Synthesis Of Indolocarbazole-Based Photosensitizers And Application Study In Dye-Sensitized Solar Cells

The electron injection energy losses of dye-sensitized solar cells(DSSCs)are among the fundamental problems hindering their successful breakthrough application.Photosensitive dye is the core part of the DSSCs,which controls the processes of light absorption and electron conversion.The design and development of photosensitizers with high efficiency and electron injection efficiency are of great significance to improve the photovoltaic performance and realize the industrial application of DSSCs.In view of this,several indole-carbazoles based organic photosensitizers have been designed and synthesized.The effects of the photoelectric physical properties and charge transfer properties of dyes on the photovoltaic performance of the DSSCs have been systematically studied.Firstly,photosensitizers ZL002,ZL004 and ZL006 with a wide spectral response,using indolo[3,2-b]carbazole as the electron donor,Z-type cyanoacetic acid(CA)or rigid 4acetylenyl benzoic acid(EBA)as the electron acceptor,have been designed and synthesized.The devices based on ZL002 and ZL004 showed higher IPCE response,moreover,dye ZL004 obtained a higher photocurrent density(Jsc)due to the stack effect between the dye load on TiO2 film and the red shift of UV-vis absorption spectra.The dye ZL004 can effectively inhibit the electron recombination between the interfaces of devices to achieve higher open-circuit photovoltage(Voc)from the analysis of electrochemical impedance spectroscopy(EIS).Finally,the devices based on dye ZL004 obtained the higher power conversion efficiency(PCE)of 11.6%.In order to explore the effect of rigid single bond and flexible Z-type double bond on the photovoltaic performance of the device,two novel triazatruxene(TAT)-based photosensitizers ZL001 and ZL003 with different ligands have been designed and synthesized.The dye ZL003 with rigid single bond showed a much faster electron injection and a smaller vibrational relaxation energy loss in the process of electron injection,especially in the locally excited state(hot injection),the ultrafast decay is more obvious,and the electron density of TiO2 is higher in the studies of electron transfer kinetics.Therefore,the devices based on dye ZL003 achieved a higher Jsc and Voc.The analysis of EIS and ultroviolet photoelectron spectrometer(UPS)again proved that ZL003 could effectively inhibit the electron recombination between the interfaces of devices,and its sensitized TiO2 film had higher Fermi energy level to obtain higher Voc.As a result,the devices based on ZL003 showed a PCE of 13.6%and the third-party certified efficiency of devices was 12.4%,all which are the highest recorded result of singledye-sensitized DSSCs to date.Two TAT-based photosensitizers with different electron acceptor groups,namely "the rigid EBA" and "the Z-type CA",have been studied on the difference of electron injection efficiency and light harvesting efficiency.In the studies of electron transfer kinetics and light capture capability,it showed that dye ZL003 with rigid EBA acceptor had a higher electroninjection efficiency and light harvesting efficiency compared with ZL005 with Z type CA acceptor to obtain higher Jsc.Finally,the devices based on ZL003 achieved the PCE of 13.4%,while ZL005 only got a PCE of 7.2%.The TAT photosensitizers ZL001 and ZL003 have been successfully used in solid-state DSSCs.The devices based on ZL003 had a large amount of dye absorption on the surface of TiO2,achieved a longer electron lifetime and a higher regeneration efficiency.Moreover,Hole transfer material(HTM)had an obvious inhibition effect on reverse electron injection processes.Consequently,the solid-state device based on ZL003 achieved the PCE of 6.6%,which is higher than the reference dye Y123.