Design Of Non-Fullerene Acceptor Based Thick Active Layers And Their Photovoltaic Performances

Organic solar cells(OSCs)have caught many researchers'eyes because of their good feasibility of light-weight,flexibility,solution-processibility,and low-cost.Recent advances in small molecular non-fullerene acceptors contribute to highly efficient OSCs with power conversion efficiency(PCE)over 18%.Currently,the state-of-the-art OSCs usually achieve the best PCE at an active layer thickness of 100 nm.A thicker active layer will significantly deteriorate the PCE,which is unfavorable for large area roll-to-roll printing at high printing rate.Therefore,it is very necessary to develop high-efficiency thick-film active layers.This thesis aims to achieve high-efficiency non-fullerene based thick-film active layers,several non-fullerene based active layers are developed to achieve high-efficiency thick-film active layers by obtaining high charge mobility and balanced charge transport.The main research contents and innovations are as follows:High-efficiency thick-film active layers are prepared through 1D/2A ternary active layers.The weak crystallinity and low electron mobility(?_e)of IT4F cause low PCE of PBOff DT:IT4F binary thick-film active layers.ID4F,a non-fullerene acceptor with strong crystallinity is introduced into the binary active layer.The PBOff DT:IT4F:ID4F ternary active layer can maintain increased PCE with a broad ID4F content,because ID4F can form an electron-transport highway which can transport electrons more effectively,resulting balanced carriers transports and suppressing the carriers recombination.As a result,PBOff DT:IT4F:ID4F ternary active layer can achieve a PCE of 10.74%with the thickness of 160 nm,and a 10.08%PCE also obtained at 380 nm;a non-fullerene acceptor IDIC and its fluorinated part ID4F are choosed to pair with PBDB-T-SF in the construction of PBDB-T-SF:IDIC:ID4F ternary active layers.The geometry difference between IDIC and ID4F is the smallest which enables the two acceptors as one“alloy”acceptor.Therefore,the ternary active layers display higher?_e,more balanced carriers transports,and optimized phase separation.The PBDB-T-SF:IDIC:ID4F active layer can achieve a high PCE of 11.52%and good thickness tolerance with PCE>10%from 85 to 250 nm.These results indicate that it is an effective method to achieve high-efficiency thick-film active layers through ternary strategy.High-efficiency thick-film active layers are prepared through reasonable selection of acceptor for a high-hole mobility(?_h)donor.The author proposes to surmount the barrier by pairing a low-bandgap and high-hole mobility(?_h)polymer Si25 with a Y-series acceptor Y14.The Si25:Y14 active layer exhibits higher?_e of 3.79×10^-3 cm² V^-1 s^-1 compare to 8.17×10^-4cm² V^-1 s^-1 for Y14 prisitine film,resulting in?_h/?_e of 2.31-3.56.The Si25-induced closer packing of Y14 molecules is observed in Si25:Y14 active layer.The high and balanced charge transports enable low FF dacay from 74.69%to 67.46%with the thickness from 320 to 600 nm.The active layer can achieve 15.39%PCE with thickness of 430 nm and provide a>15%PCE window from 430 to 600 nm.This study demonstrates that pairing high?_h polymer donors and Y-series acceptors are promising candidates to overcome the thickness sensitivity of FF.The influence of isomeric non-halogen solvents in Si25:Y14 thick-film active layers is studied.Two isomeric non-halogen solvents 1,2,4-trimethylbenzene(TMB)and 1,3,5-trimethylbenzene(MES)are introduced to prepare SI25:Y14 thick-film active layers.The Si25:Y14 active layer casts with MES(Si25:Y14-MES)can exhibit a high PCE of 14.40%with a thickness of 400 nm.Interestingly,the one prepared by TMB(Si25:Y14-TMB)only displays a PCE of 6.43%under the same condition.The author finds that the interaction between Si25and Y14 molecules are different in different solvents.For the Si25:Y14-TMB active layers,the strong crystallinity of Y14 induces poor miscibility between Si25 and Y14,resulting large phase separation,low?_e,unbalanced charge transport,and severe monomolecular or trap-assisted recombinatioin.As a result,Si25:Y14-TMB active layer demonstrates an unsatisfactory PCE.