AFM for Solar, Photovoltaics and Thermoelectrics Research

Photovoltaic (PV), thermoelectric (TE), and related materials and devices are developing rapidly, and branching into many varying fields, including PV polymers, traditional semiconductor based PV devices, and now perovskite PV materials.The characterization of these materials requires that researchers have the ability to investigate at the material, failure analysis, and device levels.  Asylum Research AFMs provide platforms for all of the major types of PV materials and devices at every stage of their development, including transparent materials, opaque materials, illumination from the top and bottom, and use of external, user provided light source.  Our electrical characterization suite, combined with our broad platform set, and topped off by our wide array of software and hardware customization tools are unmatched in the industry.
 

Capabilities

  • Kelvin Probe Force Microscopy (KPFM) - accurately measures surface contact potential difference (CPD) based on differences in the photo- or thermally- excited current
  • Electrostatic Force Microscopy (EFM) - maps variations in the gradient of the capacitance locally.  Changes photo- or thermally- excited current as a function of time can be observed using this technique
  • Conductive AFM (CAFM) - measures current through the tip as a function of an applied sample bias and as a function of illumination strength or temperature
  • Current Mapping with Fast Force Mapping - measures current at an applied sample bias during the contact segment of a fast force curve, allowing imaging of delicate PV materials without damage 
  • Scanning Microwave Impedance Microscopy (sMIM) - maps variations in local capacitance and resistance, allowing the scientist to see photo-current on 'floating' materials, or PV materials not built into a device.
 

Common Applications

KPFM
  • Measure change in local charge (~50-100 nm) variation when a sample is illuminated or heated
  • Find variations in local work function with light or heat
  • Map local domains in some materials that have n and p regions
  • Watch the change in local photo- or thermo- current with time by watching the change in potential
EFM
  • Watch the change in capacitance gradient of a sample with time after illumination or heating
  • Map the change in capacitance gradient of a sample with changes in heat or light
CAFM
  • Map photo and thermal current quantitatively
  • Map changes in mobility as a sample is illuminated
  • Map domains of variation in electron charge using fast forces with current mapping, or fast current mapping (FCM)
  • Temporally measure photo and thermal current in samples
  • Map current in domain walls in perovskite materials for PV applications
sMIM
  • Characterize a wide range of linear and non-linear materials, including conductors, semiconductors, and insulators, allowing an in depth view of PV and PT materials and devices
  • Provide contrast based on material permittivity and conductivity
  • Visualize buried structures based on capacitance variations measured at the surface
  • Map photo and thermal current on isolated PV materials

 

New Scanning Probe Techniques for Analyzing Organic Photovoltaic Materials and Devices

Organic solar cells hold promise as an economical means of harvesting solar energy due to their ease of production and processing. However, the efficiency of such organic photovoltaic (OPV) devices is currently below that required for widespread adoption. The efficiency of an OPV is inextricably linked to its nanoscale morphology. High-resolution metrology can play a key role in the discovery and optimization of new organic semiconductors in the lab, as well as assist the transition of OPVs from the lab to mass production. We review the instrumental issues associated with the application of scanning probe microscopy techniques such as photoconductive atomic force microscopy and time-resolved electrostatic force microscopy that have been shown to be useful in the study of nanostructured organic solar cells. These techniques offer unique insight into the underlying heterogeneity of OPV devices and provide a nanoscale basis for understanding how morphology directly affects OPV operation. Finally, we discuss opportunities for further improvements in scanning probe microscopy to contribute to OPV development. All measurements and imaging discussed in this application note were performed with an Asylum Research MFP-3D-BIO™ Atomic Force Microscope.

PDF 1.14MB
Photoconductive AFM for Understanding Nanostructures and Device Physics of Organic Solar Cells

Plastic solar cells are emerging as alternative energy sources for the future because of their potential for cheap roll-to-roll printing, ease of processing, lightweight and flexibility. However, their current performance is still low for practical applications which partially originate from the poor understanding of device physics and nanoscale morphology of the photoactive layer. Photoconductive atomic force microscopy is a powerful characterization tool to better understand the complex optoelectronic and morphological phenomena of organic solar cells at the nanoscale. All data for this work was obtained using the MFP-3D™ Atomic Force Microscope from Asylum Research.

PDF 2.27MB
Turnkey Glovebox Solutions for Asylum Research AFMs

Isolated environments are now essential for many research applications. Asylum Research has developed glovebox solutions for its Cypher™ and MFP-3D™ Atomic Force Microscopes. This provides a controlled environment while enabling maximum performance of the AFM. The glovebox is ideal for AFM applications including electrochemistry, batteries, photovoltaics, organic semiconductors, OLEDs, etc.

PDF 1.24MB

Asylum Research Image Gallery

Measuring Nanomechanical Properties


	AM-FM Viscoelastic Mapping Mode

AM-FM Viscoelastic Mapping Mode

Quantitatively maps storage modulus and loss tangent over a wide modulus range (~50 kPa - 300 GPa).


