In this work, we report distinct solution-state aggregate structures for donor polymer PM7 and its derivates PM7 D1 and D2. Using small angle X-ray scattering (SAXS), freeze-dried solution imaging and optical spectroscopy, we find that PM7 forms large fibrillar aggregates that are highly temperature sensitive while PM7 D1 and D2 form polymer network-like aggregates that remain stable with variations in solution temperature. Interestingly, these two types of aggregate structures lead to substantially different film morphologies and processing temperature resiliency in bladecoated non-fullerene based OSCs. Specifically, our findings suggest that forming stable polymer network-like aggregates in solution is an effective way of establishing favorable BHJ morphology with strong processing resiliency. On the contrary, large fibrillar aggregates lead to poor film morphologies which are also strongly dependent on the processing temperature. We further unveil that the ester functionalized terthiophene moieties of PM7 D1 and D2 prevent formation of large fiber-like aggregates in solution by disrupting the planarity of the backbone, thereby yielding the observed favorable morphologies with high processing temperature resiliency.