Enhancing the Durability and Carrier Selectivity of Perovskite Solar

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Enhancing Durability and Carrier Selectivity of Perovskite Solar Cells using a Blend Interlayer Dong Hun Sin, Sae Byeok Jo, Seung Goo Lee, Hyomin Ko, Min Kim, Hansol Lee, and Kilwon Cho ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 12 May 2017 Downloaded from http://pubs.acs.org on May 13, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

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

ACS Applied Materials & Interfaces

Enhancing Durability and Carrier Selectivity of Perovskite Solar Cells using a Blend Interlayer

Dong Hun Sin, Sae Byeok Jo, Seung Goo Lee, Hyomin Ko, Min Kim, Hansol Lee, and Kilwon Cho* Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, Korea

D. H. Sin, Dr. S. B. Jo, Dr. S. G. Lee, H. Ko, Dr. M. Kim, H. Lee, and Prof. K. Cho Department of Chemical Engineering Pohang University of Science and Technology (POSTECH) Pohang, 790−784, Korea E-mail: [email protected]

Keywords: adhesive interface, durable interface, electron-selective interface, ZnO:PEG blend, perovskite solar cells

ACS Paragon Plus Environment


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

Abstract Mechanically, thermally stable and electron-selective ZnO/CH3NH3PbI3 interface is created via hybridization of a polar insulating polymer, poly(ethylene glycol) (PEG), into ZnO nanoparticles (NPs). PEG successfully passivates the oxygen defects on ZnO and prevents direct contact between CH3NH3PbI3 and defects on ZnO. Uniform CH3NH3PbI3 film is formed on soft ZnO:PEG layer after dispersing the residual stress from the volume expansion during CH3NH3PbI3 conversion. PEG also increased the work of adhesion of CH3NH3PbI3 film on ZnO:PEG layer and held CH3NH3PbI3 film with hydrogen bonding. Furthermore, PEG tailors the interfacial electronic structure of ZnO, reducing the electron affinity of ZnO. As a result, selective electron-collection cathode is formed with reduced electron affinity and deep-lying valence band of ZnO, which significantly enhances carrier lifetime (473 µs) and photovoltaic performance (15.5%). The mechanically and electrically durable ZnO:PEG/CH3NH3PbI3 interface maintains the sustainable performance of the solar cells over 1 year. Soft and durable cathodic interface via PEG hybridization in ZnO layer is an effective strategy towards flexible electronics and commercialization of the perovskite solar cells.


Page 2 of 32

Page 3 of 32

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


1. Introduction Since the first observation of the photovoltaic effects of the methylammonium lead halide (CH3NH3PbX3, X=Cl, Br, and I) perovskites, a power conversion efficiency (PCE) of 20% has been achieved in perovskite solar cells (PeSCs). 1-10 This recent rapid increase in PCE was achieved by controlling the perovskite morphology and the device interfaces. Perovskite morphology is delicately influenced by the processing environment, so many studies of the fabrication of high-quality perovskite layers have been carried out.

4, 11-16

Furthermore,

charge-transferring interfaces form a built-in potential with energetic pathways for the charge carriers and selectively collect charge carriers from the perovskite layer, and thus have a critical influence on the photovoltaic parameters of PeSCs. 17-27 Selective charge collection is very important because a PeSC is basically a diode device, so for efficient power conversion the photo-generated charges should move in one direction only. 28 ZnO has a high electron mobility (10-5 ~ 10-2 cm-1 V-1 s-1) and a large band gap (~ 3.4 eV), and is therefore an appropriate material for the electron collection layer (ECL) of PeSCs. 18, 29 The conduction band (CB) of ZnO is well aligned with the CB of CH3NH3PbI3, so electron injection is favored, whereas the valence band (VB) of ZnO is high enough to block hole injection from CH3NH3PbI3. Despite these benefits of ZnO as an ECL, CH3NH3PbI3 films are mechanically and thermally unstable on ZnO. CH3NH3PbI3 films peel off from ZnO surfaces due to the poor adhesion of CH3NH3PbI3 to ZnO when PbI2 is converted to CH3NH3PbI3 because of the layer’s volume expansion during the sequential deposition method. The densities of PbI2 and CH3NH3PbI3 are 6.16 and 4.20 g cm-3, respectively, so the volume of the PbI2 film expands two-fold as a result of conversion. This volume expansion leads to incomplete perovskite conversion with a tight perovskite patch above unconverted PbI2 blocking CH3NH3I diffusion and hinders perovskite film formation on hard surface generating residual stress at the interface. 13, 30 Moreover, the methylammonium cations in CH3NH3PbI3 are deprotonated on ZnO; as a result, CH3NH3PbI3 decomposes into CH3NH3I and PbI2. 31, 32 In order to use ZnO as an efficient ECL for PeSCs, the interfacial contact between the ZnO layer and the CH3NH3PbI3 layer should be mechanically and thermally stable, which enables effective charge injection from CH3NH3PbI3 to ZnO and ensures applicability to flexible electronics and commercialization of PeSCs. Therefore, the ZnO surface must be modified to enable the fabrication of efficient PeSCs.



