Exciton Dissociation And Charge Transport In Pristine And Doped Polymer Semiconductor

The exciton dissociation and carrier transport properties of pristine as well as doped random polymer have been investigated.1 Transient photovoltage(TPV) is investigated for the sandwich device of ITO/ MEH-PPV(500nm)/Al.A negative TPV signal appears followed by a positive one when using pulse laser wavelength of 500nm.Using exciton distribution model under pulse laser with different wavelength,the exciton dissociation at ITO/ MEH-PPV interface by transfer an electron into ITO electrode is demonstrated which result in the negative TPV signal.2 The performance of TiO₂ nanotubes in bulk heterojunction of MEH-PPV:TiO₂ nanotubes is investigated.The time-of-flight result shows that the transport properties of both hole and electron are not improved.However,photoluminescence under the influence of the electric field indicates that the dissociation of excitons in the MEH-PPV:TiO₂ composite only requires a smaller electric field.It can be attributed to the facility of exciton dissociation at TiO₂ interface by transferring an electron into TiO₂.3 The MEH-PPV film is prepared under the presence of a DC electric field.The time-of-flight hole mobility enhances evidently compared with the as-prepared film. Small-angle X-ray diffraction data show that the disorder of the film prepared under electric field decreases.4 Ambipolar charge transport in bulk heterojunction of MEH-PPV:C₆₀ composite are investigated.Electron mobility is below the measurable range in pristine film. However,electron mobility can be measured when the weight ratio of C₆₀:MEH-PPV increased to 1:18.Moreover,it increases two orders of magnitude when the weight ratio of C₆₀:MEH-PPV increased to1:3.This work demonstrates that the dopant C₆₀ can form electron transport network in MEH-PPV:C₆₀ composite.5 The effects of thermal annealing treatment on carrier transport and film morphology are investigated for MEH-PPV:C₆₀ system.By analysing the temperature dependence of field dependent mobility in Gaussian disorder model(GDM),the drop of hole mobility can be attributed to the large value of both positional disorder and energetic disorder,which are 4.47 and 0.132eV,respectively.Electron mobility is below the measurable range as long as the devices experience thermal treatment.According to SEM study,the drop of electron mobility results from the discontinuity of the electron transport path due to C₆₀ aggregation and vertical segregation.The AFM result shows that thermal annealed treatment increases the roughness of the surface and enhances the virtual interface with electrode,which facilitates exciton dissociation and carrier collection for photovoltaic devices.