High Performance Perovskite Hybrid Solar Cells with E-beam

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High Performance Perovskite Hybrid Solar Cells with E-beam-Processed TiOx Electron Extraction Layer Tianyu Meng, Chang Liu, Kai Wang, Tianda He, Yu Zhu, Abdullah M. Al-Enizi, Ahmed A. Elzatahry, and Xiong Gong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b09873 • Publication Date (Web): 04 Jan 2016 Downloaded from http://pubs.acs.org on January 9, 2016

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ACS Applied Materials & Interfaces

High Performance Perovskite Hybrid Solar Cells with E-beam-Processed TiOx Electron Extraction Layer Tianyu Meng, 1 Chang Liu,1 Kai Wang,1 Tianda He,1 Yu Zhu,1 Abdullah Al-Enizi,2 Ahmed Elzatahry,3 and Xiong Gong1* 1) College of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA 2) Department of Chemistry College of Science King Saud University Riyadh 11451, Saudi Arabia 3) Materials Science and Technology Program College of Arts and Sciences, Qatar University, P O Box 2713 Doha, Qatar Abstract Perovskite hybrid solar cells (pero-HSCs) have drawn great attention in the last 5 years. The efficiencies of pero-HSCs have been boosted from 3.8% to over 20%. However, one of the bottlenecks for commercialization of pero-HSCs is to make high electrical conductive TiOx electron extraction layer (EEL). In this study, we report high performance pero-HSCs with TiOx EEL, where the TiOx EEL is fabricated by electron beam (e-beam) evaporation, which has been proved to be a well-developed manufacturing process. The resistance of the e-beam evaporated TiOx EEL is smaller than that of sol-gel processed TiOx EEL. Moreover, the dark current densities and interfacial charge carrier recombination of pero-HSCs incorporated with e-beam processed TiOx EEL is also smaller than that of pero-HSCs incorporated with sol-gel processed TiOx EEL. All these result in efficient pero-HSCs with high reproducibility. These results demonstrate that our method provides a simple and facile way to approach high performance pero-HSCs.

Keywords: Perovskite hybrid solar cells, Electron beam evaporation, Compact TiOx layer, Electron extraction layer, High short circuit current density 1 ACS Paragon Plus Environment


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*Corresponding author, Email: [email protected], Fax: (330) 9723406 Introduction Perovskite hybrid materials, CH3NH3PbX3 (where X=Cl, Br and I or combination of them) have been widely studied for realizing high efficiency solar cells.1-9 In the past 5 years, great effects have been paid to boost the efficiency of perovskite hybrid solar cells (pero-HSCs). By development of novel materials,1,9 new device architectures,2,5 and the engineering of the fabrication processes,3,4,6,7,8 the efficiencies of pero-HSCs have rapidly boosted from 3.8% to over 20 %.6 Such high efficiency indicates that pero-HSCs possesses great potentials for making commercial products.5,6 Currently, meso-superstructure (MS) and planar heterojunction (PHJ) pero-HSCs are two most widely investigated device architectures.4,5 In MS pero-HSCs with a device structure of ITO/compact TiOx/mp-TiOx/perovskite/HTL/Au9 (where ITO is indium tin oxide as the cathode, compact TiOx is used as the electron extraction layer (EEL), the mp-TiOx is mesoporous TiOx, the HTL is the hole transport layer, Au is the anode, respectively), a scaffold, mp-TiOx, is used to support the perovskite absorber for increasing the contact area between the compact TiOx EEL and perovskite active layer.10-14 It was also reported that Al2O3 layer used as an insulator to suppress charge carrier recombination and to prevent the degradation of CH3NH3PbI3 induced by moisture.15 However, the mp-TiOx layer has to be sintered at high temperature (> 500 oC).16-23 Such high temperature creates a difficulty for infiltrating perovskite materials homogeneously into the mp-TiOx layer, making the fabrication of the MS pero-HSCs is incompatible with largescale energy-effective roll-to-roll manufacturing. The PHJ pero-HSCs with a device structure of ITO/PEDOT:PSS/perovskite/PC61BM/Al (where ITO is as the anode, PEDOT:PSS is PEDOT:PSS is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, as the hole transporting

