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Keywords:

  • solar cells;
  • composite materials;
  • hybrid materials;
  • conjugated polymers;
  • zinc oxide

Abstract

The 3D nanomorphology of blends of two different (organic and inorganic) solid phases as used in bulk heterojunction solar cells is described by a spatial stochastic model. The model is fitted to 3D image data describing the photoactive layer of poly(3-hexylthiophene)-ZnO (P3HT-ZnO) solar cells fabricated with varying spin-coating velocities. A scenario analysis is performed where 3D morphologies are simulated for different spin-coating velocities to elucidate the correlation between processing conditions, morphology, and efficiency of hybrid P3HT-ZnO solar cells. The simulated morphologies are analyzed quantitatively in terms of structural and physical characteristics. It is found that there is a tendency for the morphology to coarsen with increasing spin-coating velocity, creating larger domains of P3HT and ZnO. The impact of the spin-coating velocity on the connectivity of the morphology and the existence of percolation pathways for charge carriers in the resulting films appears insignificant, but the quality of percolation pathways, considering the charge carrier mobility, strongly varies with the spin-coating velocity, especially in the ZnO phase. Also, the exciton quenching efficiency decreases significantly for films deposited at large spin-coating velocities. The stochastic simulation model investigated is compared to a simulated annealing model and is found to provide a better fit to the experimental data.