Revealing Morphology Evolution In Organic Solar Cells By Additives Or The Third Component Treatment

Organic solar cells（OSCs）have attracted a wide spread attentions in the past decades due to their unique advantages of light weight,flexibility and solution-processability,which enables low cost and potential for large-area fabrication.Recently,OSCs have made a series of breakthroughs in the power conversion efficiency（PCE）due to the development of novel active layer materials and a thorough understanding of morphology regulation.Among the aforementioned techniques,optimizing the morphology of films is crucial for improving PCE and long-term stability of devices.The ternary strategy shows great potential in regulating the morphology of the active layer and improving the performance of the devices,has become a hot spot in the field of organic photovoltaic research.So far,additives and third component have been successfully validated in TOSCs according to reports in the literature.This article aims to explore the effects of additives,liquid crystal small molecule（LCSM）and star shape small molecule on the morphology evolution of the active layer in a high efficiency system,thereby having a deeper understanding on the relationship between the morphology and device performance.It has important guiding significance for how to select a suitable third component to improve the performance of OSCs.We first take the non-fullerene system PM6:IT-4F as an example,we have designed two BHJ OSCs based on PM6:IT-4F,PM6:IT-4F:DIO,and three PPHJ OSCs based on PM6/IT-4F,PM6/IT-4F（DIO）and PM6（DIO）/IT-4F to systematically reveal the effect of solvent additive DIO on morphology regulation and device performance.Then,a simple D-A-D type LCSM DFBT-TT6 with an appropriate LC phase transition temperature is elaborately selected as a third component to construct highly efficient TOSCs based on PM6:Y6 system.To unveil the work mechanism of LCSMs on the TOSCs performance and eliminate other interferences simultaneously,a structurally similar non-LCSM DFBT-DT6 with a low glasstransition temperature is further synthesized for more clear comparison.It indicating the unique ability of LC molecules in morphology control.The aforementioned favorable morphology evolution is associated with improved crystallinity,phase separation,charge transfer,exciton dissociation and collection efficiency,ultimately boosting the PCE of TOSCs.Finally,based on the high-efficiency non-fullerene system PM6:Y6,we use star-shaped small molecule TF1 as the third component,which has a star-shaped structure and is different from the third component of the commonly used linear conjugate structure.Using TF1 as the third component to construct TOSC will play a different regulatory role than that of linear molecules..The star-shaped small molecule TF1 has a higher LUMO energy level,which helps to increase V_oc,and the TF1 has complementary absorption with the main donor and acceptor,the expansion of light absorption helps to improve the J_sc of the device.TF1has a large steric hindrance due to its own star-shaped structure skeleton,which can effectively inhibit the excessive aggregation of molecular chains during the film formation process.Optimizing morphology of the active layer is a key factor to improve the performance of the device.Exploring the work mechanism of additives and the third component on the morphology control of the active layer has guiding significance to improve device performance.