Quantum dots of lead selenide: evolution of size and geometry and influence on photovoltaic effect

Lead selenide quantum dots were synthesised by the colloidal chemical synthesis route at different reaction temperatures. The nanocrystals were characterised by X–ray diffraction (XRD), High–resolution transmission electron microscopy (HRTEM) and FTIR spectroscopy. Diameter of the PbSe quantum dots increased with reaction temperature, with average diameter varying from 30 nm to 200 nm at reaction temperatures ranging from 160ºC to 250ºC. Geometries such as sphere and square with relatively uniform size distribution have been obtained at lower reaction temperature, whereas higher reaction temperatures resulted in mixtures of pentagons and hexagons and also elongated geometries. Organic–inorganic hybrid bulk hetero junction (BHJ) thin film photovoltaic devices were designed and fabricated with PbSe quantum dots and the conducting polymer–poly 3–hexyl thiophene (P3HT). Open circuit voltages obtained for these cells confirmed existence of strong quantum confinement effect for the devices containing PbSe quantum dots with diameters below the exciton Bohr diameter.