In Situ Identification of Photo- and Moisture-Dependent Phase

Subscriber access provided by Fudan University

Letter

In-situ Identification of Photo- and MoistureDependent Phase Evolution of Perovskite Solar Cell Bo-An Chen, Jin-Tai Lin, Nian-Tzu Suen, Che-Wei Tsao, Tzu-Chi Chu, Ying-Ya Hsu, Ting-Shan Chan, Yi-Tsu Chan, Jye-Shane Yang, Ching-Wen Chiu, and Hao Ming Chen ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.6b00698 • Publication Date (Web): 09 Jan 2017 Downloaded from http://pubs.acs.org on January 10, 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 Energy Letters 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 21

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 Energy Letters

In-situ Identification of Photo- and MoistureDependent Phase Evolution of Perovskite Solar Cell Bo-An Chen,1§ Jin-Tai Lin,1§ Nian-Tzu Suen,1§ Che-Wei Tsao,1 Tzu-Chi Chu,1 Ying-Ya Hsu,2 Ting-Shan Chan,2 Yi-Tsu Chan,1 Jye-Shane Yang,1 Ching-Wen Chiu1 and Hao Ming Chen1* 1Department of Chemistry, National Taiwan University, Taipei 106, Taiwan 2

National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan

*Corresponding author: Hao Ming Chen ([email protected]) §

Authors contributed equally to the work

ABSTRACT: Photovoltaic performance of perovskite solar cell is observed to decrease with increasing humidity, which might be attributed to the formation of hydrated intermediates and further leads to a decrease in extraction of photo-carriers. However, direct evidence of the interplay between the perovskite layer and the photovoltaic performance under operating conditions (consecutive illuminating) has not yet been reported. Herein, we investigated the degradation of perovskite solar cell under operating situations through in-situ X-ray diffraction and in-situ X-ray absorption spectroscopies, which revealed that lead hydroxide iodide (PbIOH), a new phase that hasn’t previously identified as the degradation product of perovskite solar cell, was formed as end decomposition product inside the cell. The formation of PbIOH could break the interface inside and be the key reason behind the problem of reduced cell life. This work

ACS Paragon Plus Environment

1

ACS Energy Letters

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 21

illustrates that in operando direct observation of the photo- and moisture-induced effects can provide needed insights toward realizing stable perovskite solar cells.

TOC GRAPHICS

The use of fossil fuels has been revealed to be a main reason for carbon dioxide emission and becomes a globally environmental problem, and thence the increasing demands for energy source push the pursuit of renewable energy sources to substitute for fossil-fuel.1-4 An ideal way to reduce consumption of fossil fuels is to convert solar energy into electricity and/or chemical fuels. A demand for cheap and easily-fabricated solar panels has emerged, and consequently several strategies such as quantum dot, organic, inorganic-organic, and dye-sensitized solar cells have been developed to achieve this goal.1-4 Since the initial work of Kojima et al., 5 photovoltaic devices based on lead halide perovskite have experienced incredibly rapid improvement in performance with power conversion efficiencies (PCE) rising to 22 % within six years.6-16 Methylammonium lead halide perovskite offers promising potential as a breakthrough material for next generation solar cell devices owing to several critical parameters of perovskite materials


2

Page 3 of 21

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 Energy Letters

including high absorption coefficient, easy fabrication, low charge-carrier recombination rates, and long electron-hole diffusion length of more than hundred micrometers.13,17-19 One important factor in the development of perovskite solar cell, which has proven to be a critical issue in commercializing this exciting new photovoltaic technology is humidity, since CH3NH3PbI3 film rapidly decomposes upon exposure to moisture. Several reports have revealed that the CH3NH3PbI3 perovskite film underwent a rapid decomposition to PbI2 with a color change from brown to yellow, thereby leading to a considerable decline in photovoltaic performance.20-22 In addition to PbI2 phase, Christians et al. have studied the interaction of CH3NH3PbI3 film with moisture using femtosecond transient absorption spectroscopy, and found that the hydration product of CH3NH3PbI3 caused a decrease in absorption of visible light.23 As mentioned above, several approaches have been developed to investigate the degradation process and phase change of perovskite material after exposing to moisture. In practical conditions, perovskite material in a common photovoltaic cell is sandwiched between electron/hole transporting materials and undergoes photo-excitation in a confined environment. Without considering the effects of electron/hole transporting layers and operating the photovoltaic device under practical condition, it is difficult to provide a meaningful insight of the decomposition processes/mechanisms for future commercialization. With the aim of expounding such complicated photo- and moisture-induced degradation processes, as inferred from recent reports, 24-27

