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Large Grain-Based Hole Blocking Layer Free Planartype Perovskite Solar Cell with Best Efficiency of 18.20 % Haejun Yu, Jaehoon Ryu, Jong Woo Lee, Jongmin Roh, Kisu Lee, Juyoung Yun, Jungsup Lee, Yun Ki Kim, Doyk Hwang, Jooyoun Kang, Seong Keun Kim, and Jyongsik Jang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b15710 • Publication Date (Web): 17 Feb 2017 Downloaded from http://pubs.acs.org on February 17, 2017

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ACS Applied Materials & Interfaces

Large Grain-Based Hole Blocking Layer Free Planar-type Perovskite Solar Cell with Best Efficiency of 18.20 % Haejun Yu†, Jaehoon Ryu†, Jong Woo Lee‡, Jongmin Roh†, Kisu Lee†, Juyoung Yun†, Jungsup Lee†, Yun Ki Kim†, Doyk Hwang‡, Jooyoun Kang‡, Seong Keun Kim‡ and Jyongsik Jang †,* †

World Class University (WCU) Program of Chemical Convergence for Energy &

Environment (C2E2), School of Chemical and Biological Engineering, Seoul National University (SNU), 599 Gwanangno, Gwanak-gu, Seoul, 151-742 (Korea)

‡

Department of Biophysics and Chemical Biology and Department of Chemistry, Seoul National University, Seoul 151-742 (Korea)

*Corresponding author E-mail: [email protected] Tel.: (+82) 2-880-7069 Fax: (+82) 2-888-1604

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Abstract

There remains tremendous interest in perovskite solar cells (PSCs) in the solar energy field; the certified power conversion efficiency (PCE) now exceeds 20 %. Along with research focused on enhancing PCE, studies are also underway concerning PSC commercialization. It is crucial to simplify the fabrication process and reduce the production cost to facilitate commercialization. Herein, we successfully fabricated highly efficient hole-blocking layer (HBL)-free PSCs through vigorously interrupting penetration of hole-transport material (HTM) into FTO by large grain based-CH3NH3PbI3 (MAPbI3) film, thereby obtaining a PCE of 18.20 %. Our results advance the commercialization of PSC via a simple fabrication system and a low-cost approach in respect of mass production and recyclability.

KEYWORDS: hole-blocking layer free, grain size, perovskite solar cell, blockage effect, HTM infiltration, recyclability


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INTRODUCTION There has been considerable research reported over the past 3 years concerning organic– inorganic hybrid perovskite-based solar cells. A power conversion efficiency (PCE) of ca. 20% has been achieved by compositional engineering, intramolecular exchange, or chemical conversion of a bilayer structure. 1-3 Perovskite materials such as CH3NH3PbX3 (MAPbX3, X = Br, I, Cl), which is used as a light absorber in perovskite solar cells (PSCs), are of particular interest because of their outstanding light-soaking ability, direct band gap, small exciton binding energy, and excellent charge-carrier mobility.

4-9

Additionally, effective

ambipolar charge transfer and long charge diffusion in the perovskite phase have enabled the mesoscopic architecture of PSCs to be substituted with a planar heterojunction (PHJ) structure, where the perovskite was immediately coated after developing a charge-blocking layer.10-13 The PHJ-structured PSCs are of interest for numerous reasons including their simplicity of fabrication, lower commercialization cost, and potential use in flexible devices.14-16 Numerous approaches have been taken to improve and optimize a perovskite film to boost the performance of planar-type PSCs to a competitive level.17 The crystallinity, thickness, surface coverage, and grain size are critical to elevate the performance of planar-type PSCs.18-21 The remarkable PCE of ca. 19% recently reported for a planar structure indicated that a scaffold layer is not essential for high-efficiency PSCs.22 However, despite the high performance, there have been many reports that the use of metal oxide in PSCs have a crucial influence on the substandard working stability of PSCs; titanium dioxide (TiO2), mainly used as an electron-selective layer in planar-type PSCs, degrades the light stability of perovskite. This is ascribed to oxygen desorption in TiO2 by ultraviolet light.23 In addition to TiO2, zinc oxide (ZnO) aggravates structural stability because of an interaction between the perovskite 3 ACS Paragon Plus Environment


