Dry-Stamping-Transferred PC71BM Charge Transport Layer via an

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Dry Stamping Transferred PC71BM Charge Transport Layer via Interface Controlled Polyurethane Acrylate Mold Film for Efficient Planar-Type Perovskite Solar Cells Sunyong Ahn, Woongsik Jang, Soyun Park, and Dong Hwan Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b01282 • Publication Date (Web): 06 Apr 2017 Downloaded from http://pubs.acs.org on April 7, 2017

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ACS Applied Materials & Interfaces

Dry

Stamping

Transport

Transferred

Layer

via

PC71BM

Interface

Charge

Controlled

Polyurethane Acrylate Mold Film for Efficient Planar-Type Perovskite Solar Cells Sunyong Ahn†,∥, Woongsik Jang†,∥, Soyun Park†, and Dong Hwan Wang*, †

†

School of Integrative Engineering, Chung-Ang University, 221 Heukseok-dong, Dongjak-gu,

Seoul 156-756, Republic of Korea

*e-mail: [email protected] (D. H. Wang) ∥S.

Ahn and W. Jang contributed equally to this work.

KEYWORDS: Interface control, dry stamping transfer, perovskite solar cells, morphology, crystallinity, charge carrier dynamics

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ABSTRACT

The study of interlayers is important to enhance the performance of inverted perovskite solar cells (PSCs), since interlayers in PSCs align energy levels, and improve charge transport. However, previous research into applying interlayers for PSCs has only focused on wet-coated methods, such as spin coating, to form the interlayer. Here, we fabricated planar-type PSCs with deposited 6,6-phenyl-C70 butyric acid methyl ester (PC71BM) layer on to CH3NH3PbI3 (MAPbI3) layer by stamping transfer through a relatively dry process condition. We demonstrated the effects of stamping-transferred PC71BM layer using polyurethane acrylate (PUA), of which the surface energy was modified by 2-hydroxyethyl methacrylate (HEMA) to increase the transfer reproducibility. In PSCs with stamping-transferred PC71BM layer, we observed enhanced JSC and comparable power conversion efficiency (PCE), which were caused by enhanced coverage of ETL onto the MAPbI3 with preserved crystallinity, which occurs improved electron mobility and exciton dissociation. The optimized device PCE through the dry transferred PC71BM demonstrates the JSC, FF, and PCE of 21.65 mA/cm2, 76.0%, and 15.46% respectively. Moreover, morphological analysis and electrical measurement confirmed the improved durability of dry stamping transferred PSCs.


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INTRODUCTION The photovoltaic device based on perovskite materials has recently drawn much attention, because of the properties of long diffusion length,1-3 giant dielectric constant,4 low exciton binding energy,5 low-cost fabrication through solution process6 high absorption coefficient,7 and broad light absorption that is tunable by controlling chemical compositions. In organic-inorganic perovskite materials for solar cells (ABX3), A denotes an organic material, B denotes an inorganic material, and X denotes a halogen ion. Miyasaka et al. introduced CH3NH3PbI3 (MAPbI3) for solar cells with sensitized TiO2 as the hole blocking layer.9 Prof. Gratzel and co-workers developed advanced perovskite material, and focused on the increasing efficiency with interlayer systems. The normal structure of the PSCs that are generally used in TiO2 electron transport layer (ETL) requires high temperature annealing process of around ~500 °C, due to the mesoporous formation based on the dye-sensitized solar cells (DSSC) structure. In contrast, the inverted PSCs have been studied and developed for flexible electronics via low temperature and simple fabrication.10 Recently, to achieve high performance PSCs, many research groups have been making an effort to improve the quality of perovskite, such as increasing the grain size and their crystallinity,11-13 which correlated with efficient charge generation and transport pathways. In addition, the interlayer function helped energy level alignment, and improved charge transport as well as stability.14-17 For example, Prof. Huang’s groups reported improved device performances by thermal annealing and solvent annealing of PC60BM, which give rise to the functions of passivation and arrangement of the polymer interlayer.18,19 So we could recognize that the proper selection of interlayer fabrication or optimized treatment has a significant effect on the enhancement of electrical parameters. However, most of the researches until now on PSCs


