Research Of Graphene/Organic Film Composited Photodetectors

The two-dimensional materials（2 Dimensions,2D）,led by graphene,have attracted wide interests from scientists in the past ten years.Due to their high mobility,adjustable optical properties,zero band gap and broadband absorption,they have huge potential in photodetection devices.However,the great progresses have been made so far,there are still many fundamental barriers that hinder the advance of high-performance photodetectors,other photonic and optoelectronic applications;for example,graphene-based detectors have relatively low resistance,resulting in a large dark current.In order to address several current limitations of photodetectors based on graphene heterojunction,combining with organic materials with low cost,large area,flexibility and high absorption coefficient can make up or even solve some shortcomings.Moreover,this method can address the slow response speed,limited response wavelength and single function,to meet the partly demands of advanced optoelectronic chips,this dissertation considers graphene/organic detector as the main objective to explore the several aspects as follow:1.The graphene/C₆₀/Pentacene three-layer structural device is fabricated with a graphene/organic planar P-N heterojunction framework,which utilizes carrier dissociation advantage of the type-II heterojunction of C₆₀/Pentacene to improve the built-in electric field in graphene/organic single-layer heterojunction device.Compared with the inferior responsivity of the Graphene/Pentacene device,the response is improved up to 9127 A/W,the response speed is promoted down to 275μs and the detection wavelength is broadened to 1550 nm.In this framework,both the positive and negative responses（as the change of the photocurrent polarity）at different wavelengths are found.The negative responses appear at the visible light band,and the positive responses at the near-infrared band.Subsequently,the relevant factors of the positive and negative response transition point are discovered.Moreover,the materials such as Cu Pc and Sn Nc Cl₂ are successively introduced for further exploration.2.Using the graphene/C₆₀/Pentacene three-layer structure mentioned above,the structure introduces a second light source as a modulating light to tune the responsive photocurrent of the first signal light,using responsive light with opposite polarities at different wavelength bands to realize a mutual intermodulation.Compared with the existing devices that can only modulate the photocurrent amplitude and detection range broadening,the optical modulation devices can not only achieve amplitude modulation of photocurrent and response speed modulation,but also polarity modulation of photocurrent.As the optical modulation power changing,the maximum responsivity is increased from 3425 A/W to 7673 A/W.Furthermore,by using the method that the graphene oxygen vacancies can be removed through applying near ultraviolet light,the device display gradual modulation between the positive and negative responses.As the results shown,this experiment deeply reveals the carrier transport mechanism of multilayer graphene/organic devices.3.The performance and response mechanism of photodetectors with the same type of structure based on graphene/bulk heterojunction organic framework are explored.By introducing Zn O as an electron extraction layer in the design structure,device can extract photo-generated electrons from the organic heterojunction and then inject into graphene channel.In this device,both near-infrared positive-negative responses with non-memory and photo-memory functions can be realized,and they can be switched with the changing of gate voltage.Due to the higher dissociation and light sensitivity of the bulk heterojunction non-fullerene acceptor material system（IEICO-4F:PTB7）than the planar heterojunction,the graphene/organic device achieves a responsivity over 10⁶A/W and can respond even to n W/cm² magnitude of weak power light.The non-memory and photo-memory switching feature can be utilized in applications such as machine vision and bio-synaptic device.4.The device integrates other inorganic materials such as Bi₂O₂Se with the graphene/organic heterojunction to explore the further mechanism of carrier transport.Moreover,taking advantage of Bi₂O₂Se with high absorption rate in the windows of communication band,the device promotes the response ability of graphene/organic at1310 and 1550 nm.The graphene combined with type-III heterojunction detection device will be investigated and the further demonstration of optical communication by ASCII code transmission application are demonstrated.5.The use of organic donor-acceptor charge transfer complexes combined with graphene will broaden the detection range of graphene/organic devices,ultimately realizing the long wavelength detection up to 10.5μm.The detection performance and mechanism of narrow band organic materials onto graphene is explored.In summary,this dissertation comprehensively introduces various types of graphene/organic composite heterojunction devices,including planar heterojunction,bulk heterojunction,inorganic-organic heterojunction and organic charge transfer complexes.The mechanisms of various types of devices are discussed in detail,ultimately the response speed is as low as tens of microseconds,the responsivity is as high as 10⁶ A/W,and the maximum detection wavelength covers 10.5μm.And the extended the functions of different types of devices are realized,including light modulation exploration,near-infrared light memory,machine vision and communication band applications.The series of these studies will provide novel research strategies and directions for graphene/organic and other 2D material/organic heterojunctions in detection.