Fabrication And Mechanism Research Of Photomultiplication Type Organic Photodetectors With Tunable Response Range

In recent years,organic photodetectors(OPDs)have rapidly developed due to the rapid development of organic semiconductors and the optimization of device structures,which makes them promising to be the next generation of commercial photodetectors.In practical applications,photodetectors need to face complex application scenarios,and different application scenarios have different requirements for the performance of photodetectors.At present,the device structure and the working mechanism of the OPDs are relatively single,leading to that the peroformance and the spectral response range of the OPDs is limited by the organic semiconductors.This further restricts the expansion of their application scenarios.The researches in this paper are based on the photomultiplication(PM)type OPDs,and aiming at the application requirements of the PM type OPDs.The researches in this paper start from material selection and device structure design,and focus on the adjusting of optical field distribution in the OPDs.The spectral response bandwidth of the PM type OPDs was manipulated by taking advantage of the optical and electrical advantages of organic semiconductor materials and the flexibility of the preparation process.The main contents are as follows:(1)By adjusting the self-assembly process of the active layer with donor to acceptor ratio of 100:1,the arrangement of donor molecules and the distribution of trapped charges were simultaneously optimized in the active layer.When the active layer suffer from short self-assembly time,the donor molecules tend to face-on arrangement,which facilitated the hole transport along the direction perpendicular to the substrate.In addition,short self-assembly time of active layer increased the density of the electron acceptor near the upper surface of active layer.The combined effect of the two aspects enhanced the trap induced hole tunneling injection and the transport capability of the injected holes in the active layer,leading to the improved performance of the PM type OPDs.(2)By employing fullerene-free electron acceptor as electron traps,the electron trap depth and exciton dissociation efficiency were simultaneously adjusted in the active layer.The effects of the above two factors on the performance of the PM type OPDs were studied.The results indicated that deep electron traps and large exciton dissociation efficiency are beneficial for obtaining high performance PM type OPDs.In addition,the effect of 1%electron acceptor on extending the spectral response range was studied.This study has deepened the understanding of working mechanism in PM type OPDs.(3)Based on the above two works,different ratios of second donor with narrow bandgap were incorporated into the binary system of P3HT:PC71BM(100:1),the effects of different ratios of second donors on the spectral response range and performance of the PM type OPDs were investigated.The charge trapping and charge transport mechanisms between the three materials were studied.Finally,broadband response PM type OPDs with spectral response range from ultraviolet to the near-infrared wer achieved with maximum external quantum efficiency(EQE)of 38,000%in the near-infrared region,which is considered to be an effective method for obtaining high near-infrared response.(4)The concept of“charge injection narrowing(CIN)”was proposed.By adjusting the thickness of active layer in the PM type OPDs,the optical field distribution and trapped charges distribution in the OPDs were optimized.When the thickness of the active layer is 2.5?m,narrowband response was achieved with FWHM less than 30 nm,and the EQE approached 53,500%.By comparing to narrowband response photodiode(PD)type OPDs with donor to acceptor ratio of 1:1,the results indicated that the sharpness of the absorption edge plays a crucial role in the FWHM of the narrowband response.(5)Based on the above work,broadband and narrowband response were obtained,respectively.By employing transparent metal electrode as cathode,broadband and narrowband response were successfully integrated into a single OPD.When the incident light irradiated from the ITO electrode side,narrowband response was obtained.When the incident light irradiated from the transparent metal electrode side,broadband response was obtained.The EQE of the broadband and narrowband response was optimized by adjusting the thickness of the transparent metal electrode.To verify the spectral tunnability of the integrated OPDs,second donor with narrow bandgap was incorporated into the active layer,the broadband response was successfully extended to the near-infrared region,and the narrowband response was also adjusted to the near-infrared region.(6)In view of the excellent optical and electrical properties of the perovskite material and the large optical bandgap of methylamine lead halide perovskite,broadband response perovskite photodetectors(PPDs)were achieved with spectral response range from ultraviolet to the near infrared(NIR)by employing narrow bandgap perovskite as active layer in this part(Appendix A).By optimizing the thickness of the perovskite and C60 layer,EQE and specific detectivity of the PPDs were improved in the NIR region.Meanwhile,the dark current of the PPDs was also suppressed.