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Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

Published: July 8th, 2016



1Department of Chemistry and Biochemistry, St. Mary's College of Maryland, 2Department of Chemistry, U.S. Naval Academy, 3NSWC Indian Head EOD Technology Division, 4Electronics and Devices Division, Naval Research Laboratory

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 °C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136±39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

Due to their unique emerging properties, inorganic nanocrystal inks have found applications in a wide range of electronic devices including photovoltaics,1-6 light emitting diodes,7,8 capacitors9 and transistors.10 This is due to the combination of the excellent electronic and optical properties of inorganic materials and their solution compatibility on the nanoscale. Bulk inorganic materials are typically not soluble and are therefore limited to high temperature, low pressure vacuum depositions. However, when prepared on the nanoscale with an organic ligand shell, these materials ....

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Note: Please consult all relevant materials safety data sheets (MSDS) before use. Many of the precursor solutions and products are hazardous or carcinogenic. Special consideration should be directed to nanomaterials due to unique safety concerns that arise compared to their bulk counterparts. Proper protective equipment should be worn (safety goggles, face shield, gloves, lab coat, long pants and closed-toed shoes) at all times during this procedure.

1. Synthesis of Nanocrystal Precursor Inks

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Small angle X-ray Diffraction Patterns are used to verify the crystallinity and phase of the annealed nanocrystal film (Figure 1A). If crystallite sizes are below 100 nm, their crystal diameter can be estimated with the Scherrer equation (Eq. 1) and verified with Scanning Electron Microscopy (SEM),
Equation 1
where d is the mean crystallite diameter, K is the dimensionless shape factor for the material, β is the full .......

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In summary, this protocol provides guidelines for the key steps involved with building a solution processed electronic device from a spray- or spin-coating deposition. Here, we highlight new methods for solution processing transparent conductive indium tin oxide (ITO) films onto non-conductive glass substrates. After a facile etching procedure, individual electrodes can be formed before spray-depositing the photo-active layers. Using a layer-by-layer technique, CdSe and CdTe nanocrystals can be deposited in air under amb.......

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The Office of Naval Research (ONR) is gratefully acknowledged for financial support. A portion of this work was conducted while Professor Townsend held a National Research Council (NRC) Postdoctoral Fellowship at the Naval Research Laboratory and is grateful for internal support from St. Mary's College of Maryland.


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Name Company Catalog Number Comments
Oleic acid, 90% Sigma Aldrich 364525
1-octadecene, 90% Sigma Aldrich O806 Technical grade
Trioctylphosphine (TOP), 90% Sigma Aldrich 117854 Air sensitive
Trimethylsilyl chloride, 99.9% Sigma Aldrich 92360 Air and water sensitive
Se, 99.5+% Sigma Aldrich 209651
NH4Cl, 99% Sigma Aldrich 9718
CdCl2, 99.9% Sigma Aldrich 202908 Highly toxic
CdO, 99.99% Strem 202894 Highly toxic
Te, 99.8% Strem 264865
In(NO3)3.2.85H2O, 99.99% Sigma Aldrich 326127-50G
SnCl2.2H2O, 99.9% Sigma Aldrich 431508
NH4OH Sigma Aldrich 320145 Caustic
NH4NO3, 99% Sigma Aldrich A9642
HAuCl4.3H2O, 99.9% Sigma Aldrich 520918
Tetraoctylammonium bromide (TMA-Br) Sigma Aldrich 294136
Toluene, 99.8% Sigma Aldrich 244511
Hexanethiol, 95% Sigma Aldrich 234192
NaBH4, 96% Sigma Aldrich 71320
Hexanes, 98.5% Sigma Aldrich 650544
Ethanol, 99.5% Sigma Aldrich 459844
Methanol, anhydrous, 99.8% Sigma Aldrich 322415
1-propanol, 99.5% Sigma Aldrich 402893
2-propanol, 99.5% Sigma Aldrich 278475
Pyridine, > 99% Sigma Aldrich 360570 Purified by distillation
Heptane Sigma Aldrich 246654
chloroform > 99% Sigma Aldrich 372978
Acetone Sigma Aldrich 34850
Glass microscope slides Fisher 12-544-4 Cut with glass cutter
Gravity Fed Airbrush Paasche VSR90#1
Syringe needle Fisher CAD4075
Solar Simulator Testing Station Newport PVIV-1A
Software Oriel PVIV 2.0
Round bottom flask Sigma Aldrich Z723134
Round bottom flask Sigma Aldrich Z418668
Polytetrafluoroethylene (PTFE) syringe filter  Sigma Aldrich Z259926
Polyamide tape Kapton KPT-1/8
Cellophane tape Scotch 810 Tape
Polypropylene centrifuge tube Sigma Aldrich CLS430290
Silver epoxy MG Chemicals 8331-14G

