Synthesis And Application Of Polymer Hole Transport Materials With Flexible Skeleton

The certified power conversion efficiency of perovskite solar cells(PSCs)has reached 25.5%.Among them,perovskite cells with p-i-n inverted structure have the advantages of low temperature processing and low hysteresis.They have good application prospects in the fields of flexible photovoltaic devices and laminated cells.However,this kind of device still has the problems of low power conversion efficiency and poor device stability.The reason is that the polycrystalline characteristics of perovskite make it have a large number of defects,especially the defects at the interface between perovskite and charge transfer layer,which would cause serious non-radiative recombination and eventually lead to the decline of photovoltaic performance.In this paper,two kinds of polymer hole transport materials(HTMs)with flexible skeleton were constructed with binaphthyl as the polymer skeleton.By introducing multiple passivation groups into the molecule,the perovskite defects were reduced and the photovoltaic performance of the cell was improved.(1)Dibromo-n-hexane,dibromo-p-xylene,p-dicarboxyl chloride and tetrafluoro-p-dicarboxyl chloride were polymerized with binaphthol derivatives to obtain polyether(ester)-based molecules BN-3,BN-6,BN-9 and BN-12.These four kinds of molecules with flexible skeleton show good molecular degrees of freedom and good solubility in conventional solvents such as chlorobenzene and toluene.X-ray diffraction photoelectron spectroscopy(XPS)demonstrates that BN-9 and BN-12 with carbonyl groups can effectively passivate perovskite defects;X-ray diffraction(XRD)and scanning electron microscopy(SEM)show that perovskite films with good crystallinity are obtained on BN-9 and BN-12 layers.Therefore,the perovskite solar cells based on BN-9 and BN-12 have achieved power conversion efficiencies(PCEs)of 19.3% and20.38% respectively,which are higher than that of BN-3(18.03%),BN-6(18.33%)and commercial PTAA(19.50%).In addition,these devices with BN-9 and BN-12 show better device stability than PTAA.(2)Three polyamide molecules BNs,BNo-F and BNs-F were designed by introducing amide bond to replace the ether(ester)bond.Compared with BNo-F containing methoxy group,BNs and BNs-F films with thiomethyl group show better wettability of perovskite precursor.Infrared spectroscopy,XPS and defect density of states demonstrate that the above three polymer molecules can passivate defects in deposited perovskite layers.F atom can form a certain intermolecular hydrogen bond with amide bond,so BNo-F and BNs-F with F-substituted skeleton show higher hole mobility and conductivity.In addition,steady state photoluminescence(PL)and time-resolved spectroscopy(TRPL)show that the introduction of F atoms can promote the charge transfer at the interface of HTMs/perovskite.Therefore,the BNs-F-based perovskite solar cells achieve a PCE of 20.56%,which is higher than that of BNs(19.03%),BNo-F(19.07%)and commercial PTAA(19.56%).In the device stability test,after 40 days of storage in the glove box,the perovskite solar cells endowed with BNs-F maintaine an initial efficiency of more than 80%,which was better than 30% maintained by PTAA;(3)DES3-O-Hs GY,a graphene alkyne compound synthesized by metal catalytic coupling,was added to the anti solvent chlorobenzene as an additive to prepare the perovskite layer.It was demonstrated that the DES3-O-Hs GY effectively passivated the perovskite defects and improved the charge transfer efficiency.Under the same batch,the PCE of the device was increased from 20.04% to 20.24%.