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interlayer fabrication were limited by applying only wet-coated methods of spin-coating process to form the interlayer. Since spin-coating has the limitations of device size and solvent penetration, the promising process of stamping transfer via relatively dry condition has been introduced as an alternative, which can be more suitable for large area device, and can overcome an interfacial problem between the bottom and top layers by solvent diffusion during the continuous procedures. In prior research, the polymer stamps generally used poly(dimethylsiloxane) (PDMS); however, PDMS exhibited a selective restriction of solvent, owing to chemical instability from the organic solvents.20 Chu et al. transferred an active layer from silicon wafer to flexible target substrate without PDMS mold, and our group also devised polyurethane acrylate (PUA) transfer film for transfer of photoactive layer to another substrate; however, the process should be necessary for an additional solvent treatment to transfer.21-23 Moreover, due to the several advantages of PUA polymer based film such as fast curable time, transparent, and strength, we adapted for the basic supporter structure with large area for ordered nanopattern anode.24 Recently, a reproducible stamping-transferred P3HT:PCBM bulk-heterojucntion active layer had been reported through the modified hydrophilic PUA film, which surface energy was controlled by 2-hydroxyethyl methacrylate (HEMA).25,26 The UV-cured transfer film based synthesized PUA exhibits chemical stability due to the lack of coercion or solvent swelling, depending on the several polar solvents and additives. Moreover, there is no more surface energy treatment in the mother substrate (like silicon), such as 1H, 2H, 2H-Perfluorooctyltrichlorosilane (FOTS), which is widely used for reproducible transfer, because the surface property of PUA is already controlled.27,28 However, although the root mean square (RMS) of P3HT:PCBM active layer was reduced by stamping transfer, the power conversion efficiency (PCE) was decreased


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due to the higher recombination resistance.25 For the PSCs, when the PCBM is spin-coated onto the MAPbI3, the dissolved polar solvent from PCBM will be easily penetrated or located near the grain boundary of MAPbI3 layer,18,29 which cause the possibility of MAPbI3 surfaces deformation since the chlorobenzene (CB) for PCBM solution influences to the crystallinity of MAPbI3.30 Therefore, the stamping transfer of dry condition will be suitable for the fabrication of well controlled perovskite structure owing to the relatively better coverage of thin PCBM layer onto the MAPbI3. In this research, efficient PSCs with dry transferred ETL of PC71BM were fabricated through a reproducible stamping process using modified PUA film with relatively hydrophilic surface from hydroxyethyl methacrylate (HEMA). In order to compare the effect of dry stamping transferred versus wet spin-coated interlayer of PC71BM, we performed meaningful research of morphological and electrical analyzes based on atomic force microscopy (AFM), scanning electron microscopy (SEM), Impedance spectroscopy, X-ray diffraction (XRD) and Photoluminescence (PL). Moreover, the stamping transferred PC71BM ETL contributes to improved device operation, due to the different degradation behavior compared to the spincoating, which possibly affects the interfaces between perovskite and PC71BM.

EXPERIMENTAL SECTION Preparation of materials: The HEMA-PUA films were fabricated by using a synthesis method described in previous research25; the solution was prepared with 19 g of urethane diacrylate oligomer, 19 g of HEMA, and 2 g of HCPK at room temperature. Then, the solution was spread on a silicon wafer, and exposed to UV light for 10 min. For the perovskite layer; CH3NH3I (Dyesoltimo), PbI2 (99.99%, TCI. Co., Ltd.), GBL (γ- butyrolactone, Sigma Aldrich) and DMSO


