End-group Regulation Of A-D-A’-D-A Type Materials And Their Photovoltaic Properties

Organic Solar Cells(OSCs)have made rapid advances as a potential technological means to alleviate the energy crisis.In this work,we aim to construct materials with synthetic simplicity and high efficiency,and we designed and synthesized two types of small molecule materials(non-fused ring small molecule donors and fused-ring small molecule acceptors)based on the molecular design strategy of A-D-A’-D-A type molecular structure,and through the modulating the end groups of both types of materials,the optimization of optical,electrical and photovoltaic properties can be achieved.The main contents are as follows:(1)Using the design strategy of A-D-A’-D-A type backbone,two non-fused ring small molecule donors MDF-1 and MDF-2 were synthesized with fluorinated benzothiadiazole as the central acceptor unit,cyclopentadienyl dithiophene as the adjacent donor unit,and 2-ethylhexyl cyanoacetate and 3-hexyl rhodanine as the terminal units,respectively.And their optical and electrochemical properties were characterized to investigate the effect of end groups with different electron-withdrawing abilities on the molecular properties.MDF-2 due to the stronger electron-withdrawing ability end group,the intermolecular charge transfer effect is stronger,resulting in its redder absorption and deeper highest occupied molecular orbitals.Then,Y6 was selected as the acceptor material to investigate the effect of two small molecules with different end groups on their device performance.The results show that the device based on MDF-2:Y6 obtained a high power conversion efficiency(1.64%),while efficiency of the device based on MDF-1 is only 0.11%.The study shows that the modulation of electron-withdrawing ability of end groups is an effective means to improve photovoltaic performance of the materials.(2)On the basis of the above research,two A-D-A’-D-A type fused-ring third component materials were designed and synthesized using 1,3-diethyl-2-thiobarbituric acid and 1,3-dimethylbarbituric acid as the end groups,namely MAZ-1 and MAZ-2.They were doped as the third component into the efficient D18:Y6 binary system can further improve the device efficiency,mainly because the addition of the third component broadens the optical absorption range and can improve the open-circuit voltage,as well as ternary cells have more balanced carrier mobility and less charge recombination loss.The best power conversion efficiency of 17.1% and 17.9% are obtained when the MAZ-1 and MAZ-2 doping content is 10%,respectively.This work demonstrates that the modulation of the end groups of the host material to obtain structurally similar guest materials is an effective strategy to rationally design the third component and further improve the power conversion efficiency of organic cells.