| With the enhancement of mankind’s ability to transform the world,the exploitation and consumption of various energy sources,mainly fossil energy,has increased dramatically,causing many problems including energy shortage and environmental pollution.Solar energy is one of the most promising solutions to environmental and energy issues.Power conversion efficiency（PCE）of perovskite solar cells（PSCs）as a rising star in the field of solar photovoltaic technology,has reached 25.5%in just more than ten years.In the paper,the methods of extendingπconjugated skeleton,using space configuration twistedπconjugated skeleton and extending electron donor are used to improve the hole transport property by reducing the recombination energy for hole transfer and increasing the integrals of charge transfer between molecules.Furthermore,by inhibiting the structural relaxation of molecules themselves,we can obtain small organic molecule hole transport materials with high hole mobility and high glass transition temperatures.The results showed that,OTPE-OMe TPA obtained by introducing 3,4-ethylenedioxythiophene biphenyl（EDOT-Phen）fragments into tetraphenylene（OTP）based small organic molecule OTP-OMe DPA,has lower hole transfer recombination energy and larger molecular centroid distance than those of OTP-OMe DPA.And the mobility of undoped OTPE-OMe TPA film(3.9×10-5 cm2V-1 s-1)is nearly twice as high as that of undoped OTP-OMe DPA film(2.1×10-5 cm2V-1 s-1),while the mobility of doped OTPE-OMe TPA film(6.4×10-4 cm2 V-1 s-1)is 2.5 times as high as that of doped OTP-OMe DPA film(2.5×10-4 cm2 V-1 s-1).Thanks to the extension ofπconjugated skeleton of OTPE-OMe TPA molecule,the relaxation of the OTP related to the glass transition process is inhibited,affording the glass transition temperature of 193℃,higher than that of OTP-OMe DPA（141℃）by 52℃.Besides,perovskite solar cells（PSCs）based on OTPE-OMe TPA and OTP-OMe DPA achieved PCEs of 21.5%and 20.6%,exceeding or approaching of 20.9%of spiro-OMe TAD based PSC,respectively.After 1000 hours of thermal aging at 60℃,OTPE-OMe TPA based PSC remains 82%of initial PCE,larger than 70%of OTP-OMe DPA based one.It is pointed out that moreπ…πinteractions exist between small organic molecule A5H-OMe DPAs based on aza[5]helicene（A5H）with curved conjugated skeleton in single crystal,compared with NP-OMe DPA based on N-annulated perylene（NP）with planar conjugated skeleton.The difference in the spatial configurations of conjugated skeletons makes that the theoretical hole mobility of A5H-OMe DPA(2.2×10-3 cm2 V-1 s-1)is twice as high as that of NP-OMe DPA(1.0×10-3 cm2 V-1 s-1).A5H-OMe DPA film has a larger size of molecular aggregation（340 nm）and a molecular stacking mode approaching single crystal,leading to that hole transport mobility of undoped A5H-OMe DPA film(4.1×10-5 cm2 V-1 s-1)is more than 4 times as high as that of undoped NP-OMe DPA film(9.2×10-6 cm2 V-1s-1),while the hole transport mobility of doped A5H-OMe DPA film(7.1×10-4 cm2V-1 s-1)is more than 3 times as high as that of doped NP-OMe DPA film(2.1×10-4cm2 V-1 s-1).PSC based on A5H-OMe DPA with better hole transport capability achieve a higher PCE of 21.0%than 19.4%of PSC based on NP-OMe DPA.Besides chlorobenzene,PSCs based on A5H-OMe DPA films with dichloromethane,chloroform,methylbenzene and 2-methylanisole as solvents can also afford PCEs of over 18%.It is found that in the thia[5]helicenes（T5H）based small organic molecule hole transport material T5H-BMCA with dimethylcarbazolamine（BMCA）as the electron donor,the torsion relaxation related to the glass transition process is effectively controlled,offering a high glass transition temperature of 248℃.After 1000 hours of thermal aging at 85℃,T5H-BMCA based PSC still remains 88%of initial PCE（21.1%）.Good morphologic stability of T5H-BMCA hole transport layer,together with low diffusion coefficients of decomposition product of perovskite CH3I and decomposition promoting factor H2O,suppresses the decomposition of perovskite light absorption layer and concomitant performance dropment of PSCs. |
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