Abstract
In this thesis, we focus on the photophysical and physical properties of hybrid solar cells, including dye-sensitized solar cells (DSSCs), Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/Si organic/inorganic hybrid solar cells and novel perovskite solar cells. We utilized a series of measurement systems to analyze the charge recombination process and carrier concentration in DSSCs and organic/inorganic hybrid solar cells. We investigated the detailed physical properties of perovskite thin films deposited on different under-layer materials. The relationship between surface morphology of perovskite thin films and the device power conversion efficiencies is also discussed. In the first chapter, we briefly review the history of photovoltaics, especially recent development of hybrid solar cells. In the second chapter, the operation mechanisms and photovoltaic characteristics of the hybrid solar cells are described in detail. The measurement setups and principles of current-voltage curve, external quantum efficiency analysis, and transient photovoltage/photocurrent measurements are also shown in this chapter. In the third chapter, the photophysical measurement systems were employed to analyze the Ruthenium(II)-based, Osmium(II)-based and metal-free organic sensitizers in DSSCs. We find that the addition of spacial barrier in molecular structures can slow down the charge recombination from TiO2 to the electrolyte and enhance photovoltage. Besides, dye loading also affects the charge recombination. These two factors need to be considered in the future molecular design of high efficiency dye sensitizer. In the fourth chapter, the transient photovoltage/photocurrent measurements were utilized to investigate the influence of trap-state density on power conversion efficiency of PEDOT:PSS/Si organic/inorganic hybrid solar cells. We find that the SiOx passivation layer decreases the amount of trap-state density. However, thicker SiOx becomes a barrier for carrier transportation due to its non-conducting property. In the fifth chapter, we manufactured perovskite solar cells from the home-made precursor reactant CH3NH3I. We used planar ZnO thin films as an electron transporting under-layer layers. Poor efficiency was found in solution casted devices with the ZnO under-layer due to the non-uniform surface morphology of perovskite thin films. The surface morphology and surface coverage can be largely improved by vacuum evaporation of perovskite thin films on MoO3, TiO2, and PEDOT:PSS under-layers. We believe that efficient perovskite hybrid solar cells can be realized by utilizing these perovskite/under-layer pairs.