Nanomorphology and crystallinity of P3HT: PCBM solar cells doped with iron oxide nanoparticles

Organic bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C60-butyric acid methyl ester (PCBM) are processed from solution and doped with different concentrations of iron(II,III) oxide nanoparticles (Fe3O4). The power conversion efficiencies of the devices doped with low concentrations of NPs show improvements reaching up to 11% compared to the non-doped devices. The PCE raise is additionally driven by an increased fill factor (up to 12%). The improvement is caused by a lowered recombination rate, consequence of an increased effective exciton lifetime, according to the J-V characteristics and the optoelectronical analysis of the films. Advanced scattering techniques such as Grazing Incidence Small Angle X-ray Scattering (GISAXS) provide a deep insight on the evolution of the polymer/fullerene domain morphologies. After 1D-paracrystalline modelling of the studied system within the framework of the Distorted Wave Born Approximation (DWBA), the improvement in device performance could not be attributed to changes in film morphology in the mesoscale. The evolution of the solar cell short-circuit current at low doping concentrations and of the arrangement of the crystalline regions of P3HT shows a certain degree of correlation, thereby providing a reasonable picture of the functioning of the solar devices. For high doping concentrations (above 1.0 wt.%) the device performance decays rapidly. Increased leakage currents in the device caused by the presence of nanoparticles are appointed as being mainly responsible for this effect.