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layer, PC61BM is phenyl-C61-butyric acid methyl ester, as the EEL and Al is aluminum as the cathode, respectively) would possess a poor stability due to the utilization of PEDOT:PSS,24-28 which is similar to organic electronics incorporated with PEDOT:PSS.4 In order to circumvent these problems, PHJ pero-HSCs with a device structure of ITO/TiOx/perovskite/P3HT/MoO3/Ag, where ITO acts as the cathode, TiOx is the EEL and P3HT is poly(3-hexylthiophene-2,5-diyl) as the hole extraction layer (HEL), MoO3 is the electron blocking layer, and Ag is the anode, respectively, has been developed and good stability has been observed from PHJ pero-HSCs with such a device structure.29,30 However, in order to enhance the efficiency of PHJ pero-HSCs, solgel-processed TiOx EEL has to be thin enough (less than 50 nm) to ensure a good electrical conductivity of TiOx EEL. To make such thin layer homogenously by sol-gel processing is certainly incompatible with large-scale energy-effective roll-to-roll manufacturing. Therefore, to make high quality TiOx layer by low-cost, easy-and-practical-fabrication-process is crucial to manufacture pero-HSCs products. In this scenario, we report high performance PHJ pero-HSCs with a device structure of ITO/TiOx/PC61BM/CH3NH3PbI3/P3HT/MoO3/Ag, where the TiOx EEL is fabricated by electron beam (e-beam) evaporation, which has been proved to be a well-developed manufacturing process. The resistance of the e-beam evaporated TiOx EEL is smaller than that by sol-gel processed TiOx EEL. Moreover, the dark current densities and charge carrier recombination of pero-HSC incorporated with e-beam processed TiOx EEL are also smaller than those with sol-gel processed TiOx EEL, resulting in efficient pero-HSCs with high reproducibility and eliminated photocurrent hysteresis. These results demonstrate that our method provides a simple and facile way to approach high performance PHJ pero-HSCs.



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Results and Discussion Scheme 1 presents the device structure of PHJ pero-HSCs and the energy levels of TiOx, PC61BM, CH3NH3PbI3, P3HT, MoO3 and the work functions of ITO and Ag electrodes.2, 4, 30 The TiOx/PC61BM is used as the bi-EEL since high electrical conductive PC61BM (~10-7S/cm) can dramatically boost the efficiency of pero-HSCs.30 P3HT is used as the HEL and MoO3 is used as the electron blocking layer, respectively. From the band alignment, it is clearly that the lowest unoccupied molecular orbital (LUMO) energy levels of P3HT and MoO3 are higher than that of CH3NH3PbI3. Such LUMO offset is favorable for blocking the electrons being transported from CH3NH3PbI3 layer to the Ag anode. While the low-lying highest occupied molecular orbital (HOMO) energy levels of PC61BM and TiOx can effectively block the holes being transported from CH3NH3PbI3 layer to the ITO cathode. Small LUMO energy offsets between the TiOx/PC61BM EEL and CH3NH3PbI3, and negligible LUMO energy offsets between the P3HT HEL and CH3NH3PbI3 indicate that high photocurrent could be observed from pero-HSCs. The current densities versus voltage (J-V) characteristics of pero-HSCs under white light illumination with the light intensity of 100 mW/cm2 are characterized. It is noted that during the J-V characteristic measurement, the light soaking effect that improves the power conversion efficiency (PCE) is observed. Such phenomenon has been reported in pero-HSCs with a similar device structure.31-34 In our study, we first conduct the J-V characteristics of pero-HSCs instantly, and then conduct the J-V characteristics after pero-HSCs are illuminated for 10 minutes to get a constant short-circuit current density (JSC). The J-V characteristics of pero-HSCs measured instantly under white light illumination are displayed in Figure 1a. The J-V characteristics of pero-HSCs incorporated with 22 nm thickness of the TiOx EEL either processed by sol-gel or ebeam methods are shown in Figure 1b. The device performance parameters, JSC, open-circuit


