Morphology Control Of Active Layer Of Non-fulilene Organic Photovoltaic Cells

Organic photovoltaic cells based on solution?processed bulk heterojunction(BHJ)have attracted much interest due to their advantages of light weight,semitransparency,flexibility and ease of fabrication.In addition to the synthesis of donor and acceptor materials,interface engineering and device structure,the morphology of the active layer plays a crucial role in determine the power conversion efficiency(PCE)of devices.The phase separation between donor and acceptor from solution to filmss has not been studied very much.When materials with the same structure are matched,the length of the crystallization time can affect the size of the active layer phase region.The results of the study show that when materials with the same structure and different systems are combined,the crystallization time is different due to the difference in solubility of the material and the main solvent,which affects the change in morphology.When matching the acceptor,in addition to paying attention to the compatibility of the acceptor,the length of the crystallization time of the blend system in phase separation should also be considered.The additives fluoronaphthalene(FN),additives 1-8,and diiodooctane(DIO)regulate the crystallization order of the donor PBDB-TF and the acceptor IT4 F,which can effectively build a highly crystalline interpenetrating network structure.The results show that when IT4 F is crystallized first and PBDB-TF is crystallized later,the PBDB-TF crystal is inhibited by IT4 F,which causes the phase separation size of the active layer to be too large and the crystallinity to be reduced.Although the crystalline orientation is more conducive to transmission in the same direction,the advantages and disadvantages caused by each other cancel each other,so the final performance and untreated are equivalent;when PBDB-TF crystallizes first,the impact of small molecule crystallization is weakened The crystal growth is more complete,while IT4 F can be dissolved in the additive DIO,and further crystal growth can be achieved during the slow drying of DIO,thereby weakening the limitation of PBDB-TF to form a network,so the overall crystallinity is enhanced,and the highly crystalline interpenetrating network structure improves device performance.Shorten the crystallization time of the donor and acceptor through hot spin coating,and improve the highly crystalline interpenetrating network structure,thus improving the performance of photovoltaic devices.To further improve the highly crystalline interpenetrating network structure,the crystallization time was lengthened and shortened by the method of steam annealing of the tetrahydrofuran solvent and the method of hot spin coating,respectively,and the phase area size of the active layer was optimized.It was found that with the increase of crystallization time,the size of the phase region gradually increased.By means of thermal spin coating,not only the crystallization time of the donor is shortened,but also the degree of orderly aggregation of the donor in the solution is increased,resulting in an increase in the crystallinity of the films.The optimization of the morphology balances the mobility of the carriers,reduces the degree of bimolecular recombination,and thus increases the fill factor.The final device efficiency increased from 10.67% to 12.46%.