Applications Of Hot Electron Effect In Aerogel Based Light Absorbing Materials For Photo-Thermal-Electrical Conversion

Materials that can achieve strong absorption of electromagnetic waves of specific bands（super-black materials）,which is owing to either their special intrinsic electronic structure or special sub-wavelength microstructure,have broad application prospects in fields such as active stealth,solar absorption,photothermal and photoelectric conversion.Aerogel is a kind of nanoporous solid with hierarchical,fractal and subwavelength disordered microstructure.Their special structure properties endow them with many extreme properties.The super-black carbon aerogels have the lowest reflectance of 0.19%,and their reflectance is closely related to the size of microstructures.Based on this phenomenon,our research group proposed the indirect interaction hypothesis of electromagnetic wave-electron-microstructure,in which the hot electrons generated by energetic collisions of electrons under restricted conditions is a key inference.Research on the energy conversion of photo-induced electrons in aerogel-based light-absorbing materials will deepen the understanding of the interaction between microstructure and electromagnetic wave,realize the effective utilization of energy,and broaden the application range of super-black materials.In this thesis,firstly,through preparation of the carbon aerogel films,the intrinsic photo-electric response of carbon aerogels was studied.The intrinsic negative temperature coefficient of resistance(0.13–0.15%K^-1)was found and the resistance change of carbon aerogel film under laser irradiation was attributed to the synergetic effect of photo-thermal conversion and temperature-sensitive-resistance through photo-thermal-electric conversion.The photothermal conversion and electrical response of carbon aerogel films were amplified and broadened to longer wavelength electromagnetic wave due to the presence of the hot electron induced by the small size structures in carbon aerogel.It was found that carbon aerogel films show photo-thermal electric response to broadband electromagnetic wave from ultraviolet to microwave（UV at 300 nm to microwave at 3 cm）.Secondly,the photo-thermal-electric response of carbon aerogel films enhanced by hot electron effect was applied for flexible resistance-type infrared detection device.In order to achieve the patterning fabrication of the device,laser carbonization method under ambient condition was utilized for paper-based resorcinol-formaldehyde aerogel.It was found that a more portable and cheaper diode violet laser could achieve carbonization and graphitization of RF aerogel.A conductive porous carbon layer with high light absorbance could be fabricated,which was similar to the effect of infrared laser.A sensor pattern similar to Chinese character HUI（Thunder motif）was designed taking advantage of the easily patterning of laser carbonization.Compared with the traditional Serpentine type resistance sensor,this pattern showed better stability for infrared light sensing and higher sensitivity for strain sensing.It could be used as a wearable on-skin senser for gesture sensing and breath monitoring.Besides,previous study of our group showed that strong thermal conduction of pure carbon materials limited their photothermal equilibrium temperature.Thus,in addition to the hot electron effect induced by subwavelength microstructure in carbon aerogel,the LSPR hot electron in two-dimensional MXene nanomaterial was also used for strong photo-thermal conversion.A surface modified MXene/bacterial cellulose composite aerogel was fabricated.The as-prepared MXene based aerogel could make efficient thermal conversion with good thermal insulating and mechanical properties.Furthermore,the composition of MXene-based aerogel and paraffin resulted in a composite phase change film which was capable of both photothermal conversion and energy storage.The film exhibited ideal heat storage/release behavior with/without light irradiation,while maintained less paraffin leakage.Combined with the thermal insulation of Mxene-based aerogel and the thermal storage capacity of its composite phase change film,good thermal management performance could be achieved.This showed a new application approach in the field of thermal management through the controlling of energy transfer,conversion and storage/release processes.Finally,in addition to the photothermal conversion attributed to relaxation process of hot electrons,the direct photoelectrical conversion of hot electrons before relaxation in carbon aerogel was preliminary explored.The generation or gain of photocurrent induced by the emission of hot electrons on the surface and the transfer of hot electrons at the interface by the external and internal photoelectric effects were observed respectively.For external hot electron emission,through setting up a photoelectric detection device in ambient condition,photocurrent was observed using super black carbon aerogel as thermionic cathode emitter.For internal hot electron transfer,carbon aerogels were added in the device structure of all-inorganic perovskite solar cell as a single layer,placed between Ti O₂electronic transport layer and perovskite light-sensitive layer.The photocurrent gain effect was observed through the transfer and injection of hot electrons in carbon aerogel.The hot electron effect in carbon aerogel accordingly improved power conversion efficiency,realizing more efficient utilization of solar energy.Although further experiments and mechanism discussions were needed to prove the hot electron induced photocurrent,these preliminary results showed the potential application of hot electron of carbon aerogel in passive photovoltaic conversion.In general,in this thesis,based on the hot electron effect induced by the special microstructure of superblack carbon aerogel,the indirect photo-thermal-electric response of carbon aerogel enhanced by hot electron and the direct photo-electric conversion caused by hot electron were investigated.In addition,MXene nanomaterials with lower thermal conductivity were utilized as light-absorbing matrix to achieve higher photothermal conversion efficiency and effective thermal management.As a kind of macroscopic materials assembled by special nanostructures,aerogel-based light-absorbing materials are expected to play a role for photothermal conversion and photoelectric conversion,achieving more efficient utilization of solar energy.