通过控制陷阱分布实现高灵敏度窄带近红外响应有机光探测器

High-sensitivity Visible-blind Near-infrared Narrowband Organic Photodetectors Realized by Controlling Trap Distribution

近红外(NIR)窄带光电探测在机器视觉、医学检测、智能通信等领域具有重要应用.本文提出了一种基于激子解离窄化机制的改进型层级器件结构,以实现响应峰值为940 nm的近红外窄带有机光电探测器(OPD).系统研究表明,通过调节器件内部的陷阱态密度分布,可以有效地提高窄带探测器的外量子效率(EQE)峰值.最终,基于双激子耗散层结构的器件在940 nm处达到了接近60%的峰值EQE,半峰宽为79 nm,峰值比探测率为2.3×10^(13) Jones.所构筑的可见盲-近红外OPD对940 nm波段的辐射具有选择性响应,可自主屏蔽环境光干扰.此外,基于该优化的器件结构制备了柔性窄带OPD,并在反射模式下利用光容积描记技术成功地实现了无创实时心率监测,证明了这种器件结构对于实现高性能窄带光电探测功能的适用性.

Narrowband photodetectors,which only respond to the spectral bands of interest but not to other spectral ranges,are widely used in biological sensors,medical monitoring,intelligent communication and other fields.Recent developments in artificial intelligence and wearable electronic devices have fostered a growing demand for visible-blind near-infrared(NIR)narrowband photodetectors.Herein,a novel hierarchical device structure based on the exciton dissociation narrowing(EDN)mechanism is proposed to realize NIR narrowband organic photodetectors(OPDs)with a response peak at 940 nm.Compared with traditional EDN type narrowband OPDs,the new device has a significantly higher peak external quantum efficiency(EQE)at 940 nm.The transient photocurrent measurement results show that the differences in device performance arise from diversity in the dynamics of the carrier trapping and de-trapping processes.Impedance analysis shows that the central trap energy levels of the two devices are located at different trap depths.Deep Gaussian trap density of states distributions cause unfavorable space-charge effects,counteract the internal electric field,and increase the recombination loss,resulting in a significant difference in the EQE of the two devices.The visible-blind NIR OPD with optimized device structure can effectively resist the interference of ambient light,in addition,the sensitivity of the narrowband OPD in the NIR window at 940 nm has been enhanced by trap density of states distribution control.Therefore,it has a strong detection ability for weak infrared radiation.We also fabricated a flexible photodetector based on the optimized device structure with a sensitive area of 1.152 cm^(2).The device was attached to the surface of human skin,and the noninvasive real-time monitoring of human heart-rate was successfully realized by the reflective PPG technology with a flexible narrowband photodetector for the first time,demonstrating the superiority of this new structure in making high performances narrowband NIR OPDs for practical application.