we need a tool that allows realizing an in-situ visualization of this abrupt change in the

perovskite layer inside solar cell devices during realistic operating conditions. Recently, several works involving in-situ experiments that aim to investigate the degradation mechanism of lead perovskite solar cell have been reported.28-31 These experiments provided vital information especially for revealing hydrated phases (mono- and/or di-hydrated), which


3

ACS Energy Letters

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 21

could be the main cause for the failing of the lead perovskite solar cell. To the best of our knowledge, however, there is no in-situ observation of the light absorber (perovskite) inside a practical cell (with a whole construction) under operating conditions (with consecutive light illumination and moisture) to provide the direct correlation between the transformation of perovskite layer and the photovoltaic performance. In the present study, we performed both insitu X-ray diffraction and X-ray absorption spectroscopies to investigate the phase evolution and the electronic state of the perovskite layer as a function of time. The environment of perovskite layer would be very similar to a practical device in use, which allows us to directly account for the chemical state and structural change during operating. In order to study the degradation mechanism of lead-halide perovskite solar cell, a typical layer-by-layer construction of lead-halide perovskite solar cell was prepared and their structure was shown in the inset of Figure 1a. It is noticed that the CH3NH3PbI3 perovskite is polymorphic,32 and two forms (α- and β-form) of CH3NH3PbI3 exist (Figure SI-1).33 The structure and purity of as-synthesized CH3NH3PbI3 powder before and after spin-coating on compact TiO2/FTO substrate were carefully examined via X-ray diffraction technique. It clearly showed that the structure of as-synthesized CH3NH3PbI3 powder and that of deposited CH3NH3PbI3 layer (after spin-coating) were identical and confirmed to be β-CH3NH3PbI3 phase. In addition, the powder XRD pattern showed no feature of impurity, suggesting high purity of the prepared solar cell (Figure 1b). The current density (J)-voltage (V) curve of the prepared lead-halide perovskite solar cell exhibited a short-circuit current (Jsc) of 20.3 mA/cm2, an open circuit voltage (Voc) of 1.045 V and a fill factor (FF) of 67.7%. The calculated power conversion efficiency (PCE) displayed a performance of 14.4%, which was similar to most of the lead-halide solar cell


4

Page 5 of 21

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 Energy Letters

reported to date.34-36 The corresponding hysteresis and air stability measurements were included in Figure SI-2 as well. A schematic and real picture of home-made measuring device for in-situ X-ray diffraction study the cell degradation mechanism were illustrated in Figure 2a and 2b, respectively. The cell was back illuminated, and the photogenerated current and voltage were measured via two gold probes (Figure 2c), in which the structural information of the cell was detected by X-ray diffraction technique simultaneously. The relative humidity of 65 % was set to simulate a typical subtropical climate. The contour plot of two-dimensional (2-D) X-ray diffraction pattern and the cell performance along time evolution at the desired humidity were shown in Figure 2d. A distinct three stages of degradation of the prepare perovskite solar cell could be identified. In stage I, after operating for 5 hours, the Fill Factor (FF) remarkably dropped by ~25 % and resulted in lowering the PCE down to around 73 % (initial PCE was set as 100 %) while both Jsc and Voc showed a slight change below 10 %. After the first PCE drop of ~27 %, the cell performance was then stabilized until 10 hours. Although no significant signal of other phase was observed except diffraction peaks from CH3NH3PbI3 layer during stage I, it was possible that the decrease of cell performance could be attributed to the formation of hydrated CH3NH3PbI3 (i.e. CH3NH3PbI3H2O). It is noticed that the hydrate phase (CH3NH3PbI3 H2O) could transfer back to CH3NH3PbI3 by heat treatment (Figure SI-3) and the cell efficiency could be restored (although not fully recovered).28 However, judging by the intensity of the powder XRD pattern for CH3NH3PbI3, this reformed CH3NH3PbI3 showed poor crystallinity which could be one of the reasons for the cell performance decay in stage I. In the in-situ XRD experiment, the cell was consecutively illuminated, which could have a similar effect to the heat treatment. Under this


