Investigation Of Quantum Dot Sensitized Solar Cells Based On Femtosecond Laser Filamentation-Engineered TiO₂ Photoanode

Quantum dot sensitized solar cells（QDSSC）have emerged as a promising strategy for the front-runner photovoltaic technology due to the high theoretical photoelectric conversion efficiency and the multi-exciton generation effect.Nowadays,the power conversion efficiency（PCE）of QDSSC has exhibited a spectacular improvement trend to exseed 15%,while it is still far from large-scale commercial application.As a typical QDSSC photoanode material,titanium dioxide（TiO₂）is generally considered to play a role in transmitting photogenerated electrons rather than absorbing photons in photoanode due to the limitation of wide band gap.Therefore,current research on TiO₂is mainly aimed at regulating the morphology to promote the electron transfer rate.With the core goal of improving the photoelectric conversion efficiency of QDSSC,this thesis creatively proposed a new perspective from the light harvesting ability of modified TiO₂ materials,aiming to break through the limitations of TiO₂ broadband gaps and facilitate QDSSC achieving high photoelectric conversion efficiency.TiO₂was modified by intense femtosecond（fs）laser nonlinear transmission filamentation technique,and thus capable of both charge transfering and light capturing,which significantly improved the PCE of QDSSC.The physical mechanism of TiO₂ material modified by fs filamentation was explored at the same time.The specific achievements are summarized as follows:1.Optical properties and mechanism research on femtosecond laser filament modification of TiO₂ nanoparticles.Firstly,TiO₂ nanoparticles were processed using high-intensity filaments generated by ultrafast laser nonlinear propagation in the atmosphere,and the obtained black TiO₂ samples exhibited a significant improvement of the absorptivity in the spectral range between 250 and 2500 nm;secondly,the influence and effect of the absorption characteristics of black TiO₂ nanoparticles were analyzed by changing the external focusing parameters of laser pulse;finally,the mechanism of the optical properties improvement was revealed by analyses of the surface morphology,crystal structure,and chemical element composition of black TiO₂nanoparticles:after fs filamentation ablation,black TiO₂ nanoparticles formed a core-shell structure with an amorphous shell and a crystalline core;the proportion of defect states such as Ti³⁺and oxygen vacancies on the surface of black Ti O2 nanoparticles increased,resulting in a band-tailed state that narrow the Ti O2 energy gap,leading to a significant improvement in the light absorption ability of Ti O2 nanoparticles.This feasible scheme not only can overcome the harsh limitations of traditional hydrogenation processing and other technologies on experimental environments such as high temperature and high pressure,but also enable the rapid and efficient preparation of black TiO₂ nanoparticles in a large area;the physical mechanisms of fs filamentation modified black TiO₂ obtained by different characterization methods have important guiding significance for further regulating and optimizing the optical properties of black TiO₂.This series of work not only explored new application scenarios for femtosecond laser filaments,but also provided a new reliable scheme for rapidly fabricating black TiO₂ nanomaterials.2.Research on regulation and optimization of the optical properties of femtosecond filament modified black TiO₂.Firstly,the optical properties of TiO₂were regulated by modifying different crystal types,three different crystal forms of TiO₂ were processed using femtosecond laser filament processing technique,the black rutile TiO₂ exhibited the highest absorption efficiency,followed by black P25 TiO₂,and black anatase TiO₂ showed the lowest absorption efficiency;secondly,the processing environment of fs laser filamentation was changed to optimize the optical performance of TiO₂.TiO₂ samples with the same crystal form were modified by fs laser filament processing technique in deionized water and absolute ethanol environment,and it was found that the modification effect in absolute ethanol environment was better than that in deionized water or air environment;finally,the optical properties of TiO₂ were double-regulated regulated by the processing environment and TiO₂ crystal form.TiO₂samples of three crystal forms were modified in deionized water and absolute ethanol respectively,thus verified the superiority of rutile TiO₂ in terms of light utilization efficiency compared to the other two crystal forms,and the following conclusions were drawn through comparison:the filamentation-induced modification effect in absolute ethanol environment was more notable than that in the deionized water environment,and the black rutile TiO₂ fabricated in absolute ethanol showed the best optical performance,which maintained extremely high light absorbance efficiency in a wide range of 250～2500 nm.This series of work clarified the differences in optical properties among different crystal types of TiO₂,and revealed the key role of the filament processing environment in regulating and optimizing the optical performance of black TiO₂,thereby proving the potential value of black TiO₂ materialsfor photovoltaic devices,laying a theoretical foundation for further practical applications.3.Performance study of black TiO₂ photoanode in quantum dot sensitized solar cells.Firstly,the black TiO₂ photoanode films were prepared and applied in QDSSC using Cd S/Cd Se quantum dot co-sensitization strategy;secondly,the monochromatic incident photon-to-electron conversion efficiency（IPCE）test was conducted to verify whether black TiO₂ is beneficial for photoanode,and the results showed that compared to the original TiO₂ photoanode material,the superior photoelectric properties of black TiO₂ broaden the range of light conversion wavelength of QDSSC;then,the photovoltaic performance of QDSSC was obtained through photocurrent-photovoltage testing,and the best performance was achieved by device assembled with the black TiO₂ modified by fs filament in absolute ethanol,with a J_sc of28.01 m A/cm²,a V_oc of 696 m V,and an FF of 46.8%,yielding a PCE of 9.11%,which was about 6.4 times higher than that assembled with the pristine TiO₂;finally,the electrochemical performance test results showed that the improvement of the device performance can be attributed to the reduction of the series resistance and the charge transfer resistance at the TiO₂/QDs/electrolyte interface,which promoted the suppress the transport of photogenerated carriers suppresses charge recombination,thereby reducing energy loss in the cells.These results give an insight into the impact of the photoelectric performance of Ti O2 materials in the photoanode on the photoelectric conversion efficiency of QDSSC,which provides an innovative direction for achieving high-performance devices.These findings not only demonstrations the feasibility of modifying nanomaterials using fs laser filament processing technique,but also provides a rapid and novel method for the preparation of high-performance nanomaterials.In addition,it innovatively applies the fs filament modified Ti O2 nanomaterials to QDSSC,integrating the two fields of the cutting-edge femtosecond laser filament technique and novel photovoltaic devices,which has important enlightenment for other light conversion and utilization systems.