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

Page 4 of 32

The ZnO surface has previously been modified by incorporating several polar insulating polymers, namely poly(vinyl pyrrolidone) (PVP), poly(ethylene imine) (PEI), and poly(ethylene glycol) (PEG), that passivate ZnO surface defects.

33-35

Use of ZnO

nanoparticles (NPs) dispersed in alcohol-based solvent is a good strategy with solution process at low temperature because ZnO can be easily hybridized with such polar insulating polymers by simply adding them to a ZnO NP dispersion. Jo et al. hybridized ZnO NPs with PEG and fabricated organic solar cells with ZnO:PEG ECLs.

35

It was found that PEG

successfully passivates the surface defects of the ZnO NPs and tailors the CB of the ZnO NPs to the lowest unoccupied molecular orbital (LUMO) level of phenyl-C61-butyric acid methyl ester (PCBM); as a result, charges were collected effectively and selectively at the cathode. However, ZnO:PEG ECLs have only been tested in organic solar cells based on poly(3-hexyl thiophene) and a few donor molecules. 34 In order to expand the use of ZnO:PEG as an ECL in versatile applications with diverse photo-active materials, ZnO:PEG-based solar cells with other photo-active materials such as CH3NH3PbX3 perovskites should be also investigated. The modification of the charge-transferring interface also affects the charge recombination dynamics inside the PeSCs. 17, 36-39 Photo-generated charge carriers can follow several charge recombination routes before being collected at the electrode, so charge recombination dynamics critically determines the overall PCE of the PeSCs. In general, photo-generated charge carriers can recombine through the trap-assisted and bimolecular recombination mechanisms. 28, 40-42 Charged defect sites at the interface trap the charge carriers and make them recombine with the opposite charge carriers. Furthermore, poor charge injection due to an energy level mismatch at the interface leads to severe charge accumulation near the interface; the accumulated charge carriers recombine through bimolecular recombination. 43-46 Therefore, to reduce charge recombination inside the PeSCs and improve their efficiency, the number of interfacial defect sites should be reduced and the energy levels at the interface should be aligned. In this study, we hybridized ZnO NPs with a polar insulating polymer, PEG, in order to passivate their surface defects and to modify their interfacial electronic properties to prepare a mechanically, thermally stable and selectively electron-collecting cathodic interface. We systematically varied the PEG contents relative to the ZnO NP content and found that PEG successfully passivates charged surface oxygen defects of ZnO NPs and prevents direct contact between CH3NH3PbI3 and defects on ZnO. The mechanical and thermal stabilities of


Page 5 of 32

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


CH3NH3PbI3 thin films on ZnO NP layers were found to be improved significantly. In addition, hybridization of PEG into the ZnO NPs tailors interfacial electric properties of ZnO NPs by adjusting their CB to the CB of CH3NH3PbI3; as a result, an ohmic and chargeselective contact for electrons is formed, and the built-in potential increases. The charge carrier recombination dynamics was investigated by monitoring the incident light powerdependent photocurrent (Jph) and by performing transient photovoltage (TPV) and transient photocurrent (TPC) analyses. It was found that the addition of PEG results in effective and selective charge collection with an increased charge carrier lifetime (߬n) and reduced charge carrier recombination; these changes were found to result in an increased total charge carrier collection, and a rectifying property. The mechanically and electrically durable heterointerface maintained the photovoltaic performance of the PeSCs based on PEG-hybridized ZnO ECL over 1 year. These results bear the significance of soft and durable interface towards flexible electronics and commercialization.

2. Experimental details 2.1. Methylammonium iodide Synthesis CH3NH3I was synthesized by reacting 13.5 ml methylamine (40 wt% in H2O, SigmaAldrich) with 15.0 ml hydroiodic acid (57 wt% in H2O, Sigma-Aldrich) at 0 oC under N2 environment for 2h. CH3NH3I powder was obtained after solvent evaporation and washing with diethyl ether, and dried in 60 oC vacuum oven over 12 h. 2.2. ZnO NP synthesis ZnO NPs were synthesized following the sol-gel method introduced by Beek et al.