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and hydroxide groups on the ZnO surface.24 The metal oxide-driven instability is readily surmounted by removing a blocking layer having the configuration of fluorine-doped tin oxide (FTO)/perovskite/charge conductor/metal.25 In the previous report, the necessity of a compact layer was appraised for judging the prospects of HBL-free PSC, where the PCE of 13.5 % was estimated.26 Ke et al. reported that the surface properties were improved when perovskite was directly coated onto FTO that had been previously treated by UV/O3, accordingly achieving the PCE of 14.14 % in HBL-free PSC.27 However, without a compact layer, these reported PCEs were still lower than that of the blocking-layer-inserted PSC, which was attributed to failure to appropriately prevent direct contact between the holetransport material (HTM) and the FTO surface. It resulted in serious recombination of electron–hole pairs, noticeably reducing the open-circuit voltage (Voc) and the fill factor (FF).28 There is thus a great need to study the factors that affect the performance of HBL-free PSCs, e.g., thickness, grain size, crystal quality and compactness of the film. These are crucial factors to counter the unwanted penetration of the HTM. However, the deep studies associated with the aforementioned factors have not been conducted yet. Herein, we report the highly simple planar-type PSC fabricated without a metal oxidebased HBL that is commonly coated for retarding exciton recombination. To make highly efficient HBL-free PSCs, the influence of perovskite grain size and thickness on performance were examined because the perovskite film itself can function as a HBL as well as a strong sensitizer. Over the ca. 700 nm MAPbI3 grain size, the HTM was barely permeated into the film due to the enhanced compactness and decrease of grain-boundaries per area. Consequently, we obtained a remarkable PCE of 18.20 % which is the highest PCE reported to date for this type of PSC. Furthermore, these simplified-PSCs showed the better long-term stability, recyclability and performance than those of TiO2 BL-inserted PSCs.


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RESULTS AND DISCUSSION

Figure 1. (a) Schematic images representing cross-sectional configuration and (b) band-gap diagram of hole-blocking layer free perovskite solar cell. (c) FE-SEM side-view of the completed perovskite solar cell without a HBL. Overall schematic configuration of the PSCs rendered in our work is shown in Figure 1a, portraying the simple-structured PSC without a HBL. To construct the MAPbI3 film which plays a role as a HBL as well as a sensitizer, the precursor prepared with various concentration (37, 44, 51, 58 wt%) was directly spin-coated on the blank FTO substrate without coating a HBL, followed by introducing a hole transport layer (HTL) with a thickness of ca. 200 nm to allow holes to be quickly separated from the MAPbI3 phase. The HTM spread evenly in all cases, which not only facilitated a charge migration because of conformal contact of the metal with the HTL but also provided high light absorption due to 5 ACS Paragon Plus Environment


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excellent reflection by the metal.29-30 The fabrication process was completed by thermally evaporating a 60-nm-thick layer of gold. The energy level diagram for our device is illustrated in Figure 1b. The free charges generated in MAPbI3 by the sunlight absorption can be transported to the FTO or HTL by charge gradient-induced diffusion and charge shifting triggered by the built-in potential of p–i–n-type solar cells.31-32 Respective layers are clearly indicated at low and high magnifications in Figure 1c and S1b. Also, a surface of MAPbI3 with a large grain size (ca. 400–900 nm) was developed with full coverage, which is evident in the Figure S1a. A photograph of the completed device is shown in Figure S1c.

Figure 2. (a) Current density–voltage (J–V) characteristics and (b) external quantum efficiency (EQE) spectra of PSCs of different MAPbI3 thicknesses. (c) Performance and (d) EQE spectrum for the best-performing cell. The integrated current density derived from the EQE spectrum was 21.20 mA/cm2

To evaluate the effects of MAPbI3 grain size and film thickness on blockage of HTM permeation, the four types of films were prepared using the before-mentioned MAPbI3 precursors. (37, 44, 51, 58 wt%) All of the MAPbI3 films spin-coated with different 6 ACS Paragon Plus Environment

