In this thesis, I have been working with the development of nanoparticle sensitized solar cells. In the subarea of quantum dot sensitized solar cells (QDSCs), I have investigated type-II quantum dots (QDs), quantum rods (QRs) and alloy QDs, and developed novel redox couples as electrolytes. I have also proposed upconversion nanoparticles as energy relay materials for dye-sensitized solar cells (DSCs).Colloidal ZnSe/CdS type-II QDs were applied for QDSCs for the first time. The interesting features of those refer to that their photoelectrons and photoholes are located on the different parts of the dot, namely in the CdS shell and in the ZnSe core, respectively. That spatial separation between photoelectrons and photoholes can so effectively enhance the charge extraction efficiency, thus facilitating the electron injection, and also effectively expand the absorption spectrum. All these characteristics contribute to a high photon to current conversion efficiency. Furthermore, a comparison between the photovoltaic performance of ZnSe/CdS and CdS/ZnSe QDSCs shows that the electron distribution is important for the electron injection of the QDs.Colloidal CdS/CdSe QRs were applied to quantum rod-sensitized solar cells (QRSCs). They showed a higher electron injection efficiency than the analogous QDSCs. It is concluded that reduction of the carrier confinement dimensions of the nanoparticles can improve the electron injection efficiency of the nanoparticle sensitized solar cells.Two types of organic electrolytes based on the redox couples of McMT-/BMT (OS1) and TMTU/TMTU-TFO (OS2) were used for the QDSCs. By reducing the charge recombination between the electrolyte and the counter electrode, the fill factor and the photovoltage of these QDSCs were significantly improved, resulting in a higher efficiency for the studied solar cells than that with a commonly used inorganic electrolyte.Ternary-alloy PbxCd1-xS QDs used as photosensitizers for QDSCs were found to improve the photocurrent compared to the corresponding CdS and PbS QDs. By considering the effect of different ratios of Pb to Cd in thePbxCd1-xS QDs on the photovoltaic performance it was discovered that the photocurrent increases and the photovoltage decreases with the increase of the ratio in a certain range.Upconversion (UC) nanoparticles provide a strategy to develop panchromatic solar cells. Three types of UC nanoparticles employed by DSCs were confirmed to work as energy relay materials for effectively extending the light-harvesting spectrum to the near-infrared (NIR) region. They were also found to play a role as scattering centers to enhance the photovoltaic performance of the solar cells.