47

Synthesized ZnO NPs were dispersed in methanol and purified by conducting centrifugation (4000rpm, 20min) for two times, and finally dispersed in 1-butanol with a concentration of 15 mg ml-1. ZnO dispersion (15 mg ml-1 in 1-butanol) was mixed with same volumetric amount of methanol to make 7.5 mg ml-1 ZnO dispersion in a mixture of 1-butanol and methanol (1:1, v/v) before using. ZnO:PEG dispersions were prepared by mixing 1 ml ZnO dispersion (15 mg ml-1 in 1-butanol) and 1 ml PEG (Mw=6000) solution (in methanol) under ultra-sonication over 1h, generating total ZnO concentration of 7.5 mg ml-1 in a mixture of 1-butanol and methanol (1:1, v/v) with different amounts of PEG. The ZnO:PEG weight ratio was



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

systematically varied from 15:1 to 15:10 (wt:wt). 2.3. Perovskite Solar Cell Fabrication ITO coated glass was cleaned with detergent, DI water, acetone, and IPA in order with ultra-sonication for 20 min at each step. After UV-ozone treatment for 20 min, ZnO and ZnO:PEG layers were spin-casted from ZnO and ZnO:PEG dispersions. ZnO and ZnO:PEG layers were evacuated for 2h and transferred into glovebox. 460 mg ml-1 PbI2 solution was prepared in DMF at 70 oC for overnight, and 10 mg ml-1 CH3NH3I solution was prepared in IPA before using. PbI2 film was spin-casted at 4000 rpm for 90 s and reacted with CH3NH3I in IPA at 60 oC for 3 min. After reaction, perovskite film was rinsed with IPA for a second and annealed on 90 oC hot-plate for 2 min. Spiro-OMeTAD (Merck) was spin-casted from 72.5 mg ml-1 Spiro-OMeTAD solution in CB at 3500 rpm for 30 s. tBP and Li-TPSI were doped into Spiro-OMeTAD solution before spin-casing. Au (60 nm) cathode was thermally deposited under high vacuum (2×1016 cm-3) increases further (Φ=1.75) due to poor charge extraction. As a result, charge collection increases with the PEG hybridization in the ZnO ECL because charge recombination is reduced with the defect passivation on ZnO and intimate, electron-selective cathodic interface between ZnO:PEG and CH3NH3PbI3, which coincides with an increase in JSC. When FTO is used as the cathode instead of ITO, ߬n further increases from 351 to 473 µs because RS decreases and the area of the charge-transferring interface increases; these effects further reduce charge accumulation and charge recombination inside the PeSCs. Furthermore, charge carrier recombination is less dependent on charge carrier density in the FTO-based PeSCs than in the ITO-based PeSCs. With the inclusion of the highly conductive and rough FTO cathode, the electrons are effectively transferred from CH3NH3PbI3 and transported to the cathode without significant charge carrier recombination loss. As a result, charge collection becomes faster and charge collection increases as is evident in the photovoltaic parameters. 3.5. Long-Term Stability of ZnO:PEG-Based PeSCs



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

PEG in ZnO:PEG hybrid layer successfully covers surface defects on ZnO NPs and makes the hybrid layer elastic. Elastic behavior of PEG disperses the residual stress originated from the volume expansion during CH3NH3PbI3 conversion, which results in well-formed CH3NH3PbI3 film on soft ZnO:PEG layer. Direct contact between CH3NH3PbI3 and oxygen defects on ZnO is prevented by PEG and CH3NH3PbI3 layer is retained on ZnO:PEG layer through hydrogen bonding, inducing stable cathodic interface. In addition, efficient electronselective cathode significantly reduces charge accumulation near contact which focuses internal field on contact and degrades interfacial properties. As a result, photovoltaic performance of the PeSCs based on a ZnO:PEG ECL is found to be maintained at around 80% for more than 1 year in a glovebox (Figure 8). Long-term stability as well as high efficiency is a difficult issue to be solved for the PeSCs to be commercialized. With the proper passivation layer, the PeSCs based on stable ZnO:PEG ECL would be available to maintain almost initial performance over 1 year. Therefore, soft and durable interface via PEGincorporated ZnO NP layer is a capable strategy towards flexible electronics and commercialization.

4. Conclusions The roles of a polar insulating polymer, PEG, in ZnO:PEG nanocomposite layers and the optoelectronic properties of the PeSCs based on ZnO:PEG ECLs have been investigated. PEG is readily hybridized into sol-gel ZnO solution by simple mixing and successfully passivates charged surface defects on ZnO NPs with lone-pair electrons on oxygen. PEG agglomerates ZnO NPs and makes ZnO:PEG layer elastic through elastic behavior of PEG. Soft PEG disperses the residual stress arising from volume expansion during conversion from PbI2 to CH3NH3PbI3, leading to uniform CH3NH3PbI3 film on ZnO:PEG while ZnO rarely relaxes the residual stress that CH3NH3PbI3 film is detached on hard ZnO layer. Furthermore, PEG holds CH3NH3PbI3 via hydrogen bonding and prevents direct contact between CH3NH3PbI3 and oxygen defects on ZnO NPs. As a result, mechanically and thermally stable cathodic interface is formed. In addition, PEG affects interfacial electronic structure of ZnO NPs, reducing the electron affinity of the ZnO NPs, which develops the ohmic contact for electron transfer between CH3NH3PbI3 and ZnO:PEG. With the deep-lying VB of ZnO, selective electron-collection interface is created, which significantly increases carrier lifetime up to 473 µs and photovoltaic performance recording 15.5%. The mechanically and


Page 14 of 32

Page 15 of 32

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


electrically durable ZnO:PEG/CH3NH3PbI3 interface expands the working period of the PeSCs over 1 year with sustainable performance. In conclusion, the hybridization of soft polymer and metal oxide NPs is first demonstrated as an ECL for the PeSCs and found to be an effective strategy to increase mechanical and electrical durability of cathode/CH3NH3PbI3 interface, which is towards flexible electronics and commercialization of the PeSCs.

