Study On The Effect Of NGQDs Doped Mesoporous Layer On The Photovoltaic Performance Of Photovoltaic Cell

Improving the electron extraction efficiency and light absorbance is one of the effective means to improve the optoelectronic performance of perovskite solar cells.In this paper,the hole-transport layer-free perovskite solar cells are based on carbon electrodes.Aiming at the problems of insufficient matching of the band structure of the mesoporous TiO₂ layer with that of the perovskite and low extraction efficiency of photogenerated electrons,the nitrogen-doped graphene quantum dots are applied in the electron transport layer to improve its optoelectronic properties and then improve the photoelectric conversion efficiency of the solar cells.Because the nitrogen-doped graphene quantum dots can improve its optical properties by adjusting the nitrogen doping ratio and its electron extraction efficiency and conductivity are high.The specific research conclusions are as follows:（1）Graphene quantum dots and nitrogen-doped graphene quantum dots with different ratios of nitrogen doping were prepared by hydrothermal synthesis.Through TEM,XPS,UV-vis absorption spectroscopy and photoluminescence spectroscopy,it was found that the size of nitrogen-doped graphene quantum dots was 7-8 nm with the more uniform size distribution and the greatly enhanced photoluminescence properties.At the same time,as the content of pyridine nitrogen increases,its absorption intensity for near-ultraviolet light would continue to increase and the wavelength of the emitted light would red-shift.（2）The composite films of titanium dioxide and nitrogen-doped graphene quantum dots with different nitrogen doping ratios were prepared.And then XRD,capacitance-voltage,UPS,and UV-vis light absorption tests were carried out.When the ratio of amino groups is up to 4.37%,the combination of nitrogen-doped graphene quantum dots and TiO₂ would be more closely,which was conducive to the formation of electron transport channels,so that the composite film formed by combining with TiO₂ had the highest light absorption intensity.What’s more,the carrier concentration was also the largest,reaching 1.11×10²⁰ cm^-3,while the carrier concentration in it was only 4.9×10¹⁹ cm^-3 when it was not doped.The addition of nitrogen-doped graphene quantum dots could gradually increase the bottom energy level of the conduction band of the TiO₂ film,the optimal value was-3.93 e V,best matching the bottom position of the conduction band of perovskite that is-3.95 e V.（3）The NGQDs/TiO₂ composite films were applied as a mesoporous layer in perovskite solar cells,and the effects of the energy band change of the layers and the increase of electron extraction efficiency on the optoelectronic properties of perovskite solar cells were study through the analysis of tests’results such as UV-vis light absorption,incident photon conversion efficiency,electrochemical measurement and J-V curve.The results show that when the composite film of TiO₂ and nitrogen-doped graphene quantum dots with pyridine nitrogen ratio of 3.92%and amino ratio of 4.37%was used as the mesoporous layer,the performance of perovskite solar cells reaches the highest with increased open circuit voltage from 1.000 V to 1.024 V,increased short-circuit current density from 21.36 m A/cm² to 23.31 m A/cm²,increased fill factor from 59.42%to 61.03%and increased PCE from 12.69%to 14.57%.