Research On The Preparation Of N-CQDs And Their Applications In Dye-sensitized Solar Cells

Carbon quantum dots?CQDs?have triggered much attention due to unique photoluminescence properties,up-conversion luminescence,good water solubility,low toxicity and environmental friendliness,which have potential applications in optoelectronic devices.In this work,nitrogen doped carbon quantum dots?N-CQDs?were prepared via a hydrothermal method using eichhornia crassipes?ECs?and chitoson as raw material.The morphology,structure,physical phase,optical and electrical properties of quantum dots are characterized by means of TEM,XRD,Raman,PL,UV-vis and XPS.The effects of technological parameters on the properties of N-CQDs were studied.The N-CQDs were used as photosensitizers and catalysts for the photoanode and counter electrodes of dye sensitized solar cells?DSSCs?.The effects of N-CQDs on the performance of devices were studied by voltammetry,impedance spectroscopy and switching characteristic curves.The main research achievements are as follows.A series of N-CQDs were synthesized under different hydrothermal temperature employing Eichhornia crassipes?ECs?as precursor.Considering the pollution ability to water and low-cost,this study may direct the novel path to convert waste material to useful quantum dots.After measurements,outstanding optical properties have been discovered.In this fashion,solar cells are tentative to be fabricated,yielding the maximized solar-to-electrical conversion efficiency of 0.17%with a good fill factor of 67%.Meanwhile,the above-mentioned quantum dots also show the up-conversion ability,suggesting the potential application in infrared detection or broadening light-absorbing devices.We studied the role of N-CQDs as co-sensitizers in traditional DSSCs.A series of N-CQDs were prepared employing chitosan as precursor via one-pot hydrothermal technology under various times.The optimize N-CQDs are observed with an average size of 1.5nm-3nm and emited cyan light under 365nm ultraviolet light illumination.The co-sensitized solar cells based on N719 dye and optimized N-CQDs shows significantly enhanced performance,yielding a power convention efficiency as high as 9.15%under one-sun?AM 1.5G?,which is much higher than8.5%of the controlled device without N-CQDs.Pt₃Ni alloy counter electrode?CE?is one of the low-platinum but inactive catalysts as counter electrode for dye-sensitized solar cells?DSSCs?.How to optimize its structure and enhance its electrochemical activity is always a focus.Herein,the N-CQDs with up-conversion properties are used to tailor Pt₃Ni electrode,the final DSSC device yields an efficiencies of 8.63%,realizing a substantial increase for the DSSC devices without N-CQDs.The efficiency enhancement may be attributed to the increased electron concentration by N-CQDs,Moreover,the superior catalytic activity of N-CQDs-Pt₃Ni CE accelerates the internal redox reaction,and ultimately improves the efficiency of devices.