Application Of New Organic Small Molecular Hole Transport Materials In Perovskite Solar Cells

The efficiency of perovskite solar cells?PSCs?has exceeded 23%in a few years since perovskite was first used as photosensitive material in 2009.PSCs have many advantages such as wide absorption spectrum,high carrier mobility,simple manufacturing process and low manufacturing cost,which show a strong prospects for development.Hole transport layer?HTL?plays an important role in improving the efficiency of PSCs.An excellent HTL can significantly improve the extraction and transmission of photo-generated holes.It can highly improve the power conversion efficiency?PCE?and the stability of solar cells,meanwhile,the hole transport material?HTM?also significantly affect the cost of devices.Therefore,the synthesis and application study of new HTMs is an important part in PSCs research.This paper mainly studies the application of new organic small molecule HTMs in PSCs.Traditional organic small molecule HTM Spiro-OMeTAD has high synthesis cost,meanwhile the doping of LiTFSI for increase the conductivity has a negative impact on the long-term stability of PSC device.To solve this problem,we used a low-cost organic molecule X60 as HTM and synthesized a dicationic salt of X60 termed X60?TFSI?₂ as the“doping”agent to replace the previously used LiTFSI for HTM in PSCs.We found that the conductivity of HTL is proportional to the doping ratio of X60?TFSI?₂.Upon addition of 16 mol%X60?TFSI?₂,the conductivity value is increased to 4.32×10^-44 S?cm^-1,and also reach the highest PCE of19%.Because of the replacement of LiTFSI,the HTM doping with X60?TFSI?₂ shows a large water contact angle,which shows a better long-term stability of PSC device.We also contrasted the performance between two difference HTM,BDT0FMeDPA and its fluorinated molecule BDT2FMeDPA.We found that after fluorinated this small molecule,the conductivity and hole mobility of the dopant-free HTL are increased by about 3.5 times,which shows a better hole transmission and extraction ability,therefore highly enhances photocurrent.The highest PCE of device with BDT2FMeDPA as HTM is 14.5%,much higher than device with BDT0FMeDPA as HTM?11.3%?.Meanwhile,due to the introduction of fluorine atoms,BDT2FMeDPA shows a large water contact angle,with good performance in long-term stability.