5

ACS Energy Letters

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 21

effect, the CH3NH3PbI3H2O could either transfer back to CH3NH3PbI3 or subsequently be decomposed to PbI2 and caused the deterioration of the cell performance (stage I). The cell performance remained stable for 10 hours, where another significant loss of PCE was observed by about 20% (stage II). At this stage, the Jsc and Voc were observed to drop by ~18% and ~7%, respectively, while there was no considerable drop in FF. The in-situ XRD experiment clearly indicated the formation of PbI2 phase. Accompanying the formation of PbI2 phase, the signal from CH3NH3PbI3 phase gradually decreased, suggesting that CH3NH3PbI3 phase converted into PbI2 and further led to a decrease in light capturing material (CH3NH3PbI3) and resulted in the lower light absorption of the device (Figure SI-4). For this reason, a remarkable drop in Jsc was present at this stage and finally a ~ 33% PCE of the initial performance was obtained after 23 hours of operation. This observation is consistent with previous reports on the decomposition process of CH3NH3PbI3 into PbI2 under moist conditions.21,37-40 In spite of the formation of PbI2, the cell could still maintain a stable performance for more than 10 hours. This effect was even more profound when the cell was operated at relative humidity (R.H.) around 40 %, where the efficiency of the cell could be stabilized for more than 70 hours (Figure SI-5). This phenomenon, which was in line with the works from Chen et al. and Petrus et al., strongly suggested that the formation of PbI2 could act as a passivation layer on the surface of CH3NH3PbI3 layer and be able to protect the underlying CH3NH3PbI3 layer from further exposure to moisture.34, 41 After 23 hours of operation (stage III), there was a great drop in the cell performance (PCE%) with nearly 2% of initial value. Accompanying this phenomenon, an unknown phase (later on it was identified as PbIOH) was formed, which had never been reported as a degradation product of Pb-perovskite layer (stage III). Notably, the possibility that the formation of PbIOH was


6

Page 7 of 21

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 Energy Letters

caused by long-term exposure of X-ray (in-house XRD measurement) could be ruled out here, because the perovskite solar cell under identical duration of X-ray exposure could perform approximately 60% of initial value in PCE within our measured duration (40 hours), as illustrated in Figure SI-6. To identify this unknown phase, a full-spectrum Rietveld refinement to refine the powder XRD pattern of the cell at final stage (III) was performed. The corresponding diffraction peaks of this unknown phase matched perfectly with PbIOH of tetragonal space group Pnma (Figure 3a),42 and the corresponding fitting parameters were list in Table 1 and table SI-1. The whole-pattern fitting yielded a satisfactory Rwp value of 11.53% and goodness of fit (GOF) of 1.58. Another control experiment with a harsher condition (R.H. around 90 %) was conducted to ascertain the effect of moisture upon the formation of this unknown phase (Figure 3b). This PbIOH phase was quickly formed within 3 hours, indicated that the high humidity would facilitate the phase transformation from PbI2 to this PbIOH phase. In addition to the structural characterization of PbIOH, more physical properties such as XPS and UV-vis spectra of PbIOH were provided in Figure 3c and Figure SI-7. Field-emission scanning electron microscope (FE-SEM) of the top views and the crosssection views of the CH3NH3PbI3, PbI2 and PbIOH were displayed in Figure 3d, 3e, and 3f, respectively. In Figure 3d, one could readily identify the individual layers within the lead halide perovskite solar cell, and these layers were adhered with each other closely without obvious cracks or pinholes in the interfaces and layers. Moreover, the perovskite layer seemed to be homogenous and dense, suggesting a good quality of the film without obvious defects. After the cell was operated in a period of time (stage II), a significant change occurred in the perovskite layer where various irregularly particles were generated, while the rest parts still remained initial


