Design And Synthesis Of Dopant-free Hole Transport Materials And Application In Perovskite Solar Cell

As a new type of photovoltaic technology,perovskite solar cells（PSCs）have developed rapidly in the past ten years.At present,the highest power conversion efficiency（PCE）of single-cell PSCs has reached to 25.5%.The structure of a typical PSC includes Sn O₂ conductive glass doped with fluorine（FTO）as anode,electron transport layer,perovskite layer,hole transport layer and metal cathode.At present,The most widely used hole transport material is 2,2’,7,7’-tetrakis[N,N-di（4-methoxyphenyl）amino]-9,9’-spirobifluorene（Spiro-OMe TAD）.Because of the need for doping in application,the stability is poor and the price of Spiro-OMe TAD is high,the application range is greatly restricted.Therefore,the design and development of low-cost,dopant-free hole transport materials is one of the ideas for improving the stability of PSCs and realizing a wide range of applications.In this thesis,we focus on the molecular structure of materials and do research on the factors that affect the properties of materials from different perspectives.（1）Two hole transport materials coded Ph Cz-4Me OTPA and BDT-4Me OTPA based on benzocarbazole and benzodithiophene cores were synthesized.The hole mobility of Ph Cz-4Me OTPA is 1.13×10^-4 cm² V^-1 s^-1,which is higher than that of BDT-4Me OTPA(7.37×10^-5 cm² V^-1 s^-1).This is because the larger degree of distortion in the molecular structure of Ph Cz-4Me OTPA is beneficial to improve the interface contact between the hole transport layer and the perovskite layer.Furthermore,it is also benefit for the extraction of holes.The efficiencies of PSCs based on dopant-free Ph Cz-4Me OTPA and BDT-4Me OTPA are 16.04%and 8.78%,respectively.The PCE of PSC based on Ph Cz-4Me OTPA remains at 92%of the initial value after 1200 h in an environment of 80℃.It is because the glass transition temperature of Ph Cz-4Me OTPA reaches to 139°C,which ensures the thermal stability of the hole transport layer.（2）The hole transport materials coded PYR16 and PYR27 based on 1,6-dibromopyrene and 2,7-dibromopyrene were designed and synthesized.The effects of different substitution positions on the properties of the materials were studied.The molecular dipole moment of PYR16 is 2.29 D which is greater than that of PYR27（2.14D）.The greater molecular dipole moment is beneficial to the charger transfer within the molecular.The PCEs of PSCs based on dopant-free PYR16 and PYR27 are 17.00%and14.67%,respectively.The PCE of PSCs based on PYR16 and PYR27 maintained 98%and 91%of the initial values after 1080 h in an environment of 80℃.The material cost of PYR16 is calculated to be 41.27$g^-1,which is about 43%of Spiro-OMe TAD(95.99$g^-1).（3）The donor-accepter-donor（D-A-D）and donor-accepter（D-A）hole transport materials coeded NSN and ND were syethesized based on the electron accepter unit benzothiadiazole and 1,5-naphthyridine cores.The highest occupied molecular orbital（HOMO）energy level was decreased by the electron accepter unit benzothiadiazole and1,5-naphthyridine.HOMO energy levels of NSN and ND are-5.27 e V and-5.34 e V,respectively,which can achieve a well match with the valence band of MAPb I₃,conducive to the transport of holes.The root mean square roughness values of the NSN and ND films coated on MAPb I₃ layer are 20.52 nm and 27.30 nm,respectively.This is because there are multiple large planar structures in the structures of hole transport materials,the degree of molecular distortion is small,and the film morphology is poor.The PCEs of PSCs based on dopant-free NSN and ND are 11.50%and 8.11%,respectively.