Studies of Semiconductors Modified with Nanoscale Light Absorbers for Solar Cell Application

Sammanfattning: Recently, materials such as hole conductors (CuI, CuSCN) and light absorbers (Ru-complexes, CuInS2) have been actively investigated for application in nanocrystalline solar cells. In this thesis combinations of these materials have been studied.In the first part of the thesis, various methods were applied to characterize the electronic structure and photoconversion mechanism of the dye molecule Ru(dcbpyH2)2(NCS)2 when combined with materials for the use in photovoltaic devices. Specifically, the adsorption and electronic structure of the dye molecules adsorbed to semiconductors were investigated by means of photoelectron spectroscopy. The results indicate a chemical bond between the dye molecules and the hole conductors (CuI, CuSCN) via the NCS- groups. In addition, preparation of a TiO2/Ru-dye/CuI solid state model system was studied in situ. These experiments showed a partial breaking of the TiO2-dye bond caused by CuI evaporation. Photovoltage measurements were also performed. These investigations showed a shift in the light absorption threshold of the dye molecules adsorbed onto the hole conductors (CuI and CuSCN), indicating new defect states at the dye/CuSCN interface. Also, charge accumulation and transport in solar cells with CuSCN were compared to liquid electrolyte cells. Measurements showed that the lifetime and transport time of electrons in solar cells with CuSCN are much shorter than in electrolyte cells.In the second part of the thesis, the deposition of CuInS2 onto various metal oxides by spray pyrolysis has been studied with x-ray diffraction and photoelectron spectroscopy. The measurements showed that the morphologies of the substrates play a significant role in the formation of CuInS2 layers. Also, the presence of CdS at TiO2 has a positive influence on the formation of CuInS2.