Associated Content Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: ZnO NP properties, picture images of PbI2 and CH3NH3PbI3, contact angles of prove liquids, XRD of PbI2 and CH3NH3PbI3 on ZnO and ZnO:PEG layers, phase images, XRD, UV-Vis absorption of ZPx, ILP-dependent Jph of PeSCs, EQE, J-V hysteresis of PeSCs

Author Information Corresponding Author *E-mail: [email protected]

Acknowledgements This work was supported by a grant (Code No. 2011-0031628) from the Center for Advanced Soft Electronics under the Global Frontier Research Program of the Ministry of Science, ICT and Future Planning, Korea. The authors thank the Pohang Accelerator Laboratory for providing the synchrotron radiation sources at 4D, 5A and 8A2 beamlines used in this study.



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

References (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T., Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050-6051. (2) Kim, H. S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.; Moon, S. J.; Humphry-Baker, R.; Yum, J. H.; Moser, J. E.; Gratzel, M.; Park, N. G., Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2. 591. (3) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J., Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341-344. (4) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I., High-Performance Photovoltaic Perovskite Layers Fabricated through Intramolecular Exchange. Science 2015, 348, 1234-1237. (5) Gonzalez-Pedro, V.; Juarez-Perez, E. J.; Arsyad, W. S.; Barea, E. M.; Fabregat-Santiago, F.; MoraSero, I.; Bisquert, J., General Working Principles of CH3NH3PbX3 Perovskite Solar Cells. Nano Lett. 2014, 14, 888-893. (6) Hu, Q.; Wu, J.; Jiang, C.; Liu, T. H.; Que, X. L.; Zhu, R.; Gong, Q. H., Engineering of ElectronSelective Contact for Perovskite Solar Cells with Efficiency Exceeding 15%. Acs Nano 2014, 8, 10161-10167. (7) Oga, H.; Saeki, A.; Ogomi, Y.; Hayase, S.; Seki, S., Improved Understanding of the Electronic and Energetic Landscapes of Perovskite Solar Cells: High Local Charge Carrier Mobility, Reduced Recombination, and Extremely Shallow Traps. J. Am. Chem. Soc. 2014, 136, 13818-13825. (8) Edri, E.; Kirmayer, S.; Henning, A.; Mukhopadhyay, S.; Gartsman, K.; Rosenwaks, Y.; Hodes, G.; Cahen, D., Why Lead Methylammonium Tri-Iodide Perovskite-Based Solar Cells Require a Mesoporous Electron Transporting Scaffold (but Not Necessarily a Hole Conductor). Nano Lett. 2014, 14, 1000-1004. (9) deQuilettes, D. W.; Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S., Impact of Microstructure on Local Carrier Lifetime in Perovskite Solar Cells. Science 2015, 2015, 348, 683-686. (10) Malinkiewicz, O.; Yella, A.; Lee, Y. H.; Espallargas, G. M.; Graetzel, M.; Nazeeruddin, M. K.; Bolink, H. J., Perovskite Solar Cells Employing Organic Charge-Transport Layers. Nat. Photonics 2014, 8, 128-132. (11) Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Gratzel, M., Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells. Nature 2013, 499, 316-319. (12) Eperon, G. E.; Burlakov, V. M.; Docampo, P.; Goriely, A.; Snaith, H. J., Morphological Control for High Performance, Solution-Processed Planar Heterojunction Perovskite Solar Cells. Adv. Funct. Mater. 2014, 24, 151-157. (13) Zhang, T. Y.; Yang, M. J.; Zhao, Y. X.; Zhu, K., Controllable Sequential Deposition of Planar CH3NH3PbI3 Perovskite Films via Adjustable Volume Expansion. Nano Lett. 2015, 15, 3959-3963. (14) Kong, R.; Kim, J. E.; Yeo, J. S.; Lee, S.; Jeon, Y. J.; Kim, D. Y., Optimized Organometal Halide Perovskite Planar Hybrid Solar Cells via Control of Solvent Evaporation Rate. J. Phys. Chem. C 2014, 118, 26513-26520. (15) Paek, S.; Cho, N.; Choi, H.; Jeong, H.; Lim, J. S.; Hwang, J. Y.; Lee, J. K.; Ko, J., Improved External Quantum Efficiency from Solution-Processed (CH3NH3)Pbl(3) Perovskite/PC71BM Planar Heterojunction for High Efficiency Hybrid Solar Cells. J. Phys. Chem. C 2014, 118, 25899-25905. (16) Docampo, P.; Hanusch, F. C.; Stranks, S. D.; Doblinger, M.; Feckl, J. M.; Ehrensperger, M.; Minar, N. K.; Johnston, M. B.; Snaith, H. J.; Bein, T., Solution Deposition-Conversion for Planar Heterojunction Mixed Halide Perovskite Solar Cells. Adv. Energy Mater. 2014, 4, 1400355. (17) Zhou, H. P.; Chen, Q.; Li, G.; Luo, S.; Song, T. B.; Duan, H. S.; Hong, Z. R.; You, J. B.; Liu, Y. S.; Yang, Y., Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345, 542-546. (18) Liu, D. Y.; Kelly, T. L., Perovskite Solar Cells with a Planar Heterojunction Structure Prepared using Room-Temperature Solution Processing Techniques. Nat. Photonics 2014, 8, 133-138. (19) Yu, J. C.; Kim, D. B.; Baek, G.; Lee, B. R.; Jung, E. D.; Lee, S.; Chu, J. H.; Lee, D. K.; Choi, K. J.; Cho, S.; Song, M. H., High-Performance Planar Perovskite Optoelectronic Devices: A Morphological and Interfacial Control by Polar Solvent Treatment. Adv. Mater. 2015, 27, 3492-3500. (20) Sin, D. H.; Ko, H.; Jo, S. B.; Kim, M.; Bae, G. Y.; Cho, K., Decoupling Charge Transfer and Transport at Polymeric Hole Transport Layer in Perovskite Solar Cells. Acs Appl. Mater. Interfaces 2016, 8, 6546-6553. (21) Jung, J. W.; Chueh, C. C.; Jen, A. K. Y., A Low-Temperature, Solution-Processable, Cu-Doped Nickel Oxide Hole-Transporting Layer via the Combustion Method for High-Performance Thin-Film Perovskite Solar Cells. Adv. Mater. 2015, 27, 7874-7880. (22) Kim, G. W.; Kim, J.; Lee, G. Y.; Kang, G.; Lee, J.; Park, T., A Strategy to Design a Donor-piAcceptor Polymeric Hole Conductor for an Efficient Perovskite Solar Cell. Adv. Energy Mater. 2015, 5, 1500471.