	Contact Resonance Viscoelastic Mapping Mode

Contact Resonance Viscoelastic Mapping Mode

Quantitatively maps storage modulus and loss tangent over a wide modulus range (1 GPa - 300 GPa).


	Nanoindentation Option for MFP-3D AFMs

Nanoindentation Option for MFP-3D AFMs

True ISO 14577 compliant vertical nanoindenter option for MFP-3D AFMs.


	NanomechPro Toolkit

NanomechPro Toolkit

Describes the complete set of complementary tools for investigating nanomechanical properties.


Probing Electrical and Functional Behavior


	Overview of Electrical Techniques

Overview of Electrical Techniques

Overview of Asylum's full range of electrical characterization techniques.


	Conductive AFM (CAFM)

Conductive AFM (CAFM)

Detailed discussion of conductive AFM (CAFM) using Asylum’s exclusive ORCA modules.


	Piezoresponse Force Microscopy (PFM)

Piezoresponse Force Microscopy (PFM)

Detailed discussion of piezoresponse force microscopy (PFM) techniques, many exclusive to Asylum AFMs.


	Scanning Microwave Impedance Microscopy (sMIM)

Scanning Microwave Impedance Microscopy (sMIM)

Scanning Microwave Impedance Microscopy (sMIM) measures conductivity and permittivity at high resolution.


Related Webinars


	“Introduction and Innovations in High Speed Quantitative Nanomechanical Imaging”

“Introduction and Innovations in High Speed Quantitative Nanomechanical Imaging”

Capabilities and challenges of AFM techniques for measuring nanomechanical properties.


	"Contact Resonance Tools for AFM Nanomechanics"

"Contact Resonance Tools for AFM Nanomechanics"

Contact Resonance Viscoelastic Mapping Mode technology and applications.


	"Beyond Topography: New Advances in AFM Characterization of Polymers"

"Beyond Topography: New Advances in AFM Characterization of Polymers"

This webinar provides an overview of the AFM’s powerful capabilities for polymers characterization.

Selected Publications

N. Beaumont, S. W. Cho, P. Sullivan, D. Newby, K. E. Smith, and T. S. Jones, "Boron Subphthalocyanine Chloride as an Electron Acceptor for High-Voltage Fullerene-Free Organic Photovoltaics," Adv. Funct. Mater. 22, 561-566 (2011). doi:10.1002/adfm.201101782

V. W. Bergmann, S. A. L. Weber, F. J. Ramos, M. K. Nazeeruddin, M. Grätzel, D. Li, A. L. Domanski, I. Lieberwirth, S. Ahmad, and R. Berger, "Real-space observation of unbalanced charge distribution inside a perovskite-sensitized solar cell," Nat. Commun. 5, 5001 (2014). doi:10.1038/ncomms6001

J. H. Choi, K.-I. Son, T. Kim, K. Kim, K. Ohkubo, and S. Fukuzumi, "Thienyl-substituted methanofullerene derivatives for organic photovoltaic cells," J. Mater. Chem. 20, 475-482 (2010). doi:10.1039/b916597e

D. C. Coffey, and D. S. Ginger, "Time-resolved electrostatic force microscopy of polymer solar cells," Nat. Mater. 5, 735-740 (2006). doi:10.1038/nmat1712

D. C. Coffey, O. G. Reid, D. B. Rodovsky, G. P. Bartholomew, and D. S. Ginger, "Mapping Local Photocurrents in Polymer/Fullerene Solar Cells with Photoconductive Atomic Force Microscopy," Nano Lett. 7, 738-744 (2007). doi:10.1021/nl062989e

A. Fejfar, M. Hývl, M. Ledinský, A. Vetushka, J. Stuchlk, J. Kočka, S. Misra, B. O'Donnell, M. Foldyna, L. Yu, and P. R. i Cabarrocas, "Microscopic measurements of variations in local (photo)electronic properties in nanostructured solar cells," Sol. Energy Mater. Sol. Cells 119, 228-234 (2013). doi:10.1016/j.solmat.2013.07.042

I. Hancox, K. V. Chauhan, P. Sullivan, R. A. Hatton, A. Moshar, C. P. A. Mulcahy, and T. S. Jones, "Increased efficiency of small molecule photovoltaic cells by insertion of a MoO3 hole-extracting layer," Energy Environ. Sci. 3, 107-110 (2010). doi:10.1039/b915764f

C. V. Hoven, X.-D. Dang, R. C. Coffin, J. Peet, T.-Q. Nguyen, and G. C. Bazan, "Improved Performance of Polymer Bulk Heterojunction Solar Cells Through the Reduction of Phase Separation via Solvent Additives," Adv. Mater. 22, E63-E66 (2010). doi:10.1002/adma.200903677

V. S. Kale, R. R. Prabhakar, S. S. Pramana, M. Rao, C.-H. Sow, K. B. Jinesh, and S. G. Mhaisalkar, "Enhanced electron field emission properties of high aspect ratio silicon nanowire–zinc oxide core–shell arrays," Phys. Chem. Chem. Phys. 14, 4614 (2012). doi:10.1039/c2cp40238f