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voltage (VOC), fill factor (FF) and PCEs are summarized in Table 1. It is found that the VOC values for the pero-HSCs incorporated with the TiOx EEL are larger than those without the TiOx EEL, which indicates that the TiOx EEL plays an important role in enlarging the VOC. It is also found that there is no much difference in VOC for pero-HSCs incorporated with 22 nm thickness of the TiOx EEL either processed by e-beam or sol-gel methods, whereas decreased JSC are observed from pero-HSCs incorporated with sol-gel TiOx EEL, resulting in decreased PCEs from 10.29% for pero-HSCs incorporated with the e-beam processed TiOx EEL to 9.10% for peroHSCs incorporated with the sol-gel processed TiOx EEL. The decreased JSC are ascribed to the increased sheet resistance (see Table 1). Moreover, JSC, FF and PCEs of pero-HSCs incorporated with the e-beam processed TiOx EEL are increased and then decreased as along with increased thickness of the TiOx EEL. The best device performance is observed from pero-HSCs incorporated with 22 nm thickness of the TiOx EEL, exhibiting a JSC of 19.48 mA/cm2, a VOC of 0.93 V, a FF of 56.8% and a corresponding PCE of 10.29%. Thus, the device performance parameters of pero-HSCs incorporated with the e-beam processed TiOx EEL are in consistent with the values reported from pero-HSCs with a similar device structure where the TiOx EEL was processed via high temperature shintering.2 It is also found that pero-HSCs incorporated with the TiOx EEL possess the same VOC values whether they are illuminated for 10 minutes or not. With 10-minute white light illumination, however, pero-HSCs exhibit significant enhanced JSC, and consequently enhanced PCEs. For instance, pero-HSCs incorporated with 22 nm thickness of the TiOx EEL exhibit JSC of 27.83 mA/cm2, FF of 56.8%, giving rise a corresponding PCE of 14.70%, after 10-minute illumination. These results demonstrate that the light soaking effect does take place in pero-HSCs incorporated the TiOx EEL. Such phenomenon has been reported in pero-HSCs with a similar device



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structure.31-34 The light soaking effect is first reported by B. O’Regan for the TiOx/RuLL’NCS/CuSN dye-sensitized solar cells (DSSCs).32 L. Yang and P. Tiwana has also found similar effect in DSSCs incorporated with TiOx and SnO2.33,34 We are currently studying the underline of the light soaking effects in pero-HSCs and will report our findings elsewhere later.

The incident photon to current conversion efficiencies (IPCE) spectra of pero-HSCs are shown in Figure 1c. All pero-HSCs possess high IPCE values in the wavelength from 375 nm to 750 nm, while IPCE instantly drops from 750 nm to 800 nm, with the lowest IPCE values, which is in consistent with the absorption spectrum of CH3NH3PbI3.14 The IPCE values from peroHSCs incorporated with the TiOx EEL are significant higher than those from pero-HSCs without the TiOx EEL. Moreover, the IPCE values are firstly increased and then decreased along with increased thickness of the TiOx EEL, which is in consistent with the JSC variations observed from J-V characteristics (Figure 1a). It worthy to notice that the thin TiOx EEL is unable to fully cover the surface of the ITO electrode, which causes a direct contact between the ITO electrode and the CH3NH3PbI3 active layer, resulting in high leakage current and charge carrier recombination at the TIOx/perovskite interface.14 While the thick TiOx EEL would generate rough and inhomogeneous thin film, creating the surface defects, resulting in low JSC.2,14 In addition, reduced photocurrent is also expected from pero-HSCs with the thick TiOx EEL due to poor electrical conductivity of the thick TiOx EEL (10-11 S/cm). As a result, poor PCEs are anticipated in both cases. To have a better understanding of the influence of TiOx thickness on the performance of pero-HSCs, the series resistance (RS) and shunt resistance (RSH) of pero-HSCs with different thickness of the TiOx EEL processed either by e-beam or sol-gel methods, are estimated from the J-V curves as shown in Figures 1a & 1b. The results are summarized in Table 1. In solar cells, 6 ACS Paragon Plus Environment