7

ACS Energy Letters

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 21

situations (Figure 3e). The dramatic change of morphology has supported the observation from in-situ X-ray diffraction of the emergence of PbI2 phase. At the final stage of the lead-halide perovskite solar cell (stage III), the morphology has further changed from irregular shape (PbI2) to a strip-like conformation (Figure 3f), suggesting another phase transformation has been occurred and is in accordance with the finding in the in-situ X-ray diffraction pattern (formation of PbIOH). We noted that once the PbIOH phase was formed in the CH3NH3PbI3 layer, the interfaces between spiro-MeOTAD/CH3NH3PbI3/compact TiO2 were considerably interrupted and became discontinuous due to the formation of various large particles (Figure 3f). This phenomenon might result in a disrupted junction and further interfered with the charge-carrier transportation among interfaces. It is worth mentioning that the degradation of CH3NH3PbI3 to PbIOH seems to happen only in the presence of spiro-MeOTAD (Figure SI-8) regardless of Li salt is included in spiro-MeOTAD or not (Figure SI-9). This result suggests that spiro-MeOTAD seems to be a key for the formation of PbIOH, which motivates us to further investigate the influence of hole transport material. As shown in Figure SI-10, the device with hole transporting materials, P3HT and PTAA, the perovskite layers would readily transform to PbI2 after 40 hrs at R.H. 65 %. Interestingly, in the case of device with PMMA, the lead perovskite layer remains unchanged within the same time frame. This observation suggests that PMMA is a good water resist layer and can effectively protect perovskite solar cell from moisture, which is in good agreement with the finding from Prof. Snaith’s group.43 We did observe the device with PTAA, where the perovskite would transfer to PbI2 faster than the device with P3HT. Nevertheless, comparing to the device with spiro-OMeTAD, there is no sign of formation of PbIOH in these devices (with using PMMA, P3HT and PTAA) within the same time. However, we must note here that PbI2 in these devices (with P3HT and PTAA) may possibly transfer to PbIOH in a long-


8

Page 9 of 21

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 Energy Letters

term treatment (> 40 hrs). These findings suggest that replacing spiro-MeOTAD may be an effective way to improve the durability of perovskite solar cells since that may inhibit the formation of PbIOH. This result accounts for several recently reported works, in which the replacing spiro-MeOTAD with other hole-transfer layer such as carbon electrode or NiO would greatly enhance the lifetime of perovskite solar cell (due to the lack of formation of PbIOH).44,45 To further investigate the effects of light illumination and moisture toward electronic state changes of Pb ions in CH3NH3PbI3 (with presence of spiro-MeOTAD member) a reaction cell was designed and was shown in Figure 4a and 4b. In the case of light illumination without exposing to moisture (R.H. ~10%), the XANES spectra of Pb LIII edge exhibited an almost identical feature in measurement duration over 210 mins, indicating that CH3NH3PbI3 was fairly stable toward photo-excitation (Figure 4c). On the other hand, if CH3NH3PbI3 was exposed to moist situation at dark condition for 90 mins, an apparent absorption feature as illustrated in Figure 4d was observed at approximately 13,045 eV. This could be attributed to the formation of PbI2 and/or hydrate (CH3NH3PbI3•H2O) since the XANES spectra of PbI2 and hydrate phase (CH3NH3PbI3•H2O) were quite similar. Nevertheless, the color of cell turned into bright yellow, which strongly implied the formation of PbI2 (the color of PbI2 is bright yellow while the color of hydrate phase is more close to pale yellow). This assumption of PbI2 formation has further been clarified and confirmed by the X-ray diffraction studies, in which the major phase was indeed PbI2 rather than CH3NH3PbI3•H2O. The above experiment has shown that PbI2 phase would be generated in prolonged exposure to moisture in a dark condition. Once the simulated sunlight was turned on to illuminate the perovskite solar cell which has been exposed to moisture for 210 min with showing the presence of PbI2, the XANES spectra of Pb LIII edge (Figure 4e) showed a remarkable peak that indicated the formation of a species attributed to PbIOH. Keeping this


