Study On Photocurrent Spectrum And In-situ Raman Imaging Of Organic Field Effect Transistor

Organic field effect transistors(OFETs)have been developed as attractive,low cost and flexible electronic components,especially in the field of optical signal detection,due to their high flexibility,solution processing,low preparation temperature and easy to achieve large area processing.The unique photoelectronic properties of organic semiconductors have great potential for development,innovation and disruptive applications.However,because organic semiconductors are more complex than traditional inorganic semiconductors in terms of conductivity,carrier transport and electronic structure,band theory cannot well explain the carrier transport of organic materials.Therefore,it is very important to study the carrier transport mechanism and photoelectric properties of organic field effect transistors under light conditions.In this paper,by combining in-situ Raman spectroscopy characterization and electrical testing of organic field effect transistors,the micro-area photoelectric characteristics and micro-area photocurrent in the channel of organic field effect transistors are studied.The experimental observation of three potential distributions and the experimental estimation of the Debye length of OFET are achieved by surface-enhanced Raman spectroscopy.The work of this paper mainly includes the following three aspects:1.The photo response behavior of OFET was studied by using 405 nm wavelength laser.The optical current of OFET increases with the increase of light intensity,and has obvious photo response and photoelectric conversion characteristics.Further,we found that the interface trap density decreases with the increase of light intensity and the threshold voltage moves in a positive direction,which constitutes the main source of optical current.In addition,the Raman intensity of TIPS-Pentacene is positively related to the grid voltage in the in-situ Raman spectrum of the channel of the OFET device.These results provide a good basis for in-depth micro-area photoelectric and Raman imaging analysis.2.The change of micro-region photocurrent in the channel of TIPS-Pentacene OFET device was studied by micro-region photocurrent experiment.When there is no external electric field in the device channel,the photocurrent is small as a whole.When illuminating near the source and drain poles,the free drift current of the photogenerated carrier is detected,and the direction of the source and drain current is opposite.Under different grid voltage and different source leakage voltage conditions,the intensity and spatial distribution of micro-region photocurrent spectrum are very sensitive to the change of voltage,which can be used to analyze and characterize the working mechanism of the device.Essentially,the splitting efficiency of photo exciton is determined by the potential at the corresponding location of the channel.The intensity of the photocurrent depends on the potential or the electric field intensity at the corresponding location.This method can be used to analyze and describe the electric field distribution at different locations of the channel.In this paper,the change of electric field intensity at the edge of channel is successfully analyzed using this method.3.In situ surface enhanced Raman spectroscopy was used to observe the three-dimensional distribution of potential in an organic field effect transistor with pentacene as the active layer.The SERS spectra of OFET devices were obtained by introducing a silver nanoparticle layer into the active layer.It was found that the SERS intensity responded positively to the external voltage,and the logarithm of SERS enhancer had a very good linear relationship with the grid voltage.The SERS enhancer mechanism enhanced the charge transfer from silver to pentacene,which laid a good foundation for the quantitative analysis of the potential distribution.Raman imaging of OFET was further performed by in situ SERS spectroscopy,and the horizontal potential distribution and channel clamp breakpoints were observed while the device was in operation.By changing the depth of silver nanoparticles in the channel,combining the vertical potential distribution in the active layer with the transverse potential distribution in the channel obtained from SERS imaging,the three-dimensional potential distribution in the transistor channel can be obtained using in situ SERS as a visualization tool.Finally,we estimated the Debye shielding length of OFET by SERS enhancement probe and established an experimental method for L_D measurement.