Synthesis And Device Characterization Of Organic Hole Transport Materials With Sulfone-based Sulfur Passivation Units

Over the past decade,due to their simple preparation process and wide application fields,perovskite solar cells（PSCs）have attracted great interest from researchers.The photoelectric conversion efficiency（PCE）of PSCs has increased from 3.8%to 25.7%.However,poor stability and high manufacturing cost limit its further development and commercialization.The PTAA（poly-[bis-（4-phenyl）（2,4,6-trimethyl-phenyl）amine]）and Spiro-OMe TAD（2,2’,7,7’-tetrakis[N,N-di-（4-methoxyphenyl）amino]-9,9’-spirobifluorene）are commonly hole-tran sport materials（HTMs）which also have been criticized for their negative effects on device stability and high synthesis costs.Therefore,developing simple and low-cost dopant-free hole-transport materials is an important topic for PSCs.The PCE and stability of the PSCs devices can be improved through the reasonable design of HTM.Based on this,a linear structure that is easy to synthesize has been chosen as the backbone of the HTM,and introduced the passivation unit as sulfone and sulfur atom into the structure of HTM.The HTM will play both the role of hole-transfer and passivation effect on the active layer,and thus improving the PCE and stability of the device.The specific research contents are as follows:1.The DBTO-MTP was designed and synthesized with dibenzo[b,d]sulfoxide as the central unit and bis（4-methanethiol）phenylamine as the terminal group,to explore the feasibility of introducing sulfone groups into HTM,the interaction with perovskite,and its effect on device performance.By the CV（Cyclic Voltammetry）and SCLC（the space-charge-limited current）test,the HOMO（highest occupied molecular orbital）energy level of DBTO-MTP is-5.4 e V,and the hole transport mobility is 3.75×10^-4（88）.According to the Lewis acid-base theory,it is confirmed by FTIR and XPS that the sulfone group can be anchored with the free Pb²⁺ions in the perovskite active layer.The highest PCE of DBTO-MTP-based p-i-n PSCs was 18.73%,with the open-circuit voltage(V_OC)of 1.13 V.2.Three linear HTMs based on fluorenyl core were designed through the side chain engineering with different alkyl length chains substituted in the middle carbon atom,from methyl（FMT-M）to hexyl（FMT）to dodecyl（FMT-D）.The aim is to explore the effect of different alkyl chain lengths on the properties of hole-transport materials.The HOMO levels of FMT-M,FMT,and FMT-D are-5.03 e V,-5.20 e V,and-5.37 e V,respectively.And the hole mobilities are 3.78×10^-5（88）,9.5×10^-5（88）,1.14×10^-4（88）.After a series of characterizations,the crystallization of the perovskite on top of FMT-D was improved due to the FMT-D owning closer intermolecular stacking and enhanced interfacial contact.Therefore,the PCE of p-i-n PSCs based on FMT-M,FMT,and FMT-D is 16.68%,18.57%and 19.99%,respectively.The stability of the device in nitrogen and air is also enhanced.It manifests that the design strategy of side chain engineering is effective,which provides ideas for the future design of efficient HTM.