9

ACS Energy Letters

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 21

perovskite solar cell under simulated sunlight for 150 min in a moist environment, one could observe an increasing intensity of peak attributed to lead hydroxide iodide (PbIOH) and simultaneously a decreasing intensity of peak corresponding to the PbI2. It was worth noting that the existence of an isosbestic point indicated a clean transformation between PbI2 and lead hydroxide iodide (PbIOH) phase. The reference spectrum for all the mentioned phases here are shown in Figure 4f. Using the in-situ X-ray absorption, we were able to conclude that the PbI2 clearly underwent an irreversible transformation into lead hydroxide iodide (PbIOH) in the presence of sunlight and moisture. This light-induced transformation was also confirmed by above control experiment, where no PbIOH phase was present except for PbI2 and CH3NH3PbI3 ・H2O even though the perovskite cell was stored in the condition of R.H. 65% without consecutively illuminating for more than 40 hours (Figure SI-6(b)). As a result, we can conclude that, in device conditions (in the presence of illuminating and moisture), the CH3NH3PbI3 layer reacts with water to form CH3NH3PbI3•H2O and leads to a drop in FF rather than Voc and Jsc in early stage. The formation of CH3NH3PbI3•H2O intermediate showed a feature of reversible nature between hydrate of CH3NH3PbI3•H2O and CH3NH3PbI3 phase, suggesting that perovskite absorber remained stable and was able to perform at an acceptable efficiency even if perovskite layer was exposed to a low amount of moisture. Once the CH3NH3PbI3•H2O/CH3NH3PbI3 intermediates were exposed to more moisture, the CH3NH3PbI3•H2O would irreversibly decompose to PbI2 first and caused a deterioration of the device, in which the formation of PbI2 resulted in a decrease in both Jsc and Voc owing to degrading of CH3NH3PbI3. The PbI2 phase would successively decompose to PbIOH phase due to the existing of illumination and moisture. The detail of crystal structures and possible degradation paths for those mentioned phases were provided in supporting information. (Figure


10

Page 11 of 21

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 Energy Letters

SI-11). In addition to light illumination and moisture, the presence of spiro-MeOTAD is another key factor to facilitate this transformation to generate PbIOH. Once the PbIOH phase was generated within device, the cell would become invalid since the formation of PbIOH would destroy interface between electron and hole transport layers and further break down the junction inside the cell.


11

ACS Energy Letters

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 21

Figures and captions.

Figure 1. (a) The current density (J)−voltage (V) curve and the schematic representation of layer-by-layer architecture lead-halide perovskite solar cell. (b) The X-ray diffraction patterns of as-synthesized CH3NH3PbI3 powder and CH3NH3PbI3 layer after spin-coating on compact TiO2/FTO substrate.


12

Page 13 of 21

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 Energy Letters

Figure 2. (a) Schematic illustration of in-situ X-ray diffraction experiment set up. (b) Photograph of in-situ X-ray diffraction setup with designed cell. (c) Close look of schematic representation of the lead halide perovskite solar cell, the direction of the flows for the photogenerated electron (red sphere) and hole (green sphere) were indicated (black arrow) as well. (d) Contour plots of in-situ X-ray diffraction measurement and the corresponding cell performance along time evolution at R.H. 65 % and 25 °C under nitrogen environment.


13

ACS Energy Letters

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 21

Figure 3. (a) Full-spectrum Rietveld refinement of lead halide perovskite solar cell in final stage. The theoretical diffraction peaks for Au, FTO, PbI2 and PbIOH were marked as green, orange, red and dark blue rectangular bars at the bottom, respectively. (b) Contour plots of in-situ X-ray diffraction measurement at R.H. 90 % and 25 °C under nitrogen environment. (c) XPS spectra of PbIOH from Pb and I. FE-SEM images of top views and the cross-section views of relevant phases (d) CH3NH3PbI3, (e) PbI2, and (f) PbIOH formed in lead halide perovskite solar cell at different stages.


