Selective Photodetection Using Organic Field-Effect Transistor Memories

Photoelectric detection research has been receiving much attention.Meanwhile,Organic device also comes into the visions with its unique advantages such as flexibility,light weight,low cost and large-area manufacturing.Therefore,photodetection research based on organic electronic devices has developed rapidly in recent years,which has been applied in diverse fields,for example,large-area array image sensing,wide-spectrum photodetector devices and photoelectric switching transistors.In this field,it is still challenging for the research on selective photodetection.And the potential studies such as electrical simulation of optic nerve and ultraviolet content detection have attracted great interest from researchers.The photo-induced memory window in organic transistor memories provides a new strategy for selective photodetection in UV-visible spectrum.In this paper,small molecule electron acceptor material,fullerene derivative[6,6]-phenyl-C61-butyric acid methyl ester,PCBM,is mixed into the electret polymer material polymer poly(2-vinylnaphthalene)PVN.The charge trapping layer is spin-coated in the organic transistor memory.According to the amount of PCBM mixed,the responsing spectrum of the device extends from the deep-ultraviolet spectrum to near-ultraviolet and visible spectrum.In the absence of PCBM,Device A only shows a threshold voltage shift after programming/erasing under 254 nm deep ultraviolet illumination.By increasing the PCBM content to 2.5%and 30%,Device B and Device C begin to exhibit similar phenomena at 420 nm and 740 nm wavelengths.Various factors were optimized for the concentration and wavelength selection in the device.The interference of 520 nm green light on the cut-off response wavelength of the device under low concentration conditions was excluded,and the light at 850 nm could not make the device response.The memory window ensures the reliability of the device behavior.In terms of working mechanism,combined with UV absorption spectroscopy,atomic force microscopy characterization results and device electrical behavior,an energy band structure model was proposed.PCBM dispersed in PVN acts as a trap-like state,which reduce charge barrier of trapping electrons/holes.Therefore,electrons can be injected into the charge trapping layer under excitation of longer wavelengths.This model well explains the device performance.In terms of device application,there are two main applications in this work.(1)Based on the performance that the source-drain current increases linearly with the testing time under illumination and the relationship between the source-drain current and the threshold voltage,it can be calculated that there is a good linear relationship between the number of trapped charge and the light exposure.Due to this phenomenon,the device can be applied in radiation dosimeters.(2)Because the responsing spectrum of Device B is included in Device C,according to the ratio of the threshold voltage shifts of the device B and C under mixed white light,the content of the near-ultraviolet spectrum in the mixed light can be estimated.Finally,The result matched well with PR670 SpectraScan Colorimeter,which could be a convenient way to test UV content in sunlight.In summary,this paper proposes a filter-free photo-induced memory device in multi-wavebands.Which can selectively achieve dose monitoring of light.It also has the potential as a specific wave band detection.Therefore,this research provides a new and effective strategy for wearable light monitoring electronics in the future.