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the RS comes from the contact resistance between the metal electrode and photo-active layer, and the resistance inside the circuit, which dissipates output power and lowers JSC, VOC and FF, hence PCE.30 The RSH is originated from charge carrier recombination and leakage current.30 In general, low RS and high RSH are expected for solar cells with high PCEs.35, 36 The pero-HSC with 22 nm thickness of the TiOx EEL processed by e-beam method possesses the lowest RS (102 Ωcm2) and the largest RSH (489 Ωcm2) as compared to other pero-HSCs incorporated with e-beam processed TiOx EEL. Thus, the highest PCE is observed from the pero-HSCs with ~ 22 nm TiOx EEL. Moreover, the RS and RSH observed from pero-HSCs incorporated ~ 22 nm thickness of sol-gel processed TiOx EEL are 213 Ωcm2, and 293 Ωcm2, respectively. As compared with the pero-HSCs incorporated with e-beam processed TiOx EEL, the larger RS and smaller RSH observed from pero-HSCs incorporated with sol-gel processed TiOx EEL indicate the electrical conductivity of e-beam processed TiOx EEL is higher than that of sol-gel processed TiOx EEL, resulting in enhanced JSC and consequently high PCEs. The transmittance spectra of TiOx films are measured to get a deeper insight into the influence of TiOx thickness on the performance of pero-HSCs. Figure 2 presents the transmittance spectra of TiOx films with different thickness. It’s clear that in the wavelength ranging from 450 nm to 600 nm, the transmittance decreases with the increased thickness of the TiOx EEL, which can be regarded as one of the origins for the deteriorated performance of peroHSCs incorporated with the TiOx EEL with the thickness from 22 nm to 30 nm. While in the region from 600 nm to 800 nm, which is the lowest absorption region for CH3NH3PbI3,14 the transmittance remains almost the same for the TiOx EEL with different thickness, indicating that the TiOx transmittance plays minor role in determining the device performance in this region. It’s noteworthy that the transmittance value over 100% from the wavelength of 550 nm to 700 nm



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indicates TiOx thin films possess better transmittance than that of bare ITO, which is probably due to the antireflective phenomenon by destructive coherent light.19-21 Figure 3 presents the atomic force microscope (AFM) images of TiOx thin films processed either by e-beam or sol-gel methods. From the height images, the root mean square roughness (RMS) can be observed. The RMS values are ~1.08 nm, ~1.62 nm, ~4.10 nm, ~5.28 nm, and ~12.5 nm for the e-beam processed TiOx EEL with the thicknesses of ~4 nm, ~8 nm, ~13 nm, ~22 nm, and ~30 nm, respectively. The RMS values are ~0.85 nm, ~1.3 nm, ~2.35 nm, ~3.50 nm and ~5.32 nm for the sol-gel processed TiOx EEL with the thicknesses of ~4 nm, ~8 nm, ~13 nm, ~22 nm, and ~30 nm, respectively. The rough surface of e-beam processed TiOx EEL is probably due to poor film mechanical properties. From the phase images, we can see that the domain size of e-beam processed TiOx is getting larger while the film thicknesses are increased, which indicate that a thicker TiOx film can fully cover the entire surface of the ITO substrate. Also, a similar RMS observed from 4 nm TiOx with that of the bare ITO surface (RMS ~0.9 nm) indicates that thin layer (4 nm) of TiOx cannot fully cover the surface of the ITO electrode, which results in poor PCEs. While too thick TiOx films possess large RMS, which inevitably lead to leakage current at the TiOx/CH3NH3PbI3 interface and consequently detriment the device performance. Thus, PCEs are firstly enhanced with the augment of TiOx thickness but then diminished, as demonstrated in Figure 1a. Whereas, for sol-gel processed TiOx EEL, the smaller domain size and homogeneous thin films are observed. The impedance spectroscopy (IS) is further applied to study the internal series resistances (RS) of pero-HSCs with different thickness of the TiOx EEL.37-39 The RS consist of the sheet resistance (RSH) of the electrodes, the charge-transport resistance (RCT) which exists at the interface between the ITO electrode and the TiOx EEL, the TiOx EEL and perovskite active layer,


