The Investigations Of The Photophysical Propertise Of Organic Semiconductor Blend

Organic semiconductor materials possess the advantages of low cost, simple and large-area fabrication, realization of flexible devices, and etc. They can be applied in the developments of light-emitting displays, solar cells and thin film transistors. However, the mobility of the charge is considerably low in organic semiconductors. This leads to the low efficiency of the optoelectronic devices and lowers the speed of the industrialization of the organic optoelectronic devices. To solve this issue, the first thing we should do is to completely understand the mechanisms of the charge generation, transmission and dissociation in the organic semiconductor blends with different morphologies and configurations. Whereas, the photophysics is one of the important method to resolved this issue.In this thesis, we investigate the photophysical properties of the polymer blend of poly (9, 9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly (9,9'-dioctylfluorene-co-bis-N, N'-(4-butylphenyl)-bis-N,N'- phenyl-l,4 - phenylenediamine) (PFB) by a comparison between the microscopic and spectroscopic analyses:(1) The dependence of the optical spectral properties of the exciplex emission in the polymer blends of F8BT and PFB on the excitation wavelengths, on the composite ratios, and on the annealing temperatures. The following conclusions can be drawn from the experimental results:â‘ changing the excitation wavelength can modify the energy transfer at the interface between the two blend polymers, thus, favors the formation of the exciplex;â‘¡changing the composite ratios and the annealing temperatures may have actually changed the phase separation in the blend film, which is responsible for the modified mechanisms for the formation of the exciplex. (2) The influence of particle plasmon resonance (PPR) of Au nanoislands structures on the exciplex emission in the polymer blend of F8BT: PFB. The results show that when the spectral range of the PPR of the Au nanoislands overlaps the spectral range of the exciplex emission, significant enhancement and longer lifetime of the photoluminescence have been measured. We can conclude that:â‘ the scattering by the Au nanoislands enhanced the output coupling of exciplex emission;â‘¡the PPR of the Au nanoislands has increased the lifetime of the exciplex emission, implying that some new mechanisms should be considered here: modulation of the phase separation or interfacial states by the gold nanostructures; modulation of the charge-transfer or exciton-diffusion length by the localized field induced by the PPR; modulation of the charge or exciton distribution on the interface by the localized field induced by the PPR;(3) The changes of the photophysical properties of the blend of FB8T: PFB under the strong excitation in the air. The photoluminescence of the blend is found shift to about 550 nm. This can be attributed to the keto defect in the polyfluorene. This may destroy or weaken the mechanisms for the formation of exciplex in the blend.(4) The fabrication and characterization of the photoconductive device using the blend of F8BT: PFB.These investigations are important for understanding the processes of the energy transfer, charge generation and transfer in organic blend film. Furthermore, these investigations can provide an effective guidance for the development of high-efficiency organic optoelectronic devices.