Recently, Nature Communications published the latest research findings on thermal stability of organic solar cells by Min Jie’s team from the Institute for Advanced Studies, Wuhan University. The paper is entitled Simultaneous Enhanced Efficiency and Thermal Stability in Organic Solar Cells from a Polymer Acceptor Additive. This paper demonstrates a simple and universal approach to improving both the efficiency and thermal stability of organic solar cells.
Yang Wenyan, a postgraduate student from Min Jie’s team and Luo Zhenghui from Yang Chuluo’s team are the joint first authors; and Prof. Min Jie is the independent corresponding author. Wuhan University is the first author affiliation. The work was supported by the National Natural Science Foundation of China and the independent research project of Wuhan University.
It is said that organic solar cells (OSCs) have attracted much attention due to their light weight, flexibility and rich color. In particular, non-fullerene receptor materials are widely used in the field of organic photovoltaic, improving the energy conversion efficiency (PCE) of OSCs to more than 17%, meeting the basic requirements for commercialization. However, there remain insufficient studies on the device stability, far from the requirements of commercial applications.
Typically, the actual operating temperature outside of the battery assembly is as high as 50 to 70oC, and can reach 100oC in some areas. Therefore, heat is an important stress factor for OSCs attenuation and the problem of thermal instability is expected to be properly solved. Through methods like regulating molecular structure, improving glass transition temperature of the material, adding cross-linking agent or compatibilizer, and introducing thermal cracking group, the thermal stability of several key photovoltaic systems has been significantly improved. However, these methods have some disadvantages such as complex synthesis, poor repeatability and low universality, which limit their wide application.
In this study, the author utilized the advantages of the third component material, which can effectively reduce the interface free energy and inhibit the donor-receptor phase separation, adopted the strategy of solidifying the interface region of the donor-receptor by intermolecular force, and selected the polymer receptor material PZ1 with high molecular weight, long alkyl chain and planar conjugation to increase the compatibility of the donor-receptor interface of pm6:bttt-2cl photovoltaic system. The results show that by controlling the content of PZ1, the phase separation structure can be optimized, the crystallinity of the donor-acceptor can be increased, the carrier transport can be promoted, and the PCE of PM6: BTTT-2Cl photovoltaic system can be increased from 13.80% to 15.10%. More importantly, as a solid additive, PZ1 can significantly inhibit the accumulation of acceptor molecules, solidify the microstructure of blends, and improve the thermal stability. After heating the undoped active layer at 150oC for 24 hours, PCE is reduced to half of the initial efficiency. In contrast, the efficiency loss of PZ1-doped active layer is only 12% after heating at 150oC for 800 hours. Furthermore, PZ1-doped PM6: BTTT-2Cl photovoltaic system also shows good thermal stability under extreme thermal cycling conditions, indicating that it is suitable for outer space use. In addition, studies of four other photovoltaic systems have shown that PZ1 is a “master key” to simultaneously improve the efficiency and thermal stability of the active layer.
In summary, the authors developed a simple and universal doping method to improve the thermal stability of photovoltaic systems by using the polymer acceptor PZ1 as a dual function additive. Furthermore, the designed high-performance doped photovoltaic system has potential for outdoor and spatial applications. Further research is needed to design specific dual function additives for different types of photovoltaic systems, which is of great significance to the optimization and research of the efficiency and thermal stability of photovoltaic devices.
PM6: BTTT-2Cl photovoltaic system, PZ1 additive and optimized efficiency and thermal stability of devices
Paper Link: http://www.nature.com/articles/s41467-020-14926-
Rewritten by Chen Muying
Edited by: Wu Buer, Shen Yuxi and Hu Sijia