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precursors were crystallized with the solvent annealing procedure to ensure better electrical performance.22, 33 The MAPbI3 films were solvent-annealed for 1h to guarantee maximum MAPbI3 grain size for each precursor concentration. From FE-SEM images of the prepared films as shown in Figure S2, the thickness of films was increased from ca. 330 nm (37 wt%) to 870 nm (58 wt%) at the indicated spin-coating rate. (Figure S2a-d) And it is also evident from Figure S2e-f and Figure S3 that the grain size simultaneously followed the same trend as thickness, which is in good agreement with previous findings.33 While the grain size of the MAPbI3 obtained from the 37 wt% precursor solution was ca. 200–300 nm horizontally, that from the 58 wt% precursor solution was significantly greatened up to ca. 1000 nm. On the basis of MAPbI3 grain size and film thickness information, the performance of assembled devices was estimated under 1 sun illumination. Figure 2a exhibits that cell performance was improved with increasing concentration of stock solution. Average performance was confirmed for 25 devices prepared at each concentration. (Figure S4) All photovoltaic parameters were comparatively poor for the 37 wt%-based PSCs. The parameters were steadily increased with thickening stock solution, and reached saturated values in the 51 wt%-based PSCs. At greater than the optimal concentration, although the Jsc was exiguously reduced because of mismatch between the perovskite absorption depth and diffusion length of charge carriers, the significant reduction of Jsc could be avoided and sufficiently high performance was maintained in the 58 wt%-based PSCs. The Voc, that is conventionally defined as the difference between the lowest unoccupied molecular orbital (LUMO) level of the perovskite and the highest occupied molecular orbital (HOMO) of the HTM, typically exceeded 1.05 V in all cases.34 There would have been negligible changes in the HOMO or LUMO levels of the films because the same type of perovskite and HTM were applied to fabricate the PSCs. However, the much improved Voc 7 ACS Paragon Plus Environment


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was obtained in the concentrated film-based PSCs (51, 58 wt%), which was possibly ascribed to decrease of non-radiative recombination due to the large grain and heavy thickness of MAPbI3.35-36

The obtained photocurrents were in good agreement with the external quantum efficiency (EQE) spectra (Figure 2b). The champion efficiency of 18.20% was achieved with Jsc of 21.45 mA/cm2, Voc of 1.127 V, and FF of 0.751 (Figure 2c). The EQE spectra and integrated photocurrent were consistent with those acquired from the J–V characteristics (Figure 2d). The hysteretic behaviors of the HBL-free PSCs were also evaluated using the PSCs fabricated by 51 wt% based-MAPbI3 film (Figure S5a). The ratio between the forward- and reverse-scan PCEs was ca. 0.8, which was a low level hysteresis in consideration of absence of n-type HBL and was comparable with that of the previously reported result.27 However, the extent of hysteresis in HBL-free PSC was quite serious compared with that of TiO2 BLinserted PSC due to the slightly slow charge extraction rate (Figure S5b),7 and accordingly further works are in progress to achieve the hysteresis-less HBL-free PSC. To accurately approve the confidence of performance measured from HBL-free PSC, and assure the extent of device hysteresis, the steady-state photocurrent density and PCE were estimated at maximum power output (0.925 V deduced from reverse scan result) for 80 s in Figure S6. The stabilized photocurrent density (black) of HBL-free PSC was 16.86 mA/cm2, corresponding to a power output of 15.59 mW/cm2 (= PCE of 15.59 %). The stabilized PCE is close to the average value of efficiencies obtained from forward and reverse scan direction, which denotes the performance credibility of HBL-free PSC. To clarify key factor on the improved performance in this simplified type, the perovskite grain size dependent J-V characteristics were tested under a condition of the fixed film thickness (Figure S7). On the contrary to the solvent annealed film (Figure S7d), the normally 8 ACS Paragon Plus Environment

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annealed MAPbI3 films were built with very small grains (Figure S7a and S7c), and the completed devices indicated the humble PCE which is ca. 80 % of the PCE obtained from solvent annealed device. Furthermore, to understand the effect of film thickness in HBL-free PSCs without a big variation in grain size, the performance of 37 wt% based-PSCs (ca. 330 nm thickness, solvent annealing) could be compared with the normally annealed film shown in Figure S7a (51 wt%, ca. 650 nm thickness). The latter showed the slightly increased Jsc, FF and PCE than those of the former (Figure S8), and it can be seen that film thickness slightly contributed to optimization of the efficient HBL-free PSC. From these results, it was proved that the MAPbI3 grain size is a more decisive factor than film thickness for realization of the highly efficient HBL-free PSC and for effective interruption of HTM penetration. As corroborated above, the outstanding PCE was acquired from 51 and 58 wt% based PSCs, which implies that the penetration of HTM is completely prevented from the MAPbI3 film on condition that the perovskite is crystallized with an ideal grain size (0.6 ~ 1 µm) and perfect coverage. Moreover, these highly crystalline grains intrinsically have lots of merits such as the long diffusion length of charge carriers and fewer defects.33, 35, 37 This is why the high performance is continued in 58 wt%-based PSCs over the optimum concentration (51 wt%).

