Influence Of Interface Characteristics Of Organic Thin Film Transistors On Their Sensing Properties

Organic thin-film transistors?OTFTs?have attracted considerable attention due to their advantages of low cost,light-weight,flexibility,soluble processing and diversity of organic functional materials design,and become to one of the key devices of modern organic electronics.As an important application of OTFTs,the OTFTs-based gas sensors have been greatly developed in the past few decades and become a research hotspot in the field of sensitive electronics and sensing technology.Physical/chemical interactions between gas analytes and the organic functional materials possess a strong influence on the charge carrier transportation of the OTFT.On the other hand,OTFT can act as both signal transducer and amplifier,and realize multiparameter detection.Based on the recent development of OTFT,this paper reviews the current research status and strategy of OTFT gas sensors,and then introduces zinc oxide?ZnO?nanoparticles,polar polymer dielectric materials,and polymer blend film systems to modulate the interfaces of OTFT,as a result,high-performance OTFT gas sensors were prepared.This paper was divided into the following three parts:1.The influence of poly?methyl methacry??PMMA?and ZnO nanoparticles hybrid dielectric on the performance of OTFT gas sensors was studied.An OTFT ammonia?NH₃?gas sensor based on ZnO/PMMA hybrid dielectric was fabricated.The response of 75 ppm NH₃ was nearly 10 folds higher than that using pure PMMA.Moreover,the environmental stability of the OTFT sensors was measured after stored in the atmosphere for 40 days.Then,Copper?II?phthalocyanine?CuPc?was introduced to fabricate heterojunction structure with pentacene,high response OTFT NO₂ sensors were realized using the synergistic effect of hybrid dielectric and heterojunction.Moreover,after stored in the atmosphere for 30 days,the variation of saturation current increased more than 10 folds at 0.5 ppm NO₂.2.The influence of the polar polymer dielectric layer on the performance of OTFT gas sensors was studied.A polar polymer layer,poly?vinyl alcohol??PVA?or poly?4-vinylphenol??PVP?containing hydroxyl groups,was inserted between two PMMA dielectric layers.The field-effect mobility???had been raised more than 10 times in n-type devices?3 times in the p-type ones?,and the threshold voltage had been lowered almost 8 times in p-type devices?2 times in the n-type ones?.The on-off ratio of all the devices had been enhanced by almost two orders of magnitude;Secondly,the?of?-sexithiophene??-6T?based OTFT using PMMA/PVA/PMMA dielectric structure was almost 8 folds higher than that with PMMA single dielectric layer.Meanwhile,the?kept almost no change after exposed to the atmospheric environment;Finally,OTFT NH₃ gas sensors using PVA as a gas accumulation layer were fabricated.The response of drain current was50.3%at 0.5 ppm NH₃,which was over 10 folds higher than that of pure PMMA dielectric.Moreover,the response increased to 66.9%under 0.5 ppm NH₃ after applied a gate voltage bias.The adsorption and desorption process of the OTFT ammonia gas sensor can be promoted by changing the bias direction of the gate preset,and the sensor exhibits non-volatile characteristics.3.The influence of polymer blend film on the performance of OTFT gas sensors was studied.Poly?3-hexylthiophene-2,5-diyl??P3HT?:polystyrene?PS?blend films prepared from different solvents were prepared to systematically analyze the relationship between the molecular arrangement,aggregation and charge transport in P3HT:PS blends with the boil-points and solubility of different solvents;Then,OTFT NH₃ gas sensors based on P3HT/PS blend films were fabricated.When the effective concentration of P3HT in PS is 1.6 mg/mL,the device got the same ability as the pure P3HT device?8 mg/mL?.In addition,this OTFT sensor can still work efficiently after being placed in the atmosphere for 40 days;Finally,a hole-transport material,poly?9-vinylcarbazole??PVK?,was used to blend with P3HT for the semiconductor layer of OTFT NO₂ sensors.This sensors can work in two modes by adjusting the gate voltage at room temperature,the highest response is?20000%for 30 ppm??700%for 600 ppb?with the 1:1P3HT:PVK blend,it's almost 40 times greater than that with the pure P3HT.In summary,to overcome the relative low gas sensitive response,poor selectivity,poor air stability and high preparation cost of OTFT-based gas sensors,high performance OTFT gas sensors were obtained by improving the interface characteristics of OTFT by various methods,which pave the way for the extensive applications of OTFT in the field of sensitive electronics and sensing technology.