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(dimethyl sulfoxide, Junsei) were used to synthesize the CH3NH3PbI3 (MAPbI3) solution. The hole transport layer of PEDOT:PSS (AI 4083 was supplied by ECS group) and electron transport layer of 6,6-phenyl-C71 butyric acide methyl ester (PC71BM)/TiOx (precursor: Titanium(Ⅵ) isopropoxide, Sigma Aldrich) were used for an efficient cascade structure. 1-hydroxycyclohexyl phenyl ketone (HCPK, Aldrich) and aliphatic urethane diacrylate oligomer (EB 9270, ENTIS), 2-hydroxyethyl methacrylate (HEMA, Aldrich) were used for synthesis of the modified (hydrophilic) polyurethane acrylate (PUA) mold films. The modified PUA film with relatively hydrophilic property was fabricated using a previously reported method.25 Fabrication of inverted perovskite solar cells: ITO glass substrates were cleaned with dishwasher detergent and ultrasonication process with deionized water, acetone and isopropanol in regular sequence for 20 min, respectively. For spin-coating of PEDOT:PSS onto the ITO, cleaned ITO were exposed to UV ozone for 20 min for surface modification. PEDOT:PSS were then spin-coated on ITO at 5000 rpm for 40 s. The PEDOT:PSS deposited ITO substrates were annealed on hotplate at 140 °C for 10 min to generate thin film with a thickness of 30 nm. The MAPbI3 solution was composed of CH3NH3I and PbI2 (1.06:1 mol.%) in GBL and DMSO (7:3 v/v) with molar concentration of 1.4 mol/L at room temperature for 12 h. Figure 1a shows that to form the MAPbI3 layer, a solution of MAPbI3 was spun on PEDOT:PSS film at 1000rpm for 30s, then 5000 rpm for 30 s with the additional process of toluene drop casting. Then, the substrates were placed on hot plate at 100 °C for 15 min to fabricate the MAPbI3 film with a thickness of 300 nm. In order to compare the stamping transfer and spin-coating of PC71BM, the PC71BM solution was dissolved in chlorobenzene with concentration of 20 mg/mL, and coated onto the HEMA-PUA or surface of MAPbI3, respectively, at 2000 rpm for 40 s with a thickness of 30 nm. Then, the transferred PC71BM was generated from the coated HEMA-PUA to MAPbI3


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surface under 100 °C conducted by a roller via a uniform stamping and rubbing process. The TiOx layer with a thickness of ~10 nm was formed at 5000 rpm for 40 s using a molar concentration of 25 mmol/L. Finally, an Al cathode was thermally deposited under 1.9 x 10-6 Torr with a thickness of 100 nm through the thermal evaporator. Characterizations and additional measurements: The performances of the PSCs were measured by solar simulator (Peccell Technologies, Inc., PEC-L01) with Air Mass 1.5 Global (AM 1.5 G) at an intensity of 100 mW/cm2 that was calibrated by silicon reference cell, and the current density-voltage characteristics of PSCs were analyzed by electrical measurement system (ZIVE SP1). The device area was confirmed at 0.118 cm2, based on the deposited Al cathode from the mask pattern. The EQE was measured after power calibration (ABET Technologies, Inc., LS150) with a mono-chromator (DONGWOO OPTRON Co. Ltd., MonoRa-500i). The surface morphology and roughness of several thin film layers were observed by the noncontact mode from an AFM (Park NX10) and SEM (SIGMA model from Carl Zeiss, Inc.) at 5 kV, respectively. The crystallinity of perovskite thin film was measured by XRD (Bruker-AXS, New D8-Advance). The PL spectra were measured by Raman microscopy (Xperam200 (Nanobase Inc.)). The laser wavelength was 642 nm and power was 0.3 mW for each device. The magnification of the object lens was 40x power. We calculated the average of ten datasets of Raman spectra in the same position for each sample.

RESULTS AND DISCUSSION Figures 1a–c show the formation method of the perovskite (MAPbI3) active layer, sequential device structure, and energy band gap of PSCs. In this study, for planar-type PSCs, the PEDOT:PSS and PC71BM/TiOx layers were used for the hole and electron transport layers,


