Quantum-dot Sensitized Solar Cells: Fabrication And Structrual Optimization

Third Generation Photovoltaic Solar Cells are much more economical andapplicable due to their higher theoretical conversion efficiency limit andlarge scale production attributed to the introduction of nanotechnology.Among these, Quantum dot sensitized Solar Cells (QDSSC), employing theexcellent photoelectrical properties of quantum dot (Quantum Effect andMultiple Exciton Generation), exhibits enormous potential. However, theconversion efficiency of QDSSC (~5%) still lags behind most commercialsolar cells leaving a huge gap between the real applications. Besides, eachpart of the device lacks optimization as well as the abstruse mechanism.This research, based on the device mechanism, innovated the noveltystructure possessing a high value for the photoelectrical property of QDSSC.This research originated from the working principle of QDSSC, focusedon the structure optimization with the purpose of promoting conversionefficiency and time stability of QDSSC.Firstly, CdS quantum dot sensitized TiO2nanorod solar cells werefabricated. Through the photoelectrical characterization and cogent analysis,the key elements including the electron injection and recombination thatconstraining the performance of cells were examined. Besides, the effects ofpreparation method to the final device performance are analyzed. Based onthe cell performance, we proposed two mechanisms regarding the electroninjection process which were further proved by electron transmit time andlifetime. Furthermore, ZnS post treatment was conducted and the effect onelectron recombination was revealed.Secondly, Ag2S QDs was deposited on TiO2nanorod array by a two-stepphotodeposition. By controlling the photoreduction period, we obtainedAg2S sensitized TiO2with a large coverage and superiorphotoelectrochemical properties. QDSSCs based on the Ag2S sensitizedTiO2nanorod array were fabricated. Under optimal condition, theAg2S-QDSSC yields a Jscof10.25mA/cm2with conversion efficiency of0.98%at AM1.5solar light of100mW/cm2.Finally, CoS/graphene counter electrode was prepared by assembleCoS/graphene nanocomposite layer by layer. The incorporation of graphene plays a key role in modifying the nanostructure of the electrode. TheCoS/graphene electrode possesses high charge exchange density towardpolysulfide electrolyte and yield excellent electrochemical property that isfavorable for the QDSSCs. This layered nanocomposite provides apromising direction toward developing nanostructure for highelectrocatalytic counter electrode.