Sb2S3

Subscriber access provided by TUFTS UNIV

Article

Band Diagram and Effects of the KSCN Treatment in TiO2/Sb2S3/CuSCN ETA cells Yafit Itzhaik, Tatyana Bendikov, Douglas A. Hines, Prashant V. Kamat, Hagai Cohen, and Gary Hodes J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b09233 • Publication Date (Web): 04 Dec 2015 Downloaded from http://pubs.acs.org on December 9, 2015

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.

The Journal of Physical Chemistry C 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 39

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

The Journal of Physical Chemistry

Band Diagram and Effects of the KSCN Treatment in TiO2/Sb2S3/CuSCN ETA Cells Yafit Itzhaik,1 Tatyana Bendikov,2 Douglas Hines,3† Prashant V. Kamat,3 Hagai Cohen,2* and Gary Hodes1* 1

Department of Materials and Interfaces and 2 Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, 76100, Israel 3

Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA †

Present address: Lycoming College, 700 College Place, Williamsport, PA 17701

*Corresponding authors: [email protected] Tel. 972 8 9342076 [email protected] Tel. 972 8 9343422

ACS Paragon Plus Environment

1


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

Page 2 of 39

Abstract Thiocyanate ion treatment, usually either LiSCN or KSCN, of the absorbing semiconductor before deposition of a CuSCN hole conducting layer is known to improve the performance of extremely thin absorber (ETA) solar cells by reducing the cell resistivity. However, in spite of several hypotheses, the mechanism behind this treatment outcome remains elusive. In this study, the interface between Sb2S3 and CuSCN in an ETA cell is now investigated with surface spectroscopy and transient absorption spectroscopy to establish the mechanistic aspects of the KSCN treatment and role it plays in improving the photovoltaic performance. The prominent factors that dictate the cell performance are (a) doping the interfacial CuSCN and thus preventing the formation of a sub-µm depleted layer and (b) passivating charge traps at the Sb2S(O)3 surface, which increases the rate of hole transfer from the absorber to the hole conductor. In addition we further show that the treatment works just as well in improving photovoltaic performance when carried out after CuSCN deposition (post-treatment).


2

Page 3 of 39

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


Introduction A relatively new concept in photovoltaic (PV) cells, based on the dye-sensitized solar cell (DSC), is the extremely thin absorber (ETA) cell: An ultra-thin absorber layer (500 ps), which may be more relevant for the ‘slow’ CREM data (on the scale of many seconds). Hence, since the appearance of electron traps in oxides is rather common and, since their passivation by the electron-donating KSCN treatment is intuitively expected, interpretation of the TAS data showing the role of KSCN in passivating electron traps is reasonable. Thus, the combined interpretation of TAS data, the induced absorption and the bleaching, both hole and electron traps have been invoked.


32

Page 33 of 39

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


Conclusions

The KSCN treatment, a key factor in interfacial engineering in Sb2S3 ETA cells, affects the CuSCN layer, its morphology, interfacial crystal phase and infiltration into the pores, thus resulting in enhanced Sb2S3/CuSCN interfacial area. Cell aging has been observed to improve cell performance, which might be connected with recrystallization of the CuSCN layer with storage time (under vacuum). However, while these effects are interesting in their own rights, these are not the determining factors in the cell performance, since untreated cells can be treated with KSCN after the CuSCN deposition and, thus, improve their performance without CuSCN recrystallizing, or changing the pore-filling degree in the cells. The most obvious mechanism by which the KSCN treatment affects the cell is through doping of the interfacial CuSCN inside the pores. This mechanism is possibly connected with the observed K+ ion diffusion (which suggests also SCN– co-diffusion) into the CuSCN layer. By constructing the energy band alignment of an untreated cell, using XPS and CREM analyses, it was found that a depletion layer (ca. 250 meV potential loss) was formed in CuSCN due to its constrained size in the pores. This depletion layer at the Sb2S3/CuSCN interface is realized as an increase in cell resistance, explaining the lower cell performance observed in these cells. Finally, our CREM and TAS data point to the passivation of charge traps at the CuSCN/Sb-oxide interface by the KSCN treatment, which improves hole evacuation to the top electrode significantly. We note that the utility of the KSCN treatment is not limited to ETA cells: Any cell (or indeed device) that uses CuSCN (and maybe other thiocyanates) may benefit from the treatment.


33


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 34 of 39

Supporting Information Available

Description of CuSCN layer properties and characterization of CuSCN inside the pores; additional information on cell band structure and surface Sb2O3; additional information on cell aging. This information is available free of charge via the Internet at http://pubs.acs.org

Acknowledgements

We thank Dr. Yishay Feldman for XRD support and invaluable discussions, and Dr. Alon Givon and Dr. Jaykrushna Das for experimental assistance. This research was funded by the US–Israel Binational Science Foundation and the Sidney E. Frank Foundation through the Israel Science Foundation. This is NDRL No. 5083 from Notre Dame Radiation Laboratory, which is supported by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy through the award DEFC02-04ER15533.