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and inside of perovskite active layer.39 In this work, the difference in RCT is only at the interface between the TiOx EEL and perovskite active layer. Figure 4a presents the Nyquist plots of peroHSCs measured the voltage closes to the open-circuit voltage. The related electric circuit is inserted into Figure 4a. It is clearly that the RCT is firstly decreased and then increased along with increased thickness of TiOx EEL. The smallest RCT of 6 kΩ is observed from the pero-HSCs with 22 nm thickness of TiOx EEL. The rising in RCT is attributed to the descending charge carrier recombination and leakage current.35, 38 As the TiOx thicknesses is further increased, large RCT from pero-HSCs with over 22 nm thickness of TiOx EEL is probably originated from poor electrical conductivity of TiOx with such large thickness. The Nyquist plots of pero-HSCs incorporated with either the sol-gel processed or the e-beam processed TiOx EELs are displayed in Figure 4b. The RCT for pero-HSCs incorporated with the sol-gel processed TiOx EEL is ~ 8.5 kΩ, which is larger than that of pero-HSCs incorporated with the e-beam processed TiOx EEL. The increasing RCT is ascribed to the enlarged resistance of the sol-gel processed TiOx and increased leakage current. We further study the photocurrent hysteresis of pero-HSCs incorporated with e-beam processed TiOx EEL. In pero-HSCs, a significant issue is photocurrent hysteresis. Z. Xiao et al., and H. J. Snaith et al., have found that the photocurrent hysteresis of pero-HSCs was probably originated from the defects inside devices acts as the traps for electrons and holes, ferroelectric properties of organometal trihalide perovskites materials and excess of ions,4, 31 which affect the performance of pero-HSCs. To investigate the photocurrent hysteresis in pero-HSCs, we measured the J-V curves under forward scan (from negative bias to positive bias) and reverse scan (from positive bias to negative bias). As shown in Figure 5, a PCE of 13.26 % with a VOC 0.95 V, a JSC 25.30 mA/cm2, and a FF 55.2% is observed from pero-HSCs under the forward



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scan, while a PCE of 14.70 % with a VOC of 0.93 V, a JSC of 27.83 mA/cm2, and a FF of 56.8% is observed from pero-HSCs under the reverse scan. The difference in PCE is less than 1.5%, which indicates that pero-HSCs incorporated with e-beam processed TiOx EEL possess less photocurrent hysteresis than those reported values.35 Since one of the most distinguished advantages of e-beam evaporated TiOx EEL over those from the sol-gel processed TiOx is that TiOx EEL is highly homogeneous and extremely compacted, which could result in pero-HSCs with high reproducibility. In order to confirm it, over 100 of the pero-HSCs with 22 nm thickness of TiOx EEL are investigated. As shown in Figure 6, very high reproducibility and low deviation in device parameters (VOC, JSC, FF and PCE) are observed from pero-HSCs with e-beam evaporated TiOx EEL as compared with those from pero-HSCs based on sol-gel processed TiOx EEL. These results demonstrate that e-beam evaporated TiOx EEL is extraordinarily favorable for the large area production of pero-HSCs. Conclusion In summary, we reported high performance pero-HSCs incorporated with the TiOx EEL, where the TiOX EEL is processed by the e-beam evaporation, which is a well-developed manufacturing method. In contrast to the traditional sol-gel processed TiOx EEL, highly homogeneous and extremely compacted e-beam evaporated TiOx EEL suppress the dark leakage current densities and interfacial charge carrier recombination, resulting pero-HSCs with 10.29 % efficiency, very high reproducibility. Thus, our work certainly offers a facile route for boosting the commercialization of pero-HSCs with high performance.

