Research Of Ternary Heterojunction Organic Solar Cells Based On PBDB-T-SF:IT-4F System

In recent years,in order to improve the efficiency of organic solar cells?OSCs?,the ternary strategy has been valued by more and more scientific research teams as an effective method.In this thesis,the non-fullerene materials ITIC-Th and IEICO-4F are incorporated into the highly efficient binary organic solar cells?PBDB-T-SF:IT-4F?as the third component.The effects of the ratio of doped materials and the up-side-down solvent vapor annealing?USD-SVA?process on the performance of OSCs were studied.Firstly,the open-circuit voltage(V_OC)was increased by energy cascading.And the non-fullerene material ITIC-Th was incorporated into the binary system?PBDB-T-SF:IT-4F?.The effects of different doping ratios on various parameters of the binary organic solar cell were studied.The prepared ternary organic solar cells?PBDB-T-SF:IT-4F:ITIC-Th?has the best performance when the doping ratio of ITIC-Th reaches 20 wt%.At this time,the optimal ternary OSCs has an open-circuit voltage(V_OC)of 0.80 V.The corresponding short circuit density(J_SC)of the device is 21.07 mA/cm².The fill factor?FF?of the device is 65.08%.The energy conversion efficiency?PCE?of the device is10.99%,which has a 10%improvement over binary system?9.84%?.The improvement of device performance is mainly because ITIC-Th has a higher lowest unoccupied molecular orbital?LUMO?energy level than IT-4F.While increasing the open circuit voltage,the LUMO energy levels of the three materials in the active layer of the device are well aligned.That is what we call the energy cascade.Thanks to this the charge transportation will be improved.In addition,the incorporation of ITIC-Th makes the originally rough surface of the active layer smoother and flatter,and improves the energy conversion efficiency of the device.Subsequently,the short circuit density(J_SC)was increased by broadening the absorption spectrum.And the non-fullerene material IEICO-4F was incorporated into the binary system?PBDB-T-SF:IT-4F?.It was found that its performance was reduced with only conventional thermal annealing was used on the device.In order to improve the performance of the ternary OSCs,an up-side-down solvent vapor annealing?USD-SVA?process was used on the device before thermal annealing process.The active layer was treated to study the effect of different annealing times on the morphology of the active layer.When the USD-SVA time is 5 minutes,the device performance has been greatly improved.At this time,the V_OC of the device is 0.77 V.The J_SC of the device is 21.60mA/cm².The FF of the device reaches 65.23%,and the PCE of the device increased to11.0%.USD-SVA process can effectively regulate the surface morphology of the mixed film,making its surface morphology more orderly,smaller molecular aggregation domains,and more uniform phase separation.The smoother surface reduce the charge transport barrier and promote free charge transport.In summary,the non-fullerene materials ITIC-Th and IEICO-4F are used to dope the binary system of PBDB-T-SF:IT-4F,and the USD-SVA method was used on the film of active layer.It can effectively improve the performance of the device and provide new ideas for the research of high-performance organic solar cells.