34

Page 35 of 39

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)

Dittrich, T.; Belaidi, A.; Ennaoui, A. Concepts of Inorganic Solid-State Nanostructured Solar Cells. Sol. Energy Mater. Sol. Cells 2011, 95, 1527–1536.

(2)

Hodes, G.; Cahen, D. All-Solid-State, Semiconductor-Sensitized Nanoporous Solar Cells. Acc. Chem. Res. 2012, 45, 705–713.

(3)

Itzhaik, Y.; Niitsoo, O.; Page, M.; Hodes, G. Sb2S3-Sensitized Nanoporous TiO2 Solar Cells. J. Phys. Chem. C 2009, 113, 4254–4256.

(4)

Nezu, S.; Larramona, G.; Choné, C.; Jacob, A.; Delatouche, B.; Péré, D.; Moisan, C. Light Soaking and Gas Effect on Nanocrystalline TiO2/Sb2S3/CuSCN Photovoltaic Cells Following Extremely Thin Absorber Concept. J. Phys. Chem. C 2010, 114, 6854–6859.

(5)

Christians, J. A.; Kamat, P. V. Trap and Transfer. Two-Step Hole Injection Across the Sb2S3/CuSCN Interface in Solid-State Solar Cells. ACS Nano 2013, 7, 7967–7974.

(6)

Ito, S.; Tsujimoto, K.; Nguyen, D.-C.; Manabe, K.; Nishino, H. Doping Effects in Sb2S3 Absorber for Full-Inorganic Printed Solar Cells with 5.7% Conversion Efficiency. Int. J. Hydrog. Energy 2013, 38, 16749–16754.

(7)

Moon, S.-J.; Itzhaik, Y.; Yum, J.-H.; Zakeeruddin, S. M.; Hodes, G.; Grätzel, M. Sb2S3-Based Mesoscopic Solar Cell Using an Organic Hole Conductor. J. Phys. Chem. Lett. 2010, 1, 1524–1527.

(8)

Chang, J. A.; Rhee, J. H.; Im, S. H.; Lee, Y. H.; Kim, H.; Seok, S. I.; Nazeeruddin, M. K.; Gratzel, M. High-Performance Nanostructured Inorganic-Organic Heterojunction Solar Cells. Nano Lett. 2010, 10, 2609–2612.

(9)

Fukumoto, T.; Moehl, T.; Niwa, Y.; Nazeeruddin, M. K.; Grätzel, M.; Etgar, L. Effect of Interfacial Engineering in Solid-State Nanostructured Sb2S3 Heterojunction Solar Cells. Adv. Energy Mater. 2013, 3, 29–33.


35


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 36 of 39

(10) Muto, T.; Larramona, G.; Dennler, G. Unexpected Performances of Flat Sb2S3-Based Hybrid Extremely Thin Absorber Solar Cells. 2013, 6, 1–4. (11) Choi, Y. C.; Lee, D. U.; Noh, J. H.; Kim, E. K.; Seok, S. I. Highly Improved Sb2S3 Sensitized-Inorganic–Organic Heterojunction Solar Cells and Quantification of Traps by Deep-Level Transient Spectroscopy. Adv. Funct. Mater. 2014, 3587–3592. (12) Boix, P. P.; Larramona, G.; Jacob, A.; Delatouche, B.; Mora-Seró, I.; Bisquert, J. Hole Transport and Recombination in All-Solid Sb2S3-Sensitized TiO2 Solar Cells Using CuSCN As Hole Transporter. J. Phys. Chem. C 2012, 116, 1579–1587. (13) Darga, A.; Mencaraglia, D.; Longeaud, C.; Savenije, T. J.; O’Regan, B.; Bourdais, S.; Muto, T.; Delatouche, B.; Dennler, G. On Charge Carrier Recombination in Sb2S3 and Its Implication for the Performance of Solar Cells. J. Phys. Chem. C 2013, 117, 20525– 20530. (14) O’Mahony, F. T. F.; Lutz, T.; Guijarro, N.; Gómez, R.; Haque, S. A. Electron and Hole Transfer at Metal oxide/Sb2S3/spiro-OMeTAD Heterojunctions. Energy Environ. Sci. 2012, 5, 9760.

(15) Christians, J. A.; Leighton, D. T.; Kamat, P. V. Rate Limiting Interfacial Hole Transfer in Sb2S3 Solid-State Solar Cells. Energy Environ. Sci. 2014, 7, 1148–1158. (16) Itzhaik, Y.; Hodes, G.; Cohen, H. Band Alignment and Internal Field Mapping in Solar Cells. J. Phys. Chem. Lett. 2011, 2, 2872–2876. (17) Larramona, G.; Choné, C.; Jacob, A.; Sakakura, D.; Delatouche, B.; Péré, D.; Cieren, X.; Nagino, M.; Bayón, R. Nanostructured Photovoltaic Cell of the Type Titanium Dioxide, Cadmium Sulfide Thin Coating, and Copper Thiocyanate Showing High Quantum Efficiency. Chem. Mater. 2006, 18, 1688–1696.


