Quad-rotor-shaped non-fullerene electron acceptor materials to enhance the photoelectric performance of organic solar cells

Solar energy is rapidly growing as an alternative clean and renewable source of energy. In particular, the lightweight and low-cost bulk-heterojunction organic solar cells have been widely researched over the past few decades. Due to the increasing demand for high performance, the development of new and effective donors and acceptors has recently increased. This has resulted in a shift from fullerenes acceptors due to their low power conversion efficiency to non-fullerene-based acceptors.  The latter exhibits high electron affinity and increased visible and near-infrared absorptivity.

Among the available non-fullerene acceptors, fused-ring electron acceptors have been identified as promising candidates for the fabrication of high performance organic solar cells through variation of the electron-withdrawing end groups and fused-ring cores. However, the limited optimum thickness of the active fused-ring electron acceptor (FREA) layers due to the low electron mobility still remains a challenge. As such, developing new fused-ring electron acceptors with high electron mobility is highly desirable.

Herein, researchers at Yangtze Normal University: Dr. Chuang Yao, Yezi Yang, Lei Li, Dr. Maolin Bo and Dr. Cheng Peng in collaboration with Dr. Jinshan Wang at Yancheng Institute of Technology fabricated two new quadrotor-shaped fused-ring electron acceptors: BFTT-N and BFTT-TN using a combination of the two-dimensional fused-ring core with four strongly electron-withdrawing end groups. The main objective was to investigate the feasibility in enhancing the photoelectric performance of organic solar cells. The work is published in the journal, Journal of Materials Chemistry A.

Compared to the widely used fullerene acceptor (ITIC), the two fused-ring electron acceptors exhibited significantly enhanced capabilities: high electron mobility and affinity, smaller exciton binding energy and higher absorption coefficients. This ensured stronger absorption in the visible and near-infrared spectral regions which was ideal in increasing the absorption of solar radiation. Additionally, the lowest unoccupied molecular orbital energy levels accelerated the collection of free electrons at the cathode.

It was necessary to investigate the center-of-mass radial distribution functions of ITIC to determine the crystallization properties of BFTT-N and BFTT-TN amorphous films. Unlike ITIC crystals, they did not exhibit strong peaks with increasing distance indicating the absence of long-range order. However, at short distances, the fused-ring electron acceptors exhibited some weak peaks that confirmed the existence of slight agglomeration at short distances in BFTT-N and BFTT-TN. This was attributed to the larger planar structure which facilitates stacking in the quad-rotor shaped materials.

Based on the results, the authors concluded that the quad-rotor-shaped fused-ring electron acceptors are suitable electron acceptors for the fabrication of high-performance organic solar cells. Therefore, highlighting the importance of their study, Dr. Chuang Yao the lead author in a statement to Advances in Engineering observed that the quad-rotor-shaped fused-ring electron acceptors are a promising candidate for the development of future high-performance organic solar cells.