Syntheses And Applications Of Novel Spiro-based Functional Materials In Organic Optoelectronics

Conjugate materials with spiro structure have been a class of molecules that can not be neglected in the design of organic optoelectronic materials.With the most common spirofluorene(SBF)system as an example,the center carbon adopts sp3 hybridized,resulting in the conjugated planes on both sides exhibiting orthogonal structure and possessing excellent thermal property.However,one obvious disadvantage of SBF is its relatively weak electrical activity.This problem can be solved through the introduction of electron-donating or electron-withdrawing groups to modify the fluorene unit.Hence,spiro-fluorene-triphenylamine(STF)moiety was proposed in this work with triphenylamine and fluorene appending on opposite side to the sp3 carbon atom.As to the modification from this STF block,it can be derived from the triphenylamine side,fluorene ring side or both to obtain materials with particular characteristics.In this thesis,by developing molecules based on STF skeleton,we successfully obtained materials that can be used as hosts in OLEDs and as hole-transporting materials in perovskite solar cells and achieve high performance.Here are the details:(1)SAFNDCZ and SAFDCZ were designed and synthesized by derivatizing the carbazole and azo-carbazole groups in the para-position of spiro-triphenlyamine.Their photophysics,photochemistry,thermal stability,and electroluminescence properties were systematically studied and summarized.From the results we can see that it is very different from the derivatives in the fluorenyl moiety in which the derivatization on the triphenylamine moiety can significantly improve the thermal stability of the target molecule at the same time maintain its higher triplet energy.In addition,due to the different electron-donating/withdrawing capacity of carbazole and azo-carbazole,the bipolar feature of the host material can be well adjusted.Due to its high triplet energy and excellent thermal stability,SAFNDCZ and SAFDCZ show excellent device performance.Among them,SAFNDCZ-based devices show a superior result for which the external quantum efficiency of blue devices reached 15.5%.These results show that the derivatization on the triphenylamine partis a good way to improve its thermal stability at the same time maintain high triplet energy.(2)We designed a new spiro skeleton by inserting an oxygen atom into the spirofluorene triphenylamine system.Compared with the previous spiro skeleton(STF),this new skeleton has a stronger electron-donating ability,more rigid structure and smaller ?Est.Besides,by derivatizing the nonconjugated phosphorus oxide(PO)group at the fluorene part,we successfully obtained host material with thermally activated delayed fluorescence(TADF)properties.Due to the smaller AEst and lower singlet energy of target materials,blue phosphorescent devices based on these materials achieve power efficiency(PE)up to 58 lm W-1 and turn-on voltage as low as 2.9 V.In addition,thanks to the lower voltage of the material,the efficiency roll-off of the device is also particularly flat.When the device brightness rose from 1000 cd m-2 to 10000 cd m-2,the device's external quantum efficiency only dropped by about 2%.In addition,when the host material is used in two-color based white devices,excellent performance is also achieved.It is worth noting that in this device,a warm white light with CIE of(0.45,0.43)and color temperature of 2921 K and EQE over 20%is successfully achieved.In addition,the efficiency roll-off based on the white device has also been significantly improved.These excellent device properties demonstrate that this new spiro skeleton has great potential in developing thermally activated delayed fluorescent materials.It provides a new way for future design of thermally activateddelay fluorescent materials or host materials.(3)By utilizing spirofluorene-triphenlyamineas(STF)as skeleton and the method we utilized in first section,we designed and synthesized a hole-transporting material with high hole mobility,good thermal stability and suitable energy level.Due to these advantages,when utilizing this material in device,power conversion efficiency of 16.73%under the doping conditions and 12.39%of the power conversion efficiency under undoped conditions were successfully achieved.In addition,the hydrophobicity of the material is further enhanced due to the insertion of the nitrogen atom and the phenyl group.The perovskite solar cells based on SAF-OMe hole-transporting materials can maintain more than 60%PCE at end of 240 h.Regardless of efficiency and stability,performance based on this material are significantly superior to that of commercialized hole-transporting material(Spiro-OMeTAD).Based on these excellent results,we believe that SAF-OMe is likely to make an important contribution to the future development of perovskite solar cells.