In this thesis, we discuss n-type doping of organic semiconductor thin films using organic small molecules as dopants by coevaporation. Novel dopants (cationic\ndyes and their bases) for n-type doping of electron transport materials with low-lying LUMO were investigated. Our results show that cationic dyes and their bases\nare efficient n-type dopants for electron transport materials such as C60, F16ZnPc, NTCDA and others.\nFirstly, we presented detailed investigations on a new approach for n-type doping of organic thin films using cationic dyes as dopants. Cationic dyes can form strong\ndonors in situ by sublimation. Spectroscopic investigations reveal that the leuco bases of cationic dyes are formed in situ during evaporation of xanthene cationic dyes and triphenylmethane cationic dyes. A conductivity study of organic electron transport materials (with low lying LUMO) doped with the cationic dyes has been carried out. All dopants used in the study give rise to an increase of several orders of magnitude in conductivity with dopant concentration, accompanied by a decrease in activation energy. This means that cationic dyes are effective dopants\nfor n-type doping of organic electron transport materials with moderate acceptor strength. From a combined MS, UV/VIS/NIR and FTIR spectroscopy study, we identify the colorless reduced forms of the cationic dyes as the main constituent of vacuum deposited layers. The leuco forms are transformed back to the dye cation upon oxidation in air or by a stronger acceptor, TCNQ. Irreversible charge transfer\nreaction between electron donor and acceptor leads to obvious n-type doping effect.\nDeep donor states are formed in weakly acceptor-type matrices. Furthermore, we showed that fullerene C60 can be effectively doped with LCV by the coevaporation technique. An increase of six orders of magnitude in conductivity of\ndoped C60 has been achieved, compared to undoped C60. LCV gives similar doping effect in C60 to CV. Electron transfer following hydride transfer from LCV to the\nmatrices gives rise to n-type doping. For TCNQ:LCV blend layers, TCNQ anions and CV cations are clearly observed in UV/VIS/NIR absorption and FTIR spectra. A one-electron transfer from LCV to TCNQ can be found. When C60 is doped with LCV, C60 anions are identified in NIR absorption and FTIR spectra. For weaker acceptors like C60, it is obvious that a combined hydride and electron transfer reaction has\nto be supported by outer activation (light or heating). When C60 accepts hydrogen atoms or radicals, it can be reduced to hydrofullerene. An irreversible electron transfer reaction leads to a stable n-doping effect in organic thin films of C60 doped with LCV.\nFinally, doping of fullerene C60 thin films with acridine orange (AO) and acridine orange base (AOB) by the coevaporation technique are reported. AO and AOB\ngive rise to obvious doping effect in C60. EI MS shows that AOB is a main product after AO is thermally dissociated in vacuum. It is found that the dark conductivity\nof C60 doped thin films can be enhanced by a light-induced activation of dopant precursor AOB: A conductivity up to 6e-2 S/cm at 30°C is achieved when a diffusive illumination is provided in the vacuum chamber during the evaporation.\nThe field effect and Seebeck measurements confirm the n-type conduction of C60 thin films and show that deep donor states are formed in AOB-doped C60 films. A field effect mobility of 0.19 cm²/Vs is achieved for a doping level of 2 mol%. NIR\nand FTIR spectra demonstrate electron transfer from the dopant to the matrix: For C60 doped with AOB, C60 is present in NIR absorption and FTIR spectra. On the other hand, a peak corresponding to acridine orange (AO+) is also observed in the FTIR spectrum of C60:AOB. Electrochemical data of AOB and AO in acetonitrile suggest that the AOB radical cation is not stable but is rapidly transformed into a compound with similar properties to AO. We assume that, in the codeposited layers, this compound is a dyad of AOB+ and C60 connected by a C-N chemical bond.