D. A. Kamkar, M. Wang, F. Wudl, and T.-Q. Nguyen, "Single Nanowire OPV Properties of a Fullerene-Capped P3HT Dyad Investigated Using Conductive and Photoconductive AFM," ACS Nano 6, 1149-1157 (2012). doi:10.1021/nn204565h

J. H. Kim, P.-W. Liang, S. T. Williams, N. Cho, C.-C. Chueh, M. S. Glaz, D. S. Ginger, and A. K.-Y. Jen, "High-Performance and Environmentally Stable Planar Heterojunction Perovskite Solar Cells Based on a Solution-Processed Copper-Doped Nickel Oxide Hole-Transporting Layer," Adv. Mater. 27, 695-701 (2014). doi:10.1002/adma.201404189

Y. Liang, D. Feng, Y. Wu, S.-T. Tsai, G. Li, C. Ray, and L. Yu, "Highly Efficient Solar Cell Polymers Developed via Fine-Tuning of Structural and Electronic Properties," J. Am. Chem. Soc. 131, 7792-7799 (2009). doi:10.1021/ja901545q

F. Liu, W. Zhao, J. R. Tumbleston, C. Wang, Y. Gu, D. Wang, A. L. Briseno, H. Ade, and T. P. Russell, "Understanding the Morphology of PTB7:PCBM Blends in Organic Photovoltaics," Adv. Energy Mater. 4, 1301377 (2013). doi:10.1002/aenm.201301377

F. Ma, Y. Ou, Y. Yang, Y. Liu, S. Xie, J.-F. Li, G. Cao, R. Proksch, and J. Li, "Nanocrystalline Structure and Thermoelectric Properties of Electrospun NaCo2O4 Nanofibers," J. Phys. Chem. C 114, 22038-22043 (2010). doi:10.1021/jp107488k

L. S. C. Pingree, B. A. MacLeod, and D. S. Ginger, "The Changing Face of PEDOT:PSS Films: Substrate, Bias, and Processing Effects on Vertical Charge Transport," J. Phys. Chem. C 112, 7922-7927 (2008). doi:10.1021/jp711838h

L. S. C. Pingree, O. G. Reid, and D. S. Ginger, "Imaging the Evolution of Nanoscale Photocurrent Collection and Transport Networks during Annealing of Polythiophene/Fullerene Solar Cells," Nano Lett. 9, 2946-2952 (2009). doi:10.1021/nl901358v

S. C. Price, A. C. Stuart, and W. You, "Low Band Gap Polymers Based on Benzo[1,2-b:4,5-b']dithiophene: Rational Design of Polymers Leads to High Photovoltaic Performance," Macromolecules 43, 4609-4612 (2010). doi:10.1021/ma100051v

O. G. Reid, K. Munechika, and D. S. Ginger, "Space Charge Limited Current Measurements on Conjugated Polymer Films using Conductive Atomic Force Microscopy," Nano Lett. 8, 1602-1609 (2008). doi:10.1021/nl080155l

S. Schumann, R. A. Hatton, and T. S. Jones, "Organic Photovoltaic Devices Based on Water-Soluble Copper Phthalocyanine," J. Phys. Chem. C 115, 4916-4921 (2011). doi:10.1021/jp109544m

G. Shao, M. S. Glaz, F. Ma, H. Ju, and D. S. Ginger, "Intensity-Modulated Scanning Kelvin Probe Microscopy for Probing Recombination in Organic Photovoltaics," ACS Nano 8, 10799-10807 (2014). doi:10.1021/nn5045867

H. M. Stec, R. J. Williams, T. S. Jones, and R. A. Hatton, "Ultrathin Transparent Au Electrodes for Organic Photovoltaics Fabricated Using a Mixed Mono-Molecular Nucleation Layer," Adv. Funct. Mater. 21, 1709-1716 (2011). doi:10.1002/adfm.201002021

T. Sun, J. Ma, Q. Yan, Y. Huang, J. Wang, and H. Hng, "Influence of pulsed laser deposition rate on the microstructure and thermoelectric properties of Ca3Co4O9 thin films," J. Cryst. Growth 311, 4123-4128 (2009). doi:10.1016/j.jcrysgro.2009.06.044

N. K. Unsworth, I. Hancox, C. A. Dearden, T. Howells, P. Sullivan, R. S. Lilley, J. Sharp, and T. S. Jones, "Highly conductive spray deposited poly(3, 4-ethylenedioxythiophene):poly (styrenesulfonate) electrodes for indium tin oxide-free small molecule organic photovoltaic devices," Appl. Phys. Lett. 103, 173304 (2013). doi:10.1063/1.4826651

P. Zhao, J. Xu, H. Wang, L. Wang, W. Kong, W. Ren, L. Bian, and A. Chang, "Calcium manganate: A promising candidate as buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems," J. Appl. Phys. 116, 194901 (2014). doi:10.1063/1.4901636