Figure 3. (a) Nyquist plots of the blocking layer-free PSC as a function of precursor concentration under dark condition at 0.7 V bias. (b) An illustration depicting the penetration of the HTM into a perovskite film through a crevice. (Left) The penetration of the HTM can be disturbed by large grains densely located along an orthogonal path in a high-thickness 9 ACS Paragon Plus Environment


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film. (Right) On the other hand, the HTM can easily reach the FTO surface through many penetration pathways (grain boundaries).

To assure our hypothesis about the recombination between HTM and FTO, electrochemical impedance spectroscopy (EIS) was measured from 1 Hz to 1 MHz under dark and illumination conditions at 0.7 V bias. Under the dark condition (Figure 3a), the transport of HTM in the high-frequency region and recombination resistance between FTO and HTM in the low-frequency region were analyzed.38 It was challenging to characterize the difference in charge transport behavior because the arcs were indistinct in the high-frequency region. However, the main arcs in the lowfrequency region clearly indicated that recombination resistance was elevated with increasing the grain size of MAPbI3. It stands for that harmful contact of HTM with FTO frequently occurred in the small MAPbI3 grain-based PSCs. Accordingly, the Voc, FF and PCE of HBL-free PSC could be enhanced in 51 and 58 wt% based-PSCs consisting of large grains.35 In other words, as can be seen from Figure 3b, the performance variation stems from the difference of an HTM blockage ability determined by MAPbI3 grain size. In case of the 37 and 44 wt%-based PSCs, it is awkward to effectively inhibit the penetration of the HTM to the FTO, and there is a high probability of electron-hole recombination at the interface. It would be a main reason of poor performance in PSCs fabricated by stock solution of 37 wt%. However, over the ca. 700 nm of MAPbI3 grains (51, 58 wt%), the outstanding performance was achieved, which demonstrated that the hole-blocking effect of MAPbI3 film could be feasible if a satisfactorily large grain MAPbI3 films were prepared with perfect surface coverage. The MAPbI3 film consisting of large grains has a small number of crevices per unit area, which can reduce the passage for HTM infiltration and alleviate damaging recombination 10 ACS Paragon Plus Environment

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provoked at interface between FTO surface and HTM. Additionally, it is reckoned that the infiltrating HTM may frequently collide with the MAPbI3 grains in a thick film and stop penetrating, thereby minimizing the likelihood of arrival at FTO. Even though the thickness is judged as a minor factor compared with grain size from the results of Figure S6b and S7, it is imperative to harmoniously combine the two factors for excellent photovoltaic performance.

Figure 4. Surface AFM images (a–d) showing MAPbI3 films prepared by stock solutions of 37, 44, 51, and 58 wt% respectively. The projected area of the AFM images is 25 µm2 (5 × 5 µm). The RMS means root mean square roughness of the films. (e) X-ray diffraction (XRD) patterns, (f) ultraviolet-visible (UV-Vis) absorption spectra, and (g) time-resolved photoluminescence (PL) decay curves for MAPbI3 thin films deposited using various precursor solution concentrations. The asterisks and rhombuses in the XRD pattern indicate the characteristic peaks for FTO and MAPbI3, respectively. The sample for time-resolved PL consists of FTO/MAPbI3/SpiroOMeTAD layers.

To scope out the subsidiary causes of photovoltaic performance in detail, the surface roughness of MAPbI3 was firstly characterized by atomic force microscope (AFM) images (Figure 4a–d). Lower film roughness was apparent for larger grain sizes because the ratio of large grains with smooth surfaces was greater. Smooth films 11 ACS Paragon Plus Environment


