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Nanometric Organic Photovoltaic Thin Film X-Ray Detectors for Clinical KVp Beams

B Elshahat

Bassem Elshahat1*, Ilya Filipyev2 , Suman Shrestha2,3 , Jurgen Hesser4 , Hardeep Gill1 , Jayant Kumar1 , Andrew Karellas3 , Piotr Zygmanski2 , Erno Sajo1 (1) University of Massachusetts Lowell, Department of Physics and Applied Physics, Lowell, MA, (2) Brigham and Women's Hospital, Boston, MA, (3) University of Massachusetts Medical School, Worcester, MA, (4) Department of Radiation Oncology, University Medical Center Mannheim, Germany


SU-E-CAMPUS-I-1 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:To fabricate and test nanometric organic photovoltaic (OPV) cells made of various active-layer/electrode thicknesses and sizes; to determine the optimal material combinations and geometries suitable for dose measurements in clinical kilovoltage x-ray beams.

Methods:The OPV consisted of P3HT:PCBM photoactive materials sandwiched between aluminum and Indium Tin Oxide (ITO) electrodes. Direct conversion of x-rays in the active layer composed of donor and acceptor semiconducting organic materials generated signal in photovoltaic mode (without external voltage bias). OPV cells were fabricated with different active layer thicknesses (150, 270, 370 nm) and electrode areas (0.4, 0.7, 0.9, 1.4, 2.6 cm²). A series of experiments were preformed in the energy range of 60-150 kVp. The net current per unit area (nA/cm²) was measured using 200 mAs time-integrated beam current.

Results:The net OPV current as function of beam energy (kVp) was proportional to ~E⁻⁰'⁴⁵ when adjusted for beam output. The best combination of parameters for these cells was 270 nm active layer thicknesses for 0.7 cm² electrode area. The measured current ranged from 0.69 to 2.43 nA/cm² as a function of x-ray energy between 60 and 150 kVp, corresponding to 0.09 – 0.06 nA/cm²/mGy, respectively, when adjusted for the beam output.

Conclusion:The experiments indicate that OPV detectors possessing 270 nm active layer and 0.7 cm² Al electrode areas have sensitivity by a factor of 2.5 greater than commercial aSi thin film PV. Because OPV can be made flexible and they do not require high-voltage bias supply, they open the possibility for using as in-vivo detectors in radiation safety in x-ray imaging beams.

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