Page 16 of 32

Page 17 of 32

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


(23) Nguyen, W. H.; Bailie, C. D.; Unger, E. L.; McGehee, M. D., Enhancing the Hole-Conductivity of Spiro-OMeTAD without Oxygen or Lithium Salts by Using Spiro(TFSI)2 in Perovskite and Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2014, 136, 10996-11001. (24) Wang, K. C.; Shen, P. S.; Li, M. H.; Chen, S.; Lin, M. W.; Chen, P.; Guo, T. F., Low-Temperature Sputtered Nickel Oxide Compact Thin Film as Effective Electron Blocking Layer for Mesoscopic NiO/CH3NH3PbI3 Perovskite Heterojunction Solar Cells. Acs Appl. Mater. Interfaces 2014, 6, 11851-11858. (25) Lim, K. G.; Kim, H. B.; Jeong, J.; Kim, H.; Kim, J. Y.; Lee, T. W., Boosting the Power Conversion Efficiency of Perovskite Solar Cells Using Self-Organized Polymeric Hole Extraction Layers with High Work Function. Adv. Mater. 2014, 26, 6461-6466. (26) Heo, J. H.; Lee, M. H.; Han, H. J.; Patil, B. R.; Yu, J. S.; Im, S. H., Highly Efficient Low Temperature Solution Processable Planar Type CH3NH3PbI3 perovskite flexible solar cells. J. Mater. Chem. A 2016, 4, 1572-1578. (27) Oh, L. S.; Kim, D. H.; Lee, J. A.; Shin, S. S.; Lee, J. W.; Park, I. J.; Ko, M. J.; Park, N. G.; Pyo, S. G.; Hong, K. S.; Kim, J. Y., Zn2SnO4-Based Photoelectrodes for Organolead Halide Perovskite Solar Cells. J. Phys. Chem. C 2014, 118, 22991-22994. (28) Jo, S. B.; Kim, M.; Sin, D. H.; Lee, J.; Kim, H. G.; Ko, H.; Cho, K., Carrier-Selectivity-Dependent Charge Recombination Dynamics in Organic Photovoltaic Cells with a Ferroelectric Blend Interlayer. Adv. Energy Mater. 2015, 5, 1500802. (29) Kim, J.; Kim, G.; Kim, T. K.; Kwon, S.; Back, H.; Lee, J.; Lee, S. H.; Kang, H.; Lee, K., Efficient Planar-Heterojunction Perovskite Solar Cells Achieved via Interfacial Modification of a Sol-Gel ZnO Electron Collection Layer. J. Mater. Chem. A 2014, 2, 17291-17296. (30) Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G., Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties. Inorg. Chem. 2013, 52, 9019-9038. (31) Yang, J. L.; Siempelkamp, B. D.; Mosconi, E.; De Angelis, F.; Kelly, T. L., Origin of the Thermal Instability in CH3NH3PbI3 Thin Films Deposited on ZnO. Chem. Mater. 2015, 27, 4229-4236. (32) Cheng, Y. H.; Yang, Q. D.; Xiao, J. Y.; Xue, Q. F.; Li, H. W.; Guan, Z. Q.; Yip, H. L.; Tsang, S. W., Decomposition of Organometal Halide Perovskite Films on Zinc Oxide Nanoparticles. Acs Appl. Mater. Interfaces 2015, 7, 19986-19993. (33) Small, C. E.; Chen, S.; Subbiah, J.; Amb, C. M.; Tsang, S. W.; Lai, T. H.; Reynolds, J. R.; So, F., High-Efficiency Inverted Dithienogermole-Thienopyrrolodione-based Polymer Solar