Characterizations And Applications Of Narrowband Organic Photodiodes

Organic semiconductors are very suitable to develop narrowband photodiodes due to its adjustable energy gap.With the development of information society,narrowband organic photodiodes?OPD?are becoming favorable candidates for narrowband detection to meet the new requirements on detectors,such as simple structure,higher color discrimination,flexible fabrication and lower power consumption.In this paper,we put emphasis on design and fabrication of narrowband OPDs while taking the improvement of device performance and stability into account.First,this paper studies the method of improving the device performance and reducing the dark current based on a heterojunction-structure OPD.Then a simple and effective strategy,using the material with intense and sharp absorption and simple single-layer structure,is proposed to realize narrowband OPDs.And it can overcome the problem of nonnegligible absorption in unwanted regions caused by introduction of two or more materials with different absorption in narrowband OPDs with common heterojunction structure.At last,through the application of narrowband OPDs,a multi-channel visible light communication system and a multiple signal superposition device are designed and achieved.The main work of the paper can be summarized as follows:?1?A blue-light OPD based on rubrene and C₆₀,which possess not only high blue-and green-light absorption and little red-light absorption,but also high mobility,is fabricated.By doping material with very low Fermi level-MoO₃,the electron injection barrier in the electrode interface is increased,and the dark current of the device is effectively decreased without affecting the photocurrent.The optimized device has a maximum EQE of 54%at-1 V and the detectivity can be 2.5×10¹² Jones with a cutoff frequency of up to 1 MHz.?2?A narrowband OPD with single-layer structure is designed and fabricated based on 1,3-bis[2,3,3-trimethyl 1-H benzopyrrole]squarylium?ISQ1?,a material with intense and sharp red-light absorption.And through the optical field distribution simulation,we enhance the narrowband response performance of the device successfully.The full width of half maximum?FWHM?of the finally optimized device was only 80nm.The device also has a very good stability.Furthermore,we synthesized the 1,3-bis[?3,3-dimethylpyrrole?]squarylium?PSQ?by changing the substituent group of ISQ1.With PSQ and the single-layer structure,a new narrowband device is developed.The peak EQE of the device is located at 600 nm with a FWHM value of 110 nm.The detectivity is up to 7.7×10¹² Jones at-2.5 V.The repeatedly successful application of narrowband material and single-layer structure has proved that this strategy is effective for designing and developing narrowband OPDs.?3?Based on ISQ red-light and rubrene blue-light OPDs combining with matching wavelength-selective OLEDs,we achieve an all-organic multi-user visible light communication?VLC?system.The VLC system possesses a red-light channel and blue-light channel,and the two channels can transmit data simultaneously.In addition,A multiple signal superposition device is designed using ISQ1 OPD.Due to the excellent linear response performance of OPD and electric isolation of the whole device,the device realizes superposition of two signals with 100 V potential difference.