Synthesis And Properties Of Small Molecular Donor Materials Based On Diester-terthiophene ?-Bridge

All-small-molecule organic solar cells(ASM-OSCs)have become aresearch hotspot in the optoelectronic field owing to their advantages of definite structures,good batch-to-batch repeatability and broad industria-lization prospects.In comparison with other types of solar cells,OSCs exhibited lower open circuit voltage(V_OC)and power conversion efficiencies.Thus,it is very important to develop small molecule donors(SMDs)with deeper highest occupied molecule orbit(HOMO)energy levels.This dissertation reviewed the current situation of donor and acceptor materials in OSCs and proposed a new design concept for constructing SMDs.As a result,a series of A-?-D-?-A type SMDs was designed and synthesized using thiophene or benzodithiophene as electron-donating(D)central core,as well as alkyl-rhodanine or 2-ethylhexyl cyanoacetate as electron-accepting(A)end-capping unit.The effect of the D core,the A end-capping group and?-bridge structure on thermal stability,crystallinity,optical physics,electrochemistry,device morphology and photovoltaic performance was studied.High performance SMDs and their corresponding ASM-OSCs devices were obtained.The main research contents and results of this dissertation are listed as follow.1)Using thiophene or 7,8-bis(5-alkylthienyl-2-)benzodithiopehene as central D unit,diesterterthiophene as?-bridge and 3-ethylrhodanine as end-capping A unit,an A-?-D-?-A type of SMDs named TER2 and BER2 was designed and synthesized.The effect of the D core on thermal stability,crystallinity,optical physics,electrochemistry,and photovoltaics was studied.The results show that the central D unit has little impacts on the HOMO and the lowest unoccupied molecule orbit(LUMO)energy levels,which are-5.39e V/-3.03 e V and-5.37 e V/-2.97 e V,respectively.The corresponding bulk hetero-junction(BHJ)OSCs exhibited a high V_OCvalue of 0.98 e V using fullerene(PC₇₁BM)as acceptor.Therefore,it is available to lower HOMO energy levels and improve the V_OCvalue of ASM-OSCs through introducing diesterterthiophene as?-bridge.2)Using 7,8-bis(5-alkylthienyl-2-)benzodithiopehene as central D unit,diesterterthiophene as?-bridge and 3-hexylrhodanine as end-capping A unit,an A-?-D-?-A-type SMD named BER6 was designed and synthesized.In comparison with BER2 and BER6,the impact of alkyl chain attached to rhodanine on crystallinity,thermal stability and photovoltaics was studied.The results show that the growth of alkyl chain length can effectively improve the SMD's solubility.The BHJ-OSCs constructed by BER6 and non-fullerene acceptor IDIC exhibited a high V_OC of 0.97 e V with an advanced PCE of9.03%.Therefore,it is available to enhance the V_OC and PCE values of ASM-OSCs devices through introducing diesterterthio-phene as?-bridge and optimizing alkyl structure on rhodanine.3)Using 7,8-bis(5-alkylthienyl-2-)benzodithiopehene as central D unit,diesterterthiophene as?-bridge and 2-ethylhexyl cyanoacetate as end-capping A unit,an A-?-D-?-A-type SMD named BECN was designed and synthesized.In comparison with BER2 and BECN,the impact of end-capping A unit on thermal stability,crystallinity,optical physics,electro-chemisty and photovoltaics was studied.The results show that the HOMO and LUMO energy levels of BECN are-5.44 e V/-2.99 e V,and the end-capping group of2-ethylhexyl cyanoacetate has a great influence on HOMO energy level.It also did harm to molecular planarity and crystallinity,affecting the device morphology.The BHJ-OSCs constructed by BECN and IDIC exhibit a decreased PCE of 5.52%.