Regulation Of Charge Transfer Performance Of Perovskite Solar Cells By Functionalized Carbon Dots

Our country is rich in coal resources,but its development cost and environmental impact are rising year by year,the strategic adjustment of energy supply side is imminent.Photovoltaic energy has incomparable advantages over other energy sources in green,environmental protection and sustainable development.As one of the high-tech solutions to the world energy crisis in the 21st century,it is gaining momentum.Researchers found that perovskite solar cells（PSCs）have outstanding photoelectric absorption properties,good carrier mobility,adjustable optical band gap and other bright spots,and perovskite solar cells with different structures are formed based on the bipolar carrier conductivity of perovskite materials.Good charge transfer is one of the important factors to determine the battery performance.Inefficient charge transfer will reduce the charge extraction efficiency of perovskite active layer,resulting in the decomposition of perovskite,and intensifying the charge recombination in the interface and transport layer,thus affecting the device performance.At present,for mesospheric perovskite solar cells,the electron transport layer material is mainly TiO₂,and the hole transport layer material is Spiro-OMe TAD.However,with the development of PSCs,TiO₂ not only has slightly inadequate charge transfer performance but also suffers from many surface defects.The hole transport layer material Spiro-OMe TAD is also questioned because of the gap between the energy level structure and the perovskite absorption layer material.Therefore,it is urgent to modify the charge transport layer with appropriate methods to adapt to the rapid development of the current PSCs.Carbon dots（CDs）is a new type of carbon material with particle size less than 10 nm.Due to their abundant surface functional groups,stable optical properties and high visible light transmittance,they are widely used in PSCs.In perovskite solar cells,carbon dots can not only promote the level matching degree between various functional layers and improve the efficiency of charge extraction,but also play a role in passivating interface defects and inhibiting the effect of water and oxygen in the environment on device erosion,and play a non-negligible role in synchronously improving the photoelectric conversion efficiency and stability.Based on this,the specific research content of this paper for functional carbon point on perovskite solar cells is as follows:（1）The self-made anatase TiO₂ and commercial Spiro-OMe TAD were used as electron transport layer and hole transport layer respectively to construct mesoscale perovskite solar cells to explore the influence of perovskite absorption layer technology on device performance.Through the photocurrent-voltage characteristic test,electrochemical impedance,repeatability test and other aspects of its performance were tested,it was found that the one-step reverse solvent method has more advantages in the synthesis of high-quality photoactive layer thin film,more conducive to the preparation of high-efficiency perovskite solar cells.（2）TiO₂ independently synthesized by the one-step hydrothermal method can be used as electron transport layer material for perovskite devices replacing commercial TiO₂.However,the electron transport capacity of such TiO₂ is limited by surface defects,so in this paper,orange fluorescent carbon dots prepared by p-phenylenediamine are used as a modifier to regulate the electron transport process of TiO₂ in perovskite solar cells.The results show that an appropriate amount of CDs in the electron transport layer of TiO₂ can effectively reduce the interfacial electron recombination,promote the lattice growth of perovskite,effectively extract electrons from perovskite to TiO₂,and increase the electron mobility of TiO₂ from3.00×10^-5 cm²·V^-1·s^-1to 4.13×10^-5 cm²·V^-1·s^-1.In terms of photovoltaic performance,when TiO₂-CDs were used as the mesoporous electron transfer layer,the photoelectric conversion efficiency reached 21.14%and the performance is improved by about 22%.Meanwhile,PSCs based on TiO₂-CDs have negligible hysteresis and better stability and repeatability.（3）The second part is the optimization of electron transport layer in PSCs.This part mainly studies the influence of coal-based carbon points on cell hole transport and the mechanism of action.In this paper,boron doped coal-based carbon dots（B-CDs）were added to Spiro-OMe TAD solution to optimize the energy level gap between the hole transport layer and the perovskite absorbent layer,improve carrier transport performance and regulate the charge transport performance of the hole transport layer.Experiments show that appropriate amount of CDs can reduce the valence band position of Spiro-OMe TAD by about 0.08 e V,narrow the energy level gap with the perovskite absorption layer,reduce the energy loss of the photogenerated holes in the interface transport process,and at the same time reduce the defect state density of the hole transport layer.And the hole mobility of Spiro-OMe TAD is increased.At the same time,not only has the efficiency of the device improved to 20.15%,but also the stability and repeatability of the device are better.