This project aims to manufacture third generation photovoltaic cells with the active layer made of electronic polymers thin films combined with electronegative inorganic materials. To accomplish that, we will use structures containing a transparent electrode (ITO, for example), a holes carrier layer (PEDOT:PSS), and as an active layer, electronic polymers (as polythiophene or polyphenylene-vinylene derivatives) combined with TiO2 nanoparticles or fullerenes, and finally an electric contact made of aluminum and calcium. These device structures have been termed as hybrid. Surface photonic and plasmonic effects will be produced to increase efficiency of the devices. In these cells, the photoinduced charge separation is facilitated by the large interfacial area between donor and acceptor, and hybrid films have showing great photoconversion efficiencies. The decrease of charge recombination due to the nanoparticles is the most important factor to increase efficiency of these cells. The absorption of light by a semiconductor creates an electron in an excited state and a hole in the valence band, forming an exciton, which has binding energy of several eV and can migrate about 10 nm before recombine. However, if the excited electrons are transferred to a receptor site, the absorption of light can result in photocurrent generation. The subsequent conduction process takes place by different processes: conduction of holes through polymer chain by hopping, and the electrons through nanoparticles, also by hopping. This spatial separation of charges is crucial for the efficiency of photoconversion. Nanoparticles - in this case, TiO2 - have high electronic affinity, acting as electron acceptors when combined with conductor polymers, preventing the recombination of charges. It is important to remark that the charge transfer occurs between a previously photogenerated exciton and a nanoparticle. The transfer of photogenerated electrons from the polymer segment to the nanoparticle decreases the rate of radiative recombination processes. The molecular recombination also decreases due to the difference in mobility between the two types of charge carriers. This thesis will continue the pioneering work in Bernhard Gross Polymers Group, which were results of the candidate´s masters degree dissertation. Among the results, it was developed the manufacturing techniques and characterization of organic photovoltaics, which totaled close to 4% of efficiency. Those results are being written for publication in a journal of the respective area.
News published in Agência FAPESP Newsletter about the scholarship: