Synthesis and Characterization of Bi2S3 Colloidal Nanoparticles for Photovoltaic Applications

Global energy consumption is expected to increase significantly together with the greenhouse gas emissions and the problem of fossil fuels exhaustion. Solar energy, as an alternative and renewable form of energy, has gained pop- ularity as possible solution for all these problems. Lots of materials have been studied to implement the energy conversion efficiency of the so-called third generation solar cells. These devices could be a cheaper alternatives to the silicon-based ones. Unfortunately, they are often characterized by short life- time or health hazardous materials. Bismuth sulfide(Bi2S3) is a promising n-type semiconductor for solar energy conversion.In this work,the properties of the compound will be discussed,as well as its potential for applications in solar energy technology.Wehave explored the colloidal synthesis of Bi2S3 nanocrystals,with the aim of employing them in the fabrication of solution- processable solar cells and to replace toxic heavy metals chalcogenides likePbS or CdS,that are currently employed in such devices. We compare different methods to obtain Bi2S3 colloidal quantum dots, including the useof environmentally benign reactants, through horganometallic synthesis. Surfactant-assisted colloidal synthesis(SACS) methods were used to synthesize Bi2S3 nanoparticles with different size and shape.These methods have been employed changing systematically several parameters such as temperature and timeofsynthesis, concentration ofchemical reagents and sulfur precursors. Morphological characteristics and optical properties of all the synthesized nanoparticles have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-Vis and photoluminescence (PL) spectroscopy. After the characterization of electrical properties of bismuth sulfide sam- ples together with the preliminary attempts to find the most advantageous methods for the production of homogeneous film on conductive supports, asample was chosen like standard and it was employed in building of various prototype of third generation solution processed solar cells. Dip and spin coat- ing techniques were employed to produce homogeneous film of nanoparticleson conductive support, also in combination with organic polymer such P3HT, Pedot:PSS and Spiro-OMeTAD. The resulting solar cells were tested for power conversion efficiency (PCE). Synthesis and characterizations have been carried out in Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, under the supervision of Prof. Anna Musinu and Prof. Carla Cannas. Optoelectronic characterizations and solar cells manufacturing have been carried out in Di- partimento di Fisica, Università degli Studi di Cagliari, under the supervision of Prof. Michele Saba, Prof. Andrea Mura and Prof. Giovanni Bongiovanni