Effect Of Metal Oxide As Modified Layer On Organic-inorganic Hybrid Perovskite Photodetectors

The organic/inorganic hybrid perovskites have attracted extensive attentions due to its great success in solar cells.Such materials have the advantages of adjustable band gap,large light absorption coefficient,long exciton diffusion length,and simple thin film preparation process.In thin film devices,besides the optoelectronic properties of the active layer material itself,the influence of the interface on the device performance is crucial as well.In this paper,the organic/inorganic hybrid perovskite is used as the active layer,and the modified layers are fabricated by the solution processed titanium oxide nanoparticles film,tin oxide nanoparticles film,and magnetron sputtering titanium oxide film,respectively.The main conclusions reached are as follows:（1）The rutile phase and anatase phase TiO₂ nanoparticles were prepared by the water bath method.Using these nanoparticles,the photodetectors were prepared with the structure of ITO/TiO₂/MAPbI₃/PC₆₁BM/Al.Since both TiO₂ and PC₆₁BM can block holes,they are electron-only transporting devices.The results show that the device performance of anatase TiO₂ nanoparticles is better.Under the operating voltage of-0.5 V,the dark current density of the device is 3.8×10^-8 A/cm²,the maximum switching ratio is2.36×10⁵.The linear dynamic range（LDR）of the deivce is 101.9 dB under 450 nm illumination,118.8 dB under 530 nm illumination,105.1 dB under 620 nm illumination,while only 67.2 dB under 365 nm illumination.The dark current of the device increases significantly after UV light irradiation.When a 400 nm cut-off filter is used to filter out short wavelengths below 400 nm,the dark current of the device does not increase after illumination,indicating that the increased dark current is caused by ultraviolet light.This may be due to the strong ultraviolet absorption of TiO₂ nanoparticles.Therefore,the device based on TiO₂ nanoparticles is only suitable for working in the visible light region.（2）In order to avoid the increase of dark current caused by ultraviolet light,the nano-SnO₂ layer was used to replace the nano-TiO₂ layer in the device,and the device with the structure of ITO/SnO₂/MA₃PbI₃/PC₆₁BM/Al was prepared.Under the operating voltage of-0.5 V,the dark current density of the device is 4.42×10^-8A/cm²,the switching ratio is1.67×10⁵.More importantly,the LDR of the device is 95.1 dB under 365 nm illumination,110.5 dB under 530 nm illumination,and 108.7 dB under 620 nm illumination.Compared with TiO₂ nanoparticles,the surface state of SnO₂ nanoparticles has weaker absorption of ultraviolet light,therfore it does not cause a significant increase in dark current.By annealing the nano-SnO₂ layer to reduce its surface state,it is found that the dark current of the device is significantly improved.It shows that the defect state plays an important role in suppressing the dark current of the device.Therefore,nano-SnO₂ inhibits the dark current by barrier induced blocking the injection of carriers and restricting the transport of charges through surface defects.Therefore,the perovskite device prepared by nano-SnO₂ particles can work in the ultraviolet-visible light region.（3）Nano-TiO₂ has abundant surface state.In order to determine the effect of surface state,the dense TiO₂ films were obtained by sputtering,and the perovskite photodetectors were fabricated based on this film.The dark current of the device does not increase significantly after UV irradiation,because the surface defect state of the sputtering TiO₂film is much fewer than that of the solution-processed nano-TiO₂film,which proves that its surface state is sensitive to ultraviolet light.Therefore,the abundant surface state of nano-TiO₂ is the reason that they cannot used for working in the short wavelenth region.By adjusting the sputtering conditions to control the thickness of the TiO₂ layer,it is found that only when the film is thicker,a lower dark current can be obtained.This indicates that there is no synergy of surface states and a larger barrier thickness is required.By changing the preparation method,the defect state of TiO₂ film is reduced,the influence of dark current after UV illumination of the device is reduced,the device can work in the ultraviolet-visible region.There are 55 figures,4 tables and 220 references.