Advanced Materials(IF32.086) Tunable Donor Aggregation Dominance in Ternary Matrix of All-polymer Blends with Improved Efficiency And Stability

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Li’s team constructed a ternary all-polymer solar cell system with PBQx-TCl as electron donor, and PY-IT and PY-IV as electron acceptors.
It is found that PY-IT can enhance the H-aggregation of PBQx-TCl, while introducing a small amount of PY-IV can inhibit its over-aggregation.
By finely controlling the ratio of the three materials, the aggregation of PBQx-TCl polymer was optimized, achieving a high power conversion efficiency of 18.81% and significantly improved device stability.

Research Background

All-polymer solar cells are considered one of the most promising types of solar cells for large-scale commercialization due to their low cost and high power conversion efficiency. However, to achieve extensive commercialization, there is still room for improvement in photoelectric conversion efficiency and long-term stability. Professor Li’s team at the Hong Kong Polytechnic University has long been engaged in the research of all-polymer solar cell materials and devices, and has been exploring new ways to improve conversion efficiency and stability. Previous studies have shown that introducing multiple components for blending in the active layer of organic solar cells is an important way to improve efficiency. In particular, polymeric small molecule acceptors have a stronger tendency to self-assemble and aggregate, which can be used to regulate the aggregation behavior of polymer donors, and this may have a positive impact on optimizing device performance. The research results of Professor Li’s team were published in the journal Advanced Materials on July 7, 2023, with the original link being https://doi.org/10.1002/adma.202304632.

Research Results

Li’s team selected PBQx-TCl as the electron donor polymer material, and PY-IT and PY-IV, two structurally similar polymeric small molecule materials, as electron acceptors to construct a ternary blended all-polymer solar cell system. Experiments have found that when the content of PY-IT is higher, PBQx-TCl exhibits strong H-aggregation; when PY-IV dominates, PBQx-TCl exhibits J-aggregation. By finely adjusting the ratio of the three materials, the researchers eventually found an optimized mass ratio of 1:1.2:0.2, under which the ternary blended system achieved a record high power conversion efficiency of 18.81%.

The research team used advanced characterization techniques such as in-situ reflection spectroscopy, AFM, and GIWAXS to track the evolution of the thin film morphology. The results show that PY-IT can enhance the close H-aggregation of PBQx-TCl, while the addition of PY-IV appropriately inhibits over-aggregation, allowing PBQx-TCl to maintain optimal aggregation. The effect of thermal annealing is mainly reflected in further enhancing the aggregation of PBQx-TCl, rather than affecting the receptor material. The introduction of PY-IV can also adjust the phase separation degree and control the glass transition temperature of the thin film. Integrating various experimental results, the research team summarized the efficiency-enhancement mechanism: PY-IT maintains PBQx-TCl’s H-aggregation while PY-IV inhibits over-aggregation; thermal treatment optimizes donor aggregation; introducing PY-IV adjusts phase separation and glass transition temperature. Based on the above multiple synergistic control effects, the modified ternary system has been greatly improved in both conversion efficiency and stability.

Research Methods

Material selection and ratio control(omitted)

Preparation of solar cell devices(omitted)

Testing and characterization of devices

In order to fully evaluate the photoelectric conversion performance of the ternary blended all-polymer solar cells, the research team performed a series of testing and characterization. In terms of testing, they measured key parameters of the devices such as open circuit voltage, short circuit current, and fill factor, and constructed current density-voltage curves to calculate power conversion efficiency. In terms of characterization, the researchers conducted external quantum efficiency testing and electroluminescence testing to determine the photoelectric conversion characteristics of the devices. These tests provided important basis for fully evaluating the efficiency enhancement and mechanisms of the ternary system solar cells. In the testing process, the research team used Enlitech’s newly developed QE-R quantum efficiency optical instrument and SS-X series AM1.5G standard spectrum solar simulator to obtain more accurate and repeatable test results.

Thin film morphology and structure testing(omitted)

Aggregation properties and interaction testing(omitted)

Device stability testing(omitted)

Conclusion

This study results show that the structurally similar polymer acceptors PY-IT and PY-IV have different effects on the aggregation modes of donor PBQx-TCl. PY-IT can enhance the H-aggregation of PBQx-TCl, while the introduction of PY-IV appropriately inhibits its over-aggregation. By controlling the ratio of the three, the research team optimized the morphology of the all-polymer blended thin film to achieve higher conversion efficiency and good stability.

Specifically, the solar cell of the 1:1.2:0.2 ternary blended system achieved a record power conversion efficiency of 18.81%. This is not only the highest efficiency achieved by the all-PSC system so far, but also shows good photo-thermal stability. Experimental results show that compared to binary systems, the ternary blended system enhances operational stability. Thermal analysis results also reveal the impact of PY-IV on thermal stability.

In summary, this study elucidates the new mechanism of cooperative regulation of polymer acceptors on donor aggregation, providing an important way to construct high-efficiency, high-stability all-polymer solar cells. Follow-up work will further improve conversion efficiency and device lifetime through material and interface optimization based on this. It is believed that this strategy is applicable not only to all-polymer systems, but also to other types of organic photovoltaic devices.