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respectively. To observe the main effect of dry transferred interlayer, the PC71BM ETL with hydrophobic film was deposited onto the perovskite layer via stamping process from HEMAPUA with controlled hydrophilic surface through the proposed interaction of functional groups in Figure 1d. The contact angle of HEMA-PUA versus pristine PUA had been studied from previous reports.25,26 For this reason, the stamping transferred ETL would be successful, because the HEMA-PUA is expected to show a relatively weaker attraction with PC71BM, which contributes to better attachment to the hydrophobic perovskite layer with large area coverage and great reproducibility, as shown in Figure S1. Figure 2 shows the current-voltage (J-V) curve and the external quantum efficiency (EQE) data by two different fabrications of PSCs, which applied deposition by spin-coating and stamping transfer of PC71BM, respectively. Table 1 shows the electrical parameter and power conversion efficiency (PCE) based on Figure 2a. For the PSCs with spin-coated PC71BM, the open circuit voltage (VOC), short circuit current (JSC), fill factor (FF), and PCE showed 0.962V, 19.81 mA/cm2, 78.9% and 15.05%; whereas, the stamping transferred PC71BM onto perovskite layer exhibited the increased JSC and PCE of 21.65 mA/cm2 and 15.46% but slight decreased FF and Voc of 76.0% and 0.940V, respectively. The average value of electrical parameters through the spin-coating and stamping transfer was revealed in Figure S2 and Table S1, and showed the corresponding tendency to the Figure 2a. The slight VOC drop could possibly be due to the different interfaces between the perovskite and PC71BM from the relative dry condition during the transfer, compared to the direct wet coating. The EQE of Figure 2b confirmed the improved JSC of the transferred PC71BM, because of the larger width of EQE following the overall wavelength of the PSCs. The maximum peak is 86.9% (spin-coating) versus 94.0% (dry transfer) at 520 nm.


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The tendency of EQE and measured JSC between the spin-coating and dry transfer corresponds well with Figure 2 and Table 1. Figure S3 shows the dark J-V curve with comparison of spincoating versus stamping transfer, and the PSCs via transferred ETL exhibited increased series and decreased shunt resistance, which correlated to decreased FF. Therefore, although the FF and Voc value decreased slightly by stamping transfer method, the dry transferred PC71BM proved to have positive effects on the JSC values, and contributed to the comparable PCE of 15.46% with ~ 2.7% increase compared to the common spin-coating. Since the electrical parameters are influenced by the composed layer morphology, AFM and SEM images of surfaces from perovskite, spin-coated PC71BM, and dry transferred PC71BM onto the PEDOT:PSS layer were investigated, as shown in Figures 3 and S4. Figure 3a and S4a shows surface images of MAPbI3 on which transferred PC71BM ETL are formed. However, the PC71BM layers were firstly formed on different bottom surfaces, such as flat HEMA-PUA film or directly onto the MAPbI3, respectively; and the transferred PC71BM shows a smoother RMS value of 0.776 nm compared to the spin-coated layer of 2.845 nm onto the perovskite, as shown in Figures 3. Thus, the increased Jsc was also caused by the uniform surface morphology and proper thin film formation of PC71BM from the dry transfer using modified PUA film via stamping process onto the MAPbI3 layer. In Figure 4, X-ray diffraction (XRD) was measured in order to analysis the change of perovskite crystallinity during the spin-coating and stamping transferred PC71BM. Since the CB solvent causes the possibility of MAPbI3 surfaces deformation,30 only CB was dropped and coated onto the MAPbI3 layer. In cases of the MAPbI3 after the coated CB as shown in Figure 4 (red line), the intensities of XRD peaks exhibited clearly reduced compared to the pristine MAPbI3 (black line). Thus, we confirmed the CB can change the crystallinity of MAPbI3 which


