Precise Regulation Of Active Layer Morphology And Stability For High Performance Ternary Organic Solar Cells

In recent years,the power conversion efficiency(PCE)of the single-junction bulk heterojunction organic solar cells(OSCs)has exceeded 16%.The ternary strategy used to fabricate the OSCs could not only improve the absorption of sunlight,but also optimize the morphology of active layers,leading to highly efficient solar cells.However,the thickness of active layer for the most OSCs is only about 100 nm.After fabrication into thick active layer,the performance of the OSCs will sharply depress.In addition,the factors of light,air and heat will seriously affect the lifetime of cells.Aimed at solving the above problems,the article tries to use the ternary strategy to precisely modulate the morphology of active layer,especially of the vertical distribution of different components,in order to fabricate the highly efficient OSCs insensitive in thickness.First,a highly crystalline molecule DRCN5 T was involved into PTB7-Th: PC70 BM system to fabricate the large-area OSCs whose blend film thickness is up to 270 nm,achieving an impressive performance of 11.1%.The significant improvement of OSCs after adding DRCN5 T is due to the formation of interconnected fibrous network with decreased ?-? stacking and enhanced domain purity,in addition to the optimized vertical distribution of PTB7-Th and PC70 BM,producing more effective charge separation,transport and collection.The optimized morphology and performance are actually determined by the miscibility in different components,which could be quantitatively described by the Flory-Huggins interaction parameter of-0.80 and 2.94 in DRCN5T:PTB7-Th and DRCN5T:PC70BM blends,respectively.It is indicated that DRCN5 T and PTB7-Th are miscible while DRCN5 T and PC70 BM are miscible.The novel finding in this work could potentially guide the selection of appropriate third additive for high-performance OSCs for the sake of the large-area printing and roll-to-roll fabrication from the view of miscibility.The TBD-PDI-C11-Se molecules were then incorporated into PBDB-T-F:IT-4F systems,to afford a ternary OSCs with highest PCE value of 13.9%.It is found that the small molecules could effectively restrict the aggregation of IT-4F,leading to the improvement of stability of active layer.In the condition of air environment and 140 °C thermal annealing,the ternary OSCs exhibited of better stability than binary OSCs.After treating in air environment for 900 h,the PCE of ternary OSCs could still remain 85% of its original value while the binary device obviously reduced to 71%.Upon thermal annealing at 140 °C for 12 h,the ternary OSCs device could retain 88% of its original value,in contrast to the binary OSCs device of 78%.The related research could provide novel strategy to the fabrication of highly efficient and stable organic solar cells.