Design Of P-Type Conjugated Molecules For Organic/Perovskite Solar Cells

Material design and revolution of conjugated small molecules(SMs)have attracted intensive interest due to their unique properties,including easy functionalization and purification,low-cost and low-temperature solution processablity,defined physicochemical property and so on.In this dissertation,series of small molecules have been synthesized and applied into organic/perovskite solar cells as donors/hole transport layers(HTLs).The structure-property relationship has been carefully studied.In chapter 2,three acceptor-donor-acceptor(A-D-A)type small molecule donors have been synthesized with 4,8-functionalized BDT as D core and 3-ethylrhodanine as A ending group.Side-chain engineering on BDT core exhibits small but measurable effect on the optoelectronic properties,molecule packing as well as hole mobility.After solvent vapor annealing,organic solar cells fabricated with a structure of ITO/PEDOT:PSS/SM:PC₇₁BM/PFN/Al achieve a champion power conversion efciency(PCE)of 6.99%.In chapter 3,three novel small molecules donors(named DR3TDST,DRCN3TDST andDB3TDST)based on BDT core are designed and synthesized with different electron-withdrawing ending-groups.By introducing bisalkylthiothienyl side-chain to BDT core,all three molecules behave deep highest occupied molecular orbital(HOMO)energy levels around-5.40 e V,leading to a highest V_OC of 1.07 V.The influence of ending-groups on absorption,energy level,morphology,hole transport and device performance are systematically investigated.Bulk heterojunction solar cells using DRCN3TDST give a highest PCE of 5.17%after a combination post-treatment of thermal annealing and solvent vapor annealing.In chapter 4,a new truxene-based small molecule HTL,TRUX-E-T,has been reported with a facile synthesis and outstanding optoelectronic properties.The unit cost of TRUX-E-T used in perovskite solar cells(PVSCs)is only one-fortieth(1/40)of commonly used2,2?,7,7?-tetrakis(N,N-di-p-methoxyphenylamino)-9,9?-spirobifluorene(spiro-OMe TAD).Besides,TRUX-E-T exhibits better hole extracting and transporting property than spiro-OMe TAD,leading to a remarkable fill factor(FF)up to 82%(78.7%for spiro-OMe TAD).The champion PVSC device with TRUX-E-T HTL achieved a maximum PCE of 18.35%(16.44%)under reverse(forward)voltage scan.Moreover,the un-encapsulated cells kept 96.4%of their initial efficiency after 20 days storage,indicating good stability.In chapter 5,a simple carbazole-based HTL material named CZ-TA has been designed and synthesized.The solution-processed n-i-p PVSCs with 50 nm CZ-TA contributes a champion PCE of 18.32%,comparable to the most widely used spiro-OMe TAD(150 nm,18.28%).The enhanced hole extracting,transporting property as well as reduced recombination make CZ-TA-based PVSCs present impressive FF over 81.0%.Importantly,the unit cost of CZ-TA as HTL in PVSC is only 1/60 of spiro-OMe TAD,indicating the great application potential of CZ-TA.In chapter 6,a new CZ-TA derivate(CZ-STA)was synthesized by replacing all methoxy group with methylthiol group.The introduction of S atom in CZ-STA not only downshifts HOMO energy level(-5.333 e V)but also builds stronger Pb-S interaction,leading to stronger surface passivation and reduced hysteresis.To maximize the device performance,a simple binary strategy for acquiring ideal HOMO level is proposed.By tuning the weight ratio of CZ-TA(HOMO=-5.170 e V)and CZ-STA blend to 90:10(HOMO=-5.199 e V),PVSCs achieve a maximum PCE of 19.85%(18.32%for CZ-TA).The un-encapsulated PVSCs using CZ-TA:CZ-STA(90:10,w/w)binary HTL maintain over 82%of their initial PCE after 60 days'storage(under?50%relative humidity in air).Therefore,this strategy provides new thoughts on pushing forward the evolution of PVSCs.