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results in the surface deformation. Additionally, the XRD peaks of the PC71BM on MAPbI3 by spin-coated (blue line) and stamping-transferred (green line) were observed in the different tendency of the XRD peaks. The stamping transferred PC71BM film reduces the intensity of each peak position more than the spin coated PC71BM film does. This phenomenon could reflect the PC71BM was coated onto the perovskite thin film with better surface coverage. Therefore, the increased Jsc caused by he uniform surface coverage of PC71BM which contribute to the favourable role of ETL with preserved crystalline MAPbI3. Since the charge generation efficiency is proportional to the dissociation of excitons in PSCs into free charge carriers, we analyzed the characteristics of the photoluminescence (PL) of PC71BM onto the perovskite layer, in order to compare the spin-coating and dry transfer process. Figures 5a and b show PL intensity-mapping data that was measured in the region of 40 × 40 µm, which enabled comparison of the efficiency of PL quenching depending on the layer coverage of stamping-transferred PC71BM. In order to compare the PL intensity, the structure of Figure 5 was fabricated from the composition of ITO / PEDOT:PSS / MAPbI3 / spin-coated or stampingtransferred PC71BM, respectively. A bright color of PL intensity-mapping data represents a high PL intensity, and Figure 5c shows the average PL spectra based on the PL intensity-mapping data. PL quenching is a simple analysis that can be used to observe whether the excitons in MAPbI3 successfully dissociate into free charge carriers.31 At around 780 nm, the stampingtransferred PC71BM exhibited decreased PL intensity, which represents an enhanced charge separation within the MAPbI3 / PC71BM layers. Therefore, we could determine that stamping transferred PC71BM is attributed to more efficient dissociation of excitons to free charge carriers than the spin-coated PC71BM, which leads to improved charge generation efficiency.


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In order to investigate the charge carrier dynamics through the stamping transferred ETL, we measured and analyzed the electron mobility and photocurrent density (Jph) as a function of the internal voltage (Vint), as shown in Figure 6 and Table 2. Electron-only devices from the structure of ITO / PEI / MAPbI3 / spin-coated or dry transferred PC71BM / TiOx / Al were fabricated to measure the electron mobility, which was analyzed by space- charge-limited current (SCLC),32 which showed a characterized J-V curve, respectively, as shown in Figure 6a.33,34 In the high voltage region, J-V curves are expressed by the Mott-Gurney law, which shows equation (1).

=

( )

exp (

)

(1)

Thus, the equation is summarized as equation (2), where εr is the dielectric constant of MAPbI3 ≈ 21.2,35 ε0 is the permittivity of vacuum ≈ 8.854 × 10-12 F·m-1, and L is the thickness of MAPbI3 layer ≈ 190 nm 26.

=

(2)

By substitution in the principle, the PSCs with stamping-transferred PC71BM ETL presented increased electron mobility from 6.08 x 10-5 to 7.81 x 10-5 cm2V-1s-1, as summarized in Table 2. We also measured hole-mobility which presented 1.84 x 10-4 cm2V-1s-1 in the device structure of Figure S5 and revealed the improved charge carrier balance of the device with stampingtransferred PC71BM. From this result, the organic transport layer of PC71BM through the dry transfer affects the electron transport and charge carrier balance more effectively in the PSCs which leads to the enhanced photo-current density. Moreover, the Jph via Vint was measured to characterize the charge collection and generation through the comparison of spin-coated and stamping transferred PC71BM, respectively. The Jph can be presented by the equation Jph = JL – JD, where JL and JD are the current density measured


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under AM 1.5G and dark condition, respectively. Also, Vint depended on the formula Vint = V0 – Vappl. V0 is the voltage when Jph is the zero position, while Vappl means the applied voltage. Figure 6b shows that for the overall range of Vint, we observed different Jph in PSCs between the stamping-transferred and spin-coated PC71BM. In the case of low Vint point, higher Jph generally indicates that the property of charge collection is higher than for the other PSCs, which also contributes to increased JSC.36 Thus, we confirmed that dry transferred PC71BM ETL enhanced the property of charge collection efficiency, which correlated with the electron mobility. Furthermore, PSCs of the photo-generated excitons were expected to be transferred to the charge carrier at high Vint (1.98V), due to the increased saturation of Jph from low to high Vint.37 The highest Jph (20.09 mA/cm2) was revealed at PSCs with stamping transfer of PC71BM. In the case of spin-coated, the Jph value showed 19.41 mA/cm2. As a result, the increased value of Jph of the PSCs through dry transfer meant enhanced charge generation compared with the spin-coated. Thus, devising an optimized method of thin film deposition is a very meaningful approach to increase the device electrical characteristics relevant to the efficient charge carrier dynamics. In terms of FF study much reasonably, we measured the impedance spectroscope as shown in Figure 7, and show the impedance analysis, which was measured under 1 sun condition at VOC and 0V at the sample bias, respectively. In the case of 1 sun illumination and applied VOC, the formed-in electric field was offset by charge carriers injected into the film. So the frequency of charge recombination increased to the maximum. The probability of charge collection decreased to the minimum, since charge recombination prevents the photo-generated charge transport from perovskite to respective electrodes.38 Therefore, the size of the semi-circle in impedance can indicate the photo-generated charge transport resistance (RCT) of respective PSCs.39 Figure 7a


