From a novel synthesis method for bismuth tri-iodide nanoparticles to a solution-processed hybrid material: BiI3-conducting polymer

We successfully synthesized two types of bismuth tri-iodide nanoparticles: uncapped (BiI3) and capped with aniline (BiI3_ani), in order to study their potential as inorganic semiconductor for an organic–inorganic hybrid material with poly(3-hexylthiophene-2,5-diyl) (P3HT). We developed a novel direct synthesis method that avoids ligand exchange (for BiI3_ani), as well as the necessity of capping agent removal steps (for BiI3) and the formation of secondary compounds obtained by other techniques. Additionally, we evaluated and compared the properties of solution-processed P3HT:nanoparticles layers with the film sequence ITO/PEDOT:PSS/P3HT:nanoparticles, where ITO is indium tin oxide and PEDOT:PSS is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. We analyzed the layers by UV–Vis spectroscopy, X-ray diffraction, focused ion beam scanning electron microscopy and photoluminescence analysis. We proved that aniline restricts the growth of nanoparticles and improves the processability of the material compared to nanoparticles without capping agent. We demonstrated that both types of nanoparticles can be successfully suspended in a solvent in which P3HT is soluble, improve the UV–Vis absorption of P3HT and interact with this polymer leading to an improved crystalline ordering on the blends compared to pristine P3HT layers. We also demonstrated that BiI3 nanoparticles produce a nanoscopic mixture with P3HT and that it is possible to exploit the photoluminescence emission of P3HT:BiI3_ani layers. Our results show that both types of nanoparticles can be good candidates for use in solution-processed organic–inorganic hybrid material with P3HT, which could be employed for the fabrication of hybrid polymeric–inorganic solar cells with BiI3 nanoparticles as electron acceptor and P3HT as electron donor.