Cells. Nat. Photonics 2012, 6, 115-120. (34) Liang, Z. Q.; Zhang, Q. F.; Jiang, L.; Cao, G. Z., ZnO Cathode Buffer Layers for Inverted Polymer Solar Cells. Energy Environ. Sci. 2015, 8, 3442-3476. (35) Jo, S. B.; Lee, J. H.; Sim, M.; Kim, M.; Park, J. H.; Choi, Y. S.; Kim, Y.; Ihn, S. G.; Cho, K., High Performance Organic Photovoltaic Cells Using Polymer-Hybridized ZnO Nanocrystals as a Cathode Interlayer. Adv. Energy Mater. 2011, 1, 690-698. (36) Suarez, B.; Gonzalez-Pedro, V.; Ripolles, T. S.; Sanchez, R. S.; Otero, L.; Mora-Sero, I., Recombination Study of Combined Halides (Cl, Br, I) Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 1628-1635. (37) Marinova, N.; Tress, W.; Humphry-Baker, R.; Dar, M. I.; Bojinov, V.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Gratzel, M., Light Harvesting and Charge Recombination in CH3NH3PbI3 Perovskite Solar Cells Studied by Hole Transport Layer Thickness Variation. Acs Nano 2015, 9, 4200-4209. (38) Han, G. S.; Chung, H. S.; Kim, B. J.; Kim, D. H.; Lee, J. W.; Swain, B. S.; Mahmood, K.; Yoo, J. S.; Park, N. G.; Lee, J. H.; Jung, H. S., Retarding Charge Recombination in Perovskite Solar Cells using Ultrathin MgO-Coated TiO2 Nanoparticulate Films. J. Mater. Chem. A 2015, 3, 9160-9164. (39) Wang, Q.; Shao, Y. C.; Dong, Q. F.; Xiao, Z. G.; Yuan, Y. B.; Huang, J. S., Large Fill-Factor Bilayer Iodine Perovskite Solar Cells Fabricated by a Low-Temperature Solution-Process. Energy Environ. Sci. 2014, 7, 2359-2365. (40) Maurano, A.; Shuttle, C. C.; Hamilton, R.; Ballantyne, A. M.; Nelson, J.; Zhang, W. M.; Heeney, M.; Durrant, J. R., Transient Optoelectronic Analysis of Charge Carrier Losses in a Selenophene/Fullerene Blend Solar Cell. J. Phys. Chem. C 2011, 115, 5947-5957. (41) Duan, H. S.; Zhou, H. P.; Chen, Q.; Sun, P. Y.; Luo, S.; Song, T. B.; Bob, B.; Yang, Y., The Identification and Characterization of Defect States in Hybrid Organic-Inorganic Perovskite Photovoltaics. Phys. Chem. Chem. Phys. 2015, 17, 112-116. (42) Azpiroz, J. M.; Mosconi, E.; Bisquert, J.; De Angelis, F., Defect Migration in Methylammonium Lead Iodide and Its Role in Perovskite Solar Cell Operation. Energy Environ. Sci. 2015, 8, 2118-2127. (43) Mihailetchi, V. D.; Wildeman, J.; Blom, P. W. M., Space-Charge Limited Photocurrent. Phys. Rev. Lett. 2005, 94, 126602. (44) Mihailetchi, V. D.; Xie, H. X.; de Boer, B.; Koster, L. J. A.; Blom, P. W. M., Charge Transport and Photocurrent Generation in Poly (3-Hexylthiophene): Methanofullerene Bulk-Heterojunction Solar Cells. Adv. Funct. Mater. 2006, 16, 699-708. (45) Jo, S. B.; Kim, H. H.; Lee, H.; Kang, B.; Lee, S.; Sim, M.; Kim, M.; Lee, W. H.; Cho, K., Boosting



