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Concurrent Quantitative Conductivity and Mechanical Properties Measurements of Organic Photovoltaic Materials using AFM

Published: January 23rd, 2013

DOI:

10.3791/50293

1Center for Nanoscale Materials, Argonne National Laboratory, 2Institute for Molecular Engineering, University of Chicago

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution.

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. Thus, understanding of spatial variations in composition as well as electrical properties of OPV materials is of paramount importance for moving PV technology forward.1,2 In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution. Currently, materials properties measurements performed using commercially available AFM-based techniques (PeakForce, conductive AFM) generally provide only qualitative information. The values for resistance as well as Young's modulus measured using our method on the prototypical ITO/PEDOT:PSS/P3HT:PC61BM system correspond well with literature data. The P3HT:PC61BM blend separates onto PC61BM-rich and P3HT-rich domains. Mechanical properties of PC61BM-rich and P3HT-rich domains are different, which allows for domain attribution on the surface of the film. Importantly, combining mechanical and electrical data allows for correlation of the domain structure on the surface of the film with electrical properties variation measured through the thickness of the film.

Recent breakthroughs in power conversion efficiency (PCE) of organic photovoltaic (OPV) cells (pushing 10% at the cell level)3 in concert with compliance with high-throughput and low-cost manufacturing processes4 have brought a spotlight onto OPV technology as a possible solution for the challenge of inexpensive manufacturing of large-area solar cells. OPV materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials and performance of photovoltaic devices are intimately connected. Thus, understanding inhomogeneity in composition as well as electrical properties of OPV materials is of paramount i....

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1. Signal Acquisition

  1. Install sample (polymer solar cell without cathode (ITO/PEDOT:PSS/P3HT:PC61BM)) into a commercial Multimode AFM (Veeco, Santa Barbara, CA) equipped with Nanoscope-V controller.
  2. Install conductive AFM probe into Multimode AFM probe holder.
  3. Create electrical connection between the AFM probe, sample and voltage source.
  4. Route current amplifier output (current signal), Multimode AFM deflection output (force signal), Multimode AFM sample .......

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Young's modulus and resistivity maps (Figure 3) present typical results of the measurements described above. Mechanical and electrical properties of the ITO/PEDOT:PSS/P3HT:PC61BM stack were measured at negative (-10 V) and positive (+6 V) voltages applied to the AFM probe. Imaging artifacts, associated with electrostatic interaction between the AFM probe and the sample, are a common problem for quantitative measurements of functional properties using AFM. The similarity of Young's modul.......

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MPN is grateful to the Director's Fellowship Program for financial support. MPN wants to thank Yu-Chih Tseng for help with development of the protocol for solar cell processing. This work was performed at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357.

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Name Company Catalog Number Comments
Name of Reagent/Material Company Catalog Number Comments
Plextronics inks Plexcore PV 1000
ITO-coated glass substrates Delta Technologies, Inc 25 Ohms/sq
30 MHz synthesized function generator Stanfor Research Systems DS345
Current amplifier Femto DLPCA-200
Multimode AFM Veeco, Santa Barbara, CA equipped with Nanoscope-V controller
DAQ card National Instruments NI-PCI-6115
Metal Pt probes RMNano 12Pt3008
MATLAB software Mathworks
LabView software National Instruments

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