  1. Debnath, R., Bakr, O., Sargent, E. H. Solution-processed colloidal quantum dot photovoltaics: A perspective. Energy Environ. Sci. 4, 4870-4881 (2011).
  2. Tang, J., Sargent, E. H. Infrared Colloidal Quantum Dots for Photovoltaics: Fundamentals and Recent Progress. Adv. Mater. 23, 12-29 (2011).
  3. Ning, Z., Dong, H., Zhang, Q., Voznyy, O., Sargent, E. H. Solar Cells Based on Inks of n-Type Colloidal Quantum Dots. ACS Nano. 8, 10321-10327 (2014).
  4. Yoon, W., et al. Enhanced Open-Circuit Voltage of PbS Nanocrystal Quantum Dot Solar Cells. Sci. Rep. 3, (2013).
  5. Jiaoyan, Z., et al. Enhancement of open-circuit voltage and the fill factor in CdTe nanocrystal solar cells by using interface materials. Nanotechnology. 25, 365203 (2014).
  6. Kramer, I. J., et al. Efficient Spray-Coated Colloidal Quantum Dot Solar Cells. Adv. Mater. 27, 116-121 (2015).
  7. Shirasaki, Y., Supran, G. J., Bawendi, M. G., Bulovic, V. Emergence of colloidal quantum-dot light-emitting technologies. Nat. Photonics. 7, 13-23 (2013).
  8. Demir, H. V., et al. Quantum dot integrated LEDs using photonic and excitonic color conversion. Nano Today. 6, 632-647 (2011).
  9. Yu, G., et al. Solution-Processed Graphene/MnO2 Nanostructured Textiles for High-Performance Electrochemical Capacitors. Nano Lett. 11, 2905-2911 (2011).
  10. Ridley, B. A., Nivi, B., Jacobson, J. M. All-Inorganic Field Effect Transistors Fabricated by Printing. Science. 286, 746-749 (1999).
  11. Habas, S. E., Platt, H. A. S., van Hest, M. F. A. M., Ginley, D. S. Low-Cost Inorganic Solar Cells: From Ink To Printed Device. Chem. Rev. 110, 6571-6594 (2010).
  12. Townsend, T. K., Yoon, W., Foos, E. E., Tischler, J. G. Impact of Nanocrystal Spray Deposition on Inorganic Solar Cells. ACS Appl. Mater. Interfaces. 6, 7902-7909 (2014).
  13. Olson, J. D., Rodriguez, Y. W., Yang, L. D., Alers, G. B., Carter, S. A. CdTe Schottky diodes from colloidal nanocrystals. Appl. Phys. Lett. 96, 242103 (2010).
  14. Sun, S., Liu, H., Gao, Y., Qin, D., Chen, J. Controlled synthesis of CdTe nanocrystals for high performanced Schottky thin film solar cells. J. Mater. Chem. 22, 19207-19212 (2012).
  15. Chen, Z., et al. Efficient inorganic solar cells from aqueous nanocrystals: the impact of composition on carrier dynamics. RSC Adv. 5, 74263-74269 (2015).
  16. Gur, I., Fromer, N. A., Geier, M. L., Alivisatos, A. P. Air-stable all-inorganic nanocrystal solar cells processed from solution. Science. 310, 462-465 (2005).
  17. Ju, T., Yang, L., Carter, S. Thickness dependence study of inorganic CdTe/CdSe solar cells fabricated from colloidal nanoparticle solutions. J. Appl. Phys. 107, (2010).
  18. MacDonald, B. I., et al. Layer-by-Layer Assembly of Sintered CdSexTe1-x Nanocrystal Solar Cells. ACS Nano. 6, 5995-6004 (2012).
  19. Crisp, R. W., et al. Nanocrystal Grain Growth and Device Architectures for High-Efficiency CdTe Ink-Based Photovoltaics. ACS Nano. 8, 9063-9072 (2014).
  20. Townsend, T. K., et al. Safer salts for CdTe nanocrystal solution processed solar cells: the dual roles of ligand exchange and grain growth. J. Mater. Chem. A. 3, 13057-13065 (2015).
  21. Jasieniak, J., MacDonald, B. I., Watkins, S. E., Mulvaney, P. Solution-Processed Sintered Nanocrystal Solar Cells via Layer-by-Layer Assembly. Nano Lett. 11, 2856-2864 (2011).
  22. Hecht, D. S., Hu, L. B., Irvin, G. Emerging Transparent Electrodes Based on Thin Films of Carbon Nanotubes, Graphene, and Metallic Nanostructures. Adv. Mater. 23, 1482-1513 (2011).
  23. Kim, M. G., Kanatzidis, M. G., Facchetti, A., Marks, T. J. Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing. Nat. Mater. 10, 382-388 (2011).
  24. Townsend, T. K., Foos, E. E. Fully solution processed all inorganic nanocrystal solar cells. Phys. Chem. Chem. Phys. 16, 16458-16464 (2014).
  25. Yu, W. W., Peng, X. Formation of High-Quality CdS and Other II-VI Semiconductor Nanocrystals in Noncoordinating Solvents: Tunable Reactivity of Monomers. Angew. Chem. 114, 2474-2477 (2002).
  26. Brust, M., Walker, M., Bethell, D., Schiffrin, D. J., Whyman, R. Synthesis of thiol-derivatised gold nanoparticles in a two-phase Liquid-Liquid system. J. Chem. Soc., Chem. Commun. , 801-802 (1994).
  27. Smits, F. M. Measurement of Sheet Resistivities with the Four-Point Probe. Bell Sys. Tech. J. 37, 711-718 (1958).
  28. Yoon, W., Townsend, T. K., Lumb, M. P., Tischler, J. G., Foos, E. E. Sintered CdTe Nanocrystal Thin-films: Determination of Optical Constants and Application in Novel Inverted Heterojunction Solar Cells. IEEE Trans. Nanotechnol. 13, 551-556 (2014).
  29. Foos, E. E., Yoon, W., Lumb, M. P., Tischler, J. G., Townsend, T. K. Inorganic Photovoltaic Devices Fabricated Using Nanocrystal Spray Deposition. ACS Appl. Mater. Interfaces. 5, 8828-8832 (2013).
  30. Nag, A., et al. Metal-free Inorganic Ligands for Colloidal Nanocrystals: S2-, HS-, Se2-, HSe-, Te2-, HTe-, TeS32-, OH-, and NH2- as Surface Ligands. J. Am. Chem. Soc. 133, 10612-10620 (2011).
  31. Panthani, M. G., et al. High Efficiency Solution Processed Sintered CdTe Nanocrystal Solar Cells: The Role of Interfaces. Nano Lett. 14, 670-675 (2014).

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