Organic Small Molecule Hole Transportingmaterials Based On Diaryl Ketone-cored Andtheir Application In Perovskite Solar Cells

In recent years,perovskite solar cells(PSCs)have made tremendous research progress due to their advantages of high efficiency and low cost,and their power conversion efficiency(PCE)has increased from the initial 3.8% to the current 25.2%.In PSCs,the hole-transporting material(HTM)in direct contact with the perovskite layer can extract holes from the perovskite and then transport them to the counter electrode,while preventing unnecessary charge recombination at the interface.Therefore,researching and developing appropriate HTMs are meaningful for the preparation of high-performance PSCs.When designing and synthesizing HTMs,the choice of core unit is crucial.The reported core groups of HTMs are mostly electron-donating groups,such as triphenylamine,carbazole and biphenyl.And there are not many studies on electron-withdrawing core units.Electron-withdrawing groups can increase the polarity of molecules,enhance the interaction between molecules,then improve the hole transporting ability of materials.When designing HTMs,the electron-withdrawing core unit can be used to create a “3D” molecule with a twisted configuration,which enhances the interaction between molecules while ensuring that the molecule has an appropriate energy level.Therefore,in this thesis,we first introduced diaryl ketones with electron-withdrawing property as core units to synthesize new HTMs,and studied the influence of the electron-withdrawing core units on the photophysical properties,electrochemical properties and thermal stability of the molecule.The influence of molecular structure on performance of HTMs and devices has been mainly discussed in this thesis.This thesis focuses on the following two aspects:1.Designed and synthesized two organic small molecule HTMs based on diaryl ketone cores: BP-DC and PT-DC,using benzophenone and dipyridone as core units respectly.HTMs were applied to PSCs.This experiment explored the effect of different electron-withdrawing core units on the hole transporting ability of the molecules and PCE of PSCs.Pyridine has stronger electron withdrawing ability than benzene.The introduction of pyridine in the core unit makes PT-DC have stronger intermolecularinteraction than BP-DC.The results show that both molecules have excellent thermal stability.Compared with BP-DC,PT-DC has a more suitable energy level,higher hole mobility,better hole extraction and transport capability,and a smoother surface morphology.The device based on PT-DC achieves a PCE of 18.27%,which is higher than that based on BP-DC(16.70%).Moreover,the PT-DC-based device shows little hysteresis effffect.Studies show that the idea of introducing diaryl ketones into core units of HTMs is reasonable.In addition,enhancing the electron-withdrawing ability of the core unit can improve the hole transport ability of HTMs to a certain extent,thereby improving the device efficiency.2.Designed and synthesized two organic small molecule HTMs based on dipyridone cores: XJ2 and XJ3,using di(pyridin-3-yl)methanone and di(pyridin-2-yl)methanone as core units respectly.HTMs were applied to PSCs.This experiment explored the effect of the change of the substitution site on core units on the hole transporting ability of the molecules and the PCE of PSCs.The conjugation of XJ2 is better than XJ3.The results show that,compared with XJ3,XJ2 has a more suitable HOMO energy level,better hole extraction and hole transport capability,and higher hole mobility.The photovoltaic performance tests show that the PCE of XJ2-based device is 20.17%,which is higher than the PCE of XJ3-based device(18.84%).Studies show that changes in the substitution sites on the core unit can affect the performance of HTMs.It’s important to consider the appropriate substitution site when designing new HTMs.