36

Page 37 of 39

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


(18) Edri, E.; Cohen, H.; Hodes, G. Band Alignment in Partial and Complete ZnO/ZnS/CdS/CuSCN Extremely Thin Absorber Cells: An X-Ray Photoelectron Spectroscopy Study. ACS Appl. Mater. Interfaces 2013, 5, 5156–5164. (19) O’Regan, B.; Lenzmann, F.; Muis, R.; Wienke, J. A Solid-State Dye-Sensitized Solar Cell Fabricated with Pressure-Treated P25−TiO2 and CuSCN: Analysis of Pore Filling and IV Characteristics. Chem. Mater. 2002, 14, 5023–5029. (20) Sirimanne, P. M.; Tributsch, H. Thiocyanate Ligands as Crucial Elements for Regeneration and Photo-Degradation in TiO2|dye|CuI Solar Cells. Mater. Chem. Phys. 2006, 99, 5–9.

(21) Ohya, Y.; Saiki, H.; Tanaka, T.; Takahashi, Y. Microstructure of TiO2 and ZnO Films Fabricated by the Sol-Gel Method. J. Am. Ceram. Soc. 1996, 79, 825–830. (22) Bayón, R.; Guillén, C.; Martínez, M. A.; Gutiérrez, M. T.; Herrero, J. Preparation of Indium Hydroxy Sulfide Inx(OH)ySz Thin Films by Chemical Bath Deposition. J. Electrochem. Soc. 1998, 145, 2775–2779. (23) Messina, S.; Nair, M. T. S.; Nair, P. K. Antimony Sulfide Thin Films in Chemically Deposited Thin Film Photovoltaic Cells. Thin Solid Films 2007, 515, 5777–5782. (24) O’Regan, B. C.; Lenzmann, F. Charge Transport and Recombination in a Nanoscale Interpenetrating Network of N-Type and P-Type Semiconductors: Transient Photocurrent and Photovoltage Studies of TiO2/Dye/CuSCN Photovoltaic Cells. J. Phys. Chem. B 2004, 108, 4342–4350. (25) Cohen, H. Chemically Resolved Electrical Measurements Using X-Ray Photoelectron Spectroscopy. Appl. Phys. Lett. 2004, 85, 1271–1273. (26) Cohen, H.; Nogues, C.; Zon, I.; Lubomirsky, I. E-Beam-Referenced Work-Function Evaluation in an X-Ray Photoelectron Spectrometer. J. Appl. Phys. 2005, 97, 113701.


37


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 38 of 39

(27) Smith, D. L.; Saunders, V. I. The Structure and Polytypism of the β Modification of copper(I) Thiocyanate. Acta Crystallogr. B 1981, 37, 1807–1812. (28) Perera, V. P. S.; Senevirathna, M. K. I.; Pitigala, P. K. D. D. P.; Tennakone, K. Doping CuSCN Films for Enhancement of Conductivity: Application in Dye-Sensitized SolidState Solar Cells. Sol. Energy Mater. Sol. Cells 2005, 86, 443–450. (29) Jaffe, J. E.; Kaspar, T. C.; Droubay, T. C.; Varga, T.; Bowden, M. E.; Exarhos, G. J. Electronic and Defect Structures of CuSCN. J. Phys. Chem. C 2010, 114, 9111–9117. (30) Kumara, G. R. R. A.; Konno, A.; Senadeera, G. K. R.; Jayaweera, P. V. V.; De Silva, D. B. R. A.; Tennakone, K. Dye-Sensitized Solar Cell with the Hole Collector PCuSCN Deposited from a Solution in N-Propyl Sulphide. Sol. Energy Mater. Sol. Cells 2001, 69, 195–199.

(31) Page, M.; Niitsoo, O.; Itzhaik, Y.; Cahen, D.; Hodes, G. Copper Sulfide as a Light Absorber in Wet-Chemical Synthesized Extremely Thin Absorber (ETA) Solar Cells. Energy Environ. Sci. 2009, 2, 220–223. (32) Shard, A. G.; Wang, J.; Spencer, S. J. XPS Topofactors: Determining Overlayer Thickness on Particles and Fibres. Surf. Interface Anal. 2009, 41, 541–548.


38

Page 39 of 39

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


TOC graphic

KSCN CuSCN Sb2S3 1 > KSCN doping 2 < traps at interface +

3 > rate of h transfer through interface

interface


39

Sb2S3

Recommend Documents