Molecular Simulation of Perylene Diimide Crystal Structure for Morphology Characterization in Organic Photovoltaics

Open Access
Author:
Dahod, Nabeel Shabbir
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Enrique Daniel Gomez, Thesis Supervisor
  • Darrell Velegol, Honors Advisor
Keywords:
  • Chemical Engineering
  • Organic Photovoltaics
  • Solar Cells
  • Morphology
  • Crystal Structure
  • Crystallinity
  • Molecular Simulation
Abstract:
Various materials often present disparate crystal structures and thus yield unique heterojunction morphologies when used in preparing the active layer for organic photovoltaic devices. The crystal structure of these materials delineates the molecular packing arrangements of these molecules within a crystal lattice, therein revealing the molecular level structure of these materials. Perylene diimide materials, should, based on their optoelectronic properties function as effective electron acceptors in organic photovoltaic devices, yet upon testing they are revealed to have extremely poor device efficiencies (0.035±0.005 %). This work investigates the potential relationship between this somewhat unexpectedly poor device performance and crystal structure, and seeks to propose that device performance and active layer crystallinity are linked via the morphology of the active layer. Using traditional glass substrates with an indium tin oxide and PEDOT:PSS coated cathode along with an evaporated aluminum anode and poly-3-hexylthiophene as the electron donating material, organic photovoltaic devices were built and device performance was optimized with respect to the perylene diimide N,N'-bis(2,5-di-tert-butylphenyl-perylene)-3,4,9,10-tetracarboxylic diimide (BTBP). Molecular simulation of crystal structure using a Monte Carlo simulated annealing algorithm was used in order to develop various potential simulated crystal structures for this perylene diimide material. Through comparison of the simulated x-ray diffraction of these simulated crystal structures to experimentally obtained x-ray diffraction data for BTBP, a correlation between the two data sets were obtained as a measure of the accuracy of the predicted crystal structures. Further refinements are needed, though, in order for this novel methodology to provide a more effective, and impactful argument regarding the close relationship between crystal structure of the materials within the active layer and organic photovoltaic device performance.