Photoelectric/Photothermal Properties And Applications Of Low Dimensional Carbon-based Nanomaterials

Carbon-based materials are widely used in people’s daily lives,due to the outstanding light absorption properties,electronic conductivity,thermal stability,chemical stability,as well as that they are abundant in raw materials,environmental friendly,nontoxic,and low-cost,etc.Low dimensional carbon nanomaterials simultaneously have size-tunable band gap,large specific surface area,and compatibility with a variety of substrates,and show unique advantages in photodetectors,solar cells,gas sensors,photocatalysts and photothermal devices.Based on the unique material and physical properties,superhigh chemical stability and facility to prepare,and low cost,inspired by the conception of cheap science,we explores the photoelectronic/photothermal properties and applications of zero-dimensional carbon nanomaterials(graphene quantum dots and carbon black).First,solution-processed graphene quantum dots(GQDs)possess a moderate bandgap,which make them a promising candidate for optoelectronics devices.However,negative photoconductivity(NPC)and hysteresis that happen in the photoelectric conversion process could be harmful to performance of the GQDs-based devices.So far,their origins and relations have remained elusive.Here,we investigate experimentally the origins of the NPC and hysteresis in GQDs.And we further explosre the applications of GQDs based on the NPC.And details are as follows:By comparing the hysteresis and photoconductance of GQDs under different relative humidity conditions,we are able to demonstrate that NPC and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture.We also demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation.Considering the pervasive moisture adsorption,our results may pave the way for a commercialization of semiconducting graphene-based and diverse solution-based optoelectronic devices.Furthermore,although NPC exists in various materials,limited applications have been explored.Here,we report on the experimental realization of GQDs based humidity sensors and ultraviolet(UV)photodetectors.We demonstrate that the conductance of the GQDs increases linearly with increasing relative humidity(RH)of the surrounding environment due to the carrier trapping effect,which forms the basis of a humidity sensor.We show that when the sensor is operated in the dark state the sensitivity can reach as high as 0.48 nS(%RH)-1,which is higher than that of the previously reported relative sensitivity of the tungsten disulfide(WS2)nanoparticle thin film based humidity sensor,and is comparable to that of the sensor based on single-walled carbon nanotubes(SWCNT).We also demonstrate that the GQDs exhibit light intensity dependent negative photoconductivity under the UV irradiation,which can be exploited for the UV-detection purpose.Furthermore,we show that as a result of the carrier trapping and de-trapping processes in GQDs,the performance of the photodetector can be significantly improved with the increasing RH,and the photoresponsivity can reach a high value of-418.1 μA W-1 in the high humid state of RH = 90%.Compared to the deep-UV(254 nm)photodetectors which rely on the PPC of the GQDs with two gold electrodes exhibiting a photoresponsivity of 4.26 μA W-1,the photoresponsivity of our proposed UV(375 nm)photodetector based on the NPC of the GQDs is enhanced almost two orders of magnitude.Second,based on the characteristics of broadband and highly effective absorption of low-cost carbon black membrane,we research the application in terms of photo-thermal conversion.We achieve the tunable plant transpiration via the absorber-leaf interfacial engineering.And details are as follows:Moreover,transpiration effect of plants not only can enable temperature adjustment to the local environment,but also contribute significantly to the water cycle via water vapor generation.Inspired by the recent progress in interfacial solar driven evaporation,here,for the first time we report that transpiration can be tuned by the interfacial solar absorber-leaf engineering,since both the heat conduction and respiration of leaf can be manipulated by solar absorption.With fine tuning of the transpiration efficiency,relative humidity and local temperature nearby the engineered plants can be artificially controlled.This demonstrates that interfacial solar absorber-leaf engineering provides a pathway for not only tuning transpiration as an important part of hydrologic cycle,but also adjusting the moisture and temperature of the local environment.