Real-Time Tracking of Polymer Crystallization Dynamics in Organic Bulk Heterojunctions by Raman Microscopy

Abstract

State-of-the-art organic photovoltaic active layers typically undergo post-treatment such as thermal or solvent vapor annealing to increase their performance by tuning the bulk heterojunction morphology. The molecular crystallinity is one of the key factors that determine the morphology.Real-time tracking of the crystallinity during the post-treatment is strongly desired for understanding the physics of the crystallization process and for optimizing the post treatment 2 protocol. Here, we report on cold crystallization dynamics of the polymer in the temperature range of 50-150 °C in polymer:fullerene blends based on poly(3-hexylthiophene) with various fullerenebased acceptors (C60, PC61BM, PC71BM, bisPC61BM, HBIM, AIM8, and IrC60) in real-time by Raman microscopy. We also reveal how different solvents, fullerene acceptors, and temperatures affect cold crystallization during thermal annealing. We further demonstrate a correlation between the fullerene derivative weight and the polymer crystallinity for the as-cast films, and also a correlation of the polymer crystallinity before and after annealing. Our findings are essential for developing efficient strategies of morphology optimization in emerging organic photovoltaic devices with the real-time Raman microscopy tracking as a valuable tool.

Baseplate Temperature‐Dependent Vertical Composition Gradient in Pseudo‐Bilayer Films for Printing Non‐Fullerene Organic Solar Cells

“…Notably, temperature-dependent evolution of D/A vertical distribution depicted in the ToF-SIMS profiles further confirms the results of the optical absorption (Figure 1B), EQE spectra (Figure S2, Supporting Information), and AFM images (Figure S4, Supporting Information) as a function of varying baseplate temperatures. Although the vertical stratification of BHJ active layers during their film-formation process generally is a complex process resulting from the synergistic effects of many factors, [7,9,[45][46][47][48][49] our results demonstrated that SD processing can more effectively control the vertical composition gradient of the active layer through baseplate temperature regulation because of the accelerated evaporation process of CF via the increase of the baseplate temperature.…”

Multiscale Evolution of Bulk Heterojunction Solar Cell Active Layers under Thermal Stress

“…T cc could then be identified to be 49 °C from the first derivative curve of the sigmoid fitting function (Figure S8). Moreover, two other critical temperatures (T cc min and T cc max ) that corresponded to the start and end of the cold crystallization process 40 were calculated (Supporting Information S3.4) to be 30 and 84 °C, respectively. The thermotropic alignment and merging of the mesoscale orientational domains were first observed at the domain boundaries (Figures 2a, S9, and S10), where a higher amorphous polymer composition existed.…”