ZnO/Spiro-MeOTAD异质结自驱动光电探测器的制备及性能(特邀)

Preparation and Properties of ZnO/Spiro-MeOTAD Heterojunction Self-powered Photodetector(Invited)

ZnO具有高稳定性、低成本、宽带隙等优点,被广泛用于光电探测器但响应速度较慢,采用Zn(TFSI)2和CNT∶TiO_(2)作为混合掺杂剂来代替Li-TFSI,以提高Spiro-MeOTAD的稳定性及光电性能,采用旋涂法制备了ZnO/Spiro-MeOTAD异质结构筑光电探测器。ZnO/Spiro-MeOTAD光电探测器在250~600 nm波长范围内,具有良好的自驱动特性。在0 V条件下,ZnO/Spiro-MeOTAD器件在368 nm的入射光照射下具有最高的光电性能,响应度为27.34 mA W^(-1),比探测率为3.62×10^(11)Jones,开关比为2029,上升/下降时间分别为0.71 s/0.55 s,相较于ZnO的光电性能(响应度为17.74 mA·W^(-1),比探测率为5.11×10^(10)Jones,开关比为63.6,上升/下降时间为11.76 s/1.49 s)分别提升提高了1.5倍、7倍、32倍。ZnO/Spiro-MeOTAD器件在550 nm处仍具有明显响应,响应度和比探测率分别为2.48 mA·W^(-1)和3.32×10^(10)Jones,对比ZnO器件提高了248倍和940倍。不同放置时间(1个月)和预处理温度(0~140℃)下光电流的变化,验证了Spiro-MeOTAD加入构筑p-n异质结,不仅可以显著提升ZnO基光电探测器的响应度、开关比和响应速度,同时使得探测器具有良好的稳定性,可以应用于较高温度工作环境。

A photodetector is a sensing element capable of converting an optical signal into an electrical signal.ZnO is widely used in photodetectors due to high stability,low cost and wide band gap,however the long response speed limits their development.The photoelectric performances of ZnO can be effectively improved by fabricating the inorganic-organic heterostructure.The Li-TFSI doped Spiro-MeOTAD as one of organic semiconductor exhibits high hole regeneration ability,high conductivity and the hole mobility,but the stability is low.In this paper,Zn(TFSI)_(2) and CNT∶TiO_(2)are used as mixed dopants to replace Li-TFSI to improve the conductivity and stability of Spiro-MeOTAD and achieve higher photoelectric performances.The doped Spiro-MeOTAD is closely combined with ZnO thin films by spinning coating method.ZnO/Spiro-MeOTAD photodetectors were prepared by Ag paste as electrodes covered on the ZnO thin films and ZnO/Spiro-MeOTAD heterojunction,respectively.The morphologies and structure of ZnO,Spiro-MeOTAD and ZnO/Spiro-MeOTAD devices were characterized by scanning electron microscope,X-ray diffractometer,Raman spectrum,UV-Vis absorption spectrum,suggesting the successful preparation of ZnO/Spiro-MeOTAD heterojunction.The thickness of the ZnO film is about 9μm,while the thickness of Spiro-MeOTAD is about 400 nm,suggesting the thin Spiro-MeOTAD is benefit to the light absoption and photodetection performances.The optical absorption coefficient of ZnO/Spiro-MeOTAD is higher than that of ZnO in the whole wavelength range,and is significantly improved in the wavelength range of 350~450 nm.The addition of Spiro-MeOTAD extends the absorption cutoff edge of ZnO and expands the response wavelength range.Under dark conditions,the forward bias voltage and the reverse bias voltage of ZnO/Spiro-MeOTAD devices have different current change rates,showing a rectification effect with the rectification ratio of 28±2.The open circuit voltage and short circuit current of the device under 368 nm illumination are 0.4 V and 14 nA respectively,indicating a good self-powered characteristic.At 0 V,ZnO/Spiro-MeOTAD device exhibits the highest photoelectric performances at 368 nm,with a responsivity of 27.34 mA·W^(−1),specific detectivity of 3.62×10^(11)Jones,switching ratio of 2029,and rise/fall time of 0.71 s/0.55 s,respectively.Compared with ZnO,the photoelectric performances of ZnO/Spiro-MeOTAD(responsivity 17.74 mA·W^(−1),specific detection 5.11×10^(10)Jones,switching ratio 63.6,rise/fall time 11.76 s/1.49 s)is improved by 1.5 times,7 times and 32 times,respectively.Compared with ZnO devices(response of 0.01 mA·W^(−1),specific detectivity of 3.53×10^(7)Jones),ZnO/Spiro-MeOTAD device still shows the responsivity and specific detectivity of 2.48 mA·W^(−1)and 3.32×10^(10)Jones at 550 nm,which is increased by 248 times and 940 times,respectively.The ZnO/SpiroMeOTAD device has a wide spectral response of UV-visible light with the addition of Spiro-MeOTAD.The p-n heterojunction can fast separate the electron-hole pairs due to the build-in potential,improving the electronic properties.The photocurrent of ZnO/Spiro-MeOTAD device without packaging protection only decreases to 78.6%of the original photocurrent after one month,and the switching ratio is 1.25 at 140℃.The comparison of ZnO/Spiro-MeOTAD-O(doped with Li-TFSI and TBP)device remains 50%photocurrent after one day,not a stable periodic cycle after one week,and switching ratio of 1.08 at 100℃.The excellent stability can be contributed to enhanced hydrophobic characteristics with doping by zinc salt not lithium salt,as well as the improved thermal stability and conductive properties by CNT∶TiO_(2)mixed dopants.The Zn(TFSI)2 and CNT∶TiO_(2)doped Spiro-MeOTAD can improve the e responsivity,switching ratio and response speed of ZnO film,and promote the thermal stability and environmental stability of the ZnO/Spiro-MeOTAD heterojunction.This preparation method provides a new idea for new composite structure heterojunction,which has theoretical research and practical application value.