Experimental Section


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Materials: Titanium was purchased from Electron Beam Welding LLC. The lead iodine (PbI2, 99.99%) was purchased from Sigma-Aldrich. CH3NH3I (methylammonium iodine, MAI) was synthesized using previous reported method in our lab29,34. Hydroiodic acid (57 wt%, 99.99%) and methylamine (33 wt %) were purchased from Sigma-Aldrich. PC61BM (99.9%) was purchased from Solenne BV. P3HT was purchased from Rieke Metals, Inc. MoO3 was purchased from Alfa Aesar Inc. All materials were used as received without further purification. TiOx preparation: Electron-beam evaporation is based on the bombardment of high speed electrons directly to the target materials. To make TiOx compact thin film, the pure metal titanium (Ti) was firstly deposited by electron-beam evaporation on the ITO substrates, followed with thermal annealing at 500℃ for one hour in the ambient environment to convert Ti to TiOx. The make of sol-gel processed TiOx as comparable device is reported previously.29 TiOx thin film characterization: The surface morphology of TiOx thin film is investigated by atomic force microscope (AFM) (NanoScope NS3A system). The thickness of TiOx is also measured by AFM. The UV-vis transmittance spectra of TiOx films are tested by HP 8453 spectrophotometer. Pero-HSCs Fabrication: Pero-HSCs are fabricated on the pro-cleaned ITO glass substrates. ~ 80 nm PC61BM layer is spin-coated on the top of TiOx EEL from 2 wt% 1, 2-dichlorobenzene (oDCB) solution. After that, ~280 nm CH3NH3PbI3 film is prepared by two-step method. Firstly, PbI2 layer is casted on the top of PC61BM layer from 40 wt % dimethylformamide solution followed with thermal annealing at 70oC for 10 minutes. Afterward, MAI layer is spin-coated in the top of PbI2 layer from 3.5 wt % isopropanol solution and then thermal annealed at 100 ℃ for 2 hours. The MAI was synthesized in our lab.29,34 After that, ~100 nm P3HT layer is casted on the top of perovskite layer from 2 wt% o-DCB solution. Lastly, ~10 nm MoO3 and ~100 nm Ag



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are sequentially deposited in the vacuum with base pressure of 4 ×10-6 mbar. The device area is measured to be 0.045 cm2. Pero-HSCs characterization: pero-HSCs are characterized under an AM 1.5 G calibrated solar simulator (Newport model 91160-1000) with light intensity of 100 mW/cm2, which is calibrated by a mono-silicon detector (with KG-5 visible color filter) of National Renewable Energy Laboratory. The J-V characteristic is tested and recorded by Keithley 2400 source meter. The incident photon to current efficiency (IPCE) is measured by ESTI for cells and mini-modules. The impedance spectrometry (IS) is tested by HP 4194A impedence/gain-phase analyzer. The devices for IS testing are conducted in dark, with oscillating voltage of 10 mV and frequency of 1 Hz to 1 MHz. Acknowledgments The authors would like to thank National Science Foundation (Grant No. 1351785) for financial support. TUM acknowledges Ms. Tong Li for assisting in AFM measurement.


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References 1) Yella, A.; Heiniger, L -P.; Gao, P.; Nazeeruddin, M. K.; Gratzel, M. Nanocrystalline Rutile Electron Extraction Layer Enables Low-Temperature Solution Processed Perovskite Photovoltaics with 13.7% Efficiency. Nano Lett. 2014, 14, 2591-2596. 2) Conings, B.; Baeten, L.; Dobbelaere, C. D.; D’Haen, J.; Manca, J.; Boyen, H -G. PerovskiteBased Hybrid Solar Cells Exceeding 10% Efficiency with High Reproducibility Using a Thin Film Sandwich Approach. Adv. Mater. 2014, 26, 2041-2046. 3) Liu, D.; Kelly, T. L. Perovskite Solar Cells with a Planar Heterojunction Structure Prepared using Room-Temperature Solution Processed Techniques. Nat. Photonics 2014, 8, 133-138. 4) Xiao, Z.; Bi, C.; Shao, Y.; Dong, Q.; Wang, Q.; Yuan, Y.; Wang, C.; Gao, Y.; Huang, J. Efficient, High Yield Perovskite Photovoltaic Devices Grown by Interdiffusion of SolutionProcessed Precursor Stacking Layers. Energy Environ. Sci. 2014, 7, 2619-2623. 5) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskite as VisibleLight Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050-6051. 6) 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, 542-546. 7) Zhao, Y.; Zhu, K. Charge Transport and Recombination in Perovskite (CH3NH3)PbI3 Sensitized TiO2 Solar Cells. J. Phys. Chem. Lett. 2013, 4, 2880-2884. 8) Gonzalez-Pedro, V.; Juarez-Perez, E. J.; Arsyad, W –S.; Barea, E. M.; Fabregat-Santiago, F.; Mora-Sero, I.; Bisquert, J. General Working Principles of CH3NH3PbX3 Perovskite Solar Cells. Nano Lett. 2014, 14, 888-893. 9) Grätzel, M. Dye-sensitized Solar Cells. J. Photochem. Photobiol., C 2003, 4, 145-153. 13 ACS Paragon Plus Environment