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shows that PSCs with stamping transfer of PC71BM exhibited a smaller semi-circle than did spincoated PC71BM. Therefore, we could conclude that the dry transferred PC71BM increases RCT. In the case of the other condition, AM 1.5G and 0.0V of sample bias, we could measure the bulk (Rbulk) and recombination resistance (Rrec) values, where Rbulk is related to RCT of PSCs,38, 40 and Rrec functions as a shield to avoid charge recombination.38 Figures 7b show small semicircles depending on Rbulk, and also show large semi-circles depending on Rrec at the high and low frequency regions, respectively. Figure 7b and Table 3 show that the PSCs of stampingtransferred PC71BM showed more deteriorated Rbulk and Rrec. Moreover, the impedance data was reasonable by comparison with the tendency of the J-V curve under dark. As a result, we could conclude that dry transferred PC71BM caused the slightly decreased FF by the charge transport and recombination resistance. Through the results of Jph via Vint, SCLC, PL quenching/mapping and impedance analysis, we can demonstrate that the PSCs from a dry transferred PC71BM exhibited improved JSC as well as comparable PCE, from 19.81 mA/cm2 and 15.05% to 21.65 mA/cm2 and 15.46%, respectively from the reasons of improved electron mobility, and efficiency of electron mobility, charge generation and separation. Since the relatively dried PC71BM was transferred onto the MAPbI3, while the spin-coating method largely gave rise to the permeation of CB for PC71BM solution into the MAPbI3 layer,41 we measured the durability test to see the efficiency drop under the average humidity of 50% (± 5%) in air without encapsulation in Figure 8, and observed the morphological changes of ETL surfaces depending on time (hours) in the inset figures (left; the spin-coated ETL and right; dry transferred ETL). The surface of spin-coated ETL showed unstable and poor morphology compared to the dry transferred ETL after 300 hours, due to the pin-holes that were generated. Interestingly, though the same ETL material was used for forming the electron transport layer,


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we could observe the improved stability of PSCs depending on the dry transfer method. Additionally, we investigated the chemical state of the thin film surface (the full structure is the same as the ITO / PEDOT:PSS / MAPbI3 / PCBM / TiOx device) comparing the fresh and after 1 week under average humidity of 50% (± 5%) in air through XPS. Figure S6 shows that the XPS results present the analogous peak positions of chemical states at the surface, even though different forming methods of ETL are used. From these results, the different behavior of morphological changes of the surface was caused by the inter-diffusion due to the wet solvent penetration during the spin-coating. Therefore, the PSCs showed improved durability, of which PCBM dissolved CB was less diffused to the MAPbI3 layer using by dry stamping transfer which leads to improved durability of the device operation.

CONCLUSION In conclusion, we successfully fabricated PSCs using a dry stamping transfer of PC71BM ETL through the synthesized PUA, of which the surface energy was modified by HEMA. We could observe smoother morphology, better coverage of PC71BM layer by stamping-transfer onto the MAPbI3 than by the spin-coating. Here, we mainly investigated the effect of dry transferred PC71BM in PSCs, such as studies of improved electron mobility, charge carrier lifetime, charge separation from generation, transport and collection, using SCLC, impedance and PL measurements, respectively. Furthermore, the PSCs from the dry transferred ETL showed improved durability depending on the time, due to the stable morphology without pin-holes, and reduced inter-diffusion of ETL solution in the perovskite layer. Therefore, the dry transferred ETL contributes to increased JSC and device stability, as well as comparable PCE. From these effective combination factors, we expect that the stamping transfer technology can be a


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promising alternative process for high performance PSCs with many other efficient interlayer depositions, using simple device polymer transfer film.

