May 15 2019
Enhancing the efficiency of polymer solar cells (PSCs) from device physics has turned out to be a hot topic.
(a) J-V curves and (b) EQE spectra of binary and ternary PSCs. (Image credit: Science China Press)
The ternary approach offers a highly promising solution for concurrent improvement of materials selection as well as the device manufacturing process. Professor Fujun Zhang’s team has been focusing on the study of ternary PSCs since 2013. Zhang’s team has performed a sequence of studies on the ternary system, for example, polymer/polymer, polymer/small molecule, small molecule/small molecule, double acceptor, double donor, and so on. The preparation technology of the “inverted method” and the “two-step method” were successively reported, and in addition to that, certain novel techniques were developed for investigating the carrier and exciton dynamics in ternary PSCs.
Material compatibility is a major factor that impacts device performance, working mechanism¸ intermolecular interactions, and the phase separation of an active layer. The ternary PSCs’ working mechanisms are still being studied. For instance, the “alloy model” can be a macroscopic phenomenon promoted by the dissoluteness of the excited state energy level between materials, while its microscopic nature remains unchanged.
Of late, Fujun Zhang’s team has reported ternary PSCs with an efficiency of 16.27% and this has been featured on the Science Bulletin in the form of Short Communication.
Two binary PSCs—PM6:IT-4F and PM6:Y6—display complementary short circuit current density (Jsc, 19.75 mA cm-2 versus 25.08 mA cm-2), fill factor (FF, 75.1% versus 73.2%), and open circuit voltage (Voc, 0.860 V versus 0.836 V). By tuning the content of IT-4F in acceptors, the three photovoltaic parameters of the PM6:Y6:T-4F ternary PSCs can be improved. When the IT-4F content is 20 wt%, the ternary PSCs attain an improved efficiency of 16.27% with a FF of 75.9%, a Voc of 0.844 V, and a Jsc of 25.40 mA cm-2. The up-side-down solvent vapor treatment was used in this work to improve the phase separation of active layers, which Zhang’s team had proposed initially.
High repeatability and easy preparation process are the unavoidable demands for the industrialization of PSCs. Without solvent additive, the ternary PSCs exhibit excellent potential when it comes to the industrialization of organic photovoltaic. The third component, apart from improving the photon harvesting of the active layer, can also improve photo-generated excitons bulk distribution to enhance the PSCs’ performance. This study further demonstrates that the ternary approach has the potential to become the first option for the industrialization of PSCs.
The study was supported by the Fundamental Research Funds for the Central Universities (2018JBM061), National Natural Science Foundation of China (61805009, 61675017), and Beijing Natural Science Foundation (4192049).