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are desirable for better attachment between MAPbI3 and the HTM, and free holes can be efficiently extracted from MAPbI3 to the HTM. Therefore, it is obvious that largegrain-based PSCs (RMS: 17 – 19 nm) would exhibit better electrical performance than small-grain-based PSCs (RMS: 22 – 21 nm).39 X-ray diffraction (XRD) patterns were analyzed to assess the crystallinity of the MAPbI3 films (Figure 4e). All films were consistent with the tetragonal phase of MAPbI3, with diffraction peaks at 15.04 and 27.36° corresponding to the (110) and (220) planes, respectively. The (110) and (220) diffraction peaks were intensified with increasing grain size, indicating that the MAPbI3 crystal structure was highly oriented with low defect densitiy.40 Forming the superb crystals is unconditional in HBL-free structure to offset the disadvantages originated from the absence of adjacent charge transport layer (e.g. TiO2 or ZnO) Figure 4f denotes the incident light absorption properties of the prepared films. With increasing grain size and thickness, the light soaking to MAPbI3 was enhanced from the UV range to 800 nm without any band-gap shift. This was attributed primarily to the high volume of the light absorber and improved crystallinity because of the large grains.41 Time-resolved photoluminescence (TRPL) was explored to monitor the charge transfer properties of MAPbI3 with charge selective layers (Figure 4g). The configuration of the samples was glass/FTO/MAPbI3/spiro-OMeTAD, where the FTO and spiro-OMeTAD were assigned as electron- and hole-extraction layers, respectively. Carrier lifetime is grain size dependent, becoming longer with increasing precursor concentration because of grain boundary-related defects.42 When quenching layers were inserted onto the MAPbI3 interface, fast fluorescent quenching occurred and the lifetime dramatically shortened. We employed a bi-exponential decay equation 12 ACS Paragon Plus Environment

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to fit the displayed curves. The calculated decay lifetimes are summarized in Table S1. The first exponential part (fast decay) is related to non-radiative recombination (surface properties) and exciton transport to a charge collection layer, and the second part (slow decay) contributes to radiative recombination in the bulk perovskite phase.18, 43-45 The ratio of A1, which reflects the charge extraction efficiency, increased with enlarging MAPbI3 grain size. The fast decay time (߬ଵ ) of 3.0 ns for the small grain-based sample (37 wt%) decreased to 0.5 ns for the large grain case (58 wt%). The rate of PL quenching was quickened with increasing MAPbI3 grain size, which was strikingly attributed to the accelerated hole migration at the interface between MAPbI3 and HTM owing to upgraded contact by surface flatness of MAPbI3 (Figure 4a-d).

46

Further, the free charges might be efficiency extracted in the film having a

better quality of perovskite crystallites and low trap density.47-48 To support the results of TRPL and comprehend the charge transport resistance of identical PSCs, the EIS measurement was conducted under full illumination of simulated solar AM1.5 global light at 100 mW/cm2 (Figure S9). The arcs of Nyquist plots recorded in the high-frequency region indicated internal resistance at the FTO/MAPbI3, MAPbI3/HTM, and HTM/Au interfaces.49-51 Apart from the HTM/Au interface prepared by an identical process, the arc size of the Nyquist plot could be affected by the contact of the MAPbI3 layer with the HTM or FTO. Small arcs were obtained for the large MAPbI3 grain-based PSCs (51, 58 wt%), which represented excellent charge transfer between the internal layers of the device. In these devices, the electron migration from MAPbI3 to FTO was facilitated because of improved crystallinity and low trap density of perovskite.47-48 Furthermore, the HTM was more efficiently deposited on the MAPbI3 films having flat and uniform surface. According to the result of AFM (Figure 4a-d), the 51 and 58 wt%-based MAPbI3 have low 13 ACS Paragon Plus Environment


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surface roughness, and this accelerated hole-migration into the HTM. From this characterization, we determined that the current density could be improved by more effective charge transport as well as incident light harvesting level. This EIS result was consistent with the trends in the TRPL data (Figure 4g) and the photovoltaic performances. Also, the influence of perovskite crystallinity on PCE is need-to-know factor to verify our hypothesis. As shown in Figure S10, after DMSO annealing, the PCE of TiO2 BL-inserted-PSC increased by 7 % due to the enhanced crystallinity of MAPbI3 with enlarging grain size. However, the increase of 21 % in PCE was confirmed in case of HBL-free PSC, which demonstrates that the effect of HTM blockage was significantly involved in performance improvement as a pivotal factor besides the enhanced crystallinity. In brief, the control of HTM permeation through increasing MAPbI3 grain size is a more reasonable cause for the improved performance.

