Organic solar cells (OSCs) have attracted widespread attention at home and abroad due to their advantages such as light weight, intrinsic flexibility, and solution processability, and have made significant progress in the past decade, but their power conversion efficiency (PCE) still lags behind. For inorganic and perovskite solar cells, this is mainly due to their larger non-radiative energy loss resulting in lower open circuit voltage. Among them, the formation of triplet excitons is considered to be one of the main sources of non-radiative energy loss, limiting the further development of OSCs.

Figure 1. a-f Energy disorder of organic solar cells, energy difference between 3CT and T1, coupling and reverse charge transfer rate

In response to the above challenges, the research team has effectively reduced the reverse charge transfer rate by reducing the energy disorder of the charge transfer state, inhibited the generation of triplet excitons, reduced non-radiative energy loss, and improved the performance of OSC. In this work, the team used the ternary strategy to regulate the energy disorder of the charge transfer state as a starting point. Through in-depth research, it was clarified that the reduction of the energy disorder of the charge transfer state leads to a more delocalized distribution of polaron pairs in space, reducing the spatial overlap with the localized triplet excitons and reducing coupling. According to the Marcus semi-empirical formula, the reverse charge transfer rate of the system is reduced, providing time for the dissociation of triplet charge transfer excitons, thereby reducing the generation of triplet excitons. Ultimately, the ternary organic solar cell device using this strategy achieved a non-radiative energy loss of 0.183 eV and a PCE of 20.25% (certified efficiency of 19.82%), setting a record for single-junction devices. At the same time, the non-radiative energy loss obtained is the minimum value of the PCE system exceeding 19% reported so far in OSC. This work not only proposes a new strategy to suppress triplet exciton formation and non-radiative energy loss by reducing charge transfer state disorder, but also provides valuable insights for improving the performance of OSCs.

The relevant research results were recently published in the journal Nature Communications under the title "Highly efficient organic solar cells enabled by suppressing triplet exciton formation and non-radiative recombination". Dr. Li Congqi from the research group is the first author of the work, Yao Guo (Nanjing University) and Dr. Gu Xiaobin from the research group are the co-first authors, and Professor Huang Hui and Associate Professor Cai Yunhao are the corresponding authors. The above work was funded by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and the University of the Chinese Academy of Sciences.

Article link: https://doi.org/10.1038/s41467-024-53286-2