 1939, 56, 978. (26) Zhang, C.; Zhang, J.; Hao, Y.; Lin, Z.; Zhu, C. A Simple and Efficient Solar Cell Parameter Extraction Method from a Single Current-Voltage Curve. J. Appl. Phys. 2011, 110, 064504. (27) Haruyama, J.; Sodeyama, K.; Han, L.; Tateyama, Y. Termination Dependence of Tetragonal CH3NH3PbI3Surfaces for Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 2903-2909. (28) Li, C.; Wei, J.; Sato, M.; Koike, H.; Xie, Z. Z.; Li, Y. Q.; Kanai, K.; Kera, S.; Ueno, N.; Tang, J. X. Halide-Substituted Electronic Properties of Organometal Halide Perovskite Films: Direct and Inverse Photoemission Studies. ACS Appl. Mater. Interfaces 2016, 8, 11526-11531. (29) Metzger, W. K.; Wanlass, M. W.; Ellingson, R. J.; Ahrenkiel, R. K.; Carapella, J. J. Auger Recombination in Low-Band-Gap N-Type InGaAs. Appl. Phys. Lett. 2001, 79, 3272. (30) Pascoe, A. R.; Duffy, N. W.; Scully, A. D.; Huang, F.; Cheng, Y.-B. Insights into Planar CH3NH3PbI3 Perovskite Solar Cells Using Impedance Spectroscopy. J. Phys. Chem. C 2015, 119, 4444-4453. (31) Bisquert, J.; Fabregat-Santiago, F.; Mora-Sero, I.; Garcia-Belmonte, G.; Gimenez, S. Electron Lifetime in Dye-Sensitized Solar Cells: Theory and Interpretation of Measurements. J. Phys. Chem. C 2009, 113, 17278-17290. (32) Dong, Q. F.; Fang, Y. J.; Shao, Y. C.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. S. ElectronHole Diffusion Lengths > 175 µm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347, 967-970. (33) Wang, Y. W.; Zhang, Y. B.; Zhang, P. H.; Zhang, W. Q. High Intrinsic Carrier Mobility and Photon Absorption in the Perovskite CH3NH3PbI3. Phys. Chem. Chem. Phys. 2015, 17, 1151611520. (34) Oga, H.; Saeki, A.; Ogomi, Y.; Hayase, S.; Seki, S. Improved Understanding of the Electronic and Energetic Landscapes of Perovskite Solar Cells: High Local Charge Carrier


17


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 25

Mobility, Reduced Recombination, and Extremely Shallow Traps. J. Am. Chem. Soc. 2014, 136, 13818-13825. (35) Li, Y.; Yan, W.; Li, Y.; Wang, S.; Wang, W.; Bian, Z.; Xiao, L.; Gong, Q. Direct Observation of Long Electron-Hole Diffusion Distance in CH3NH3PbI3 Perovskite Thin Film. Sci. Rep. 2015, 5, 14485.


18

Page 19 of 25

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


Table of Contents Graphic and Synopsis


19


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

Figure1 114x69mm (300 x 300 DPI)


Page 20 of 25

Page 21 of 25

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


Figure 2 763x400mm (72 x 72 DPI)



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

Figure3 62x93mm (300 x 300 DPI)


Page 22 of 25

Page 23 of 25

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


Figure 4 213x160mm (300 x 300 DPI)



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

Figure5 175x248mm (300 x 300 DPI)


Page 24 of 25

Page 25 of 25

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


Figure 6 151x111mm (300 x 300 DPI)


Carrier Transport Improvement of CH3NH3PbI3 Film by Methylamine

Recommend Documents