14

Page 15 of 21

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 Energy Letters

Figure 4. (a, b) The schematic illustration and real picture of in-situ X-ray absorption experiment set-up. The X-ray absorption spectra of lead halide perovskite solar cell at different condition as time evolved. (c) illuminating only, (d) humid gas (nitrogen) only, (e) humid gas (nitrogen) and then illuminating, and (f) comparison with reference spectra.


15

ACS Energy Letters

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 21

Table 1. Crystallographic data and refinement parameters for PbIOH. Empirical formula

PbIOH

Fw, g mol-1

351.108

Crystal system

Orthorhombic

Space group

Pnma (No. 62)

λ, Å

1.54056

T, K

300(5)

a, Å

7.81152(68)

c, Å

4.21177(89)

V, Å3

10.45823(84)

GOF on F2

1.58

RP

0.0792

RWP

0.01153


16

Page 17 of 21

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 Energy Letters

ASSOCIATED CONTENT Supporting Information The Supporting Information includes experimental method, XRD patterns of α- and βCH3NH3PbI3 phase, hysteresis and air stability measurements of the prepared lead perovskite solar cell, phase transformation experiment between CH3NH3PbI3•H2O and CH3NH3PbI3 with spiro-MeOTAD, time-dependent UV-vis measurement of prepared lead perovskite solar cell, contour plot of in-situ X-ray diffraction measurement and the corresponding cell performance along time evolution at R.H. 40 % and 65 % conditions w/o consecutively illuminating and corresponding XRD patterns, UV-vis spectrum of PbIOH, phase stability experiment of βCH3NH3PbI3 w/o spiro-MeOTAD layer and with PMMA, P3HT and PTAA, the influence of Lisalt in the spiro-MeOTAD toward phase degradation and crystal structural evolution from CH3NH3PbI3 to PbIOH. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ACKNOWLEDGMENT We acknowledge support from the Ministry of Science and Technology, Taiwan (Contracts No. MOST 104-2119-M-002-005 and MOST 104-2113-M-002-011-MY2).


17

ACS Energy Letters

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 21

REFERENCES (1) Dresselhaus, M. S.; Thomas, I. L., Alternative energy technologies. Nature 2001, 414, 332337. (2) Gray, H. B., Powering the planet with solar fuel. Nat. Chem. 2009, 1, 7-7. (3) Listorti, A.; Durrant, J.; Barber, J., Artificial photosynthesis: solar to Fuel. Nat. Mater. 2009, 8, 929-930. (4) Anscombe, N., Solar cells that mimic plants. Nat. Photon. 2011, 5, 266-267. (5) 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. (6) Zhang, W.; Saliba, M.; Moore, D. T.; Pathak, S. K.; Hörantner, M. T.; Stergiopoulos, T.; Stranks, S. D.; Eperon, G. E.; Alexander-Webber, J. A.; Abate, A.; Sadhanala et al., Ultrasmooth organic–inorganic perovskite thin-film formation and crystallization for efficient planar heterojunction solar cells. Nat. Commun. 2015, 6, 6142. (7) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I., Highperformance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 2015, 348, 1234. (8) Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K. et al. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals. Science 2015, 347, 519. (9) Nie, W.; Tsai, H.; Asadpour, R.; Blancon, J.-C.; Neukirch, A. J.; Gupta, G.; Crochet, J. J.; Chhowalla, M.; Tretiak, S.; Alam, M. A. et al., High-efficiency solution-processed perovskite solar cells with millimeter-scale grains. Science 2015, 347, 522. (10) Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-b.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y., Interface engineering of highly efficient perovskite solar cells. Science 2014, 345, 542. (11) Sum, T. C.; Mathews, N., Advancements in perovskite solar cells: photophysics behind the photovoltaics. Energy Environ. Sci. 2014, 7, 2518-2534. (12) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I., Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells. Nat. Mater. 2014, 13, 897903. (13) Green, M. A.; Ho-Baillie, A.; Snaith, H. J., The emergence of perovskite solar cells. Nat. Photon. 2014, 8, 506-514. (14) Gao, P.; Gratzel, M.; Nazeeruddin, M. K., Organohalide lead perovskites for photovoltaic applications. Energy & Environmental Science 2014, 7, 2448-2463.


