Pre-aggregation Matchingin Solution And Ternary Strategy Accounting For Thermally Stable Solar Cells

Attributing to the rapid development of novel donors and acceptors,the power conversion efficiency（PCE）of the single bulk-heterojunction organic solar cells has achieved 18%.Unfortunately,the operating temperature of the organic solar cells upon illumination always reach to 90°C,how to fabricate organic solar cells showing of high PCE value as well as excellently thermal stability remains to be the key factor determining the commercialization.The article incorporated the perylene diimide derived molecules into the fullerene and non-fullerene systems,serving as the third additive.It is found that the preaggregation matching of components in solvents is the vital factor to realize the highly-efficient and thermally stable organic solar cells.First,the three-dimensional TBDPDI-C₁₁ molecule was incorporated into the classical PTB7-Th:PC₇₁BM system,and the PCE value slightly increased from 8.60%to 8.90%.In addition,the TBDPDI-C₁₁ could effectively restrict the aggregation of PC₇₁BM upon thermal annealing treatment.After annealing at 120°C for 1 h,the PCE value of the device could still remain 83.1%of its original value,showing that TBDPDI-C₁₁ could improve the thermal stability of PTB7-Th:PC₇₁BM.Then,the mechanism of how the solvent type influencing photovoltaic performance and thermal stability of non-fullerene organic solar cells remains to be unexplored.The well-known PTB7-Th was selected as donor while F8IC was used as acceptor.The PTB7-Th:F8IC processing from chloroform（CF）exhibited superiorly higher power conversion efficiency（PCE）of 10.5%,in contrast to the specimen from chlorobenzene（CB）of 6.8%.In addition,upon thermal annealing at 160℃ for 120min,the device processing with CF was more stable than that with CB.The incorporation of perylene diimide derivative TBDPDI-C₁₁ serving as third additive could also obviously improve the PCE value and thermal stability of PTB7-Th:F8IC processing with CB.According to ultraviolet（UV）spectra,atomic force microscope（AFM）,transmission electron microscope（TEM）and grazing incidence wide-angle X-ray scattering（GIWAXS）analysis,the enhanced photovoltaic performance and thermal stability is mainly attributing to formation of PTB7-Th nanofibers and appropriate aggregation of F8IC.The interaction free energy calculating by water and diiodomethane contact angles reveals that PTB7-Th well disperses in CB and tends to aggregate in CF,while F8IC facilitates to aggregate strongly in CB.The pre-aggregation matching of donor and acceptor in solution is essential for the optimization of morphology,efficiency and thermal stability.The finding in this article could provide useful guidelines to fabricate efficient and thermally stable organic solar cells simply by analyzing the surface energy of components processing from different solvents.