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19) Bao, X.; Sun, L.; Shen, W.; Yang, C.; Chen, W.; Yang, R. Facile Preparation of TiOx Film as an Interface Material for Efficient Inverted Polymer Solar Cells. J. Mater. Chem. A 2014, 2, 1732-1737. 20) Im, S. H.; Kim, H –J.; Kim, S. W.; Kim, S. –W.; Seok, S. I. All Solid State Multiply Layered PbS Colloidal Quantum-Dot-Sensitized Photovoltaic Cells. Energy Environ. Sci. 2011, 4, 4181-4186. 21) Mergel, D.; Buschendorf, D.; Eggert, S.; Grammes, R.; Samset, B. Density and Reflective Index of TiO2 Films Prepared by Reactive Evaporation. Thin Solid Films 2000, 371, 218-224. 22) Bao, X.; Yang, Y.; Yang, A.; Wang, N.; Wang, T.; Du, Z.; Yang, C.; Wen, S.; Yang, R. Antireflection and Band Gap Extension Effects of ZnO Nanocrystalline Films Grown on ITO-Coated Glasses by Low Temperature Process. Mater. Sci. Eng., B 2013, 178, 263-266. 23) Bi, D.; Moon, S. –J.; Häggman, L.; Boschloo, G.; Yang, L.; Johansson, E. M. J.; Nazeeruddin, M. K.; Grätzel, M.; Hagfeldt, A. Using a Two-Step Deposition Technique to Prepare Perovskite (CH3NH3PbI3) for Thin Film Solar Cells Based on ZrO2 and TiO2 Mesostructures. RSC Adv. 2013, 3, 18762-18766. 24) Jeng, J. –Y.; Chiang, Y. –F.; Lee, M. –H.; Peng, S. –R.; Guo, T. –Z.; Chen, P. Wen, T. –C. CH3NH3PbI3 Perovskite/Fullerene Planar-Heterojunction Hybrid Solar Cells. Adv. Mater. 2013, 25, 3727-3732. 25) Seo, J.; Park, S.; Kim, Y. C.; Jeon, N. J.; Noh, J. H.; Yoon, S. C.; Seok, S. I. Benefits of Very Thin PCBM and LiF for Solution-Processed p-i-n Perovskite Solar Cells. Energy Environ. Sci. 2014, 7, 2642-2646.



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1 2 3 4 Thickness 5 of TiO x 6 (nm) 7 0 8 4±0.2 9 8±0.2 10 13±0.2 11 22±0.2 12 30±0.2 13 22±0.2# 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

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Table 1. Characteristics of pero-HSCs VOC (V) 0.80±0.06 0.96±0.07 0.93±0.06 0.93±0.07 0.93±0.08 0.95±0.07 0.92±0.06

JSC (mA/cm2) W/O 11.44±0.82 18.30±0.81 18.77±0.67 19.29±0.76 19.48±0.61 17.50±0.64 18.02±0.55

FF (%)

W/ * 16.35±0.82 26.14±0.81 26.81±0.67 27.55±0.76 27.83±0.61 25.00±0.64 25.23±0.52

PCE (%)

39.2±2.0 46.8±1.7 54.7±1.6 55.2±2.3 56.8±2.6 54.0±2.6 54.9±2.1

W/O 3.58±0.50 8.22±0.31 9.54±0.38 9.90±0.39 10.29±0.54 8.97±0.48 9.10±0.49

W/ * 5.12±0.50 11.74±0.31 13.64±0.38 14.14±0.39 14.70±0.54 12.82±0.48 12.74±0.49

*

RSH (Ωcm2) W/O W/ * 67 112 157 257 344 430 410 520 489 626 158 223 293 395

RS (Ωcm2) W/O W/ * 682 549 251 189 197 132 135 105 102 78 185 110 213 165

: with the light soaking effect for 10 minutes (AM 1.5 G calibrated solar simulator with the light intensity of 100 mW/cm2 ) # : pero-HSCs with 22 nm thickness of the sol-gel processed TiOx EEL