18

Page 19 of 21

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 Energy Letters

(15) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J., Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science 2012, 338, 643. (16) NREL, Best Research-Cell Efficiencies www.nrel.gov/ncpv/images/efficiency_chart.jpg 2015. (17) 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. (18) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J., Electron-hole diffusion lengths > 175 μm in solution-grown CH3NH3PbI3 single crystals. Science 2015, 347 (6225), 967. (19) 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. et al., Efficient inorganic-organic hybrid heterojunction solar cells containing perovskite compound and polymeric hole conductors. Nat. Photon. 2013, 7, 486-491. (20) Zhao, Y.; Zhu, K., Optical bleaching of perovskite (CH3NH3)PbI3 through room-temperature phase transformation induced by ammonia. Chem. Commun. 2014, 50, 1605-1607. (21) Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I., Chemical management for colorful, efficient, and stable inorganic–organic hybrid nanostructured solar cells. Nano Letters 2013, 13, 1764-1769. (22) Bass, K. K.; McAnally, R. E.; Zhou, S.; Djurovich, P. I.; Thompson, M. E.; Melot, B. C., Influence of moisture on the preparation, crystal structure, and photophysical properties of organohalide perovskites. Chem. Commun. 2014, 50, 15819-15822. (23) Christians, J. A.; Miranda Herrera, P. A.; Kamat, P. V., Transformation of the excited state and photovoltaic efficiency of CH3NH3PbI3 perovskite upon controlled exposure to humidified air. J. Am. Chem. Soc. 2015, 137, 1530-1538. (24) Kirshenbaum, K.; Bock, D. C.; Lee, C.-Y.; Zhong, Z.; Takeuchi, K. J.; Marschilok, A. C.; Takeuchi, E. S., In situ visualization of Li/Ag2VP2O8 batteries revealing rate-dependent discharge mechanism. Science 2015, 347, 149. (25) Tung, C.-W.; Hsu, Y.-Y.; Shen, Y.-P.; Zheng, Y.; Chan, T.-S.; Sheu, H.-S.; Cheng, Y.-C.; Chen, H. M., Reversible adapting layer produces robust single-crystal electrocatalyst for oxygen evolution. Nat. Commun. 2015, 6, 8106. (26) Bergmann, V. W.; Weber, S. A. L.; Javier Ramos, F.; Nazeeruddin, M. K.; Grätzel, M.; Li, D.; Domanski, A. L.; Lieberwirth, I.; Ahmad, S.; Berger, R., Real-space observation of unbalanced charge distribution inside a perovskite-sensitized solar cell. Nat. Commun. 2014, 5, 5001.