Figure 5. (a) Comparison of (a) long-term stability and (b) recyclability of PSCs fabricated as (a) the HBL-free and (b) TiO2 BL-inserted types. All samples were not encapsulated, and the performance was measured without an UV-blocking filter. Long-term stability (air and sunlight) was characterized under ambient condition (25 °C, 35 % RH), and the PCEs obtained at each time point were estimated after sunlight exposure for 7 min. 14 ACS Paragon Plus Environment

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Figure 5 investigates the long-term stability and recyclability of both HBL-free PSCs and TiO2 thin layer-inserted PSCs to suggest the potentiality for commercial application. The HBL-free PSCs had strong durability from attack by sunlight or moisture compared with the TiO2 BL-inserted type, and it can be seen that a TiO2 layer mainly destroys MAPbI3 at the interface by an UV light-induced photocatalytic effect and trap-charge driven degradation (Figure 5a).23, 52 After illuminating sun light on the samples structured with FTO/MAPbI3 or FTO/BL-TiO2/MAPbI3 for 6 h, the peak of PbI2 was soared in case of the TiO2-inserted sample while there was little change of XRD patterns in the TiO2-free sample (Figure S11). In addition to long-term stability, it was confirmed that the PCE of HBL-free PSC measured at reverse scan direction was comparable with TiO2 BL-inserted PSCs with an augmentation of Voc from 1.09 to 1.12 averagely (Figure S12), even though the photocurrent was decreased by low electron extraction rate from perovskite due to large energy barrier between FTO and perovskite.53 This Voc enhancement was caused by reducing the capacitive current and trapped charges accumulated in defects of TiO2 BL, and the static electrons have trouble in jumping over the TiO2 BL, which can trigger the unwanted non-radiative recombination and voltage drop.54,55 In case of FF, the distinct gap was not observed in our experiment and the quite high values were obtained in all cases. Consequentially, the superiority of PCE were fluctuated depending on the values of Jsc and Voc, which is meaningful that the performance of HBL-free PSC is quite close to the PCE of BLinserted PSC in that the commercialization was innovatively facilitated in terms of production cost and process simplification. For the sake of validating cell recyclability (Figure 5b), we washed off the layered thin films from the completed cells just using DMF, DI water, acetone and 2-propanol, which differed from the previous report in that high temperature calcination process is excluded.56 The performance of TiO215 ACS Paragon Plus Environment


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inserted cell was dramatically debased after just one recycle, which was attributed to existence of residual polar protic solvents and PbI2 on TiO2 surface,56 whereas the performance of HBL-free cell was equally maintained with that of the initial cell after four recycles (Figure S12). These highly simple and efficient HBL-free PSCs are very suitable to a commercial solar cell model in terms of economic and environmental values.


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CONCLUSION In summary, we successfully fabricated a simple and efficient PSC in spite of eliminating a HBL. The MAPbI3 film was directly deposited on a blank FTO glass, and the formation of large grain and thick film were material to outstanding performance of HBL-free PSCs. The grain size of MAPbI3 grew up to ca. 1 µm by using a 58 wt% stock solution while maintaining the high crystallinity. A large grain based-MAPbI3 film hindered HTM permeation effectively, enabling a reduction in exciton recombination. Consequently, the topperforming HBL-free PSC, with grain size of ca. 700 nm and a MAPbI3 film thickness of ca. 650 nm, had a PCE of 18.20 %, Jsc of 21.45 mA/cm2, Voc of 1.127 V, and FF of 0.751. This PCE is the highest performance compared with the same type of PSCs and is most closely matched with a previous simulation research.57 Furthermore, it is proved that the exclusion of TiO2-BL not only boosts the average photovoltaic performance, but also has practical benefits from a perspective of long-term stability, recyclability and cost. In addition to the convenient and economical merits, our approach has a potential to be applied to the flexible and roll-to-roll systems, and consequently opens a gate for the successful commercialization of PSC.



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ASSOCIATED CONTENT Supporting Information. Experimental section, Digital photograph of the assembled cells, SEM images, XRD patterns of perovskite, Grain size distribution, photovoltaic properties and J-V curves results under various cell conditions, Hysteresis behavior test, Recyclability result of our PSCs, EIS measurement of HBL-free PSCs under illumination condition. Summarized TRPL decay parameters.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ACKNOWLEDGMENT This work was supported by Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Education,

Science

and

Technology,

Korea

(2011-0031573,

NRF-

2014M3A6A7060583)


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Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-b.; Duan, H.-S.; Hong, Z.; You, J.; Liu,

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