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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


b

a

Scheme 1. (a) Device structure of pero-HSCs, ITO/TiOx/PC61BM/CH3NH3PbI3/MoO3/Ag and (b) the LUMO and HUMO energy levels of TiOx, PC61BM, CH3NH3PbI3, P3HT, MoO3 and the work functions of ITO and Ag electrodes



0

0 0 nm TiO

a

x

b

4 nm TiO

Sol-gel processed TiO

8 nm TiO

E-beam processed TiO

2

Current Density (mA/cm )

2

Current Density (mA/cm )

x x

13 nm TiO

-5

x

22 nm TiO

x

30 nm TiO

x

-10

-15

x x

-5

-10

-15

-20 -20 0

0.2

0.4

0.6

0.8

1

0

Voltage (V)

0.2

0.4

0.6

0.8

1

Voltage (V)

80

c 70 60

IPCE (%)

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

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50 40 30

0 nm TiO 4 nm TiO

20

8 nm TiO

X X X

13 nm TiO 10

22 nm TiO 30 nm TiO

X X X

0 400

500

600

700

800

Wavelength (nm)

Figure 1. (a) J-V characteristics of pero-HSCs incorporated with e-beam processed TiOx EEL, (b) J-V characteristics of pero-HSCs incorporated 22 nm thickness of TiOx EEL processed by ebeam and sol-gel methods and (c) the incident photon-to-current conversion efficiency (IPCE) spectra of pero-HSCs incorporated with incorporated with e-beam processed TiOx EEL.


Page 21 of 26

100

Transmittance (%)

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


80

60

4 nm TiO 40

8 nm TiO

X X

13 nm TiO 22 nm TiO 20

0 450

30 nm TiO

500

550

600

650

700

X X X

750

800

Wavelength (nm)

Figure 2. Transmittance spectra of e-beam processed TiOx EEL.



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

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Figure 3. AFM height images of e-beam processed TiOx with thickness of (a) 4 nm, (b) 8 nm, (c) 13 nm, (d) 22 nm, and (e) 30 nm and AFM phase images of e-beam processed TiOx with thickness of (f) 4 nm, (g) 8 nm (h) 13 nm, (i) 22 nm, and (j) 30 nm, and AFM height images of sol-gel processed TiOx with thickness of (k) 4 nm, (l) 8 nm, (m) 13 nm, (n) 22 nm and (o) 30 nm, and AFM phase images of sol-gel TiOx with thickness of (p) 4 nm, (q) 8 nm, (r) 13 nm, (s) 22 nm and (t) 30 nm


Page 23 of 26

4

4 10

(a)

R 0 nm TiO

4

3.5 10

4 nm TiO 8 nm TiO

4

3 10

CT

R

X

S

X X

-lm Z (Ohm)

13 nm TiO 22 nm TiO

4

2.5 10

30 nm TiO

X

C

X X

4

2 10

4

1.5 10

4

1 10

3

5 10

0 0

3

5 10

4

4

4

4

4

4

4

1 10 1.5 10 2 10 2.5 10 3 10 3.5 10 4 10

Re Z (Ohm) 1 10

4

R

(b)

CT

R S

8 10

3

C

-lm Z (Ohm)

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


6 10

Sol-gel processed TiO

3

x

E-beam processed TiO

4 10

3

2 10

3

0 0

2 10

3

4 10

3

x

6 10

3

8 10

3

1 10

4

Re Z (Ohm)

Figure 4. (a) Nyquist plots of pero-HSCs incorporated e-beam-processed TiOx EEL and (b) Nyquist plots of pero-HSCs incorporated 22 nm thickness of TiOx EEL either processed by ebeam or sol-gel methods. The measurement is conducted at V≈VOC.



0

Current Density (mA/cm2)

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

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Forward scan

-5

Reverse scan -10

-15

-20

-25

-30 0

0.2

0.4

0.6

0.8

1

Voltage (V)

Figure 5. J-V curves of pero-HSCs incorporated with e-beam processed TiOx EEL under forward and reverse scan directions


Page 25 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Histograms of photovoltaic parameters for pero-HSCs (a) VOC, (b) JSC, (c) FF, and (d) PCEs



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Table of Contents (TOC)


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High Performance Perovskite Hybrid Solar Cells with E-beam

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