19

ACS Energy Letters

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 21

(27) Chen, Q.; Mao, L.; Li, Y.; Kong, T.; Wu, N.; Ma, C.; Bai, S.; Jin, Y.; Wu, D.; Lu, W. et al., Quantitative operando visualization of the energy band depth profile in solar cells. Nat. Commun. 2015, 6, 7745. (28) Leguy, A. M. A.; Hu, Y.; Campoy-Quiles, M.; Alonso, M. I.; Weber, O. J.; Azarhoosh, P.; van Schilfgaarde, M.; Weller, M. T.; Bein, T.; Nelson, J. et al., Reversible hydration of CH3NH3PbI3 in films, single crystals, and solar cells. Chem. Mater. 2015, 27, 3397-3407. (29) Song, Z.; Abate A.; Watthage S.; Liyanage G. K.; Phillips A.; Steiner U.; Grätzel, M.; Heben M., Perovskite solar cell stability in humid air: partially reversible phase transitions in the PbI2-CH3NH3I-H2O system. Adv. Energy Mater. 2016, 6, 201600846. (30) Yang, J.; Siempelkamp, B. D.; Liu D.; Kelly T. L., Investigation of CH3NH3PbI3 degradation rates and mechanisms in controlled humidity enbiroments using in situ techniques. ACS Nano 2015, 9, 1955-1963. (31) Kim, H.-S.; Seo, J.-Y.; Park, N.-G., Impact of selective contacts on long-term stability of CH3NH3PbI3 perovskite solar cells. J. Phys. Chem. C 2016, 120, 27840-27848. (32) Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G., Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties. Inorg. Chem. 2013, 52, 9019-9038. (33) Onoda-Yamamuro, N.; Yamamuro, O.; Matsuo, T.; Suga, H., p-T phase relations of CH3NH3PbX3 (X = Cl, Br, I) crystals. J. Phys. Chem. Solids 1992, 53, 277-281. (34) Xiao, M.; Huang, F.; Huang, W.; Dkhissi, Y.; Zhu, Y.; Etheridge, J.; Gray-Weale, A.; Bach, U.; Cheng, Y.-B.; Spiccia, L., A fast deposition-crystallization procedure for highly efficient lead iodide perovskite thin-film solar cells. Angew. Chem. Int. Ed. 2014, 53, 9898-9903. (35) Ke, W.; Fang, G.; Wang, J.; Qin, P.; Tao, H.; Lei, H.; Liu, Q.; Dai, X.; Zhao, X., Perovskite solar cell with an efficient TiO2 compact film. ACS Appl. Mater. Interfaces 2014, 6, 1595915965. (36) Jung, H. S.; Park, N.-G., Perovskite solar cells: from materials to devices. Small 2015, 11, 10-25. (37) 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 Letters 2014, 14, 4158-4163. (38) Mei, A.; Li, X.; Liu, L.; Ku, Z.; Liu, T.; Rong, Y.; Xu, M.; Hu, M.; Chen, J.; Yang, Y. et al., A hole-conductor-free, fully printable mesoscopic perovskite solar cell with high stability. Science 2014, 345, 295-8. (39) Niu, G.; Guo, X.; Wang, L., Review of recent progress in chemical stability of perovskite solar cells. J. Mater. Chem. A 2015, 3, 8970-8980.


20

Page 21 of 21

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 Energy Letters

(40) Niu, G.; Li, W.; Meng, F.; Wang, L.; Dong, H.; Qiu, Y., Study on the stability of CH3NH3PbI3 films and the effect of post-modification by aluminum oxide in all-solid-state hybrid solar cells. J. Mater. Chem. A 2014, 2, 705-710. (41) Petrus, M. L.; Hu, Y.; Moia, D.; Calado, P.; Leguy, A. M. A.; Barnes, P. R. F.; Docampo, P., The influence of water vapor on the stability and processing of hybrid perovskite solar cells made from non-stoichiometric precursor mixtures. ChemSusChem 2016, 9, 2699-2707. (42) Zhu, G.; Liu, P.; Hojamberdiev, M.; Zhou, J.-p.; Huang, X.; Feng, B.; Yang, R., Controllable synthesis of PbI2 nanocrystals via a surfactant-assisted hydrothermal route. Appl. Phys. A 2009, 98, 299. (43) Habisreutinger S.; Leijtens T.; Eperon G. E.; Strankks, S. D.; Nicholas R. J.; Snaith H. J., Carbon nanotube/polymer composites as a highly stable hole collection layer in perovskite solar cells. Nano Lett. 2014, 14, 5561-5568. (44) You, J.; Meng, L.; Song, T.-B.; Guo, T.-F.; Yang, Y.; Chang, W.-H.; Hong, Z.; Chen, H.; Zhou, H.; Chen, Q. et al., Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers. Nat. Nanotechnol. 2016, 11, 75-81. (45) Chen, W.; Wu, Y.; Yue, Y.; Liu, J.; Zhang, W.; Yang, X.; Chen, H.; Bi, E.; Ashraful, I.; Grätzel, M. et al., Efficient and stable large-area perovskite solar cells with inorganic charge extraction layers. Science 2015, 350, 944.


21

In Situ Identification of Photo- and Moisture-Dependent Phase

Recommend Documents