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Optimizing the morphology of the active layer is crucial for achieving high photovoltaic conversion efficiency in all-polymer solar cells (APSCs). Solvent vapor annealing (SVA) is an essential post-treatment strategy for controlling active layer morphology. However, most current SVA are conducted ex situ, limiting their ability to accurately reveal the morphological evolution of active layers of APSCs. In this study, in situ synchrotron radiation GIWAXS and in situ UV-vis spectroscopy combined with GISAXS is used to monitor the morphological evolution of PM6/PY-IT blends during the SVA process in real-time. Results showed that the PY-IT absorption peak exhibited a red shift under a nonpolar carbon disulfide vapor, while a blue shift is observed during the SVA process with a polar chloroform vapor. The SVA process can be divided into three stages: solvent swelling, recrystallization, and molecular rearrangement. For thermally pre-annealed samples subjected to chloroform SVA, the power conversion efficiency (PCE) increased by 15.1%. The improved PCE stems from reduced crystal plane spacing (d-spacing), enhanced crystal coherence length, and optimal phase separation via SVA. Pre-annealing suppresses excessive swelling, emphasizing the reordering dynamical role in the morphology of APSCs. This study offers insights into balancing SVA conditions to maximize performance and minimize adverse effects.
Hao et al. (Mon,) studied this question.