In the context of increasing interest in faster material screening and blend component selection for organic solar cells, this thesis explores thermal analysis as a tool towards a more in-depth understanding of the relationship between material structure, phase behavior and performance in organic solar cells (OSCs). Firstly, the phase behavior of PffBT4T-2DT/O-IDTBR polymer donor/non-fullerene acceptor (NFA) system is investigated using differential scanning
calorimetry. The observed monotectic temperature-composition (T-Φ) diagram is used to rationalize optimal donor/acceptor (D/A) ratio in devices based on morphological changes, and is supplemented by transient absorption spectroscopy and X-ray techniques to probe the morphology in thin films directly. It was found that a D/A ratio within the inferred miscibility gap induces excessively large polymer domains which are not well interconnected, thus limiting performance.
Secondly, the relationship between phase behavior and device performance is further explored in P3HT blends with either O-IDTBR or EH-IDTBR, where it was found that the dependence of eutectic composition on Mw in blends with the former acceptor correlates with a dependence of performance, while both eutectic composition and performance are largely invariant in blends with the latter. This difference was attributed to the difference in degree of crystallinity of the two acceptors, which is further explored in the fourth chapter where acceptor crystallization kinetics and phase structure are investigated using differential scanning calorimetry and variable temperature X-ray diffraction. It was found that O-IDTBR crystallization persists at faster rates
compared to EH-IDTBR. The latter acceptor was found to form a liquid crystalline phase that is
more robust towards fast rates compared to the crystalline phase.