Organic solar cells (OSC) have unique advantages such as light weight, wide absorption range, simple preparation process and no pollution. The rapid development of photovoltaic materials and device engineering has accelerated the industrialization of organic solar cells. Effectively improving the stability of organic solar cells is a problem faced by practical applications. Unlike inorganic solar cells, organic solar cells can be used in the fields of flexible and wearable electronics, and therefore impose stricter requirements on the active layer. The active layer materials, molecular arrangement and network morphology, which are the core of the photoelectric conversion of organic solar cells, are important factors that affect their flexibility and stability. Under normal circumstances, the active layer has a metastable structure, and the molecules will be distorted and wriggle over time, leading to delamination between materials, thereby affecting exciton dissociation and charge extraction. In addition, due to different working environments or substrates, the interlayer interaction between the active layer and the transport layer is also particularly important for the thermal and mechanical stability of the device. Therefore, adjusting the molecular accumulation and entanglement in the active layer and changing the internal and surface characteristics of the active layer are of great significance to improving the mechanical and thermal stability of the device.
Recently, the Advanced Organic Functional Materials and Devices Research Group of Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences used two polymer donors with different side chains (PBB1-Cl, PBB2-Cl) as the third component to fine-tune the activity. Layer internal and surface characteristics to improve the performance of organic solar cells. The good planarity of PBB1-Cl and PBB2-Cl significantly increases the overlapping area of ​​the intermolecular arrangement. In particular, PBB1-Cl has one-dimensional side chains, which can reduce the steric hindrance between the molecules, so that the molecules of the active layer are closely packed and integrated. The tangles are significantly enhanced. Studies have shown that after adding 20·wt% of PBB1-Cl, the elongation at break of the ternary blend film based on PM6:PBB1-Cl:Y6-BO-4Cl is increased by 4.6 times (26.86%), and the conversion efficiency of the corresponding device (PCE) increased from 15.83% to 17.36%. The small difference in surface energy γs between the PBB1-Cl-based ternary blend film and the transmission layer has the possibility of reducing the separation between layers. At the same time, the glass transition temperature Tg of the ternary blend film is increased, and the temperature sensitivity of the absorption spectrum is reduced, so that the thermal stability of the active layer is improved. The PCE of the PBB1-Cl-based flexible ternary organic solar cell remains at more than 74% within 24 hours of 500 bends or 100°C annealing at a diameter of 10·mm. The results show that enhancing the intermolecular overlap and close packing in the active layer to optimize the internal and external characteristics of the active layer has potential for improving the photovoltaic performance, mechanical stability and thermal stability of organic solar cells.
Related results were published in Energy & Environmental Science. The research was supported by the National Natural Science Foundation of China, the National Key R&D Program and the Exploration Fund Project of Shandong Energy Research Institute.
Using a ternary strategy to build ultra-high stretchability organic photovoltaic cells
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