Fabrication And Characterization Of Thin-film Transistors Based On Metal Halide Perovskite Semiconductors

Metal halide perovskite semiconductors are very attractive for fabricating high-performance thin-film transistors（TFTs）because of their excellent optoelectronic properties,good solution processability,and high intrinsic carrier mobility(>100 cm²V^-1 s^-1).Metal halide perovskite TFTs have been developed for more than two decades,and the field-effect mobility of the devices has exceeded 50 cm² V^-1 s^-1,which is the current hot spot in transistor device research.However,on the way to the further development and application of metal halide perovskite TFTs,there are still some problems（transistor devices cannot operate normally and stably at room temperature,poor device stability and devices not friendly to the environment,etc.）that need to be faced and solved by systematic research work.In view of this,this thesis aims to improve the device performance and stability of metal halide perovskite TFTs and conducts corresponding research work.In addition,this thesis also explores the application of metal halide perovskite TFTs in the field of photonic synapses and photodetectors.The specific research works are described as follows.（1）To understand the effects of spin-coating process and material components on the quality of three-dimensional lead halide perovskite（3D LHP）films and the performance of the corresponding transistor devices,this work investigates the differences in surface morphology,grain size,crystallinity and light absorption of 3D LHP(MAPb I₃ and（FAPb I₃）_0.97（MAPb Br₃）_0.03)films prepared by different spin-coating processes.It is shown that the two-step spin-coating method helps to form high-quality 3D LHP films with larger grain size,smaller surface root mean square（RMS）roughness,higher crystallinity and stronger light absorption than the one-step spin-coated perovskite films,and the resulting transistors have higher field-effect mobilities and smaller hysteresis.Based on this,this work investigates the photoresponse performance of（FAPb I₃）_0.97（MAPb Br₃）_0.03 TFTs prepared based on two-step spin-coating method,and the devices exhibited excellent photoresponse performance with a maximum specific detectivity of 6.63×10¹² Jones.As a result,this work further constructs the photonic synaptic transistors based on perovskite/organic semiconductor heterojunctions by a simple solution spin-coating process.It is shown that the（FAPb I₃）_0.97（MAPb Br₃）_0.03/PDVT-10 heterojunction-based photonic synaptic transistors can simulate the basic functions of biological synapses（excitatory postsynaptic current（EPSC）,paired-pulse facilitation（PPF）,short-term plasticity（STP）,long-term plasticity（LTP）,and the transition from STP to LTP）by tuning the parameters of light stimulation,including the intensity,width,interval,and numbers of light pulse.Our research provides a convenient method for fabricating metal halide perovskite-based photonic synaptic transistors,showing their great potential for neuromorphic computing.（2）To address the problem of two-dimensional lead halide perovskite（2D LHP）TFTs that cannot operate at room temperature,this work proposes a simple strategy for fabricating 2D LHP TFTs.With this device fabrication strategy based on Sn O₂interlayer and NH₄Cl additive,2D LHP TFTs that can operate well at room temperature are achieved.It is revealed that the Sn O₂ interlayer can effectively regulate the growth orientation of 2D LHP films and induce parallel orientation of the inorganic layers in the perovskite materials,and the introduction of NH₄Cl additive will further enhance the parallel orientation of the perovskite films and thus improve the crystallinity of the films,as well as produce a doping effect on the perovskite films to effectively passivate the traps in the films.Overall,this device fabrication strategy not only effectively suppresses the ion migration effect in 2D LHP films,but also improves the charge transfer efficiency in the perovskite films,based on these optimizations to achieve good operation of 2D LHP TFTs at room temperature.As a result,the general applicability of this device fabrication strategy is further investigated in this work,and the results show that both BA₂MA_n-1Pb_nI_3n+1 and PEA₂MA_n-1Pb_nI_3n+1 TFTs with different n values can operate at room temperature,with the best device(BA₂MA₃Pb₄I₁₃ TFT)having mobility up to 5.73×10^-3 cm² V^-1 s^-1,with on/off ratio of about 10⁴ and negligible hysteresis.Based on this,this work also demonstrates that such TFTs have excellent bias-stress stability（+1.8 V shift after biased for 3600 s）and storage stability（91.2%current retention after 350 days in glovebox without encapsulation）.In addition,large-area TFTs（>20 cm²）by solution spin-coating process show outstanding uniformity in device performance and demonstrate their potential as light detection arrays for image detection.Our research paves the way for developing high-performance 2D LHP TFTs and further advances 2D LHP TFTs toward practical applications.（3）To optimize the device performance and stability of metal halide perovskite TFTs,this work proposes a solution for the fabrication of transistor devices using 2D Dion-Jacobson（DJ）phase tin halide perovskites（THPs）.Specifically,this work adopts2D DJ phase perovskite BDASn I₄ with BDA²⁺diamine cations as organic cations in terms of the perovskite structure and studied in comparison with 2D Ruddlesden-Popper（RP）phase perovskite PEA₂Sn I₄.The results show that BDASn I₄ perovskite has larger grain size,lower defect density and better charge transport property compared to PEA₂Sn I₄ perovskite.Based on this,this work further optimized the device performance of BDASn I₄ TFTs by interfacial engineering（Alkylammonium Salt Interlayers,ASIs）and additive engineering（NH₄SCN additives）.It is shown that the ASIs can effectively optimize the quality（crystallinity and grain size）of BDASn I₄films,thereby reducing the defect density and suppressing the nonradiative recombination behaviors in the films,and the introduction of NH₄SCN additive further passivates the defects and increases the grain size of the films.The resulting best device has a room temperature hole mobility as high as 1.61 cm² V^-1 s^-1 and on/off ratio of4.7×10⁶.In addition,the device exhibits excellent storage stability（the on-current of the device remains unchanged after 150 h of storage in a"double 45"environment）and photoresponse performance(the detectivity up to 1.59×10¹⁷ Jones).Our research demonstrates a high performance,high stability and environmentally friendly 2D THP TFTs,offering new possibilities for the development of transistor devices with long-term stability.