界面种子层修饰策略制备高性能CsPbIBr_(2)光电探测器

Preparation of High-Performance CsPbIBr_(2) Photodetector via Interfacial Seed Layer Modification Strategy

在相对湿度低于90%(<90%RH)的大气环境下,通过界面种子层修饰策略,利用气动喷涂法制备出高结晶度、界面接触良好、结构稳定的CsPbIBr_(2)厚膜。界面种子层的引入对CsPbIBr_(2)厚膜的光学带隙(2.10~2.12 eV)没有太大的影响,但明显增强了其对光的吸收和发射,并且荧光寿命也明显延长(从0.95 ns到4.49 ns)。由此厚膜制备的二极管型光电探测器(p-n CsPbIBr_(2)-ITO)具有非常低的暗电流(5.70×10^(-10)A),并且展示出高效的光电探测性能:高开关比(1.8×10^(4))以及微秒级别的响应时间(上升时间和下降时间分别为9μs、13μs)。当未封装的CsPbIBr_(2)光电探测器处在<90%RH的大气环境下,其表现出强的抗水抗氧能力:储存60 d后,其仍能保持初始开关比的83%。所提方法为在大气环境下制备低成本、高性能、长效稳定的二极管型CsPbIBr_(2)光电探测器提供了一种有效的途径。

Objective Photodetectors can convert incident light into electric signals and are widely used in many fields such as image sensing,optical communication,environmental monitoring,and biological detection.In recent years,allinorganic metal halide perovskite CsPbIBr_(2) has been concerned in photoelectric detection due to its high light absorption coefficient,high charge carrier mobility,and low defect density.On the one hand,CsPbIBr_(2) film is susceptible to ambient humidity,so it is not usually prepared under an atmospheric environment but in glove boxes by methods such as spin coating.On the other hand,on account of uncontrolled nucleation during crystallization,CsPbIBr_(2) film has poor morphology and crystallinity,which results in weak photoelectric characteristics and instability of its photodetector.In order to overcome these problems,the morphology,crystallinity,and water/oxygen resistance of CsPbIBr_(2) thick film can be improved by additives and interface layer strategies.In this study,we employ an interfacial seed layer modification strategy under an atmospheric environment with relative humidity(RH)below 90%to prepare one highquality CsPbIBr_(2) thick film with high crystallinity,excellent interfacial contact,and stable structure.We hope that our findings can help fabricate lowcost,highperformance,and longlasting photodiodetype CsPbIBr_(2) photodetectors under an atmospheric environment.Methods CsPbIBr_(2) thick films with controllable thicknesses in the range of 0.5-100μm are prepared under an atmospheric environment with RH below 90%by pneumatic spraying.Prior to spraying,the interfacial seed layers are formed on the substrates by spincoating followed by annealing.During spincoating,the density distribution of the interfacial seed layers is realized by controlling the concentration of precursor solution.In this strategy,the interfacial seed layers act as the nucleating points for crystal growth,which improve the crystallization of the thick films in preparation processing.The morphology and the phase structure of the thick films are analyzed by scanning electron microscopy(SEM)and Xray diffraction.Compared with the thick film without an interfacial seed layer,these films with interfacial seed layers have high crystallinity,excellent interfacial contact,and stable structure.In order to assess the effect of interfacial seed layers on the optical properties of the thick films,these thick films are investigated by absorption,photoluminescence(PL),and timeresolved PL spectra.In order to verify the feasibility of the thick films for photodetection,their photodiodetype photodetectors of Au/ITO/CsPbIBr_(2)/Au are fabricated and measured.The IV and response time curves of the photodetectors are examined under laser excitation of 405 nm.In order to characterize the longterm stability,tracing measurements on the onoff ratio of the devices are made,and the nakedeye photographs of the corresponding thick films are recorded.Results and Discussions Compared with the control film with smallsize crystal grains and a large number of holes on the surface,the modified films by introducing interfacial seed layers exhibit largesize crystal grains and dense morphology[Fig.1(a)].From the crosssectional SEM images,the improved interfacial contacts between the modified films and the substrates lead to columnar growth features[Fig.1(b)].The modified films show a preferred orientation on the(110)diffraction plane,especially for 0.3 mol/L,which is consistent with the SEM results[Fig.1(c)].Once seed layers are inserted between the thick films and the substrates,the absorption coefficients and PL peak intensities increase significantly in the whole visible range,and the fluorescence lifetime increases from 0.95 ns to 4.49 ns(Fig.2).The dark current from the control device to the modified devices decreases from 2.05×10^(−7) to 5.70×10^(−10)A,while the onoff ratio significantly increases from 490 to 1.8×10^(4)[Fig.3(a)].By fitting the IV curves under light illumination,it is proved that the modified device of 0.3 mol/L has a stronger light response(n=0.87)and larger response range(RLD=80 dB)than the control device(n=0.60 and RLD=34 dB)[Fig.3(b)-(e)].The rising and falling time(ton and toff)from the control device to the modified devices decreases from 38μs to 9μs and from 110μs to 13μs,respectively[Fig.3(f)].After lasting 60 days,the modified device of 0.3 mol/L still retains a high onoff ratio of 1.5×104,which is 83%of the initial onoff ratio,and the nakedeye photographs of the thick films do not change significantly(Fig.4).Conclusions In this study,under an atmospheric environment with RH below 90%,highquality CsPbIBr_(2) thick films are prepared by pneumatic spraying via an interfacial seed layer modification strategy.In this strategy,the interfacial seed layer acts as the nucleating points for crystal growth,which results in the improvement of the crystallinity,interfacial contact,and structural stability of the CsPbIBr_(2) thick films.Furthermore,the introduction of interfacial seed layers has no significant effect on the optical band gaps of CsPbIBr_(2) thick films,ranging from 2.10 eV to 2.12 eV.It is worth noting that the absorption coefficient of visible light and the PL intensity are enhanced significantly,and meanwhile the fluorescence lifetime is increased(from 0.95 ns to 4.49 ns).The photodiodetype CsPbIBr_(2) photodetector(pn CsPbIBr_(2)-ITO)shows a low dark current(5.70×10^(−10) A)and possesses highperformance photodetection parameters,namely high onoff ratio(1.8×104)and microsecondlevel response times(9μs and 13µs).Moreover,the unpackaged CsPbIBr_(2) photodetector is strongly resistant to water and oxygen under an atmospheric environment with RH below 90%,which is 83%of the initial onoff ratio after lasting 60 days.These results can provide an effective way to prepare lowcost,highperformance,longlasting,and stable photodiodetype CsPbIBr_(2) photodetectors under an atmospheric environment.