Competition between recombination and extraction of free charges determines the fill factor of organic solar cells

Among the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter θ, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor:acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over…

• DF
  Deutsche Forschungsgemeinschaft

  Award: SPP 1355
• BF
  Bundesministerium für Bildung und Forschung

  Award: FKZ 03|S2151D
• NO
  Nederlandse Organisatie voor Wetenschappelijk Onderzoek