The Study Of Hybrid Organic-inorganic Perovskite Based Photodetectors

Photodetectors,which can convert incident light into electric signals,have a wide range of industrial and scientific applications.Recently,based on the characteristics of different wavelength light,photodetectors have been widely used in various fields includes environmental pollution monitoring,ozone hole monitoring,security inspection,optical communication,medical treatment,flame detection,infrared night vision,etc.Among the photodetector materials,hybrid organic-inorganic perovskite CH3NH3PbX3(X=Cl,Br,I),has attracted extensive interest due to their narrow direct band gap,large absorption coefficient,low exciton binding energy,and can detect a broad spectrum from ultraviolet(UV)to near infrared(NIR)light.The position of the energy band can be adjusted by tuning different ion ratio to match the energy band of different semiconductor materials.Due to the high carrier mobility and long charge difffusion length of perovskite,the carriers can be separated and transported more effectively.In addition,good solution processability and low-temperature crystallinity make perovskite suitable for various preparation methods and can be combined with a large number of high temperature resistant materials.Therefore,it is very important to design and fabricate perovskite based photodetector to meet the new development trend(self-powered,flexible,and multi-functional).In this paper,the hybrid structure based on perovskite and other materials were designed to remedy the disadvantages and broaden the application scope of perovskite.Based on the views of carrier dynamics(generation,separation and transmission of carriers),the integration between perovskite and the materials with different characteristics improves the performance of photodetectors and provides a way to design perovskite-based photodetectors for the later practical applications.In this context,we have designed a series of hybrid structures and carried out relevant research work,including a rigorous characterization and analysis.The results are summarized as follows:1.Carrier generation from absorbed photons is the basis of spectral response of semiconductors.However,the properties of perovskite limit its absorption of infrared light,which makes it impossible for perovskite to generate photogenerated carriers in infrared light.In order to further broaden the spectral response range,we integrate perovskite with silicon material.In this process,TiO2 was introduced to reduce the recombination which caused by the energy mismatch between silicon and perovskite.The perovskite/TiO2/Si trilayer heterojunction structure was prepared by atom layer deposition(ALD)and spin coating method.Suitable TiO2 thickness can suppresses dark current,and enhances the carriers'separation and transmission at the interface.Basically,the spectrum response range of the optimal hybrid photodetector extended to 1150 nm,and the response time and detectivity up to 50 ms and 6 × 1012 Jones,respectively.2.For subsequent carrier separation problems,we have designed and fabricated a ferroelectric semiconductor SrTiO3 and perovskite film hybrid structure-based photodetector.SrTiO3 ferroelectric layers can be polarized by an external electric field and generate internal electric field,which promote the bending of energy band at the SrTiO3/perovskite interface and improve the separation of photogenerated charge carriers.The optoelectronic measurements reveal that both the responsivity and the response speed of the devices strongly depend on the direction of polarized field.After the proper positive poling,the optimum device exhibits a large photocurrent and fast response speed of 0.956 mA and 0.1 s under white light illumination.The responsivity as high as 0.73 A W-1 at 550 nm.These parameters are higher than the unpoled devices and the devices without SrTiO3 interlayer.3.As mentioned above,improve the separation ability of self-powered devices often require a complex process.In order to simplify the preparation process,reduce the preparation steps and interface recombination,we mixed organic ferroelectric material P(VDF-TrFE)with perovskite to form a bulk heterojunction.A stronger built-in electric field will be generated after polarization,which can separate and transport of photogenerated carriers more effectively.After proper poling treatment(5 V for 5 min),the optimum device exhibits a high responsivity(20 mA W-1),a large detectivity(1.4×10-3 Jones),and fast response time(92/193 ?s)under 650 nm light illumination.Moreover,the device shows an outstanding stability under different bending angles from 0 to 180°and bending cycles up to 200.4.For transport problems,it's well known that one-dimensional(ID)materials can be used as carrier transport path,while fewer nanowire junctions in nano fiber arrays can further reduce interface recombination.Thus we designed and fabricated ZnO nanowire/perovskite film photodetectors to improve the separation and transport capacity of photogenerated carriers,shorten the response time,reduce the carriers' recombination,and improve the responsivity.ZnO nano wires were prepared on ITO with a 0.5 mm etched channel by electrospinning equipment.The orientation and density of ZnO nanofibers can be controlled by the appropriate receiving device and the electrospinning time,respectively.Then,perovskite film was spin-coated on ZnO nanowires to prepare ZnO nanowires/perovskite films hybrid photodetectors.The optimal ZnO nanowire/perovskite film hybrid photodetectors show a fast response speed(0.2 s),high responsivity(0.1 A W-1)and large detectivity(1013 Jones).5.To improve the photodetector performance under self?power condition,we can't just focus on carrier separation or transmission.O gradient doped CdS nanorod array was adopted to form continuous energy band bending in CdS nanorod from shell to core.After hybrid with perovskite,it can facilitates the separation and transport of photogenerated carriers,hinders the backflow of electrons.Noted that when the oxygen doping is excessive,the conduction band position of O-gradient doped CdS surface will higher than that of perovskite and forms an energy barrier,which hinder the electrons transport from perovskite to CdS.The optimal sample exhibits a high response rate(0.48 A W-1),a large detectivity(2.1 × 1013 Jones)and a fast response speed(0.54/2.21 ms)at 700 nm wavelength.In this paper,we have designed and fabricated many hybrid structure based on perovskite and other materials to improve the carriers generation,separation and transport aptitude of perovskite devices.These results provide some ideas for the design and fabrication of high performance,broad spectrum,self?driving,flexible,ultra-long stability photodetector.