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

Photon Harvesting in Organic Solar Cells with Highly Oriented Molecular Crystals via Graphene-Organic Heterointerface. Acs Nano 2015, 9, 8206-8219. (46) Lin, Y. Y.; Chu, T. H.; Li, S. S.; Chuang, C. H.; Chang, C. H.; Su, W. F.; Chang, C. P.; Chu, M. W.; Chen, C. W., Interfacial Nanostructuring on the Performance of Polymer/TiO2 Nanorod Bulk Heterojunction Solar Cells. J. Am. Chem. Soc. 2009, 131, 3644-3649. (47) Beek, W. J. E.; Wienk, M. M.; Kemerink, M.; Yang, X. N.; Janssen, R. A. J., Hybrid Zinc Oxide Conjugated Polymer Bulk Heterojunction Solar Cells. J. Phys. Chem. B 2005, 109, 9505-9516. (48) Baikie, T.; Fang, Y. N.; Kadro, J. M.; Schreyer, M.; Wei, F. X.; Mhaisalkar, S. G.; Graetzel, M.; White, T. J., Synthesis and Crystal Chemistry of the Hybrid Perovskite (CH3NH3)PbI3 for Solid-State Sensitised Solar Cell Applications. J. Mater. Chem. A 2013, 1, 5628-5641. (49) Navamathavan, R.; Kim, K. K.; Hwang, D. K.; Park, S. J.; Hahn, J. H.; Lee, T. G.; Kim, G. S., A Nanoindentation Study of the Mechanical Properties of ZnO Thin Films on (0001) Sapphire. Appl. Surf. Sci. 2006, 253, 464-467. (50) Zhao, Y. C.; Wei, J.; Li, H.; Yan, Y.; Zhou, W. K.; Yu, D. P.; Zhao, Q., A Polymer Scaffold for SelfHealing Perovskite Solar Cells. Nat. Commun. 2016, 7, 10228. (51) Kang, B.; Lim, S.; Lee, W. H.; Jo, S. B.; Cho, K., Work-Function-Tuned Reduced Graphene Oxide via Direct Surface Functionalization as Source/Drain Electrodes in Bottom-Contact Organic Transistors. Adv. Mater. 2013, 25, 5856-5862. (52) Zhao, B. X.; Kwon, H. J., Adhesion of Polymers in Paper Products from the Macroscopic to Molecular Level - An Overview. J. Adhes. Sci. Technol. 2011, 25, 557-579. (53) Bi, C.; Wang, Q.; Shao, Y. C.; Yuan, Y. B.; Xiao, Z. G.; Huang, J. S., Non-Wetting Surface-Driven High-Aspect-Ratio Crystalline Grain Growth for Efficient Hybrid Perovskite Solar Cells. Nat. Commun. 2015, 6, 7747. (54) Raoufi, D., Synthesis and Photoluminescence Characterization of ZnO Nanoparticles. J. Lumin. 2013, 134, 213-219. (55) Ono, L. K.; Schulz, P.; Endres, J. J.; Nikiforov, G. O.; Kato, Y.; Kahn, A.; Qi, Y. B., Air-ExposureInduced Gas-Molecule Incorporation into Spiro-MeOTAD Films. J. Phys. Chem. Lett. 2014, 5, 1374-1379. (56) Koch, B. M. L.; Amirfazli, A.; Elliott, J. A. W., Wetting of Rough Surfaces by a Low Surface Tension Liquid. J. Phys. Chem. C 2014, 118, 23777-23782. (57) Kim, J. B.; Kim, P.; Pegard, N. C.; Oh, S. J.; Kagan, C. R.; Fleischer, J. W.; Stone, H. A.; Loo, Y. L., Wrinkles and Deep Folds as Photonic Structures in Photovoltaics. Nat. Photonics 2012, 6, 327-332. (58) Chen, H. W.; Sakai, N.; Ikegami, M.; Miyasaka, T., Emergence of Hysteresis and Transient Ferroelectric Response in Organo-Lead Halide Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 164-169. (59) Credgington, D.; Hamilton, R.; Atienzar, P.; Nelson, J.; Durrant, J. R., Non-Geminate Recombination as the Primary Determinant of Open-Circuit Voltage in Polythiophene:Fullerene Blend Solar Cells: an Analysis of the Influence of Device Processing Conditions. Adv. Funct. Mater. 2011, 21, 2744-2753. (60) Bartesaghi, D.; Perez, I. D.; Kniepert, J.; Roland, S.; Turbiez, M.; Neher, D.; Koster, L. J. A., Competition between Recombination and Extraction of Free Charges Determines the Fill Factor of Organic Solar Cells. Nat. Commun. 2015, 6, 7083. (61) Ameri, T.; Heumuller, T.; Min, J.; Li, N.; Matt, G.; Scherf, U.; Brabec, C. J., IR Sensitization of an Indene-C60 Bisadduct (ICBA) in Ternary Organic Solar Cells. Energy Environ. Sci. 2013, 6, 1796-1801.