Figure 1. (a) Scheme of the formation method of the MAPbI3 layer with chlorobenzene treatment during the spin-coating of MAPbI3. (b) The structure of the PSCs composed of ITO/PEDOT:PSS/MAPbI3/PC71BM/TiOx/Al. (c) Schematic energy level diagram based on the


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structure of PSCs. (d) Scheme of HEMA-PUA-based stamping transfer of PC71BM and PEDOT:PSS layers, respectively.


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Figure 2. (a) J-V characteristics of PSCs fabricated with and without stamping transfer of PC71BM layer under AM 1.5G irradiation at 100 mW/cm2. (b) EQE spectra of PSCs depending on J-V characteristics.


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Figure 3. AFM image of the several layer surface of (a) MAPbI3 (RMS = 7.716 nm), (b) spincoated PC71BM (RMS = 2.845 nm), and (c) stamping-transferred PC71BM on MAPbI3 (RMS = 0.776 nm).


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Figure 4. XRD spectrum of MAPbI3 layer (black), MAPbI3/CB spin-coating (red), spin-coated PC71BM layer on MAPbI3 (blue), stamping transferred PC71BM layer on MAPbI3 (green).


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Figure 5. (a) and (b) PL intensity-mapping data for sample composed of ITO/PEDOT:PSS /MAPbI3/spin-coated and stamping-transferred PC71BM, respectively, in region of 40 x 40 µm. (c) Average PL intensity of (a) and (b.).


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Figure 6. (a) Electron mobility of the electron-only device with PC71BM formed by spin-coating and stamping transfer. (b) The photocurrent density (Jph) versus internal voltage (Vint) characerization of PSCs with and without stamping transfer.


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Figure 7. Impedance response of PSCs composed of spin-coated and stamping-transferred PC71BM layer under condition of AM 1.5G with (a) sample bias VOC, and (b) 0.0V.


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Figure 8. Stability tendency of PSCs based on ETL fabricated by spin-coating and stamping transfer without encapsulation, respectively. Insets show SEM imagery of ETL layers fabricated by spin-coating (left) and stamping transfer (right) after 300 hours.


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Table 1. Electrical parameters of PSCs fabricated with and without stamping transfer of PC71BM layer depending on J-V curve. Fabrication Condition Spin-coated PC71BM Dry-transferred PC71BM

Voc (V)

Jsc (mA/cm2)

IPCE (mA/cm2)

FF (%)

PCE (%)

0.962

19.81

19.18

78.9

15.05

0.940

21.65

20.96

76.0

15.46


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Table 2. Electron mobility and Jph value of PSCs fabricated with and without stamping transfer. Fabrication Condition Spin-coated PC71BM Dry-transferred PC71BM

Jph (mA/cm2) (Vint= 1.98V) 19.41

Electron mobility (cm2V-1s-1) 6.08 x 10-5

20.09

7.81 x 10-5


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Table 3. Electron mobility for electron-only device with PC71BM formed by spin-coating and stamping transfer, with Impedance parameters of PSCs with spin-coated and stampingtransferred PC71BM layer. Fabrication Condition Spin-coated PC71BM Dry-transferred PC71BM

RCT (Ω Ω)

Rrec (kΩ Ω)

14.7

8.97

19.6

6.23


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ASSOCIATED CONTENT Supporting Information Available. Detailed morphological and electrical study of dry stamping transferred PCBM charge transport layer via interface controlled polyurethane acrylate mold film planar-type perovskite solar cells are included. This information is available free of charge via the internet at http://pubs.acs.org/.

AUTHOR INFORMATION Corresponding Author *e-mail: [email protected] (D. H. Wang)

ACKNOWLEDGMENT This research was supported by the Basic Science Research Program, through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT & Future Planning (2017R1A1A1A05000772).

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TOC figure


34

Dry-Stamping-Transferred PC71BM Charge Transport Layer via an

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