Polycarbazoles Hole Transporting Materials:Design,Synthesis,and Applications In Inverted Perovskite Solar Cells

Inverted（p-i-n structure）PSCs have been becoming more and more attractive,owing to their easy-fabrication,cost-effectiveness,and suppressed hysteresis characteristics.Poly（bis（4-phenyl）（2,4,6-trimethylphenyl）amine）（PTAA）is a polymer HTMs that is widely used in inverted PSCs due to its high hole mobility and high optical transmittance.It is necessary to design and synthesize novel polymer HTMs for inverted PSCs.In this work,by using carbazole as the main unit,we designed and obtained a series of novel polymer HTMs for inverted PSCs.The main research contents are as follows:（1）3,6-PCzTPA,2,7-PCzTPA and 3,6-2,7-PCzTPA were synthesized by the Suzuki coupling reaction using the carbazole unit as the polymer backbone and the triphenylamine unit as the peripheral group.The cell based on 3,6-PCzTPA shows a relatively low efficiency of 16.4%,mainly stemming from a low open-circuit voltage(V_OC)of 0.96 V probably due to the highest HOMO level of 3,6-PCzTPA in three polycarbazole HTMs.Nevertheless,the 2,7-PCzTPA cell exhibits a PCE of 17.1%,primarily due to a low fill factor（FF）of 73.2%,which is possibly related to the relatively low hole extraction and transport ability of 2,7-PCzTPA HTL.Benefiting from the appropriate energy alignment with perovskites,good hole extraction and transport ability,as well as excellent film morphology,3,6-2,7-PCzTPA achieves a champion PSC with a PCE of 18.4%.This work shows that by using the more curved polycarbazole as HTL,the p-i-n type PSCs demonstrated a higher power conversion efficiency.（2）We report the synthesis of two types of carbazole and p-Methoxyaniline based polymers,namely 3,6-PCzTPA-OMA and 2,7-PCzTPA-OMA,by C-N coupling reaction.Both of the 3,6-PCzTPA-OMA and 2,7-PCzTPA-OMA exhibit a PCE of 8%andtheinvertedPSCsdevicestructureis ITO/HTM/（FAPbI₃）_0.85（MAPbBr₃）_0.15/PCBM/C₆₀/BCP/Ag.This work shows that3,6-PCzTPA-OMA and 2,7-PCzTPA-OMA displayed the same optical and electrochemical properties in spite of the different connectivity mode of the carbazole unit.（3）We report the synthesis of two types of carbazole and Dioctyl-fluorene based polymers,namely 3,6-PCzTPA-F and 2,7-PCzTPA-F,by Suzuki coupling reaction.Despite the same chemical composition,3,6-PCzTPA-F and 2,7-PCzTPA-F displayed different optical and electrochemical properties due to the different connectivity mode of the carbazole unit.The inverted PSCs device structure is ITO/HTM/（FAPbI₃）_0.85（MAPbBr₃）_0.15/PCBM/C₆₀/BCP/Ag.This work shows that the device based on 3,6-PCzTPA-F showed better photovoltaic properties with the PCE of 10.46%than that based on 2,7-PCzTPA-F.This could be due to its more suitable highest occupied molecular orbital（HOMO）level and higher hole mobility.