1. Investigate the current development of NFA OSCs via plenty of literatures.
2. Divide the part of Emerging Approaches in Enhancing the Efficiency of NFA OSCs in two parts:
① Emerging Strategies for High JSC and FF
② How to maximize VOC?
3. Divide the part of Emerging Approaches in Enhancing the Device Stability in NFA OSCs in four parts:
① NFA molecular structure
② Morphology
③ Film Processing
④ Interfacial Contacts and Device Configuration
4. Give a status analysis and highlight some aspects that might need further attention for breakthroughs
An overview of the results:
I. A wide range of narrow bandgap NFAs have been developed with great efforts to modify the donor moiety and electron-withdrawing end groups. These new NFAs, blended with donors having complementary absorption, are now increasingly closing the gap between OSCs and perovskite/inorganic solar cells, especially in terms of JSC and FF. In order to realize industrial applications, it is of critical importance to decrease the cost of NFAs, which can preferably be processed from green solvents and show good thickness tolerance. Along this line, more efforts should be dedicated to the simplification of the synthetic routes (for reduced cost), modification of the structures (for processing with green solvents), and improvement of the crystallinity of NFAs (for high mobility and hence thickness tolerance).
II. The energy losses have also been significantly decreased in NFA-based OSCs compared with those based on fullerene derivatives. In order to further decrease the energy losses to a level close to that of high-efficiency inorganic and perovskite solar cells, the key is to develop NFAs with strong photoluminescence, so that the non-radiative recombination losses can be suppressed. However, the relationship between the molecular structures and emission properties of NFAs remains unclear, and hence further efforts are needed to guide the design of highly emissive NFAs that maintain efficient charge generation at the same time. Meanwhile, it is quite interesting to note that some third components or additives can help to reduce non-radiative losses, although the underlying mechanism needs further clarification. It might be intriguing to have a deep understanding of device physics in this case, so that we can also suppress the energy losses from the point of device engineering. In addition, the relationship between the morphology and energy losses, though discussed in some previous reports on fullerene-based OSCs, might also deserve further investigation in OSCs based on NFAs.
III. The stability of NFA OSCs is closely related to the organic materials and the morphology. The photo-oxidation of NFAs accounts for the degradation of devices, as they contain more active photo-oxidation reaction sites than the fullerene counterparts. It has been demonstrated that the photostability of NFAs can be improved by choosing the end groups and the donor moiety rationally. The structure-stability relationship requires more investigations so that the photostability of NFAs can be further enhanced. In terms of the morphology stability, it is important to optimize the miscibility of D/A materials or introduce a third component to adjust the interaction of D/A materials. In addition, developing efficient and low-cost encapsulation is also very important for the commercial application of OSCs.
Exploitation and dissemination of the results:
I have taken the following three approaches to effectively disseminate the research results achieved from this project. Firstly, publication in the high-impact journal of Advanced Energy Materials (IF: 25.245) will facilitate to disseminate the knowledge gained from this project. This will help me and EU to achieve a good scientific reputation and stimulate other researchers for more novel ideas. Secondly, I have presented these results in national and international conferences via oral presentations or posters. The conferences include the European Conference on Molecule Electronics meeting in Linkoping (2019), Sweden, and the Energy Materials Conference (2021) in Hefei, China. Thirdly, I have also utilized academic social media like MaterialsViews and ResearchGate to spread the research results generated in this project.