Page 18 of 32

Page 19 of 32

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 Captions Figure 1. SEM images (left) and peeling test with scotch tape (right) of CH3NH3PbI3 films on (a) ZnO and (b) ZnO:PEG layers. (c) Schematic mechanism of CH3NH3PbI3 conversion on ZnO and ZnO:PEG layers. Figure 2. The indentation loading-unloading curve and corresponding SEM image of ZnO layer (inset) Figure 3. (a) AFM images, (b) PL, and UPS (c) secondary and (d) valence spectra of ZnO layers with various PEG contents. Figure 4. (a) Schematics of device architecture. (b) J-V Characteristics of PeSCs with ZnO ECLs with various PEG contents. (c) Energy diagrams inside PeSCs with ZnO and ZnO:PEG. Figure 5. (a) JSC, (b) VOC, (c) FF, and (d) PCE of PeSCs with ZPx ECLs depending on PEG contents. Figure 6. AFM images of (a) ITO and (b) FTO substrates. (c) Cross-sectional SEM image of ZP2.5-based PeSC on FTO cathode. (d) J-V Characteristics of ZP2.5-based PeSCs with ITO and FTO cathodes. Figure 7. (a) TPV, (b) TPC, and (c) ߬n-n relation. Figure 8. JSC, VOC, FF, and PCE stabilities of ZP2.5-based PeSC stored in glovebox. Table 1. Elastic modulus and hardness of ZnO and ZnO:PEG layers. Table 2. Photovoltaic parameters of PeSCs with ZnO ETLs with various PEG contents. Table 3. Photovoltaic parameters of ZP2.5-based PeSCs with ITO and FTO cathodes. Table 4. Recombination parameters extracted from TPV and TPC.



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 1.


Page 20 of 32

Page 21 of 32

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


Figure 2.



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 3.


Page 22 of 32

Page 23 of 32

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


Figure 4.



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

Figure 5.


Page 24 of 32

Page 25 of 32

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.



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 7.


Page 26 of 32

Page 27 of 32

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 8.



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

Elastic Modulus [GPa]

Hardness [GPa]

ZnO

163.6 ± 10.7

8.0 ± 0.8

ZnO:PEG

143.3 ± 8.6

6.9 ± 0.5

Table 1.


Page 28 of 32

Page 29 of 32

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


S parameter

JSC [mA cm-2]

VOC [V]

FF [%]

PCEmax (PCEave)* [%]

RS [Ω cm2]

RSh [Ω cm2]

Vo-V = 0.5 V

Vo-V = 2 V

ZnO

11.70 ± 2.17

0.61 ± 0.04

30.0 ± 3.1

3.1 (2.1 ± 0.76)

30.2

94

-

-

ZP1

19.65 ± 0.68

1.00 ± 0.01

55.8 ± 2.7

11.6 (11.0 ± 0.51)

13.5

1622

0.953

0.962

ZP2

20.14 ± 0.45

1.01 ± 0.01

58.2 ± 2.5

12.3 (11.8 ± 0.44)

11.7

2446

0.950

0.962

ZP2.5

19.75 ± 0.42

1.02 ± 0.01

63.0 ± 1.9

13.1 (12.7 ± 0.39)

9.4

3155

0.956

0.969

ZP5

17.92 ± 0.64

1.02 ± 0.01

54.0 ± 2.7

10.6 (9.9 ± 0.47)

17.3

3470

0.943

0.966

ZP7.5

16.47 ± 1.19

1.02 ± 0.01

53.0 ± 3.6

9.5 (8.9 ± 0.57)

16.4

1784

0.940

0.957

0.816

0.953

15.53 1.02 47.4 8.1 19.6 918 ± 1.33 ± 0.01 ± 4.0 (7.5 ± 0.58) *The values in parentheses represent the average PCEs with standard devications from over 8 devices. ZP10

Table 2.



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

ZP2.5/ITO

Page 30 of 32

S parameter

JSC [mA cm-2]

VOC [V]

FF [%]

PCEmax (PCEave)* [%]

RS [Ω cm2]

RSh [Ω cm2]

Vo-V = 0.5 V

Vo-V = 2 V

19.75 ± 0.42

1.02 ± 0.01

63.0 ± 1.9

13.1 (12.7 ± 0.39)

9.4

3155

0.956

0.969

0.967

0.978

20.48 1.05 70.0 15.5 6.4 2205 ± 0.25 ± 0.01 ± 1.0 (15.1 ± 0.27) *The values in parentheses represent the average PCEs with standard devications from over 8 devices. ZP2.5/FTO

Table 3.


Page 31 of 32

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


Overall reaction order

Charge carrier density [1016 cm-3]

Charge carrier lifetime [µs]

ZnO/ITO

1.46 ± 0.10

5.92 ± 0.18

248 ± 19

ZP2.5/ITO

1.41 ± 0.03

8.28 ± 0.13

351 ± 11

ZP2.5/FTO

1.31 ± 0.04

13.73 ± 0.25

473 ± 19

Table 4.



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

Graphic for manuscript


Page 32 of 32

Enhancing the Durability and Carrier Selectivity of Perovskite Solar

Recommend Documents