Design Of Organic Small-molecule Acceptor Photovoltaic Materials And Modulation On Photoelectric Properties

In the past decade,owing to their outstanding electron transport properties,fullerene derivatives have been dominant electron acceptors in organic solar cells?OSCs?.However,some intrinsic drawbacks,including poor absorption and high cost,have limited the further improvement of their photovoltaic performance.By means of easy synthesis and purification,easy adjustment of optical absorption and energy levels,Non-fullerene small molecule acceptors have shown great development prospects.In recent years,rapid developments have been made in the area of small-molecule acceptors,and the photovoltaic devices based on small-molecule acceptors have achieved the record PCE of 16.02%.In this paper,three design strategies of molecular design,including the fluorination on molecular backones,the modulation of?-bridge sequences and the extension of conjugated backones,were employed to synthesize ten small-molecule acceptors,and the influence of structural modulation on photoelectric properties were investigated by density functional theory?DFT?and time-dependent?TD-DFT?calculations,ultraviolet-visible?UV?absorption spectra and cyclic voltammetry?CV?measurements.The details are as follows:?1?six A₁-?-A-?-A₁ type molecules,incorporating 2,1,3-benzothiadiazole?BT?unit or 1,2,3-benzotriazole?BTz?with no,one or two fluorine atoms as the core,2-ethylhexyl-substituted phenylimide?PI?as the terminal moiety and ethynyl functionalized thiophene as the?-linker,were synthesized to explore the effect of fluorination on photoelectric properties.We found that fluorination on molecular backbones can decrease both the HOMO and LUMO energy levels efficiently and has little effect on the ability to absorb photons.?2?On the basis of?PIAT?₂dfBT,the electron-donating fluorene was chosen as the core to synthesize two A₁-?-D-?-A₁ type molecules with different?-bridge sequences,and their photoelectric properties were fully explored as well.These two molecules shows different molecular configurations,which can affect the degree of?-conjugation and electron density in molecules,resulting in their different absorption properties and molecular energy levels.?3?On the basis of?PIAT?₂dfBT,we chose diketopyrrolopyrrole?DPP?with extended structure to design two extended type molecules,and investigated their photoelectric performance.Enlarging the conjugated backbone can broaden the absorption profiles efficiently with minimizing the influence on molecular LUMO levels,satisfying the requirements for preparing acceptor materials.?4?poly?3-hexylthiophene??P3HT?was chosen as the electron donor material pairing with these molecules,and preliminary device fabrication and investigation of photovoltaic performances were performed.The results demonstrate that our materials show great potential in being electron acceptors in OSCs,and further research on device fabrication and optimization can help improve their photovoltaic performance.